Comparison study on mechanical properties of powder metallurgy titanium materials with nitrogen solutes and TiN dispersoids

Abstract

Two types of Ti-based materials with (1) N solutes and (2) TiN particles, as used in powder metallurgy (PM), were prepared from the same pre-mixed pure Ti and TiN powders. An optimized post heat treatment (HT) was applied to the forged samples to completely dissolve the N, originating from TiN particles existing as solid-solution atoms, into the Ti matrix. XRD analysis clearly indicated that only the (0002) α-Ti peak shifted to a lower diffraction angle after HT due to lattice expansion on the c-axis caused by N atoms in solution. Ti-based materials with N solutes showed a large increment in their tensile and compression strengths. Ti composites with TiN dispersoids, however, showed only a very small stress increment. For example, 20 MPa should be the incremental strength rather than the final tensile strength with the addition of 2-mass% TiN particles. Quantitative evaluation of the strengthening mechanism of the Ti-based materials with N solutes using the Hall-Petch equation and the Labusch model revealed that the N solid solution strengthening factor was 90–95% of the total increment in the tensile yield stress. The N solid-solution is thus highly effective in improving the strength of PM Ti materials, relative to Ti composites reinforced with TiN particles.