Intergrowth microstructure and superior wear resistance of (TiB + TiC)/Ti64 hybrid coatings by gas tungsten arc cladding

Abstract

For the sake of enhancing hardness and wear resistance of Ti based materials, 50 vol% (TiB + TiC)/Ti64 composite coatings with different TiB/TiC ratios were fabricated by gas tungsten arc cladding (GTAC) on the network structured 3.5 vol% TiBw (TiB whisker)/Ti64 substrate. The results showed that primary TiB and TiC exhibited much larger sizes than their eutectic counterparts, and the two-scale reinforcements formed by the dissolution-precipitation mechanism predominated the hybrid coatings. In particular, most TiC was embedded within the TiB prism displaying an intergrowth structure with “dissimilar-joining” characteristic, which contributed to the hardness and wear resistance improvement. The remarkable hardness improvement was attributed to the following three-fold mechanisms: (a) load transfer strengthening from the primary TiB and TiC; (b) Orowan strengthening from the eutectics; and (c) Hall-Petch strengthening from the refined Ti64 matrix. Moreover, the plastic deformation resistance was significantly improved by the hybrid reinforcements, leading to the enhanced the anti-abrasion performance. Consequently, the coating exhibited a comparatively low wear rate (7.35 × 10−5 mm3·N−1·m−1) compared with the substrate (54.89 × 10−5 mm3·N−1·m−1), and the corresponded wear mechanisms are summarized as: brittle debonding, oxidation and slight micro-ploughing. Keywords: Titanium matrix composite coatings, Hybrid TiB + TiC reinforcements, Gas tungsten arc cladding, Microstructure, Hardness, Wear