Andrew Cassese

High Pressure Prepares Parts for Space

/ AEROSPACE HEAT TREAT, AEROSPACE HEAT TREAT TECHNICAL CONTENT, FEATURED NEWS, HIPING TECHNICAL CONTENT

Dive into the role and benefits of HIP and HPHT™ in the space industry, highlighting how these key processes are shaping the future of space applications.

This Technical Tuesday article by Andrew Cassese, applications engineer, Quintus Technologies was originally published in Heat Treat Today’s March/April 2024 Aerospace print edition.

The realm of space exploration and technology is rapidly evolving, pushing the boundaries of what’s possible in engineering and material science. Among the key players in this revolutionary change are hot isostatic pressing (HIP) and High Pressure Heat Treatment™ (HPHT™). These processes have become indispensable in manufacturing components that can withstand the harsh conditions of space. In this demanding environment, the longevity and reliability of components are paramount.

Reducing Risk

Space missions have put increasing focus on the need to minimize risk and improve mission safety. Some well-documented, safety-related events include:

  • Outer space
    • Soyuz 11 decompression in 1971
  • Earth’s atmosphere
    • Soyuz 1 parachute failure in 1967
    • X-15 controls failure in 1967
    • Space Shuttle Challenger launch
      booster failure in 1986
    • Space Shuttle Columbia re-entry
      disaster in 2003

Structural integrity is therefore in focus for every single component involved in space missions, with exacting demands on quality and function. Material failure is not an option, and therefore component qualification is one of the main areas of focus. Predictable properties that are reliable and with minimal variation are critical for mission safety. Hot isostatic pressing helps to guarantee this by reducing the spread and variation in mechanical properties.1 It works to do this by using high temperatures and pressures to close internal defects in mission critical parts after casting or additive manufacturing. This increases the density of components and gives them a more anisotropic microstructure which in turn results in more consistent mechanical properties.2

What Properties Are Most Important

The harsh environment of space demands components with exceptional properties. They must withstand extreme temperatures, resist radiation, endure vacuum pressures, and cope with mechanical stress from vibrations and accelerations. HIP processing plays a pivotal role in this, enhancing material properties to meet these challenges. Space manufacturers also must think about thermal expansion/contraction due to temperature variations, compressive stresses, irradiation, and space debris. All of these can affect mission success and can ultimately prevent loss of life, see Figure 1.

Figure 1. Challenges that space-bound materials must endure

Through HIP, components gain increased fatigue life, improved ductility, and enhanced fracture toughness, which are crucial for surviving in space.

Common Materials and HIP Processing Requirements

Materials commonly processed by HIP for space applications include titanium, aluminum alloys, nickel-based superalloys, refractory alloys, shape memory alloys, and ceramics. High-strength aluminum and titanium alloys are used due to their high strength to weight ratio which is key for space missions to conserve fuel efficiency, increase payload capacity, and improve maneuverability.3 Nickel-based superalloys are used in exhaust valves and turbine rotors due to their exceptional creep resistance properties at high temperatures. Refractory alloys like Nb-C103 and TZM are used in high-performance rocket nozzles because of their high melting point and excellent strength at high temperatures. Newer shape memory alloys developed by NASA can recuperate their original shape when heating above specific critical temperatures, and their applications are expanding beyond just actuators.4

As new alloys and materials are developed in the space industry, certifications and standards are necessary for their adoption. HIP effectively eliminates porosity in these materials, ensuring structural integrity and performance under the extreme conditions of space. This means HIP recipes need to be developed and optimized for materials to be tested with their greatest potential in mind.

Challenges in Processing Space Components

Processing components for space via HIP is not without its challenges. Th e extreme conditions required for HIP, including high temperatures and pressures, demand robust and sophisticated equipment. Quintus Technologies applications centers utilize a graphite furnace capable of heating to 3632°F (2000°C), while maintaining pressures of 30,000 psi (200 MPa). The process requires precise control to ensure uniformity of properties across the component. Specifically, the graphite uniform rapid cooling© (URC©) furnace can maintain temperature uniformity while controlling to a specified cooling rate.

Another challenge with processing space components in HIP can be oxidation of parts in the HIP furnace atmosphere. Niobium, for example, can suffer from substantial oxidation at elevated temperatures. In practice, tantalum foil is typically used to wrap the niobium components during HIP and to prevent oxidation from any residual moisture in the argon atmosphere. New products, like the Quintus Purus©, can reduce the amount of oxidation seen on parts aft er HIP while saving valuable time and resources by not having to wrap parts with getter materials like stainless steel, titanium, or tantalum.

