Heat Treat Today publishes eight print magazines a year and included in each is a letter from the publisher, Doug Glenn. This letter first appeared in Heat Treat Today'sDecember 2021 Medical and Energy print edition.
Doug Glenn Publisher and Founder Heat TreatToday
It’s December. Another year is mostly in the rearview mirror — unbelievable! Second only to COVID-19, America’s embattled supply chain has been top-of-mind for pretty much everyone in the North American heat treat industry. Just yesterday, a frantic heat treater called me asking where he could get a certain type of quench fluid necessary for aluminum processing. His go-to supplier ran out and he was in dire need of enough fluid to completely refill his rather large quench tank. It’s not good when the shelves are bare at the industrial grocery store.
The supply chain troubles will most likely not end soon. After shuttering the economy for nearly a year, we should not be surprised.
Nevertheless, as 2021 winds down, there is MUCH for which we should be thankful.
Thankful for Ancestors Who Fought to Defend Freedom
You’re reading this in December; I’m writing in mid-November, just prior to the oft-forgotten holiday of Thanksgiving. In fact, just yesterday was Veterans Day here in the United States and Remembrance Day in Canada — a time to remember and give thanks for the sacrifices made by men and women who fought to defend their and our freedom. When we stop and think about all the freedoms that we continue to have because of their sacrifice, we should be immensely thankful. Beyond being thankful, I hope many of us will be as brave as them and continue the fight to keep us free from internal and external enemies . . .of which there are many.
Most of the time, defending freedom doesn’t look like war or armed combat. Most of the time, it simply involves saying “no” to the little intrusions that well-intended civil authorities attempt to press on us. It’s not a popular position to hold in 21st century America, but our Founding Fathers, who had a much better sense of the latent evil in ALL men, had a healthy skepticism about those in authority. Get this… they understood that ALL men were sinners (evil by nature) and would tend to use any power granted to them for their own good and at the expense of others. I’m thankful for people who still think like our ancestors and are willing to sacrifice so much for our freedoms.
Thankful for Colleagues and Industry Friends
I’m also very thankful for colleagues and friends in the North American heat treat industry who make being in this industry so enjoyable. There are a lot of very good people in this industry. As I tell many newbies, “There are just a lot of very nice people in this industry. You’ll fit right in!” There are countless numbers of you who invest time and energy into helping others. One of my favorites is Mike Shay. Mike is no longer active in the industry, but for years, he worked for Hauck Manufacturing and was also a fully invested Scout leader. Mike spent untold hours helping young boys mature into thoughtful, freedom-loving men. Mike is just ONE example. There are MANY more.
Although supply chain issues will undoubtedly continue, the one supply chain that will never run dry is the supply chain of thankfulness. Thank you for being a Heat Treat Today reader. And thank you for the time you invest helping others enjoy their time in this great industry. Happy Thanksgiving, Merry Christmas, and Happy New Year! The Heat Treat Today team wishes (and prays) for a good and prosperous 2022 for each of you.
Direct thermal measurement of temperatures within a turbine is limited due to many factors. Some thermal sensing systems are not able to measure the lower end of the spectrum, while other systems are not able to measure the higher end. In this article, learn how Nanmac and Rhenium Alloys, Inc. worked together to discover a thermal sensing system in hydrogen atmospheres that solved these issues and more.
Today's Technical Tuesday was written by Herbert Dwyer, chief technical officer of Nanmac and president of Herb Dwyer & Associates, LLC., and Todd Leonhardt, metallurgist and director of Research & Development at Rhenium Alloys, Inc. This article was originally published in Heat TreatToday’s December 2021 Medical & Energy print edition.
Introduction
Todd Leonhardt
Metallurgist and Director of Research & Development
Rhenium Alloys, Inc.Herbert Dwyer
CTO, Nanmac
President, Herb Dwyer & Associates
Direct thermal measurement of temperatures within the turbine (both fixed and aviation) and on the test stand, has been limited to 2642°F (1450°C). This uses a precious metal thermocouple composed of platinum (Pt) and rhodium (Rh) which are very expensive and have limited life above 3182°F (1750°C).
