In-situ TiC and γ′-Ni3(Al,Ti) triggered microstructural modification and strengthening of Ni matrix composite by reactive hot-press sintering pure Ni and Ti2AlC precursor

Abstract

In the present study, a novel type of Ni-based composites was successfully fabricated from pure Ni and Ti2AlC powder mixtures by hot-press sintering route at 1400 °C and 30 MPa. The microstructural analysis indicates that the initial reinforcement Ti2AlC particles transformed into TiC phase, while the additional AlTi atoms decomposed from Ti2AlC diffused into the Ni matrix. The de-intercalated AlTi atoms would subsequently react with Ni to give rise to the formation of γ′-Ni3(Al,Ti) precipitates according to element compositions. SEM observations on 30 vol%Ti2AlC/Ni composite after etched showed that L12-centered γ′ phase is ultrafine (about 100 nm) and uniformly distributed in the Ni matrix. The mechanical behavior in relationship with the different fractions of Ti2AlC (10 vol%, 20 vol%, 30 vol% and 40 vol%) were carefully investigated. Yield strength, ultimate compressive strength, flexural strength and Vickers hardness except for fracture strain and toughness increased with the increasing Ti2AlC content; the optimal values for 30Ti2AlC/Ni composite were approximately 1056 ± 29 MPa, 1776 ± 33 MPa, 1284 ± 59 MPa, and 4.06 ± 0.07 GPa respectively, with 19.37 ± 0.75% fracture strain and 26.31 ± 2 MPa m1/2 fracture toughness. The enhancement of mechanical properties was attributed to the synergistic effect of fine-grain strengthening, austenitic solid-solution strengthening and dispersion strengthening mechanism.