Microstructure And Mechanical Properties Of In Situ TiB_w +TiC_p Reinforced (Ti-4.0Fe-7.3Mo-xCr) Matrix Composites

Titanium alloy has a wide application as its low density,but with the bad abrasion resistance. The in situ titanium matrix composites, (TiB_w+TiC_p) / (Ti-4.0Fe -7.3Mo-xCr) composites, have been produced by hot pressing sintering utilizing the reaction between B₄C, C, Cr₃C₂ and titanium powders, in 1300℃/ 20MPa/1h/Ar atmosphere protective conditions. Microstructure and mechanical properties of the composites have been investigated. The influence of Cr content and the volume fraction of TiB_w+TiC_p in the composites on microstructure have been studied to obtain a better understanding on the strengthening mechanisms and abrasion resistance.Microstructure analysis shows that particle size of TiC_p decreases with the increasing of Cr content. TiB whisker aspect ratio increases with the increasing of Cr content, but decreases with the volume fraction increased by in situ reaction. Matrix of the composite is comprised of theα-Ti andβ-Ti phase and the content ofβ-Ti phase increases with the increasing of the Cr content, but decreases with the volume fraction increased by in situ reaction.Mechanical properties test shows that with the increasing of Cr content, both the bending strength and fracture toughness increase, the Young's modulus decreases and hardness remained unchanged at 580kg·mm-2. With increasing of the volume fraction of the in situ formed TiB_w and TiC_p, the flexural strength and fracture toughness first increase and then decrease. 15vol% (TiB_w+TiC_p) / (Ti-4.0Fe-7.3Mo-5.2Cr) composite has excellent strength and toughness. The bending strength is 1070.5MPa, the fracture toughness is 15.11MPa·m1/2, the Young's modulus is 160.9MPa and the hardness is 696.4kg·mm-2. With the increasing of the volume fraction, the flexural strength and toughness improve. 40vol% (TiB_w+TiC_p)/(Ti-4.0Fe-7.3Mo-5.2Cr) composite has the maximum hardness, which is 1102.5 kg·mm-2, and the flexural strength is 867.4MPa.Sliding friction tests show that wear plowing and micro-cutting are the two wear modes of the matrix. The introduction of Cr by adding Cr₃C₂ raw materials effectively raises the work hardening and shear abrasion, which makes the wear type of composite from wear plowing and micro-cutting to abrasive wear. The increasing of the volume fraction of the in situ formed TiB_w and TiC_p improves the Young's modulus of the composite, which results in resistance to plastic shear capacity of composite to improve, mainly abrasive wear. 40vol% (TiB_w+TiC_p)/ (Ti -4.0Fe-7.3Mo-5.2Cr) composite generate debris in the process of friction wear, which plays the role of solid lubricant. In the wear scar, there is the oxidation layer acting as a lubricant, which plays a role in a ball's grinding and polishing in order to reduce the contact area.