The conditions within the turbine also limit the choice of direct measurement systems due to the combustion by-products, wind speeds, pressures, shear forces, vibration, and thermal shock.
The recent focus on “green energy” gases that are more friendly to the atmosphere and offer excellent energy density per volume of gas points to a gas that has been around for many years — hydrogen. However, the use of hydrogen as a combustion gas within the turbine can be challenging as well. Molecular hydrogen is generally smaller than molecular oxygen. The by-product of the combustion of hydrogen and oxygen forms water. Water vapor is more climate friendly than carbon monoxide, carbon dioxide, or other forms of carbon found in turbines using standard jet fuels, natural gas, or combinations. Another challenge is the wide variety of temperatures to be measured at various points within the turbine, from inlet air to combustion to outlet air, the range can be from -22°F (-30°C) or lower to a predicted high of 4172°F (2300°C). No one type of thermal measuring system exists today that covers this total range. With this as a baseline, Nanmac and Rhenium Alloys, Inc. worked together to explore various combinations of material systems that could operate at the lower temperatures, plus reaching the upper temperatures of 4172°F (2300°C).
The system that could cover this range was the Type C thermocouple with a 5% tungsten and 26% rhenium wire composition. One key part of the system is the insulator which separates the two legs of the thermocouple, the second key part is the refractory sheath like tantalum or molybdenum. The range of temperature covered by this combination was from about 662°F (350°C) to 4172°F (2300°C). The actual testing temperature was performed from 1292°F (700°C) to 3992°F (2200°C).
Application and Testing Objectives:
Fixed and aviation turbines (includes direct mount and test stands)
Test temperatures above the 2642°F (1450°C) range
100% hydrogen atmospheres
Thermal shock issues
Life issues at elevated temperatures and stress
High shear stress caused by air flow
Low and high frequency vibrations
Mounting options to accommodate space issues
Atmospheric corrosion caused by particulates in combustion gases
Cold junction transition location
Mounting depth
Objectives, Equipment, Assembly, and Test Times
Of concern, as atmospheres approach the ultra-high temperatures (UHT) region above 2642°F (1450°C), there are materials interactions between the components of the thermocouple (sheath, insulators, and thermocouple wires) and the furnace environment (representing the combustion section of the turbine) at elevated temperatures. Individually, the materials have high melting points, but combining these materials within the thermocouple system can cause low melting point eutectic to form a reaction between materials to occur. These material interactions can cause the thermocouple to fail prematurely in service at unexpectedly lower temperatures than predicted.
During Nanmac’s material compatibility testing, interactions between the sheath, insulators, and Type C thermocouple wire occurred. The weak link in the thermocouple system is the high temperature insulators of hafnia, alumina, and boron nitride. As the temperature approached the 3812°F (2100°C) test temperature, the insulators decomposed. Some of the observed failures appeared to be due to the hydrogen gas penetrating the end closure welds or even through the sheath walls; some of the insulators failed at these temperatures at much lower levels than expected. Some failure modes were caused by the insulator melting and attacking the thermocouple wires leading to fractures of the junction welds and the individual thermocouple wires.
Figure 1. The hafnia insulator failed above 3542°F (1950°C)
Photo Credit: Herb Dwyer & Associates, LLCFigure 2. 99 alumina failure above 3542°F (1950°C) during the transition to 3812°F (2100°C) 6 inches back from tip
Photo Credit: Herb Dwyer & Associates, LLC
Nanmac and Rhenium Alloys, Inc. used hydrogen cover gas because of access to a furnace which used that atmosphere. The use of hydrogen as a future combustion gas gave insight into how these material systems would operate in that harsh environment. The furnace also gave insight into the thermal shock issues from quenching the furnace with hydrogen gas for rapid cooling which allowed for a quick turnaround in testing. Additionally, the processes helped evaluate the possible impact of 100% hydrogen atmosphere on the insulator’s materials, wire junction welds, and sheath end closure weld. The furnace used for compatibility testing used a calibrated control system with a reference thermocouple and a calibrated optical pyrometer.
