By Chaman Lall, Ph.D., MPP Vice President – Technology & Applications Development
Powder Metallurgy (P/M) parts are being used in increasingly demanding applications and environments which mandate optimum performance from the materials. A potent P/M approach is through the utilization of high temperature sintering. In this review, both the science base and its application to P/M parts production are considered i.e. the fundamentals and thermodynamic principles for high temperature sintering, with specific examples for stainless steels and soft magnetic alloys. In ferrous-base materials, sintering well above the traditional 2050°F (1121°C) temperature minimizes the absorption of N2 and, hence, the subsequent formation of nitrates during cooling. High temperature sintering also promotes the deoxidation/reduction of oxides that inhibit metal to metal bonding of the powder particles. In addition, the dramatic changes in diffusion rate with increasing temperature result in significant increases in the rate of grain growth, the homogenization of alloys, and the attainment of a spheroidal pore morphology. Marked improvements in the corrosion resistance of stainless steels and in the performance of soft magnetic alloys result from high temperature sintering.