Multi-scale reinforcements stimulated dynamic recrystallization and mechanical behavior of as-extruded titanium matrix composites

^a State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
^b Shanghai Key Laboratory of Advanced High Temperature Materials and Precision Forming, Shanghai 200240, China
^c AVIC Manufacturing Technology Institute, Beijing 100024, China

^* Corresponding author. Email address: hyuf1@sjtu.edu.cn (Yuanfei Han), luweijie@sjtu.edu.cn (Weijie Lu).

Abstract

Different volume fraction of TiB, TiC and La₂O₃ multiple-reinforced Ti6Al4V composites were fabricated by casting and followed by forging and hot extrusion. The microstructural evolution and mechanical behavior of (TiB+TiC+La₂O₃)/Ti6Al4V composites during hot extrusion were investigated. The microstructural observations showed that the TiB_w and TiC_p agglomeration disappeared and distributed more homogeneously in the Ti matrix after hot extrusion. Besides, TiB_w exhibited highly preferred alignment along the extrusion direction and TiC_p distributed along the same direction. Besides, two kinds of microstructure bands with distinctive spatial distributions of reinforcements were formed after hot extrusion: equiaxial bands embedded with fairly substantial reinforcements and finer basket-weave bands containing few reinforcements, in which the micron-scale TiB_w, TiC_p and submicron-scale La₂O₃ particle stimulating nucleation occurred and resulting dynamic recrystallization were the main mechanisms responsible for grain refinement. The tensile tests revealed that hot extrusion significantly increased elongation of (TiB+TiC+La₂O₃)/Ti6Al4V composites from 2.71% to 13.2% accompanied by slightly decreasing ultimate tensile strength from 954MPa to 903MPa, compared with that of the as-forged composites, which due to a complex process of reinforcements/matrix interaction during extrusion and dynamic recrystallization.