The test assemblies for compatibility testing were smaller lengths of typical thermocouple systems composed of the 0.050” walled molybdenum sheath. The insulators tested included: hafnia (HfO2); 99% alumina (Al2O3), and boron nitride (BN insulator and Type C 24 AWG [0.020]) thermocouple wire assembly, which was back filled with argon gas to prevent oxidation of the components. Test durations were one hour, two hours, and six hours, at elevated temperature and a complete post-mortem evaluation was performed on all test articles to evaluate compatibility of the thermocouple components at UHT.
Discussion:
The ASTM E20 Committee is exploring the possible increase in calibration temperatures from the existing 2642°F (1450°C) to 3182°F (1750°C) or higher. While it appears the individual materials can achieve these and even higher temperatures, tests indicate that this is not the case for all the combined thermocouple components.
Discussion of some of the material issues includes:
1. As atmospheres reach 3182°F (1750°C) and up to 4172°F (2300°C), materials are limited to refractory materials like:
Molybdenum, tantalum, platinum, and other alloys of these materials.
Ceramics like 99% alumina, zirconia, hafnia, boron nitride, silicon nitride (SiC), and others were tested.
Wire materials are limited to some alloys of tungsten (W) and rhenium (Re).
2. Combining these materials also lowers the system’s overall temperature. For example, the boron nitride, on its own, can reach temperatures up to 5252°F (2900°C), but when combined with the Type C wire and molybdenum sheath, it can only operate reliably to 3632°F (2000°C). Figures 1 and 2 are examples of failures of ceramic insulator exposed to high temperature service conditions.
NOTE: During lab analysis, at the various temperatures, it was observed that decomposition and significant degrading of the insulators had occurred. The exposure to the UHT not only attacked the ceramic insulators but also attacked the Type C wire and its sheath. Part two of this article will show some of the pictures of this attack and discuss some of the approaches to address this material issue at these UHTs, above the threshold of 3182°F (1750°C).
3. Cost now becomes a significant driver. Some of these materials, including alloys of platinum and rhodium can cost upwards of $2,000 or more per inch, are very hard to machine and form, and can contain hidden cracks and voids that under these extreme temperatures lead to reduced mechanical life.
4. The operating atmospheres have a significant impact on the alloys used, and high carbon loads from unburned fuel can also impact these refractory materials, for example:
Oxygen attacks molybdenum, tungsten, and even tantalum, although to a lesser extent than the attack on molybdenum.
Hydrogen’s small molecules can attack the insulator by penetrating the welds; the insulators exposed to this reducing gas oxidize, melt, and shrink causing potential grounding, secondary junction(s), and further mechanical failure.
Nitrogen becomes a significant factor when used above 1832°F (1000°C).
5. The operating environment is not friendly to the following:
The need to directly insert into the combustion gas flow chambers exposes the tip to very concentrated thermal and mechanical forces.
Space restrictions limit the wall thickness and lengths (to resist H2 penetration and handle the extreme heat, thicker walls and an OD of ¼ inch or higher are required).
A turbulent air flow at speeds up to 400 mph.
Air pressures to 500 psi or higher.
6. The shorter the thermocouple (TC) length, additional thermal transfer issues are exacerbated. For example, four inch or shorter lengths can adversely impact any brazed joints from the TC to extension wire [(the temperature in this area where the tip may be at 3632°F (2000°C)], can be 1832°F (1000°C) or higher. Braze joints fail at much lower temperatures.
The transition at this point may also have insulation issues since it may be difficult to control the addition of an acceptable insulator in the transition area. The potential of secondary junctions is quite high (any significant mechanical movement (expansion and contraction) can cause high stress and weak insulators.
A technique using swaging has been somewhat successful but requires materials that can be swaged, limiting options to very expensive alternatives today. Some mineral insulated (MI) cables may be acceptable but need more testing.
