Why AM Has Stricter Powder Requirements
Metal AM processes, SLM, EBM, DED, binder jetting, demand much tighter powder specifications than traditional powder metallurgy. The powder must flow uniformly across a build plate or through a deposition nozzle, fuse predictably under a laser or electron beam, and produce dense parts free of porosity and defects.
Particle Size Distribution
Typical PSD ranges: 15–45 µm for laser powder bed fusion (LPBF), 45–105 µm for electron beam melting (EBM), 20–60 µm for cold spray. These ranges are not mesh classifications, they are measured by laser diffraction (Malvern, etc.) and reported as D10/D50/D90 values.
Morphology and Flowability
Gas-atomised spherical powders dominate AM applications. High sphericity gives excellent flowability, uniform powder bed packing, and predictable melting behaviour. Hall flow rate per ASTM B213 is typically 12–20 s/50g for AM-grade powders.
Oxygen and Surface Chemistry
Surface oxide layers compromise weld pool stability. AM-grade powders typically specify O content <500 ppm, with critical alloys (Ti-6-4, IN718) at <200 ppm. Handling under argon or vacuum is standard.
Satellites and Hollow Particles
Gas atomisation is not perfect. Fine particles that collide with larger droplets still molten weld onto them as satellites, and entrapped atomising gas can leave hollow particles behind. Satellites blunt flowability by roughening an otherwise smooth sphere. Hollow particles are worse: the trapped gas is released in the melt pool and reports as porosity in the finished part. Neither is visible in a PSD figure, which is why sphericity and internal quality are assessed separately.
Powder Reuse and Degradation
AM powder is recovered and re-run, and it does not come back unchanged. Each cycle exposes powder to elevated temperature and oxygen, raising surface oxide and gradually shifting the PSD as fines are consumed preferentially. Reused powder typically flows differently from virgin powder and can drift out of specification without any single lot ever failing. Sieve between builds, blend to a documented ratio, and track cycles.
Packing Density and Layer Uniformity
A recoater spreads a layer tens of microns thick. If packing density varies across the plate, so does the amount of metal available to melt, and part density varies with it. High sphericity and a controlled distribution give consistent packing; a broad or bimodal distribution does not. This is why a nominally in-range powder can still build inconsistently.
Qualifying a Powder Lot
Qualification means more than chemistry. Ask for PSD by laser diffraction with D10/D50/D90 reported, flow rate per ASTM B213, apparent and tap density, oxygen content, and morphology assessment. A certificate that lists chemistry alone tells you nothing about whether the powder will spread.