Mechanical properties of hot isostatically pressed nanograin iron and iron alloy powders

Hot isostalic pressing (hipping) was performed on a variety of iron and iron alloy powders produced by attrition ball milling. Microhardness and compression tests were used to determine the mechanical properties. Fracture morphology was studied by scanning electron microscopy. For each specific alloy, increasing the hipping temperature causes an increase in density up to a maximum. Hipping at still higher temperatures improves the bonding without any change in density. The minimum temperature required for obtaining the maximum density depends on the initial powder composition. While iron powder processed in argon (Fe [Ar]) reached a maximum density at 580degree C, an identically processed iron carbon alloy (Fe-2C [N]) reached its maximum densityabove 850degree C. Two types of compression strain-stress curves were obtained: up to a certain temperature, most powders showed an increase in compression yield stress with temperature. Hipping above this point causes a decrease in the compression yield stress, and an increase in elongation. This behaviour is entirely different than that of a stainless steel powder (Fe-18Cr-8Ni), which shows substantial work hardening for hipping temperatures ranging between 965 and 1050degreeC.