The cold reference junction may be unacceptably close to the high temperature (1832°F or 1000°C), thus requiring a relocation further away from this point, requiring possibly a unique analog to digital converter (A/D) like those used in cars. This has not yet been fully developed at this point.
Nanmac is working on a method to carry the TC wire further into the test stand or turbine. This will address the transition issue, enable the use of existing A/Ds, and offer potential integration into the turbine engine itself.
By using this method (see d, above) on the test stand, it is possible to economically investigate this method, maintain safe operations, and make it useable once the system issues are resolved at the test stand.
The Type C was chosen for this temperature requirement (4172°F or 2300°C)
Other than the Type D or A (both of which are in very limited supply and are basically of the same alloy construction), the Type C is well known and characterized, can operate up to 4172°F (2300°C), and has some significant history of use in this temperature realm [the tungsten (W)/Rhenium (Re) alloys are used regularly in high temperature metallurgical furnaces and even within the turbines].
Type C is recognized by ASTM and NIST, its accuracy is 1%, and by comparison calibration Type C has been shown to be capable to about 0.5%, not the 0.25% of the Type S or R, but at a cost of 75% or less and its life, at elevated temperatures, is good and predictable.
Type C has existing MI cable matching extension wire.
Type C has existing A/D systems; thus, it is easier to integrate.
Type C has existing connectors, color coded wire, and terminal connections.
Can other ceramics reach 4000°F (2204° C)? Can these ultra-high temperature systems be built commercially? To find out the answers to these questions, don’t miss the second part of this article in March’s (2022) Aerospace Heat Treating magazine and learn about the results, conclusions, and next steps.
About the Authors:
Herbert Dwyer is the CTO of Nanmac, and president of Herb Dwyer & Associates, LLC. Herb specializes in international business development, electromechanical manufacturing, heat treating furnace optimization, and thermal measurements up to 4172 °F. Herb has over 50 years of experience in the field of thermal and pressure sensors for the aerospace industry.
Todd Leonhardt, a metallurgist and director of R&D at Rhenium Alloys, Inc., possesses an in-depth knowledge of high temperature refractory metal and is an expert in rhenium. As a 38-year veteran of industrial and government research in the areas of material characterization and processing refractory metals, Todd has shared his knowledge in over 25 publications including NASA technical memorandum, peer review journal articles, and conference proceedings.
Hazelett Strip-Casting Corporation of Colchester, VT in the US has become a member of a global heat treat furnace solution provider headquartered in Leonding, Austria. This happened via an acquisition of a majority interest in Hazelett.
Hazelett technology is used in metal manufacturing processes worldwide to cast aluminum, copper, zinc, and lead into metal strip and bar used to create a variety of products. The company has been involved in the design and manufacture of continuous casting machines for the global metal industries for over 100 years. Similarly, the acquiring group, EBNER Group, has been involved in the design and manufacture of thermal processing furnaces for over 70 years. Both have been family-owned throughout their histories and this merger preserves that legacy.
Mino S.p.A, based in Alessandria, Italy will remain a shareholder, and David Hazelett will also remain as both a shareholder and president. "As family-owned businesses," Hazelett commented, "Hazelett and EBNER have the freedom to take a longer view; one that encourages investment in research and development, building long-term relationships, and preserving our environment.”
Hazelett plant Photo Credit: EBNER
EBNER Industrieofenbau is a global company and market leader in heat treatment facilities for the semi-finished metal products industry. EBNER specializes in the research, development, fabrication, installation and commissioning of heat treatment facilities for the ferrous and non-ferrous industries using the most environmentally friendly and energy efficient technologies.
Welcome to Heat TreatToday’s This Week in Heat TreatSocial Media. As you know, there is so much content available on the web that it’s next to impossible to sift through all of the articles and posts that flood our inboxes and notifications on a daily basis. So, Heat TreatToday is here to bring you the latest in compelling, inspiring, and entertaining heat treat news from the different social media venues that you’ve just got to see and read!
We’re looking at the holiday posts, origami metal, and dad jokes about aluminum this week. Check it out!
