Effects of TiB 2 Particle and Short Fiber Sizes on the Microstructure and Properties of TiB 2 -Reinforced Composite Coat
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Effects of TiB2 Particle and Short Fiber Sizes on the Microstructure and Properties of TiB2-Reinforced Composite Coatings Yinghua Lin, Jianhua Yao, Liang Wang, Qunli Zhang, Xueqiao Li, Yongping Lei, and Hanguang Fu (Submitted August 9, 2017; in revised form March 8, 2018) In this study, particle and short fiber-reinforced titanium matrix composite coatings are prepared via laser in situ technique using (0.5 and 50 lm) TiB2 and Ti powder as cladding materials. The microstructure and properties of the composite coatings are studied, and the changing mechanism of the microstructure is discussed. The results reveal that particle agglomeration is prone to appear with using fine TiB2 particles. Decomposition of the particles preferentially occurs with using coarse TiB2 particles. The cracks and pores on the surface of the coating are formed at a lower laser energy density. With the increase in the laser energy density, cracking on the surface of the coating diminishes, but the coating exhibits depression behavior. The depression extent of the coating using fine TiB2 particle as the reinforcement is much less than that of the coating using coarse TiB2 particle. Moreover, the size of the aggregate and the tendency of cracking can be reduced with the increase in Ti addition. Meanwhile, short TiB fiber bundles are formed by the diffusion mechanism of rod aggregate, and randomly oriented TiB short fibers are formed mainly by the dissolution–precipitation mechanism of fine TiB2 particles. Moreover, the growth of short TiB fibers can be in an alternating manner between B27 and Bf structures. The micro-hardness and wear resistance of the coatings are evidently higher than that of the titanium alloy substrate. The wear resistance of the large size TiB2 coating is higher than that of the small size TiB2 coating under the condition of low load. Keywords
coating, laser cladding, microstructure, properties, TiB2
1. Introduction TiB short fiber with low density, high melting point, high hardness, good thermal and chemical stability, can meet double requirements of structure weight reduction and high temperature strength of the future automobile engines so that it is one of the most promising heat-resistant lightweight structural materials (Ref 1). Currently, TiB short fiber-reinforced titanium matrix composites have been in practical application. However, the wear resistance of these composites is poor in the applications of engine and mining machinery, and the main failure mode for these applications is adhesive wear (Ref 2, 3). In recent years, various studies showed that the wear resistance of short fibers was less than that of hard particles in micro-cutting or abrasion condition (Ref 4-6). Abachi et al. (Ref 7) found that the wear resistance of short fiber-reinforced metal matrix composites was very poor in the dry sliding wear experiments. Kim et al. (Ref 8) further found that the adhesive wear resistance of the materials can be improved, but the
Yinghua Lin, Jianhua Yao, Liang Wang, and Qunli Zhang,
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