Effect of boron content on microstructure and mechanical properties of Ti50Zr50 alloys

A series of as-cast (Ti50Zr50)(100-x)B-x (x = 0, 2, 4, 6, 8 at.%) alloys were fabricated by vacuum electro-arc melting method. The microstructure and mechanical properties of all as-cast specimens were investigated. Single alpha' phase was observed in the Ti50Zr50 alloy. With the adding of B element, the diffraction peaks of TiB and ZrB2 were found. The TiB and ZrB2 intermetallics with a whisker shape were mostly distributed in the prior beta grain boundaries. When the addition B content is 4%, the TiB and ZrB2 whiskers is the most smallest. In addition, the microstructures of Ti-Zr-B alloys are obviously refined with the increase B content. It may be attributed to constitutional supercooling caused by boron rejection due to a small amount of solid solubility of boron in titanium and zirconium. The tensile tests indicate that the as-cast (Ti50Zr50)(96)B-4 alloy shows the maximum ultimate tensile strength and yield strength, which increased by 27.9% and 42.3% compared with the Ti50Zr50, respectively. The strengthening mechanisms may be from two aspects of the load transfer and grain refinement. Fracture morphologies show that the brittle fracture becomes dominant in the Ti-Zr-B alloys with the increase of B concentration.