MEDICAL HEAT TREAT TECHNICAL Archives

Water Electrolysis for Hydrogen Production Facilitates Decarbonization

The thermal processing industry is a good example of how the on-site production of hydrogen by water electrolysis can be beneficial for many of its processes and for reducing the CO₂ of its plants. In today’s Technical Tuesday, David Wolff, industrial sales director at Nel Hydrogen, discusses how, from plasma spray to metal AM binder jet to annealing at rolling mills, industries across medical, automotive, and beyond are looking to water electrolysis for hydrogen production.

This informative piece was first released in Heat Treat Today’s December 2024 Medical & Energy Heat Treat print edition.

Hydrogen atmospheres are widely used in high temperature thermal processing, including annealing, brazing, PM, MIM, and binder jet AM sintering, metal-to-glass sealing, and related processes such as thermal spray. Hydrogen helps heat treaters achieve acceptable product characteristics. It’s used as a very powerful reducing agent, and it actively cleans surfaces as compared to inert gas atmospheres which only displace oxygen.

Relative to hydrogen’s use in helping plants decarbonize, it’s a fact that major OEMs buying heat treating services and heat treated products are demanding that their suppliers report their decarbonization progress. To meet the needs, hydrogen generation is becoming ever more compelling to heat treaters to ensure hydrogen for atmosphere needs inside the plant, and to help minimize their carbon footprint.

The Clean Energy Supply Conundrum

Most U.S. heat treating facilities get their atmosphere components delivered by truck. The truck emits CO₂ and the hydrogen on that truck is likely “gray” hydrogen made from natural gas. Hence, the carbon footprint from their hydrogen use is notable. Importantly, the electricity grid operators are actively seeking ways to enhance the business success of providers of low carbon electricity. The key issue with those providers — solar, wind, hydro, and nuclear — is that they cannot easily follow the ups and downs of demand. Instead, consumers get electricity from those resources when the wind is blowing, the sun is shining, or the river is high. In the case of nuclear plants, they preferentially run at near fixed output, day and night. They run continuously regardless of demand. As the grid demand is very low at night, they get very low prices for the electricity they generate. They only make money for 12 or so hours a day. That’s why a lot of nuclear plants are threatening shutting down for economic reasons.

Taking Advantage of Low Demand Period Energy Prices for Use During High Demand Hours

Consider this scenario: What if a client with electrolysis capacity to produce hydrogen, such as a heat treater, could buy electricity at lower nighttime prices to make the hydrogen it needs during the day shift for its various processes, perhaps even heating their furnaces? The clean energy provider would be pleased to have more income during its low demand, low price times. The heat treat plant is happy saving money buying decarbonized electricity at low demand prices to make clean hydrogen for its various thermal processes and to operate its furnaces. And, the heat treat company’s OEM clients demanding decarbonization are satisfied, too.

How To Get Started

The scenario described above is a practical and real one for the heat treat industry today. Nel Hydrogen recommends that a heat treat company begin with a plan. That plan may comprise several phases. It’s important to seek out a knowledgeable hydrogen partner in this endeavor to specify exactly what’s needed. For heat treat applications, users generally would want compact equipment, extreme hydrogen purity, load following, near-instant on and instant off, and sufficient hydrogen pressure that make it flexibly suited for a variety of thermal processes, and for hydrogen storage addition at a later time if desired.

Figure 1. Compact hydrogen generators using water electrolysis for thermal processing applications (Source: Nel Hydrogen)

Both batch and continuous processes can be served. Batch processes may benefit from a small amount of surge storage at the outset. By combining on-site hydrogen generation with a small amount of in process hydrogen surge storage if needed, on-site hydrogen generation can be used to meet the needs of batch processes such as batch furnaces and thermal spray. By carefully choosing generation rate and pressure, and surge storage vessel volume and pressure capacity, the combination of generation with surge storage can provide maximum process flexibility while minimizing the amount of hydrogen actually stored.

The presence of a small amount of hydrogen surge storage also protects clients’ parts in case of an electric interruption that stops hydrogen production. The surge storage hydrogen can protect the parts while they cool under a reducing atmosphere.

In practice, specific client priorities such as minimum hydrogen storage, or lowest system capital cost, or highest degree of expandability, or least amount of space occupied, can be met by choosing the specific hydrogen generator capacity and surge storage system employed for any particular production challenge.

Examples of Thermal Processors Producing Hydrogen On Site with Water Electrolysis

Decarbonization will be a near-future requirement as part of the global effort to evolve towards a cleaner, greener world. On-site hydrogen generation in industry makes great sense to align with those initiatives. Right now, the thermal processing industry is experiencing the benefits of producing hydrogen on site for its production processes, and the decarbonization demand will be easier to accommodate with that infrastructure in place.

Here are a few examples of companies performing a variety of thermal processes that have made the decision to use water electrolysis to produce hydrogen on site:

Plasma Spray of Cast Iron Cylinder Liners

One of the most compelling examples has been implemented by two different U.S. automakers to accommodate the increasing use of low-weight aluminum engine blocks in today’s high efficiency vehicles. Aluminum blocks must have a cast iron lining on the inside of the cylinder bore to maximize the durability of the engine. (Older readers may recall the notorious Chevy Vega that used an aluminum engine without a cast iron liner. The author’s wife had one Vega which burned through three engines!)

Figure 2. Plasma torch used to spray-apply metal coatings in additive manufacturing processes (Source: Shutterstock)

The traditional approach to provide a cast iron liner was to drive a sleeve into the aluminum engine block. However, a new technology has been commercialized by which the cast iron liner is spray-applied using a plasma torch. The torch uses hydrogen and argon gases to add energy and maintain the necessary low oxygen atmosphere. The plasma spray was a new addition to engine production facilities that had not previously been equipped with hydrogen supply and thus elected to generate their own to minimize delivered hydrogen and avoid the need for hydrogen inventory and extensive supply piping.

