Microstructure evolution and improved properties of laminated titanium matrix composites with gradient equiaxed grains

Abstract

With the purpose of improving both the strength and ductility, gradient equiaxed grains were successfully achieved in the matrix of the laminated TiB/Ti-TiB/Ti-6.58Al-1.76Zr-1.04V-0.89Mo composite via water quenching (WQ) and thermal compressing deformation. Gradient equiaxed grains varied from approximately 1.0 µm in TiB/Ti-6.58Al-1.76Zr-1.04V-0.89Mo layer to 5.5 µm in TiB/Ti layer. The formation of the gradient structure was related to the alloying elements diffusion during the initial sintering process, and the equiaxed shape was constructed by dynamic recrystallization during thermal compressing. WQ treatment before thermal compressing was adopted to obtain fine lamellar structure, which promoted the segmentation of a lamellae, and accelerated the dynamic recrystallization process. Raising the quenching temperature can increase the proportion of equiaxed grains in the composite, which improved both the bending strength and ductility. Compared with the as-sintered specimen, the specimen with gradient equiaxed grains exhibited nearly 30% enhancement in flexural strength (from 1719 to 2218 MPa), and the ultimate bending fracture strain was increased from 7.0% to 17.2%. This significant improvement should be attributed to the coordination deformation by interface gradient grains, the grain refinement strengthening and the good balance between strength and ductility of the recrystallized equiaxed grains.