Preparation and Tribological Properties of In-Situ TiB/Attapulgite Mineral Dual-Phase Reinforced Ti Matrix Composites

The application of Ti alloys as friction components is limited owing to their low hardness, high friction coefficient, and poor wear resistance. Generally, introducing hard reinforcement to obtain discontinuous reinforced titanium-matrix composites by single-phase or multiphase coordination is an effective way to improve the mechanical and tribological performance of titanium-matrix materials. In this study, in situ TiB/attapulgite dual-phase-reinforced Ti matrix composites were prepared using Ti, Al, B and attapulgite natural mineral powders as raw materials by spark plasma sintering (SPS). The effects of attapulgite on the microstructure, phase structure, morphology, and distribution of in situ TiB reinforcements and the micromechanical properties of the composites were studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), microhardness and nanoindentation testing. The tribological properties of the composites under oil lubrication were investigated using an SRV reciprocating sliding-wear tester. Finally, the mechanisms by which attapulgite mineral improved the mechanical and tribological properties of in situ titanium matrix composites were discussed. The results showed that the in situ TiB/attapulgite dual-phase reinforced Ti matrix composites prepared by SPS had a compact structure and uniform distribution of in-situ TiB reinforcements. The attapulgite mineral exhibited an obvious fine-grained strengthening effect on the composites. Compared with the pure in situ TiB/Ti composites, the matrix grain and in situ TiB size of the dual-phase-reinforced composites were refined after the addition of the attapulgite natural mineral. The matrix phase indentation hardness (H_IT) and composite microhardness increased by approximately 31.4% and 39.3%, respectively. Compared with pure TiB-reinforced Ti matrix composites, dual-phase reinforced composites exhibited superior tribological properties, and the friction coefficient and wear rate increased less with increasing applied load. In addition, under the same friction conditions, the friction coefficient and wear rate decreased by 16.67% and 59.26%, respectively. EDS and XPS analyses showed that the contents of Ti oxides, Fe oxides, and graphite on the worn dual-phase-reinforced Ti matrix composite surfaces were higher than those on the pure in-situ TiB/Ti composites. The worn surface hardness, elastic modulus (E), hardness/elastic modulus ratio (H_IT/E), and H_IT³/E² of the dual-phase-reinforced composites were significantly higher than those of both the worn surface of the pure in situ composites and the unworn surface. Worn surface analysis indicated that attapulgite mineral dispersed inside the titanium matrix composites formed a tribolayer composed of Al₂O₃, SiO₂, TiO₂, attapulgite mineral powder, and graphite on the worn surface through a self-dehydration reaction, group reconstruction, and tribochemical reaction between the active oxygen-containing groups and the metal on the friction surface under the action of friction-thermodynamic coupling. The tribolayer had high hardness, good toughness and plasticity, and excellent self-lubrication characteristics, and therefore improved the tribological properties of the in situ TiB reinforced titanium matrix composites.