The electrolyzers recommended for plasma spray applications are compact and produce high purity hydrogen of better than UHP grade at 200+ psig pressure, with less hydrogen stored than would fill a party balloon bouquet. About the size of a washing machine or refrigerator, depending on the model, each unit is low maintenance, compact, quiet, and can be installed nearly anywhere in a facility.

Metal Additive Manufacturing (AM) Binder Jet

One of the most exciting approaches to metal AM is the technology called binder jet, which creates a near net shape part using polymer and wax binders to adhere metal powders. After the part is formed, the binders are chemically or thermally removed. Then the part is sintered to attain near net shape and full part density. Hydrogen is required for the sintering atmosphere to prevent oxidation of the part during the sintering process. Binder jet technology promises to provide for mass production of individually customized parts at high production rates and consequently lower costs than parts produced individually.

Figure 3. Binder jet metal AM parts sintered in a hydrogen atmosphere (Source: Shuttershock)

Many new metal AM production facilities are being established in factories that are not already equipped for the delivery, storage, and internal piping/distribution of hydrogen. As such, many have chosen instead to use zero inventory hydrogen made on site to minimize infrastructure investments. Electrolyzers for small-scale applications requiring up to 230 scf/hr of hydrogen gas at 99.999+ % purity are advised for metal AM. About the size of a large refrigerator, the units require minimal facility floor space, are easy to maintain, and can be installed in any non-classified space. Applications for AM include medical, electronics, industrial, and automotive components.

Annealing at Rolling Mills

Plate and strip metal are processed in rolling mills where the thickness of the metal is reduced by alternating “cold” rolling steps followed by intermediary hot annealing steps. Cold rolling makes the metal more brittle, so it is necessary to have an annealing step following each rolling step. The metal is alternately thinned and then softened for what could be several iterations. Hydrogen is required for the annealing steps to maintain metal surface quality while heated. Because of the periodic market disruptions in delivered hydrogen from plant outages or trucking interruptions, several rolling mills have chosen to generate hydrogen on site to augment or entirely replace their delivered hydrogen supply. The benefits that the plants experience are primarily focused on supply reliability. Of course, they are also eliminating the carbon footprint associated with truck delivery. In this case, the carbon footprint of the generated hydrogen is determined by the particular electricity generating mix that serves the plant site.

Most often at rolling mills, electrolyzers that produce up to 1,140 scf of hydrogen gas at 99.999+ % purity are best suited for the hydrogen requirement. These units replace the need for hydrogen tube trailers or liquid hydrogen storage. They can be installed in the mill or can be containerized outdoors, offering flexible siting and reduced operational safety risks compared to delivered hydrogen.

Figure 4. Steel rolls are heated in an annealing step to soften the metal during production. (Source: Istock)

On Track Towards Decarbonization

Described in the examples above, once the means to generate hydrogen is chosen at a thermal processing facility, the company can move further along the decarbonization journey. This may be to apply a strategy as outlined in the electricity scenario whereby the company takes advantage of low demand rates or institutes an alternative creative idea. Certainly, as more and more clients demand proof that suppliers are reducing their carbon footprint, more strategies will be developed and implemented to serve the thermal processing industry. Simply generating hydrogen on site removes the trucking emissions factor and is a beneficial and practical starting point.

About the Author:

David Wolff
Eastern Regional Sales Manager
Nel Hydrogen

David Wolff has 45 years of project engineering, industrial gas generation and application engineering, marketing and sales experience. He has been at Nel Hydrogen for over 25 years as a sales and marketing leader for hydrogen generation technologies.

For more information: Nel Hydrogen at sales@nelhydrogen.com.

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HIP Innovation Maximizes AM Medical Potential

January 16, 2024 / FEATURED NEWS, HIPING TECHNICAL CONTENT, MEDICAL HEAT TREAT TECHNICAL / Leave a Comment

The appeal of additive manufacturing (AM) for producing orthopedic implants lies in the “ability to design and manufacture complex and customized structures for surgical patients in a short amount of time.” To complement speed of production, learn how an innovative hot isostatic pressing (HIP) application is confronting the challenges of post-processing heat treatments when creating high quality AM medical parts.

Today’s Technical Tuesday article, written by Andrew Cassese, applications engineer; Anders Magnusson, manager of Business Development; and Chad Beamer, senior applications engineer, all from Quintus Technologies, was originally published in Heat Treat Today’s December 2023’s Medical and Energy Heat Treat magazine.

AM is playing a significant role in the medical industry. It gives manufacturers the ability to create customized and complex structures for surgical implants and medical devices. Additionally, medical device manufacturers have different material factors to consider – such as biocompatibility, corrosion resistance, strength, and fatigue – when selecting a material for a given application. Each of these factors plays a significant role. It’s no wonder that the most common metallic biomaterials in today’s industry are stainless steels, cobalt-chrome alloys, and titanium alloys (Trevisan et al., 2018).

In this article, learn about the application of Ti6Al4V in the medical industry, as well as ways to address some of the challenges when producing AM medical components.

