PHASE AND STRUCTURE CHANGES DURING THE SINTERING OF COMPACTS OF HIGH-SPEED STEELS OBTAINED FROM POWDERS WITH VARIOUS RATES OF SOLIDIFICATION

摘要

An investigation was made of the phase and structure transformations in compacts of high-speed steel R6M5F3 powder fractions -630+50 #mu#m at the temperatures of solid-phase (1160-1220 deg C) and liquid-phase (1240 deg C) sintering. The structure of the compacts was crystalline or quasicrystalline depending on the degree of superheating and cooling rate of the melt during powder spraying. This was related to the presence of a cellular structure in particles of a critical size in the powder. Compacts of powder with the cellular structure experienced higher shrinkage during solid-phase sintering as a result of structure relaxation and recrystallization. The driving force of these processes is the change in chemical potential arising from the decomposition of highly supersaturated metastable solid solutions, and the excess grain-boundary energy of the quasicrystalline matrix structure.