The investigation on the fabrication and microstructure of NbTi-(NbTi)C Fe-based composite

Abstract

NbTi-(NbTi)C Fe-based composites are fabricated by in-situ diffusion reaction. The locally reinforced (NbTi)C cermet layer formed by carrying out the reaction of C + β-NbTi → (NbTi)C, which resulted in the formation of the core-annular shell structure with a ductile core (NbTi) and high hardness annular shell (cermet layer). The (NbTi)C cermet layer is composed of two zones, where ZoneⅠ, near the GCI, is composed of micron and sub-micron-sized particles; and ZoneⅡ, near the remnant β-NbTi, is composed of sub-micron-sized particles. The detailed microstructural, elemental and morphological analysis has been carried out to unveil the phase distribution and microstructural changes in the (NbTi)C cermet layer. The results reveal that the cermet layer consists of (NbTi)C particles with different Ti/(Ti + Nb) ratios, ranging from 0.6308 to 0.8330, which have different morphology: the fusiform particles and near spherical or cubic particles. Moreover, the nanoindentation results of (NbTi)C layer indicate that the maximum hardness and elastic modulus is 31.43 GPa and 473.11 GPa, respectively. It is worth mention that the remnant β-NbTi and α-Fe phases, surrounding the (NbTi)C cermet layer, render high plasticity. Therefore, the combination of β-NbTi, α-Fe and (NbTi)C phases can effectively improve the hardness and plasticity of as-prepared composites.