The Future Demands Orthopedic Implants

Figure 1. Example of AM trabecular structure on a Ti6Al4V
acetabular cup (Source: Quintus Technologies)

The medical market for orthopedic implants is predicted to grow annually by approximately 4% where joint replacement, spine, and trauma sectors are reported to account for more than two-thirds of the market. The largest portion is joint replacement with over a third of global turnover, reaching in excess of 20 million U.S. dollars in 2022 (ORTHOWORLD® Inc., 2023). This confirms an earlier study by Allied Market Research where spine, knee, and hip implants made up over 66% of the entire market, with knee implants leading the way at 26% (Allied Market Research Study, 2022). This fact, combined with the expectation that the global population aged 60+ is predicted to double between 2020 and 2050, adds to the increasing demand on manufacturers to produce better quality and longer lasting orthopedic implants (Koju et al., 2022).

These factors have increased the predicted medical implant market for Ti6Al4V and other common orthopedic materials. Using AM processes such as electron beam melting (EBM) and laser powder beam fusion (L-PBF), manufacturers can produce thin-walled trabecular structures that are fabricated to promote bone ingrowth in a growing market that is in competition with traditional production methods.

Titanium-based alloys have been increasingly used in orthopedic applications due to their high corrosion resistance and a Young’s modulus similar to that of human cortical bone (Kelly et al., 2021). The high strength-to-weight ratio and bioinert-ness of Ti6Al4V has proven it to be an ideal candidate for orthopedic and dental implants. It is a titanium alloy with 6% aluminum and 4% vanadium that has low density, high weldability, and is heat treatable. Ti6Al4V demonstrates good osteointegration properties, which is defined as the structural and functional connection between living bone and the surface of a load carrying medical implant.

Many manufacturers are using L-PBF to create thin-walled complex structures on the surface of the implant. This makes use of the osteointegration properties as the implant integrates itself into the body over time without the need for bone cement (Kelly et al., 2021). Introducing a large metallic foreign body leads to challenges such as promotion of chronic inflammation, infection, and biofilm formation. Instead, porous AM Ti6Al4V implants have a biomimetic design attempt towards natural bone morphology (Koju et al., 2022).

AM Yields Production Solutions for Medical Alloys

The medical industry has been increasing the use of AM over traditional processing methods. AM facilitates weight reduction, material savings, and shortened lead-time due to reduced machining, but these are only a few of the benefits. Improved functionality and patient satisfaction are also key aspects through tailoring of designs to take advantage of AM over traditional forging and casting techniques. Additionally, the costs of machining a strong alloy like Ti6Al4V can be expensive, and any wasted material and time in turn lead to higher cost.

One of the main reasons for the interest in AM is the ability to design and manufacture complex and customized structures for surgical patients in a short amount of time. For example, if a patient needs an implant for surgery, an MRI scan can help reverse engineer a customized implant. Engineers prepare a design of a patient-specific implant according to the patient’s anatomy that is then printed, HIPed, and finished for surgery with a reduced lead time. This is especially important for trauma victims, where the speed of repair can mean the difference between losing a limb or returning to a fully functional life. Cancer victims and those requiring aesthetic surgery to the skull, nose, jaw, etc., can also benefit from this (Benady et al., 2023).

Some of the current challenges with AM titanium in the medical industry are related to the post-processing heat treatments that are required. These treatments can leave an oxide layer on thin-walled structures that is hard to remove by machining or chemical milling. Quintus Purus®, a unique clean-HIP solution, has proven to overcome this challenge and provide clients with a robust solution that both densifies and maintains a clean surface.

When HIP Meets AM

Figure 2. AM Ti6Al4V components HIPed without getter using conventional HIP (left) and Quintus Purus® (right) (Source: Zeda)

HIP is important in the AM world as a post-process that closes porosity and increases fatigue life. For medical implants, high and low cycle fatigue life properties are key as they affect the longevity of the repair. The mechanical strength and integrity are improved significantly by HIPing the implants, reducing the need for further surgery on the same patient. Modern HIP cycles have been developed to further increase this performance. When combined with Quintus Purus®, modern HIP cycles can minimize the thin, oxygen-affected layer that can result from thermal processing on surfaces of high oxygen-affinitive materials, such as titanium.

For Ti6Al4V, this layer is often referred to as alpha-case. The brittle nature of the alpha-case negatively impacts material properties resulting in medical manufacturers requesting their AM parts in the “alpha-case free” state. Alpha-case can be formed during heat treatment. As surfaces of the payload and process equipment are exposed to oxygen at elevated temperatures, they may be oxidized or reduced, depending on the oxide to oxygen partial pressure equilibrium. During heat treatment, evaporating compounds become part of the process atmosphere, and solids are deposited or formed on other surfaces, either as particles or as surface oxides.

For titanium alloys, surface oxides are formed at logarithmic or linear rates, depending on temperature and oxygen partial pressure. At the same time, oxygen can diffuse into the surface to form the brittle alpha-case, which is detrimental to the part’s fatigue performance. Changes of the surface color can often be seen as an indication that surface reactions have occurred during processing when using traditional thermal processes (Magnusson et al., 2023).

The HIP furnace atmosphere contaminants that cause this oxidation can originate from various sources including the process gas, equipment, furnace interior, and, most importantly, the parts to be processed. The payload itself often absorbs moisture from the surrounding atmosphere before being loaded into the furnace, which is subsequently released into the HIP atmosphere during processing. Industrial practice today attempts to solve the issue by wrapping parts in a material such as stainless steel foil or a “getter” that has a high affinity to oxygen protecting the Ti6Al4V component from exposure to large volumes of process gas, thus helping minimize the pickup of the contaminates.

This method adds material, time, and labor to wrap and unwrap parts before and after each HIP cycle. Also, wrapping in getter cannot guarantee cleanliness and may result in some uneven oxidation. This is where the tools of Quintus Purus® are of assistance; these tools allow the user to define a maximum water vapor content that can be accepted in the HIP system before the process starts. The tool utilizes the Quintus HIP hardware together with a newly developed software routine, ensuring that the target water vapor level is met in the shortest time possible. The result is a cleaner payload, without the need to directly wrap components with getter (Magnusson et al., 2023).