“This technique uses lasers to apply highly localized heat treatment to temper-rolled stainless steel. It focuses on softening areas where material will need to bend. Robots then form the temper-rolled sheets into complex 3D shapes. The final forming hardens the structure in order to regain the original flat sheet’s strength.” (Thomas.net)
Click the image to watch or read about the heat treatment
2. Fascinating Heat Treat Comments and Discussions
I didn’t know social media could foster such in-depth content and comments! Have you seen these posts/shares from across social media?
3Din30: The Scary Truth About Heat Treatment Innovation
.
Hyundai Heat Treat Case Study
.
Nitriding Layers, from Pro Microstructure Photographer
3. And What Did You Do for New Year’s?
We saw a lot of you hard-working heat treaters posting on LinkedIn and Twitter during the break. Tsk tsk. Take the break! But we get it: we’re excited for 2022 with you, too!
4. What to Read
Want to have a heavier read for the weekend? Well okay. . .
An Overview of Heat Treatment in the Refining, Power, and Petrochemical Industry – Part 2: The Importance of Heat Treatment to Mechanical Integrity.
.
Heat Treat Radio Special Videos
Did you watch the videos or just listen to these two podcasts? There is something different about when you watch something versus just listening. Sometimes, one is better than the other! Other times, you’re scratching your head waiting for the transcript to load. . .
Take a look at these two widely shared podcasts from 2021.
Heat Treat Tomorrow – Hydrogen Combustion: Our Future or Hot Air?: Click to –>Watch | Listen | Learn
The Future of Heat Treat, a Conversation with Piotr Zawistowski: Click to –>Watch | Listen | Learn
.
“Industry 4.0 Implementation for Small and Medium-Sized Shops”
Over the past year, we’ve seen numerous new technologies in the way of research, new partnerships, and conversations throughout the industry. So in honor of today being #NationalTechnologyDay, we’re sharing an original content article about just several of these new technologies that are changing the work of heat treaters across North America.
Research
Using HIP to Advance Oregon Manufacturing Innovation Center Programming– “‘Today’s globally competitive manufacturing industry demands rapid innovations in advanced manufacturing technologies to produce complex, high-performance products at low cost,’ observes Dr. Mostafa Saber, associate professor of Manufacturing & Mechanical Engineering Technology at Oregon Tech.”
College Students Implement a NEW Heat Treat Solution with Induction? – “‘We were in shock,’ Dennis admitted, ‘because we didn’t expect it to [work].’ The expectation, Dennis continued, was that something would go wrong, like the lid would not be able to clamp down, or the container would leak.”
The Age of Robotics with Penna Flame Industries – “The computerized robotic surface hardening systems have revolutionized the surface hardening industry. These advanced robots, coupled with programmable index tables, provide an automation system that helps decrease production time while maintaining the highest quality in precision surface hardening.”
Heat Treat Radio: Five experts (plus Doug Glenn) discuss hydrogen combustion in this episode. An easily digestible excerpt of the transcript circulated by Furnaces Internationalhere and is available to watch/listen/read in full for free here.
Heat Treat Radio: Get on-the-ground projections of what technologies Piotr Zawistowski believes will be bringing in the future. Watch/listen/read in full here
Heat Treat Radio: HIP. The Revolution of Manufacturing, that is, according to Cliff Orcutt. Watch/listen/read in full here
Heat Treat Radio: Will indentation plastometry find its way into North America? If you’ve been listening to James Dean, it seems like it already has. Watch/listen/read in full here
Heat Treat Radio: Fluxless inert atmosphere induction brazing. That’s a mouthful! But what is it? Watch/listen/read in full here
A retrofitted vacuum furnace will now produce more metal injected molded (MIM) components with considerably less downtime.
In 2021, a North American heat treater, Solar Atmospheres of Western PA, retrofitted a vacuum furnace for use in a new metal injection molding (MIM) and additive manufacturing (AM) binder removal technology application. The goal was to build a vacuum sintering furnace with a new innovative hot zone and pumping technology that would minimize and target the deposit of detrimental binders evaporating out of MIM and AM parts.
