Exploring the potential of refractory metals in additive manufacturing

frederic larouche
Market studies project exponential growth over the coming years for refractory metals in additive manufacturing, especially for use in high-performance aerospace and military applications, and the nuclear energy sector. 

Despite many beneficial properties, they have typically been a challenge to work with over the years. Until now. Plasma atomization offers a stable and cost-efficient way to create high-quality refractory metal powders to create complex shapes and parts. 

We spoke with Fréderic Larouche, CTO at AP&C, a GE Additive company, to find out more.

What are refractory metals?
Refractory metals are a specialty class of metals and metal alloys that are characterized by having a high melting point, high density, and high hardness. Because they are hard, they tend to be brittle and in the past that has made them difficult to shape and work with. 

The standard industry definition of a refractory metal stated for long that they to have a melting point above 2,000°C, which includes niobium, tantalum, molybdenum, rhenium and tungsten, and their alloys. However, over time, other metals such as zirconium and hafnium - which also have a melting point between 1,800 and 2,000 °C - were added to the classification.

What is the potential for refractory metals in additive?
Refractory metals make excellent wear-resistant coatings, and today they can be found in use in conventionally manufactured drill bits used in the mining industry. They also exhibit good mechanical properties and their unique high temperature capabilities which is what makes them so well-suited to additive manufacturing. 

Refractory metals in additive manufacturing in several areas raise such as 3D lead-free products for collimators and anti-scatter grids for CT scanners, SPECT and gamma cameras. They also show strong potential for the production of a number of aircraft and rocket parts, as well as medical implants and instruments.

Our customers are particularly interested in tantalum and niobium. Niobium is perhaps the most interesting for the aerospace industry because of its lower weight and density.

Is it difficult to produce spherical refractory metal powder?
It’s not all that difficult to produce a refractory metal powder by crushing techniques. However, it starts to become more challenging if you want the particles to be high purity, spherical and the right size for use in additive manufacturing. 

Historically, spherical powders have been manufactured by gas atomization - a process where a metal is melted in a crucible and then poured towards a high-pressure cold gas atomization nozzle to be transformed into a fine spherical powder.

The high melting point of refractory metals prevents the efficient use of a crucible and this has limited the production of refractory metals powders. 

Why is plasma atomization well-suited to the production of refractory metal powders?
Plasma atomization has now emerged as an effective solution for producing the highly spherical and high purity powders and is fast becoming the preferred method of obtaining spherical refractory metal powder. This technique allows for the efficient atomization of high temperature refractory metals. 

AP&C’s unique process converts a wire into a powder with a high purity, high sphericity and outstanding flowability. A preheated wire enables the heating of the metal to be efficient at high temperatures. As the wire area is small in comparison with a large pool of liquid metal, the radiation heat loss is significantly reduced, and the energy efficiency increased. 

The use of the rapid hot plasma at more than 3,500 °C converts the metal into the very fine particles that are required for additive manufacturing. By comparison, traditional gas atomization techniques always have a large volume, so they unavoidably lose a lot of heat during the process.

And the overall outlook?
Companies shouldn’t let the lack of available additive materials today prevent them from moving into additive. AP&C already offers a custom atomization service to produce refractory metal powders and has experience in producing niobium, tantalum, and molybdenum powders. 

Now we have mastered the process we plan to provide niobium alloy C-103TM (90%Nb-10%Hf) as a standard product towards the end of next year.

Our plasma atomization technology can produce a refractory metal powder that is suitable for use with additive manufacturing processes at a competitive cost. 

If you’d like to find out more, please get in touch