Table 2. Results from case study productivity analysis
(Source: Quintus Technologies)

Table 1. Input to case study (Source: Quintus Technologies)

Alpha-Case Avoided: Comparing Conventional HIP and Optimized HIP Technologies

Quintus Technologies performed a study with Zeda, Inc. to evaluate Quintus Purus® on L-PBF Ti6Al4V medical implant parts. The study was performed in the Application Center in Västerås, Sweden in a QIH 21 HIP. A conventional HIP cycle was performed as well as an optimized Quintus Purus® HIP cycle, both without the use of getter. No presence of alpha-case was found on the part processed with the Quintus Purus® cycle as shown in Figure 2 below (Magnusson et al., 2023).

Quintus Purus® can be further enhanced with the use of a Quintus custom-made getter cassette supplied as part of the installation, which consumes or competes for the remainder of contaminant gaseous compounds still present in the system after all other measures such as best practice handling, adjustment of gas quality, etc., have been implemented.

Titanium is considered the getter of choice for Quintus Purus® and is included as an optional compact getter cassette placed at the optimum position in the hot zone of the HIP furnace. Although the custom-made getter cassette occupies a small space, its use can significantly increase loading efficiency. The traditional way of individually wrapping components with stainless steel or titanium foil will consume more furnace volume, through reduced packing efficiency, leading to less components per cycle when compared to the Quintus Purus® titanium getter cassette strategy. Using an average spinal implant size of 2 in3 (32 cm3), one can calculate the packing density in a standard HIP vessel assuming two shifts per day and a 90% machine uptime. For example, a Quintus Technologies QIH 60 URC with a hot zone diameter of 16 in (410 mm) and a height of 40 in (1,000 mm) can pack up to 1,280 implants per cycle, with clearances for proper spacing and load plates.

Figure 3. Quintus Technologies QIH 60 URC outfitted with
Quintus Purus® technology (Source: Quintus Technologies)

The typical Ti6Al4V HIP parameters include a soak time of two hours at 1688°F with 14.5 ksi argon pressure (920°C with 100 MPa). Accounting for heat up and cool down time, this HIP cycle can take less than eight hours, allowing two cycles per day on a two-shift work schedule. A typical case of wrapping each component in getter material adds time, cost, resources, and uses up to an estimated 50% of the load capacity. With the increased efficiency enabled by Quintus Purus®, clients have the opportunity to HIP 552,960 spinal implants per year (Tables 2 and Figure 3).

In conclusion, the growing Ti6Al4V market in the medical industry demands innovative developments to keep up with ever-increasing production volumes, whilst quality demands in lean production are becoming more significant. Solutions like the Quintus Purus® will allow manufacturers to have control over the quality of their titanium parts during a HIP cycle. It can be applied to produce alpha-case free components ensuring the optimal performance of orthopedic implants with increased service life.

References
Ahlfors, Magnus, Chad Beamer. “Hot Isostatic Pressing for Orthopedic Implants.” (2020): https://quintustechnologies.com/knowledge-center/hiporthopedic-implants/.
Allied Market Research Study performed for Quintus Technologies, 2022.
Benady, Amit, Sam J. Meyer, Eran Golden, Solomon Dadia, Galit Katarivas Levy.
“Patient-specific Ti-6Al-4V lattice implants for critical-sized load-bearing bone defects reconstruction.” Materials & Design 226 (Feb. 2023): https://www.sciencedirect.com/science/article/pii/S0264127523000205?via%3Dihub.
Kelly, Cambre N., Tian Wang, James Crowley, Dan Wills, Matthew H. Pelletier, Edward R. Westrick, Samuel B. Adams, Ken Gall, William R. Walsh, “High-strength, porous additively manufactured implants with optimized mechanical osseointegration.” Biomaterials (Dec.2021): 279, https://www.sciencedirect.com/science/article/abs/pii/.

About the Authors

Andrew Cassese is an applications engineer at Quintus Technologies. He has a bachelor’s degree in welding engineering from The Ohio State University.

Contact Andrew at andrew.cassese@quintusteam.com

Anders Magnusson is the business development manager at Quintus Technologies with an MSc in engineering materials from Chalmers University of Technology.

Contact Anders at anders.magnusson@quintusteam.com

Chad Beamer Applications Engineer Quintus Technologies

Chad Beamer is a senior applications engineer at Quintus Technologies, and one of Heat Treat Today’s 40 Under 40 Class of 2023 award winners. He has an MS from The Ohio State University in Materials Science and has worked as a material application engineer with GE Aviation for years and as a technical services manager with Bodycote. As an applications engineer, he manages the HIP Application Center located in Columbus, Ohio, educates on the advancements of HIP technologies, and is involved in collaborative development efforts both within academia and industry.

Contact Chad at chad.beamer@quintusteam.com

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Potential for L-PBI Titanium Alloy in Aero and Medical Industries

September 25, 2023 / AEROSPACE HEAT TREAT, AEROSPACE HEAT TREAT TECHNICAL CONTENT, FEATURED NEWS, MEDICAL HEAT TREAT, MEDICAL HEAT TREAT TECHNICAL, TITANIUM PROCESSING TECHNICAL CONTENT, VACUUM FURNACES TECHNICAL CONTENT

Source: TAV Vacuum Furnaces

Those familiar with vacuum heat treatments are surely acquainted with the vacuum heat treatment of titanium and how such furnaces create the ideal environment for titanium's heat treatment. However, not all titanium and its alloys are created equal. Enter the beta titanium alloy.

