Mechanical properties of hot isostatically pressed nanograin iron and ironalloy powders

Hot isostatic pressing (hipping) was performed on a variety of iron and iro n alloy powders produced by attrition ball milling. Microhardness and compr ession tests were used to determine the mechanical properties. Fracture mor phology was studied by scanning electron microscopy. For each specific allo y, 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 powde r processed in argon (Fe [Ar]) reached a maximum density at 580 degreesC, a n identically processed iron carbon alloy (Fe-2C [N]) reached its maximum d ensity above 850 degreesC. Two types of compression strain-stress curves we re obtained: up to a certain temperature, most powders showed an increase i n compression yield stress with temperature. Hipping above this point cause s a decrease in the compression yield stress, and an increase in elongation . This behaviour is entirely different than that of a stainless steel powde r (Fe-18Cr-8Ni), which shows substantial work hardening for hipping tempera tures ranging between 965 and 1050 degreesC.