Growth kinetics of ceramic grains during liquid phase sintering in Mo2FeB2-based cermets

Abstract

Mo2FeB2-based cermets with different hard phases were fabricated by reaction boronizing sintering. SEM, EDS, and TEM were utilized to evaluate the growth kinetics of Mo2FeB2 hard-phase grains with different morphologies during liquid phase sintering. During the sintering stages of L1 and L2, the growth of elongated grains along the long-axis conformed to the cubic law. Combined with the observed rough interface between the hard and binder phases, the growth mechanism along the long-axis could be identified as diffusion-controlled since atoms did not have to overcome large energy barriers to nucleate. Meanwhile, the grain growth along the short-axis was primarily accomplished via 2-D nucleation on the smooth interface, which was mainly controlled by interface reaction during the liquid phase sintering since the driving force in the short-axis direction failed to meet the requirements of critical driving force (∆Gc). In addition, the principal control mechanism of nearly equiaxed grains growing in L1 and L2 was identical to the long-axis direction of elongated grains. Nevertheless, the third phase (Fe23B6) at the interface of nearly equiaxed grains affected grain growth, resulting in variations in grain size and growth activation energy during the L1 and L2 sintering stages.