In this best of the web article from TAV Vacuum Furnaces, discover the potential applications for beta titanium alloys, as well as the effects that various vacuum heat treatments can have on the mechanical properties of the alloy. Additive manufacturing (AM) technologies, specifically laser powder bed fusion, are gaining increased interest in the treatment of beta titanium alloys, due to their efficiency and their cost-cutting potential. Learn more about the chemistry and applications of this unique material below.

An excerpt:

Beta titanium alloys have an unique combination of desirable properties: their high specific strengths, creep resistance, oxidation and corrosion resistance, excellent temperature resistance up to 600°C and hardenability, make them very attractive for aerospace applications. On the other hand, the excellent biocompatibility and low elastic modulus, closer to that of human bone compared to other alloys, make Ti beta alloys an excellent material for biomedical applications.

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A Quick Guide to Alloys and Their Medical Applications

January 8, 2023 / FEATURED NEWS, MEDICAL HEAT TREAT, MEDICAL HEAT TREAT TECHNICAL

Do you know what are the most popular alloys in the medical market? What are their applications? This medical alloys reference graphic gives a quick overview of alloys and their specialized uses in the medical industry.

Ask average people walking along the street what metal/alloy comes to mind when they think of medical uses - things like hip and shoulder joints, the orthodontia their kids might wear, the forceps used to remove stitches - they might come up with the answer "titanium." While this certainly is correct, there are lots of other metals and metal alloys that are used in the medical industry. They probably wouldn't answer "nitinol," a titanium alloy. Nitinol is actually used in the aforementioned braces! Nitinol can be found in other things too: stents, staples, septal defect devices, etc. Take a look at the graphic to see what all these alloys, in fact, can do; you might be surprised!

Such important implements, devices, and components that are used in and on the human body need to be durable and reliable. These medical pieces can improve the quality of life (to put it mildly) or actually save a life (to put it dramatically). Some of these alloys are actually used in and around the heart and blood vessel system! Only the best of the best will do to make up these medical items; lives are literally preserved and saved with them.

What alloys have you found in medical applications? Maybe you have experience with a loved one or yourself incorporating one of these medical pieces in your life? Are you a heat treater involved in the making of these products? Let Heat Treat Today know in the Reader Feedback.

Download the full graphic by clicking the image below.

Source: Heat Treat Today

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Heat Treating: The Best Medicine

January 3, 2023 / FEATURED NEWS, HIPING TECHNICAL CONTENT, MEDICAL HEAT TREAT, MEDICAL HEAT TREAT TECHNICAL

Heat treating solutions are important for more than keeping an airplane flying in the sky or a bridge suspended above the water. These two examples are high profile, but what about the heat treating solutions that do not zoom through the air or mark the skyline above rivers? In the medical industry, heat treating solutions are often unseen unless something goes wrong.

When it comes to medical implant and device heat treating, what options are available to manufacturers that will benefit patients? What should we know about the heat treating processes that make metal parts functional as knees, hips, and elbows? Find out in this expert analysis from Quintus Technologies and ECM USA, Inc.

This Technical Tuesday article was first published in Heat Treat Today's December 2022 Medical and Energy print edition.

Introduction

Dan McCurdy, former president at Bodycote, Automotive and General Industrial Heat Treatment for North America and Asia, knows full well just how much time, energy, and pain the right medical heat treating practice and alloy composition can save a patient. Dan’s wife suffered from complications due to a nickel allergy in a traditionally thermally-processed ASTM F75 knee implant. She dealt with constant inflammation, swelling, and pain. Physical therapy and a second procedure did nothing to ease the discomfort. The best medicine for Dan’s wife? A specially heat treated medical implant (more of Dan's story can be found at the end of this article).

To understand the stories behind final medical products, Heat Treat Today asked Quintus Technologies and ECM USA, Inc. to share two different approaches on medical implant and device heat treatment. These two companies at the forefront of the medical heat treating industry shared about hot isostatic pressing (HIP) with additive manufacturing, and vacuum heat treating. Read their answers to our questions and learn how, when it comes to implantable medical devices, heat treating can be the best medicine.

How do you ensure your equipment maintains the precise specifications required in the medical industry? What specifically is necessary to maintain compliance when it comes to medical implants?

Quintus Technologies

Quintus Technologies has observed a trend in bringing Nadcap to the medical industry. Historically the medical industry has focused on the standards and regulations for the quality management system of their approved supplier, but a consistent transition to technical aspects of critical processes (including HIPing) is becoming the norm. Quintus Technologies’ background is one of delivering HIP equipment in line with Nadcap and AMS2750 specifications. The medical industry requires best-in-class temperature uniformity and accuracy; systems designed with production driven flexibility (such as thermocouple quick-connectors for T/C sensor installation
to minimize downtime); HIP furnaces equipped with uniform rapid cooling (URC^®) for optimized cycle productivity; active involvement in standards committees; and working directly with the industry.

Requirements are increasing in terms of productivity and the introduction of more complex surface requirements. It is crucial to work closely with the industry to reduce oxidation of orthopedic implants during the HIP and heat treatment processes.

Steering of the HIP cycle is key, along with in-HIP heat treatments to achieve the desired microstructure for the application, which is a standard offering for High Pressure Heat Treatment™ (HPHT™) equipment.

ECM USA, Inc.

Some of the features that are most important are leak rate at deep vacuum along with a chamber and furnace design that does not contribute to any contamination. In our systems, these features, along with others, are of the utmost importance when supplying equipment for the medical implant market.

