Effect of a matrix microstructure on the high cycle fatigue properties of TiB particulate reinforced Ti3Al-Nb matrix composites

Ti3Al-based alloys, especially alloys containing large amounts of Nb to imp rove their ductility, are attractive materials for aircraft and automobile parts. However, these alloys do not have good high temperature mechanical p roperties. In the present study, Ti3Al-Nb alloys reinforced by TIE ceramic particulates were produced using blended elemental (BE) powder metallurgy ( P/M). To improve their mechanical properties, the modification of the matri x microstructure was attempted by heat treatment. Titanium powder, Niobium-Aluminum master alloy powder and TiB2 ceramic powd er were used as starting powder materials. Blended powders were cold presse d using mechanical pressing, vacuum sintered at 1823 K and finally hot isos tatic pressed (HIP'ed) at 1373 K and 200 MPa for 10.8 ks. During sintering, TiB particulates were ipl-situ formed and dispersed in the matrix homogene ously. The matrix microstructure of the composite produced by this conventi onal method showed a colony microstructure with diameters ranging from 5 mu m to 20 mu m. Modification to a uniform, finer colony microstructure with a diameter of 5 mu m was achieved by annealing the composite at 1573 K foll owed by air-cooling. This resulted in improved high cycle fatigue strength with almost no fatigue data scatter.