Effect of XD TiB2 volume fraction on the microstructure of a cast near-gamma titanium aluminide alloy

TiB2 particulate levels ranging from 0.1 to 4.6 volume percent were incorporated into the near-gamma titanium aluminide alloy Ti-47.5Al-2Nb-2Mn (at. pct) via the XD process. Material was prepared by vacuum arc remelting followed by investment casting into cylindrical bars. Results show that grain refinement occurs in alloys with XD TiB2 additions equal to or greater than 1.0 volume percent. Alloys with additions of less than 1.0 volume percent TiB2 contained boride phases having lacey and blocky morphologies. Alloys with additions of 1.0 volume percent TiB2 or greater contained needle shaped borides, blocky equiaxed borides, and lacey borides. Determination of boride phase morphology, boride type, and microstructural response were determined by backscatter electron imaging, EMPA, XRD, and optical metallography. 6 refs