***What are the top 3–5 key* requirements or compliance/quality issues needed to heat treat medical *implants?***

Quintus Technologies

There are several industry standards that have been released to establish key requirements for the HIP process that are often leveraged for medical applications demanding performance and reliability. For example, Nadcap has released AC 7102/6 which details the audit criteria for HIP. This document was developed with significant input from the industry and the government to define operational requirements for quality assurance. It offers a checklist for the HIP processing of metal products and includes requirements for:

managing the equipment per pyrometry standard AMS2750
qualifying technical instructions and personnel training
handling product during the loading and unloading operations
complying with gas purity requirements of the pressure medium
controlling temperature, including uniformity and accuracy evaluations and management

These aspects are critical to ensure product quality meeting medical customer requirements and expectations. Recent additions beyond conventional requirements highlighted above include high speed cooling in the HIP process (>200 K/min) for some materials which is important for metallurgical results.

ECM USA, Inc.

Key requirements include thermal performance (both uniformity and ramp control); real-time vacuum and gas management; traceability and production lot follow up through human machine interface (HMI); quality procedures for all sensor calibrations; and remote access for control and troubleshooting.

Can you share an example of how your equipment could be used to heat treat a medical implant/device from start to finish?

Quintus Technologies

Many medical implants — whether fabricated using conventional processing techniques such as casting, or more novel approaches such as additive manufacturing — require HIP to eliminate process related material defects. Defects include shrinkage porosity for castings and lack-of-fusion and keyhole defects for fusion based additive manufacturing techniques. These defects can have a negative impact on product quality, impacting performance and reliability. Once HIP has been applied to a material, post processing is often not complete, with additional thermal treatments required to achieve the optimum microstructure leading to the desired material properties and performance. Such thermal treatments are material and process dependent, but could include a stress relief, solution anneal, rapid cooling or quenching, and aging and are often applied in separate heat treat equipment.

Hot Isostatic Press QIH 60 offering our most advanced Uniform Rapid Cooling (URC®) furnace technology with industry leading temperature control and accuracy

Quintus Technologies has introduced HIP systems providing capabilities beyond conventional densification. Decades’ worth of work in equipment design, system functionality, and control now offers an opportunity to perform HIP and heat treatment in a combined cycle, referred to as HPHT. Combined HIP and heat treatment for castings and AM implants can mitigate the risk of thermally induced porosity, as well as grain growth, which can offer advantages for mechanical and chemical properties in implants. This methodology provides a more sustainable processing route with improved productivity and energy efficiency. A joint HIP and heat treatment offers significant advantages with lead time, and this improvement in lead time couples well with the demands placed on the personalized medical implants. It also offers opportunities to further optimize microstructures for improvement in material properties coupled with ease of manufacturability. HPHT and modern HIP equipment may allow for a higher performing material system, which produces an implant with improved reliability and life.

Within the medical industry, fine grain AM microstructure, repeatability, and low porosity are key concerns. There are many reported benefits by applying the combined HPHT route such as reduced number of process steps, reduced cycle time and lead time, and improved process and quality control. Other advantages include spending less time at elevated temperatures helping to preserve the fine grain AM microstructure by minimizing grain growth. Tight control and steering of the cooling rates during the different steps of the HPHT cycle ensures repeatability of the properties. Manufacturability can be improved through HPHT as this approach reduces the cooling or quench severity during cooling segments which can often lead to part distortion or cracking. Improved functionality and
control go hand-in-hand with the high quality and reliability demanded in the medical industry.

ECM USA, Inc.

We have several customers making titanium alloy prothesis for various applications: shoulders, hips. Our furnaces are used for post printing processes, such as stress relieving and solution annealing.

Given concerns of metal poisoning, do you know of any changes in alloy composition of medical devices over the last decade?

Quintus Technologies

There are some metals that are becoming more common for implants, including tantalum, magnesium, CP Titanium, etc., and there have been major steps in improving ceramic materials to compete with metals for many applications.

ECM USA, Inc.

As a vacuum furnace equipment supplier, we are not deeply involved in the entire process of material selection. In the early stages of 3D printing joint replacements, from 2013 to 2014, we saw cobalt being part of some alloys. Lately it seems, indeed, that there is a trend in removing that element from the finished parts.

A Happy Ending

Dan McCurdy
Former president, Bodycote, Automotive and General Industrial Heat Treatment for North America and Asia

(The rest of Dan's story from the beginning of the article....) The effects of metal poisoning and metal allergies post-surgery can be
devastating. In the narrative below, Dan McCurdy shares the story of his wife’s struggle with an allergic reaction to a knee implant, and the heat treating solution that proved to be the best medicine for her.

My wife, an avid runner up and down the hills of Cincinnati, was diagnosed with osteoarthritis in both knees at the age of 53. Her orthopedist suggested a knee replacement for the most degraded one. The replacement was a well-known brand, made from investment-cast ASTM F75 (nominally a Co-Cr-Mo alloy) with full FDA-approval. After a successful surgery and diligent physical therapy, her recovery plateaued, and she experienced chronic inflammation, swelling, and pain.

A blood test, designed to detect allergies to materials used in orthopedic implants, showed a reaction to nickel that was nearly off the charts. We were surprised, as she had previously tested negative for nickel allergies through skin patch testing. The ASTM F75 specification allows for up to 0.5% bulk nickel as a tramp element in implantable devices; however, depending on foundry practices, the concentration of tramp alloys at any point on the surface of a casting can vary significantly. Titanium implants may be the solution to this, but FDA-approved titanium alloys can still contain up to 0.1% Ni.

The solution for my wife, as it turned out, was a different material, originally developed for the nuclear industry, along with an innovative heat treatment process. Created with an alloy of zirconium and niobium (with a maximum nickel content of 0.0035%), her new knee was heat treated at a high temperature in an oxidizing environment, which converts the soft zirconium surface into hard
ceramic zirconia, increasing hardness and wear resistance. With this specially heat treated implant in place, my wife is back to nearly 10K steps a day.

