Rheological behavior and processability assessment of Cu–Al–Ni shape memory alloy feedstocks for powder injection molding

Cu–Al–Ni shape memory alloys (SMAs) have been produced by casting and conventional powder metallurgy, but their fabrication by powder injection molding (PIM) has not yet been established. This study explores PIM for Cu–Al–Ni SMAs by developing feedstocks with suitable rheological behavior for defect-free green-part formation. The critical powder volume concentration (CPVC) of an 84Cu–12Al–4Ni (wt.%) powder mixture was determined as 69.7 vol.%, and feedstocks containing 64, 66, and 68 vol.% powder were prepared. All feedstocks exhibited pseudoplastic behavior. Differences in the flow behavior index among the formulations were temperature dependent. The 64 vol.% feedstock exhibited the lowest flow activation energy (11.00 kJ/mol). At 190 °C, it also showed the lowest instability index (0.025) and Casson apparent yield stress (24.96 kPa), together with the highest moldability index (8.4696 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>×</mml:mo> </mml:math> 10 −6 Pa −1 s −1 K −1 ). Accordingly, the 64 vol.% feedstock was identified as the most favorable rheology-based candidate, while the 68 vol.% feedstock showed a narrower processing window because of its proximity to the CPVC. Preliminary injection molding of the 64 vol.% feedstock produced green parts without visible molding defects. Semi-quantitative spatial analysis of the exported EDS maps identified Al as the element with the greatest regional signal variation in both the initial powder mixture and the injected green part. The feedstock and green-part densities were 4.73 and 4.67 g/cm 3 , respectively.