Tensile and fracture behavior of boron and carbon modified Ti-15-3 alloys in aged conditions

This work illustrates the effect of boron and carbon addition on the mechanical behavior of a beta Ti alloy, Ti-15V-3Cr-3Al-3Sn (Ti-15-3), in differently aged conditions. The alloys were prepared by consumable vacuum arc melting followed by forging and hot rolling. These were subsequently solution treated and aged at different temperatures above 500 °C for 8 h. Standard tensile and plane strain fracture toughness tests were carried out to understand the mechanical behavior of the alloys and its correlation with the microstructural features characterized by scanning and transmission electron microscopy. Both the boron- and the carbon-containing alloys exhibit improved strength with comparable elongation to failure values as compared to the base Ti-15-3 alloy. The presence of TiB and TiC precipitates in a matrix of fine α with β results in lower fracture toughness (KIC) in the boron- and carbon-containing alloys as compared to the base alloy. However, at higher aging temperatures KIC improves due to more tortuous crack path because of the presence of coarse α-phase. An empirical relationship has been proposed correlating KIC with the volume fraction, size and interspacing of α in these alloys.