References

[1] Magnus Ahlfors and Chad Beamer. “Hot Isostatic Pressing for Orthopedic Implants.” quintustechnologies.com/knowledge-center/hot-isostatic-pressing-for-orthopedic-implants. Quintus Technologies. 2020.

[2] Chad Beamer and Derek Denlinger. “Hot Isostatic Pressing: A Seasoned Player with New Technologies in Heat Treatment — Expert Analysis.” www.heattreattoday.com/processes/hot-isostatic-pressing/hot-isostatic-pressing-technical-content/hot-isostatic-pressing-a-seasoned-player-with-new-technologies-in-heat-treatment-expert-analysis/. Heat Treat Today. 2020.

For more information

Contact Chad Beamer at chad.beamer@quintusstream.com

Contact Dennis Beauchesne at DennisBeauchesne@ECM-USA.COM

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

Heat Treating: The Best Medicine Read More »

Corrosion Behavior of DMLS Titanium Alloy for Orthopedic Applications

December 20, 2022 / FEATURED NEWS, HIPING TECHNICAL CONTENT, MEDICAL HEAT TREAT, MEDICAL HEAT TREAT TECHNICAL, SINTERING POWDER/METAL TECHNICAL CONTENT, TITANIUM PROCESSING TECHNICAL CONTENT

In this article, explore the importance of alternative advanced manufacturing processes and the effects of post-process heat treating of DMLS titanium alloy parts. In a recent study, a team at Worcester Polytechnic Institute (WPI) evaluated the effects of these processes. Read along to see what they found.

This Technical Tuesday article was first published in Heat Treat Today's December 2022 Medical and Energy print edition.

Jianyu Liang
Professor of
Mechanical and Materials Engineering
at Worchester Polytechnic Institute
Source: WPI

According to Markets and Markets reports, the metal implants and medical alloys market¹ will reach $17.64 billion by 2024, at a CAGR of 9.4%, with titanium metal implants and medical alloys accounting for the largest share of the market. Since it was first reported in the 1940s that titanium had excellent compatibility with human bones, titanium has been used in a wide range of biomedical applications, including arthroplasty and bone replacement, prostheses, craniofacial, maxillofacial, and dental implants, as well as surgical instruments and healthcare goods.^2,3

Although Ti-6Al-4V alloy was originally developed for aerospace applications, its many attractive properties — such as high strength-to-weight ratio, satisfactory biocompatibility, and good corrosion resistance — resulted in it being one of the most widely used biomedical alloys.⁴

However, Ti-6Al-4V alloy is very difficult to machine. Traditional Ti-6Al-4V manufacturing processes include casting, wrought (forging/milling from ingots), and powder metallurgy (P/M), with wrought products accounting for 70% of the titanium and titanium alloy market.⁵

In recent decades, additive manufacturing (AM) processes have been rigorously

Richard Sisson
Key Heat Treat
Researcher and Lecturer at Worchester
Polytechnic Institute
Source: WPI

developed as an alternative advanced manufacturing process for Ti-6Al-4V, especially in personalized biomedical applications. Alternate processes, including powder-bed fusion (PBF), directed energy deposition (DED), and sheet lamination (SL) have been applied in AM processing of titanium and its alloys.⁶ Direct metal laser sintering (DMLS), a PBF technology, was the first commercial rapid prototyping method to produce metal parts in a single process and is one of the most widely used AM technologies to manufacture Ti-6Al-4V parts.⁷ However, even with the protective oxide film (mainly TiO2), titanium alloys still suffer from pitting and crevice corrosion. Localized breakdown of the protective film leads to the formation of pits. These pits can grow and propagate into macroscopic cracks, which lead to catastrophic failure in orthopedic applications.^8,9

It was reported that post-heat treatment of Ti-6Al-4V parts fabricated by AM techniques could improve its mechanical properties, especially increasing ductility and fatigue strength.

Yangzi Xu
Yield & Module
Process Engineer at Intel Corporation
Source: WPI

However, the changes in corrosion behavior with various post-heat treatments of Ti-6Al- 4V parts fabricated by AM techniques have not been fully understood. In a recent study, a team at Worcester Polytechnic Institute (WPI) evaluated the effects of various post-process heat treatments (including solution treatment and aging, annealing, stress relief, and hot isostatic pressing (HIP)), on the corrosion behavior of Ti-6Al-4V parts manufactured by DMLS. The researchers then proposed a desirable posttreatment procedure that can obtain a good combination of mechanical properties and corrosion behavior of as-printed parts in a simulated body environment.^10,11,12

Ti-6Al-4V dumbbell-shaped tensile testing bars were fabricated by DMLS, according to ASTM standards. The microstructure, phase fraction, porosity, and residual stress of as-printed parts were examined and compared to those of the commercial Grade 5 alloy. It was found that the as-printed samples, mainly composed of acicular α’ martensite phase with a small amount of nano-scaled β precipitates, dispersed in the α’ matrix due to rapid cooling during laser processing, whereas the Grade 5 alloy has an α + β two phase with an equiaxed microstructure. The β phase fractions in the as-printed and Grade 5 alloy were 1.6% and 20%, respectively, based on the results of x-ray diffraction refinement. Furthermore, porosity and defects due to lack of fusion or entrapped gas were observed in the DMLS samples. The rapid cooling rate also resulted in residual tensile stress in the as-printed parts.

The microstructure and phase changes due to different heat-treatment processes were examined and compared to those of the commercial Grade 5 alloy. The corrosion behavior of the heat-treated DMLS parts was studied in simulated body fluid by well-established electrochemical methods.