Robert (Bob) Hill, FASM President Solar Atmospheres of Western PA
The hot zone, after a month of repeated 2400°F sintering cycles, remains clean. The problematic binders coalesced at the targeted area within a separate heated pumping port while keeping the primary pump and booster uncontaminated. Most importantly, the client reported that their sintered parts processed in this new furnace never looked better. The MIM parts were extremely bright and met their critical density and dimensional requirements.
The heat treater anticipates considerable maintenance savings on this dedicated furnace versus processing sintering and AM work with binders in a traditional vacuum furnace. Working in a traditional furnace meant added labor and material costs coupled with the lost production time and degradation on the life of the hot zone, which cost the company more than $180,000 per year. The projected maintenance costs on this newly designed sintering furnace will be $10,000 per year.
"Knowing the effects," reported Bob Hill, president of Solar Atmospheres of Western PA, "of what MIM and certain AM processing had done to our equipment in the past, Bill Jones and the engineers at Solar Manufacturing developed an innovative solution for us. Having this newly designed vacuum furnace will be an asset for our future in MIM and AM processing."
This Technical Tuesday column appeared in Heat Treat Today’s December 2021 Medical and Energyprint edition.
Introduction
Dan Herring
"The Heat Treat Doctor"
The HERRING GROUP, Inc.
Medical devices (e.g., dental, and orthopedic implants, instruments) employ literally hundreds of different types of fasteners to hold their assemblies together. Even though the components in the medical devices are small or even tiny, when a fastener fails, the device will almost always fail as well.
Medical devices fall into two broad categories: surgical/non-implant devices and implantable devices. The alloys and heat treatments for the fasteners involved in both are explained below.
Surgical & Non-Implant Medical Devices
Surgical and dental instruments are examples of non-implant medical devices typically manufactured from austenitic stainless steels where good corrosion resistance and moderate strength are required. Examples include: canulae, dental impression trays, guide pins, hollowware, hypodermic needles, steam sterilizers, storage cabinets, work surfaces, and thoracic retractors, to name a few. These applications often use a variety of stainless steels that can be easily formed into complex shapes. (The heat treatment of stainless steels was covered in Heat Treatment of Fasteners for the Petrochemical Industry, Fastener Technology International, October 2013.)
Specific grades of austenitic stainless steel and high-nitrogen austenitic stainless steels are used for some surgical implants. Examples include: aneurysm clips, bone plates and screws, femoral fixation devices, intramedullary nails and pins, and joints for ankles, elbows, fingers, knees, hips, shoulders, and wrists.
However, the vast majority of orthopedic implants worldwide are manufactured from titanium (e.g., Ti-6Al-4V alloy) or cobalt-based alloys (e.g., ASTM F75, a cobalt-based alloy or cobalt-chromium-molybdenum alloys). They are manufactured from castings, forgings, or bar stock.
Medical application examples include pins, bone plates, screws, bars, rods, wires, posts, expandable rib cages, spinal fusion cages, finger and toe replacements, hip, and knee replacements, and maxillofacial prosthetics.
Figure 3. Dental implant posts
Photo Credit: Dentist in Goa via Flickr
Other Uses for Titanium Alloys
Titanium and its alloys have experienced rapid growth in the industrial (38%), commercial aerospace (29%), and military aerospace (23%) segments. The benefits of titanium include its strength, strength-to-weight ratio, corrosion resistance, non-toxicity, biocompatibility, excellent fatigue and fracture resistance, non-magnetic characteristics, life, cost, flexibility, and elasticity that rival that of human bone.
Non-medical applications include:
Manned and unmanned aircraft (e.g., commercial and military aircraft, rotorcraft)
Artillery (e.g., howitzers)
Military vehicles (e.g., tanks, hovercraft)
Naval and marine applications (e.g., surface vessels, submarines)
Turbines (e.g., power generation)
Chemical processing plants (e.g., petrochemical, oil platforms)
The heat treatment of titanium and titanium alloys is complex and demands an understanding of the end-use application, desired microstructure, and process variables.
