Effects of TaC Addition on the Microstructure Transformation and High-Temperature Wear Resistance of Laser Cladding Ti₂AlNb Coatings

Ti₂AlNb-based coatings with different TaC additions (0, 1.25, 2.5 and 5 at%) were prepared on Ti-6Al-4 V alloy to improve its surface properties by laser cladding. The effects of TaC addition on the morphology, microstructure transformation and mechanical properties of the laser cladding TiC/Ti₂AlNb coatings were studied. The results showed that the TiC/Ti₂AlNb coatings mainly composed of matrix B2 phase, layered O phase and a small amount of TiC. In situ formed TiC effectively refined the microstructure of the coatings. When the TaC addition increased from 0 to 5 at%, with the amount of in situ formed TiC increased from 0 to 20%, the grain size of B2 decreased from ~ 400 μm to ~ 50 μm, and the grain size of O phase decreased from ~ 3 μm to ~ 1 μm. The microhardness and wear resistance of TiC/Ti₂AlNb based coatings improved when the TaC addition increased from 0 to 2.5 at%. The average microhardness for the sample with 2.5 at% TaC addition (602.18 HV_0.5) was 1.06 times that of the sample without TaC (568.36 HV_0.5), while the wear mass loss (16.28 mg) at 25 ℃ was only 43.4% that of the sample without TaC (37.50 mg). When the samples worn at 400 ℃ and 800 ℃ for 45 min, the wear mass losses of the sample with 2.5 at% TaC addition were only 15.13 mg and 13.50 mg, which were 50.9% and 51.5% these of the sample without TaC addition, respectively. The wear mass loss of sample with 5 at%TaC addition increased up to 16.04 mg and 16.4 mg, which means the large amount coarse TiC (dendrites) and the decrease of O phase fraction lowed the wear resistance of the TiC/Ti₂AlNb coatings, though it still less than that of the Ti₂AlNb coating (29.68 mg and 26.2 mg).