Effect of TiC on microstructures and mechanical behaviors of low-density Nb-Ti-Al alloys fabricated by laser solid forming

Ultra-high temperature Nb alloys are prospective for practical applications as aircraft materials. Sufficient efforts must be made to improve their manufacturing technologies and properties. The Nb-Ti-Al alloys with TiC addition were fabricated by laser solid forming (LSF) in this work. LSFed Nb-Ti-Al-TiC alloys which were composed of Nbss and (Nb,Ti)C had excellent formability and metallurgical quality. There were columnar and equiaxed Nbss grains in Nb-37Ti-10Al-3TiC and Nb-37Ti-10Al-5TiC while there were entire equiaxed Nbss grains in Nb-37Ti-10Al-8TiC. Expectant columnar-to-equiaxed transition was realized by the addition of TiC. Moreover, the grain sizes gradually decreased from the addition of 3TiC to 8TiC, and the average grain size of Nb-37Ti-10Al-8TiC decreased to 22.08 μm. The strip-like and particle-like (Nb,Ti)C precipitation coexisted in Nb-37Ti-10Al-3TiC and Nb-37Ti-10Al-5TiC, but only particle-like (Nb,Ti)C formed in Nb-37Ti-10Al-8TiC. The tensile strength, compression strength and fracture toughness of all Nb-Ti-Al-TiC alloys increased with the increase of TiC content. For Nb-37Ti-10Al-8TiC, the maximum tensile strength of 754.14 ± 3.84 MPa, compression strength of 3310.0 ± 55.28 MPa and fracture toughness of 34.96 MPa·m^1/2 were obtained. The simultaneous increase of strength and fracture toughness was mainly attributed to fine grain strengthening by TiC addition. Compared with Nb alloy with the addition of Ta, W, Mo and Hf, the LSFed Nb-Ti-Al-TiC alloy had considerably high strength and was of low density. This confirmed the feasibility of preparing Nb alloy by LSF technology and adjusting the microstructure and property.