Investigation of Ti3AlC2 formation mechanism through diffusional reaction between carbon and Mo-modified Ti6Al4V

Abstract

Carbon and Mo-coated Ti6Al4V alloy diffusion couple was used to investigate Mo-modified diffusion reaction between carbon and Ti6Al4V. Randomly dispersed carbide particles were observed in Ti6Al4V alloy after 900℃ exposure. Carbide particles were found evolving from defective TiCx (x<1) to mixture of TiCx and defective Ti3AlC2. Although Mo atoms were hardly detected in particles, their dilution effect along Ti alloy grain boundary (GB) is beneficial to carbon diffusion and carbide formation along GB. Based on high-resolution TEM (HRTEM) imaging, high density stacking faults (SFs) and nanotwins were observed in TiCx particles which explain Raman activation of defects in TiC. Formation of SFs and nanotwins in TiCx is attributed to carbon vacancies, which inversely promotes incoherent twin boundary (ITB) formation. Transformation from TiCx to Ti3AlC2 is considered driven by Al indiffusion along ITBs. Intergrowth of TiCx in defective Ti3AlC2 is the compromise to low Al concentration in Ti6Al4V.