The influence of six processing sequences on the microstructure, mechanical properties and heat treatment response of the Ti-7Al~4Mo alloy has been studied. The information developed demonstrates the critical effects of processing history in controlling the material performance levels and emphasizes the importance of such considera¬tions in attaining "optimum" values.nForging entirely above the beta transus produced the usual Widmanstatten type of structure found in titanium alloys after such processing. As expected, the creep resistance of this structure was excellent; however, heat treatment response and tensile ductility were poor, and a reduction in Charpy impact strength of 3/4" rod was noted for all thermal treatment conditions. Forging entirely below the beta transus developed an equiaxed microstructure and generally good properties except for reduced creep resistance. Duplex forging, i.e., forging initially above the beta transus, cooling to room temperature, and reheating to below the beta transus for finish forging, produced a nearly equiaxed microstructure and general property levels quite similar to all below-beta forging but with improved creep resistance.nIn general, notch tensile and notch stress rupture did not show any direct relationships with processing history. Notch rotating beam fatigue tests for above-beta forged material showed more scatter than those on material forged below the beta transus though the endurance limit was not greatly affected.
展开▼
