Determining the particle size distribution of metal powders
Wet and dry dispersion on the Mastersizer 3000
If we look at some of the most interesting and inspiring innovations in modern engineering, Additive Manufacturing (AM), in my opinion, has to be up there with the best. For metallic products, increased design freedom, ever more complex designs and much smaller amounts of raw material consumption are just some of the major selling points when compared to more traditional metal machining techniques. Bicycle frames, golf clubs and intricate vehicle parts are just some of the multitude of products that we can come across in everyday life that are now being manufactured using AM.
Why is particle size in Additive Manufacturing key?
The most common raw materials used in Metal AM processes are metal powders, for which there are often strict specifications for both physical and chemical properties, especially for medical and aerospace applications. The particle size in the powders is a very important factor here since packing density needs to be maximised – think of trying to achieve the maximum packing density between different sized balls in a box.
The flowability and compressibility of the powder are also directly affected and optimized by the particle size ratio. Along with packing density, all three characteristics are essential in powder bed fusion (PBF) AM processes. They ensure uniformity and must be optimized to create a product that is free from defects such as pores, cracks, inclusions, residual stresses and unwanted surface roughness. Knowledge of the particle size distribution and how it impacts the inherent properties of powdered metal, and ultimately the final product, is therefore vital for ensuring that the powder is suitable for an application. This is where Malvern Panalytcal’s Mastersizer 3000 (MS3000) can help.
Particle sizing by Laser Diffraction
The Mastersizer 3000 measures particle size through the technique of Laser Diffraction. A sample of particulate material scatters incoming light at different angles depending on the sizes of the particles involved. So by measuring the angular variation in intensity of the scattered light it is possible to determine the particle size distribution of that sample.
Our most recent application note “Determining the particle size distribution of metal powders using wet and dry dispersion on the Mastersizer 3000” details how we can use laser diffraction and the Mastersizer 3000 to measure the particle size distributions of metal powders for AM and other powder metallurgy processes, and why it is such an important and versatile quality control tool.
The full picture: Morphology, structure and elemental composition
Particle size distribution is key for powder bed additive manufacturing and is one of the key specifications for both powder producers and end-users alike, as any deviations can adversely affect the build process and integrity of the built part. However, particle size in only one part of the puzzle with particle morphology, including particle shape and surface roughness, also important factors. These factors influence the flowability and packing of the powders, with smooth spherical particles often preferred. We look at this in more detail in our other recent application note “Characterising the particle size and shape of metal powders for additive layer manufacturing”.
Furthermore, we also need to assess whether the selected metal powders have the desired elemental composition, since powders need to comply with the alloy composition of the material specified. The microstructure of finished products is also important to ensure that the built parts have the desired phase composition, texture and are free from residual stress. These are areas where Malvern Panalytical’s X-ray fluorescence (XRF) and X-ray diffraction (XRD) technologies find common use, and you can take a look at how they are applied to powdered metals and processes in one of our previous webinars.
And, if you enjoyed this blog, make sure to read our other AM stories which we’ve listed for your convenience in this blog: A look back at this year’s best additive manufacturing blogs.