Effect of Cr contents on microstructure and mechanical properties of (TiB _w+TiC _p)/(Ti-4.0Fe-7.3Mo-xCr) composites

Titanium alloys had a wide application as their good toughness and strength, but these alloys had relatively low abrasion resistance as the low hardness which limited their application as structure parts. The titanium matrix composites, 10% (TiB _w+TiC _p)/(Ti-4.0Fe-7.3Mo-xCr) composites with TiB:TiC=1:1, were prepared by in situ reaction between B ₄C, C, Cr ₃C ₂ and titanium powders. The mixtures were hot pressed at 1300°C, under a pressure of 20 MPa for 1 h in Ar atmosphere. Microstructure and mechanical properties of the composites were investigated. The results showed that by changing the proportions of Cr ₃C ₂, B ₄C, and C, the content of Cr from Cr ₃C ₂ could affect both the matrix and reinforcing phase. The composite was comprised of the α-Ti and β-Ti phase, and the content of β-Ti phase increased with the content of Cr from Cr ₃C ₂ increased by in situ reaction. With the increase of Cr content from Cr ₃C ₂ varied from 2.2% to 5.2%, the strength increased significantly, up to 908.7 MPa, while the Young's modulus decreased from 170 to 150 GPa, but the hardness (HRC) of the TMCs was much higher than that of the matrix alloy and remained steadily at 55. Additionally, the introduction of Cr ₃C ₂ could also influence the distribution and morphology of in situ formed TiB _w and TiC _p reinforcements. With the increase of Cr content from the Cr ₃C ₂, the aspect ratio of the TiB _w rose, and the granularity of the TiC _p declined which enhanced the strength and toughness of the composites.