Types of Titanium Alloys
Titanium alloys are classified in four main groups based on the types and amounts of alloying elements they contain:
Alpha (α) alloys — cannot be strengthened by heat treatment; low-to-medium strength, good notch toughness, and good creep resistance (superior to beta alloys) at somewhat elevated temperatures; formable and weldable
Near alpha phase alloys — medium strength and good creep resistance
Alpha-beta (α - β) alloys — strengthened by heat treatment; medium-to-high strength, high formability, good creep resistance (but less than most alpha alloys), alloys with beta content less than 20% are weldable; most familiar alloy in this category is Ti-6Al-4V
Beta (β) alloys — strengthened by heat treatment, high strength, and fair creep resistance
Figure 5. Load of bone reamers after heat treatment
Photo Credit: Solar Atmospheres, Inc.Figure 6. HIP repair screw after heat treatment
Photo Credit: Midwest Thermal-Vac
Standard heat treatments are typically done in vacuum style furnaces or in inert (argon) atmosphere furnaces and include:
Annealing — increases fracture toughness and ductility (at room temperature) as well as dimensional stability and improved creep resistance. Annealing may be necessary following severe cold work and to enhance fabrication and machining.
Homogenizing — for improved chemical homogeneity in castings.
Solution Treating and Age Hardening (Aging) — a process of heating into the beta or high into the alpha-beta region, quenching, and then reheating again to the alpha-beta region. A wide range of strength levels is possible, fatigue strength increases while ductility, fracture toughness, and creep resistance are enhanced.
Stress Relief — used to reduce residual stresses during fabrication or following severe forming or welding to avoid cracking or distortion and to improve fatigue resistance. Strength and ductility will not be adversely affected and cooling rate is not critical.
Tempering — When titanium is quenched from an elevated temperature, reheated to a temperature below the beta transus, held for a length of time and again quenched, it is said to have been tempered. Three variables exist in tempering: the phases present, the time held, and the tempering temperature.
Figure 4. Load of knee implants after heat treatment
Photo Credit: Solar Atmospheres, Inc.Figure 7. Typical vacuum furnace
Photo Credit: Solar Atmospheres, Inc.
Custom heat treatments include:
Beta Vacuum Annealing and Vacuum Aging — improves fatigue and yield strength as well as elongation in alloys such as Ti-5553 (Ti-5Al-5V-5Mo-3Cr).
Brazing — induction, resistance, and furnace brazing in an argon atmosphere or in vacuum; torch brazing is not applicable. Cleanliness is important to avoid contamination.
Creep Forming — takes advantage of the fact that titanium moves and takes a set-at temperature.
Degassing — involves removing of entrapped gases such as hydrogen (to under < 50 ppm) to avoid embrittlement.
Diffusion bonding — primarily in powder metallurgy where individual particles fuse together from intimate contact of their surfaces.
Hydriding/Dehydriding — the deliberate addition of hydrogen to embrittle the material followed by the removal of the hydrogen after crushing the material into powder. These are the basic steps in the production of titanium powders.
Isothermal Transformation — involves quenching an alloy from the all beta region into the alpha-beta field, holding, and then continuing to quench to room temperature. Treatment in this way causes precipitation of the alpha phase from the beta.
Sintering — typically involving hot isostatic pressing and laser sintering of powder particles to form near net share components
Practical Considerations — What’s Important
The heat treatment of titanium and titanium alloys is most often done in a vacuum furnace (Figure 7). Heat treat furnace capacity is an important consideration since many titanium parts are volume-limited rather than weight-limited. Load support is a critical issue in many applications to prevent creep or other dimensional changes, especially on intricate or complex part geometries typical in a medical fastener.
Temperature measurement and control must be exact, usually ± 10 °F (5.5°C) or better throughout the entire working zone of the furnace. Work thermocouples are needed; part temperature, not just the furnace temperature, must be known. Caution: when heating parts over 1730°F (943°C), titanium cannot be in contact with a nickel alloy or stainless steels since eutectic melting will occur.
