Mechanism of Grain Growth at Sintering Stage of Fe-44.4%Mo-4.9%B-2.5%Cr-2.9%Ni-Based Cermets
Mo2FeB2-based cermets,synthesized from Mo,Fe,Cr,Ni,FeB,and C via a reaction boronizing sintering technique,are characterized by their exceptional hardness,strength,and toughness,coupled with comparatively economical production costs.This study delved into the fabrication of Fe-44.4%Mo-4.9%B-2.5%Cr-2.9%Ni-based cermets utilizing a vacuum liquid phase sintering method and meticulously examined the morphological evolution,growth processes,and underlying mechanisms of the cermet's hard phase at both solid and liquid phase sintering stages.The results reveal that below 600℃,Fe amalgamates with lamellar FeB,initiating the formation of the Fe2B phase and marking the onset of solid-phase sintering.As the temperature ascends to 900 ℃,Mo commences nucleation at the Fe2B interface,leading to the formation of Mo2FeB2 characterized by spiral growth patterns and the emergence of growth steps.Further temperature elevation to 1 000℃ propels the enlargement of Mo2FeB2 grains,surpassing critical radii and instigates the precipitation of diminutive Mo2FeB2 grains.At 1 050 ℃,ongoing dissolution and precipitation processes result in the development of Mo2FeB2 grains with hexagonal cross-sections.Throughout this thermal trajectory,Mo2FeB2 grain growth traverses through four stages:nucleation,spiral growth,dissolution-precipitation,and the eventual establishment of hexagonal cross-sectional grains,culminating in the formation of hexagonal Mo2FeB2 grains derived from Mo,FeB,and Fe2B phases.Beyond 1 050℃,the cermets transition into the liquid phase sintering stage,characterized by columnar growth of the Mo2FeB2 hard phase.The growth activation energies determined for the long and short axes of the grains are 317 kJ/mol and 402 kJ/mol,respectively,suggesting a pronounced propensity for Mo2FeB2 grains to elongate along their long axis,ultimately yielding elongated grain structures.
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