Microstructure and Mechanical Properties of Ti-Nb Alloys Prepared by Mechanical Alloying and Spark Plasma Sintering

摘要

The effect of Nb content on microstructure, mechanical properties and superelasticity was studied in Ti-Nb alloys fabricated by powder metallurgy route using mechanical alloying and spark plasma sintering. In the microstructure of the as-sintered materials, undissolved Nb particles as well as precipitations of alpha-phase at grain boundaries of beta-grains were observed. In order to improve the homogeneity of the materials, additional heat treatment at 1250 degrees C for 24 h was performed. As a result, Nb particles were dissolved in the matrix and the amount of alpha-phase was reduced to 0.5 vol.%. Yield strength of the as-sintered alloys decreased with Nb content from 949 MPa for Ti-14Nb to 656 MPa for Ti-26Nb, as a result of the decreasing amount of alpha-phase precipitations. Heat treatment did not have a significant effect on mechanical properties of the alloys. A maximum recoverable strain of 3% was obtained for heat-treated Ti-14Nb, for which A(s) and A(f) temperatures were - 12.4 and 2.2 degrees C, respectively.