Ongoing Research and Unknowns

Collaborations with universities and national labs on projects at low TRLs will help set the foundation for HIP in the space industry. Quintus Technologies, through its application centers, is actively engaged in research to further enhance the capabilities of HIP for space applications. Optimizing the HIP process to reduce costs and improve efficiency through HPHT is one area where the company has already found success, see Figures 2 and 3.

Figure 2. Typical thermal processes for additively manufactured parts
Figure 3. High pressure heat treatment with solution heat treatment (SHT) process for the same parts, using an integrated heat treatment approach

The HPHT process can combine stress relief, solution annealing, HIP, and aging into one cycle. Aft er a ramp up in pressure and temperature, the part is held for a specified amount of time before being rapidly cooled in the URC furnace. Aft er this, the temperature of the machine can be brought up to the aging temperature of the material for the completion of an in situ heat treatment.

A Space Case – Launcher Engine-2 Rocket Engine

Table 1. CuCrZr vs. GRCop-42: A Comparison

One application of this is on the Launcher Engine-2 (E-2) rocket engine.

Quintus Technologies, EOS Group, and Launcher worked together to develop a tailored HPHT cycle for Launcher’s 3D printed E-2, first vetted out in an applications center at small scale. The powder alloy in question, CuCrZr, was developed by EOS and printed on an AMCM M4K machine. EOS compared CuCrZr to the NASA alloy of GRCop-42 and found that the CuCrZr alloy was a more economically viable solution for thermal applications with lower strength requirements, see Table 1. The rapid cooling at 200°C/min in the QIH 122 URC furnace at Aalberts surface technologies allowed the team to HIP and solution heat treat the CuCrZr combustion chamber in a single step. The aging treatment was also performed in the QIH 122 directly aft er the solution.5

In October 2020, a full-scale test firing of the E-2 injector and combustion chamber was conducted at the Launcher NASA Stennis Space Center test stand. On April 21, 2022, Launcher’s E-2 liquid rocket engine was able to demonstrate full thrust. Continued tests from Launcher have been successful with performance boost testing
and the first fully integrated engine was ready for shipping on October 12, 2023.6

Figure 4. Aalberts QIH-122 MURC in Greenville, SC (Source: Aalberts Surface Technologies)

Conclusion

As humanity reaches further into the cosmos, the role of HIP and HPHT in manufacturing space-bound components becomes increasingly significant. These processes not only enhance the essential properties of materials for space applications but also address the unique challenges of manufacturing for an environment as hostile as space. With ongoing research and development, HIP and HPHT continue to evolve, promising to unlock new possibilities in space exploration and technology, and their contribution will ensure the success of space missions, safeguarding the lives of those who venture into the final frontier.

Figure 5. Test firing of the High Pressure Heat Treated Launcher Engine 2 produced using additive manufacturing

References

[1] Dominik Ahlers and Thomas Tröster, “Performance Parameters and HIP Routes for Additively Manufactured Titanium Alloy Ti6Al4V. EuroPM,” 2019. https://www.semanticscholar.org/paper/Performance-Parameters-and-HIP-Routes-fortitanium-
Ahlers-Tr%C3%B6ster/faeb46e6eb8ef3e30bc00b91cd1bd8a7c0619200.
[2] Jake T. Benzing et al., “Enhanced strength of additively manufactured Inconel 718 by means of a simplified heat treatment strategy,” Journal of Materials Processing Technology 322, (December 2023). https://www.sciencedirect.com/science/article/abs/pii/S0924013623003424?via%3Dihub.
[3] “Engineering Materials for Space Building Stronger Lighter Structures,” Utilities One, last modified November 2023. https://utilitiesone.com/engineering-materials-for-space-building-stronger-lighter-structures.
[4] Girolamo Costanza and Maria Elisa Tata, “Shape Memory Alloys for Aerospace, Recent Developments, and New Applications: A Short Review,” Materials (Basel) 13, no. 8 (April 2020): 1856. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7216214/.
[5] Mahemaa Rajasekar, “Processing Copper Alloys with Powder Bed Fusion,” LinkedIn, last modified November 2022. https://www.linkedin.com/pulse/processing-copper-alloys-dmls-technology-mahemaarajasekaran/.
[6] LAUNCHER (@launcher), “The first fully integrated E-2 engine is ready for shipping to @NASAStennis for our upcoming full engine test campaign later this year. E-2 is a 22,000 lb. (10 ft) thrust LOX/Kerosene,” X post, October 12, 2023. https://twitter.com/launcher/status/1712636548997607752.

About the Author

Andrew Cassese, Applications Engineer, Quintus
Technologies

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

For more information: Read J Shipley, “Hot Isostatic Pressing in Space – Essential Technology to Ensure Mission Safety,” 2020. Contact Andrew at andrew.cassese@quintusteam.com.

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HIP Innovation Maximizes AM Medical Potential

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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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