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H.C. Starck aiming high with refractory metals

Kip Hanson
By Kip Hanson Contributing Editor, SME Media

A conversation with Faith Oehlerking, R&D engineer for additive Manufacturing at H.C. Starck Solutions

Faith Oehlerking, R&D engineer for additive manufacturing, H.C. Starck Solutions

Faith, why are the refractory metals—tantalum (Ta), molybdenum (Mo), tungsten (W), niobium (Nb), and rhenium (Re)—important?

They are a class of metallic materials that offer superior heat resistance and melting points greater than 2,200 °C (3992 °F). They can have high corrosion resistance, high density and retain superior mechanical strength at high temperatures. These features make refractory metals the materials of choice for many challenging applications facing the most demanding environments. But, unfortunately, these great properties get in the way of manufacturing complex components efficiently and cost-effectively in traditional manufacturing, which limits adoption of refractory metals and possibly why many people know little about them.

Many machinists can attest to the extreme difficulty of milling and turning these materials. How is it to 3D print them?

Because these metals are difficult to manufacture and machine traditionally, my company, H.C. Starck, has dedicated R&D efforts into AM in order to streamline manufacturing, reduce material waste and add design complexity of refractory metals. Niobium and tantalum are all fairly ductile and easy to weld so they are good materials for laser powder bed fusion (L-PBF), and these elements and some of their alloys can be printed with high resolution and over 99.9 percent dense using this technique. Tungsten and molybdenum, on the other hand, are extremely brittle in the as-printed state and can crack easily if L-PBF technology is used. We are looking into various approaches to improve the printability of these metals, which includes alloying them with more workable elements, as well as using alternative AM techniques that consolidate the refractory powder using a binder and then sintering to full density. Using the binder/sinter strategy is similar to traditional press and sinter techniques that we use for W and Mo, so we have historical knowledge to help adopt this technique.

Do you have a favorite refractory metal?

My favorite refractory metal to print with is tantalum. It’s an extremely rare metal with very high density (2× that of steel), a high melting point 2996°C (5425°F), good mechanical strength at elevated temperatures, and is easily printable by L-PBF. Tantalum is also described as having a “lustrous blue-grey finish” and looks similar to platinum, which adds a luxurious feel. It is not every day that someone gets to work on such a unique material, and it can be applied in many different industries, including space/aerospace, medical, electronics and industrial, so I see so many potential applications for it in AM.

You’ve been named to the Women in 3D Printing (Wi3DP) organization. What advice would you give to women considering a career in manufacturing?

The AM/3D printing industry is unique because it is relatively new, so we have the opportunity to make it inclusive and collaborative from the start. I highly encourage any younger person, not just women, to get involved with Wi3DP: There many opportunities for mentorship, career development and networking with industry leaders that I don’t think you can find anywhere else. Events include regional happy hours, career fairs, mentorship cohorts, technical webinars and conferences. Make sure to follow the organization on LinkedIn or join their newsletter for updates!

You earned a bachelor’s degree in Metallurgical and Materials Engineering from the Colorado School of Mines. Why did you pursue a career in metals?

I knew I wanted to major in materials engineering because I always found it so practical. By changing a material on a microscale [the structure of its atoms] you can see the drastic effects it has on the macroscale [physical, mechanical, electrical, magnetic properties]. There are constant developments of new materials or new manufacturing techniques to make materials, too, so I always found the field to be exciting and innovative. I was attracted to the Colorado School of Mines due to their prestigious material engineering department, but it also didn’t hurt that Mines is right by the Rocky Mountains, making hiking and skiing after class extremely accessible. The smaller size was also a benefit as it let me get to know my professors on a personal level—one of whom recommended me for my first full-time job with AM. Having that background in metallurgical and materials engineering was the perfect foundation for my current career, and it helped me realize the potential of how disruptive metal AM will be going forward.

Eliana Fu of TRUMPF North America called you “an absolute badass AM engineer and 3D printing enthusiast!” That’s high praise from someone with her credentials. How did it make you feel?

That was quite an honor! Eliana is such a force within AM, and I’m privileged to know her through Wi3DP. She is so knowledgeable when it comes to metal AM and the space industry, so I always learn something new when I speak with her. In addition to her technical prowess, I really admire how Eliana is always willing to help others and give advice, no matter what title she holds. Seeing women like Eliana in leadership roles is motivating for me and my own career, and I am so glad that there are women making their voices heard in manufacturing and supporting others along the way.

This “Resistojet” nozzle segment was 3D printed from refractory metal as part of the UK Space Agency’s Project STAR (Super-High Temperature Additively-manufactured Resistojets) (Provided by H.C. Starck Solutions)

As you and others increase the mastery of 3D printing refractory metals, where do you see the biggest growth opportunities outside of aerospace, and why?

Other than aerospace, the two main areas where I see adoption of refractory metal AM is in the medical and industrial sectors.

For medical applications, specific Ta, W, and Mo alloys are known to have high biocompatibility and could be 3D printed to form porous structures that enhance bone osteointegration, tailor mechanical properties, and reduce overall part mass. Products could include orthopedic, dental and spinal implants, cardiovascular stents, and markers for radiation imaging. Tungsten and tungsten alloys are also used to produce collimators and anti-scatter grids for CT scanners, SPECT, and gamma cameras due to their high density and radiation shielding properties. We have successfully printed these structures using 3D Screen Printing technology, a process that enables us to print very small feature sizes with tight tolerances.

Refractory metals also offer very good thermal and corrosion resistant properties and can survive in extremely harsh environments. This is great for industrial applications as very complex heat exchangers and furnace parts that are exposed to corrosive fluids or high temperatures can now be manufactured efficiently with AM. In fact, H.C. Starck Solutions has demonstrated that AM can dramatically improve the performance of tantalum heat exchangers by as much as 20×.

You interned at SpaceX after college. What did you learn there, and how did it guide your future career steps?

Working there was such an amazing opportunity! I saw firsthand how private space companies like SpaceX are revolutionizing manufacturing to make functional and reusable rockets in record speed. It taught me to question every step of the manufacturing process and to challenge “the traditional way.” SpaceX’s fast-paced work culture made the job thrilling since they weren’t restricted by as many rules and regulations as government-owned space companies are, and it really felt like you were making a difference toward a larger mission. Working there opened my eyes to how exciting manufacturing can be and encouraged me to search for roles that have a focus on innovation and new technology.

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