Go with the Flow – Spheroidisation for Additive Manufacturing

Generating a component by 3D metal printing, metal Additive Manufacturing (AM), relies on building the final design through a series of many thousands of layers. To achieve good flow and high packing density Additive Manufacturing metal powders should be highly spherical with no satellites.

Whilst different metal powders can be selected according to the required performance of the final part, reproducible behaviour of the powder throughout the process is key to successful builds.

Plasma spheroidisation

LPW’s Plasma spheroidisation process improves the performance of low sphericity, irregular, angular, metal powders produced by methods such as water atomisation, chemical and mechanical routes and standard gas-atomised methods.

The effect of the optimisation process on morphology, flow and packing properties of metal powders can be seen in a recent case study, showcasing three different metal powders – pure tungsten, Ti6Al4V, and pure tantalum. The results are highlighted in the morphology of the powders shown before and after plasma treatment.

Results

As Dr Lampros Kourtis, LPW R&D Project Engineer, commented, “The results show that the morphology, flow, and packing properties are significantly improved by our carefully optimised plasma treatment, regardless of the original shape, melting point, and original powder manufacturing route.”

A typical example of the improved morphology and resulting flow characteristics is seen for one of the most commonly used Ti-based alloys: Ti6Al4V Grade 23. The powder feedstock was produced by mechanically crushing “embrittled” Ti64 ingots via a Hydride-De-Hydride (HDH) process. The shape of the powder feedstock as received is angular and elongated which leads to a flow rate which is relatively slow for the particle size. This irregular shape also contributes to the tap density value which is 50% lower than the theoretical bulk density for this material.

After controlled plasma treatment, the shape is almost perfectly spherical for the majority of the powder particles and the flow rate is less than half that of the starting material.

  Before Plasma Treatment After Plasma treatment
Product Ti6Al4V starting material(HDH and mechanically crushed) Ti6Al4V spherical
Particle Size, µm 45-105 µm 45-105 µm
Hall Flow rate, sec/g 47.31 22.3
App. Density, g/cc N/A 2.6
Tap Density, g/cc 2.2 3.0
Shape analysis Circularity: D10: 0.556, D50: 0.774, D90: 0.937
Elongation: D10: 0.083, D50: 0.260, D90: 0.428
Circularity: D10: 0.81, D50: 0.989, D90: 0.995
Elongation: D10: 0.008, D50: 0.044, D90: 0.366
Morphology SEM – x1000 mag  morphology-1  morphology-2

 

Too hot to handle?

Tungsten, with a melting point of 3695 K, has the highest melting point of all metals in its pure form, but with plasma temperatures operating above 5000 K the spheroidisation process can also be applied to refractory metals. The Tungsten metal powder feedstock, produced by reducing Tungsten Oxides, is angular but after spheroidisation it also becomes spherical, measuring significant improvements in flow and packing parameters.

Tailored powder performance

Plasma Spheroidisation is a versatile and effective method for improving a wide range of elemental and alloy powders, making them suitable for reliable metal AM, 3D printing applications.

LPW, with its wealth of Additive Manufacturing expertise, working within aerospace, biomedical, and automotive industries, has developed a suite of Plasma Spheroidisation parameters to produce highly spherical powder products with improved flow and packing density. We continue to use this expertise to deliver specific powder requirements across a broad range of industries for all AM platforms.