Microstructure: coarsening of the α lath thickness, more spherical β precipitates.
Phase identification: narrowed α characteristic peaks (reduced compressive residual stress)
Source: WPI

Transformation from α’ to α phase, coarsening of the α lath microstructure, and the development of β phase were observed in samples after heat treatments. The greatest fraction of β phase was obtained in the high temperature annealed sample. Enhanced corrosion resistance was found in all heat-treated samples. The reasons for improved corrosion resistance after heat treatments include: 1) a passive layer that was developed on the sample surface after heat-treatments; 2) increased β phase fraction and size after heat treatments that led to the reduction of the corrosion susceptible sites. Furthermore, only a single passive layer has been observed in the as-printed sample, whereas double passive layers have been observed in samples after heat treatments at temperature higher than 550°C. However, this second layer, which was largely composed of Al2O3 and V2O5, had very low corrosion resistance compared to that of the primary passive layer that was primarily TiO2.

Microstructure: coarsening of the α lath, and grain boundary can be observed
Phase identification: narrowing of α characteristic peaks (reduced microstrain, increased grain size) and evolution of β phase
Source: WPI

It was also found that the surface roughness had an exponential effect on the corrosion current density and calculated corrosion rate. A rough surface led to a higher corrosion rate, but a rough surface is known to enhance osteointegration. Therefore, surface roughness needs to be adjusted, based on specific applications.

Microstructure: no significant change in the α lath thickness
Phase identification: narrowing of α characteristic peaks (reduced microstrain), evolution of β phase
Source: WPI

The effect of porosity was analyzed by using a crevice corrosion test. After a one-month immersion in Ringer’s solution at body temperature, pits were found on the Ti-6Al-4V sample surface near the pores in the as-printed samples, which was due to the formation of localized O2 concentration cells near the pore. Porosity in the as-printed parts was confirmed to impair crevice corrosion resistance. To reduce porosity, HIP was applied at three different temperatures. Based on polarization tests and electrochemical impedance spectroscopy tests, different degrees of reduction in porosity and corrosion-current density were observed in samples after HIP; this reduction was most significant after high-temperature HIP at 799°C (1470°F).

In summary, it was found that high temperature heat-treatment enhanced the corrosion resistance of DMLS Ti-6Al-4V parts. HIP was effective in reducing porosity and improving corrosion resistance. HIP below the annealing temperature (799°C, 1470°F) was recommended as a post-treatment for DMLSprintedTi-6Al-4V, to achieve a good corrosion resistance.

References

[1] “Metal Implants and Medical Alloys Market – Global Forecast to 2024,” 2019. https://www.marketsandmarkets.com/Market- Reports/metal-implant-medical-alloy-market-256117768.html.

[2] R. Bothe, et al., “Reaction of bone to multiple metallic implants.” Surgery, Gynecology and Obstetrics, 1940, 71:598–602.

[3] M. Sarraf, E. Rezvani Ghomi, S. Alipour, et al., “A state-of-the-art review of the fabrication and characteristics of titanium and its alloys for biomedical applications,” Bio-des. Manuf., 2022, 5, 371–395. https://doi.org/10.1007/s42242-021-00170-3.

[4] L.-C. Zhang and L.-Y. Chen, “A Review on Biomedical Titanium Alloys: Recent Progress and Prospect,” Adv. Eng. Mater., 2019, 21: 1801215. https://doi.org/10.1002/adem.201801215.

[5] L. E. Murr, S. A. Quinones, et al., “Microstructure and mechanical behavior of Ti–6Al–4V produced by rapid-layer manufacturing, for biomedical applications,” Journal of the mechanical behavior of biomedical materials, 2009, 2(1), 20-32. https://doi. org/10.1016/j.jmbbm.2008.05.004.

[6] A. Hung Dang Nguyen, A. K. Pramanik, Y. Basak, C. Dong, S. Prakash, S. Debnath, I. S. Shankar, Saurav Dixit Jawahir, and Budhi Dharam, “A critical review on additive manufacturing of Ti-6Al- 4V alloy: microstructure and mechanical properties,” Journal of Materials Research and Technology, 2022, 18: 4641-4661. https://doi.org/10.1016/j.jmrt.2022.04.055.

[7] “Direct Metal Laser Sintering (DMLS) Technology,” Additive News. https://additivenews.com/direct-metal-laser-sintering-dmlstechnology/.

[8] O. Cissé, O. Savadogo, M. Wu, and L’H Yahia, “Effect of surface treatment of NiTi alloy on its corrosion behavior in Hanks’ solution.” Journal of Biomedical Materials Research, 2002, 61/ 3 :
339-345. https://doi.org/10.1002/jbm.10114

[9] Sara A. Atwood, Eli W. Patten, Kevin J. Bozic, Lisa A. Pruitt, and Michael D. Ries,”Corrosion-induced fracture of a double-modular hip prosthesis,” The Journal of Bone & Joint Surgery, 2010, 92/ 6: 1522-1525.

[10] Y. Xu, Y. Lu, K.L. Sundberg, et al., “Eff ect of Annealing Treatments on the Microstructure, Mechanical Properties and Corrosion Behavior of Direct Metal Laser Sintered Ti-6Al-4V,” J. of Material Eng and Perform, 2017, 26: 2572–2582. https://doi.org/10.1007/ s11665-017-2710-y

[11] Ibid.

[12] Z. Yang, Y. Xu, R. D. Sisson, & J. Liang, “Factors Influencing the Corrosion Behavior of Direct Metal Laser Sintered Ti-6Al-4V for Biomedical Applications,” Journal of Materials Engineering and Performance, 2020, 29/6: 3831-3839.