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 similar to 400 mu m to similar to 50 mu m, and the grain size of O phase decreased from similar to 3 mu m to similar to 1 mu m. 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 HV0.5) was 1.06 times that of the sample without TaC (568.36 HV0.5), while the wear mass loss (16.28 mg) at 25 degree celsius was only 43.4% that of the sample without TaC (37.50 mg). When the samples worn at 400 degree celsius and 800 degree celsius 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).