Characteristics of Al–Cr–Zr alloy powders made by confined nozzle atomisation

The effects of superheat and powder particle size fraction on the characteristics of Al–5Cr–2Zr (wt-%) alloy confined nozzle atomised powder particulate has been investigated. The median powder particle size decreased from 62 to 38 μm with increase in superheat from 140 to 300 K for the atomising conditions studied, with a broadening of the size distribution and the increasing presence of large irregular powder particles at the lowest superheats. Essentially featureless α-Al based microstructures in splat caps and small sized powder particles were replaced by cellular α-Al with increasing amounts and sizes of primary L1₂Al₃Zr and Al₁₃Cr₂ inclusions with increasing powder particle size. Refinement of the α-Al cell and intermetallic inclusion sizes in a fine compared with a coarse powder size fraction was consistent with the expected powder relationship between these variables. The decreased microhardness for coarser powder particle size fractions was attributed to the formation of increasingly coarse distributions of the primary aluminides at the expense of retention of Zr and Cr in extended solid solution. A notable age hardening response after 1h at 350–450°C for the 25–50 μm powder size fraction was consistent, however, with retention of 0·5–1·0 wt-%Zr in solid solution in this fine size fraction of the powder.

MST/3163