Vacuum pumping systems must be capable of reaching high vacuum levels, 1 x 10-5 Torr or lower before starting to heat. This vacuum level must be maintained while heating (requiring very slow ramp rates) as well as when at temperature. Diffusion pumping systems must be properly maintained for maximum efficiency and to avoid backstreaming.
Since titanium is a strong getter material, vacuum furnace interiors must be pristine; ideally, all metal hot zones and dedicated furnaces are desired, but graphite lined furnaces also used for other processes are typical throughout the industry as a practical necessity. Thus, fixtures and furnaces must be “baked out” (cleaned) before use typically at 2400°F (1315°C).
In Conclusion
Fasteners are at the heart of the medical device industry and heat treatment plays a critical role in the manufacturing process. Whether made of stainless steel, titanium, tungsten carbide, or superalloys, a heat treat recipe is available to maximize both mechanical and metallurgical properties for implantable and non-implantable applications.
References
[1.] Jones, Christie L., Fastening Solutions for Medical Devices, White Paper, SPIROL International Corporation.
[2.] Herring, Daniel H., Practical Aspects Related to the Heat Treatment of Titanium and Titanium Alloys, Industrial Heating, February 2007.
Dan Herring, who is most well known as The Heat Treat Doctor®, has been in the industry for over 45 years. He spent the first 25 years in heat treating prior to launching The HERRING GROUP, Inc. in 1995. His vast experience in the field includes materials science, engineering, metallurgy, equipment design, process and application specialist, and new product research. Dan holds a patent (as a co-inventor), and his consulting services in heat treating and sintering, metallurgy, operations, business management, sales and marketing, and technology have benefitted a broad range of industries.
To jump start your heat treat knowledge this year, read this list of 22 ways you can connect with industry leaders, access new technology, review old and trusted practices, and so much more. We hope this original content article is helpful to you as you return from a much needed break!
We will be celebrating the holidays with family, so look for your next Heat Treat Dailyon January 3rd.
2021 has been a transformative year! Because we love people and 2021 saw the return of in-person, face-to-face events, seeing you in and around the trade show halls has been our #1 memory from 2021! What a joy to see and talk with so many of you.
In 2022, we’re looking forward to keeping you well informed by sharing relevant and compelling technical content, industry news, and innovative trends in the North American heat treat industry.
We are thankful for you and here’s our year-end prayer for you and yours, “May you experience the peace and hope that only Christ can give. Wishing you the joy of the Lord as we celebrate the birth of the Savior.”
Welcome to Heat Treat Today's This Week in Heat TreatSocial Media: The Christmas Edition. With so much content available on the web, especially during Christmas, it’s next to impossible to sift through all of the articles and posts that flood our inboxes and notifications on a daily basis. So before you head off to celebrate with friends and family, Heat Treat Today is sharing some great Christmas-themed heat treat news from the different social media outlets!
"Tinsel, the thin sparkling strands we drape over Christmas trees, first appeared in Germany around 1610 and was originally thin strips of material extruded from real silver. According to WiseGeek.com, silver looked good but tarnished quickly and was soon replaced by other sparkly metals. Tinsel was first placed on Christmas trees to accentuate the glow of lit candles, and only the wealthiest people could afford entire garlands.
"Advances in manufacturing eventually resulted in cheaper aluminum-based tinsel, and by the early 20th century most consumers could afford tinsel garlands, as well as individual pieces of tinsel known as icicles. By the 1950s, the use of tinsel garlands and icicles nearly overshadowed the use of Christmas lights." (Thomasnet.com)
2. Christmas Chatter
Chestnuts roasting on an open fire? Sounds like a safety hazard. Check out what people are chatting about this holiday season.
3. Light Up the Night
What do you get when you mix candles with combustion?
Heat Treat Today publishes eight print magazines a year and included in each is a letter from the publisher, Doug Glenn. This letter first appeared in Heat Treat Today's December 2021 Medical and Energy print edition.
