Optimisation of powder metallurgy technology of 17-4 PH material

The density, compressive strength, and microstructure analyses of gas-atomised 17-4 PH samples produced by the press and sinter method (PSM) were investigated to evaluate the effects of various factors, including cold pressing, sintering time, and conventional sintering temperature. A challenge that arose from using 17-4 PH powder was that it produced PSM parts with significantly low density due to its extremely high hardness. The evaluation procedures included Archimedes' density method, regression analysis, microstructure observation analyses (optical, SEM, and EDS), X-ray diffraction, Vickers hardness measurements, and compression strength measurements. Despite employing a low sintering temperature of 1200 °C, the work highlighted that increasing the cold pressing and sintering time aimed to improve the sinter density to approximately 98 %. A linear regression model aligned with the actual results concerning the effect of sintering time on relative sinter density, while a polynomial regression model was developed to describe the relationship between sintering temperature and relative sinter density. Compared with the reported literature, this work achieved improvements in relative sinter density (5 %), Vickers hardness (40 %), and compressive yield strength (10 %), respectively. The low sintering temperature minimised volume shrinkage. The 7 h of sintering resulted in smoother grain boundaries compared to those of 2 h. Future research can utilise the extensive investigation data to develop a mathematical model for predicting the density of PSM 17-4 PH materials.