Fabrication of a novel multi-sized and layered (Tix,Nb1−x)C surface-reinforced layer on TiNb alloy

The multi-sized and layered (Tix,Nb1−x)C surface-reinforced layer (MLRL) was fabricated on the surface of the high temperature TiNb alloy via an in situ solid-phase diffusion reaction. The MLRL is formed by the diffusion of carbon atoms that diffuse from gray cast iron into the TiNb alloy. During the diffusion reaction, the MLRL is gradually formed in situ on the surface of the TiNb alloy. Thus, there is a good bonding interface between the MLRL and the substrate. Scanning electron microscope (SEM) analysis indicates that the MLRL is composed of three layers; the outer layer is micro-nano carbide particles, the middle layer is multi-sized carbide particles, and the inner layer is gradient micro-nano carbide particles. EDS results indicate that the different particles have different ratios of Ti/(Ti + Nb). The XRD results indicate that the MLRL is mainly composed of (Tix,Nb1−x)C particles; the diffraction peaks are located at 2θ positions between the corresponding peaks of TiC and NbC. Nanoindention test results show that the hardness of the MLRL obviously increases (compared to that of TiC or NbC); the highest micro-hardness of the MLRL is nearly 2366 HV0.05. Benefited from the solid-solution strengthening, the multi-sized and layered structures, the relationship between the strength and toughness of MLRL can be improved. Meanwhile the high hardness and volume fraction of (Tix,Nb1−x)C will obviously enhance the wear resistance of the reinforced layer.