Abstract
The aim of the present investigation was to produce highly fatigue tolerant P/M Ti-5Al-2.5Fe by the microstructure-controllable Blended Elemental (BE) method, in which as-sintered preforms are quenched from the beta phase region prior to HIP'ing. An extra low chlorine titanium powder and a 53.6Al-26.3Fe-21.1Ti master alloy powder were used as starting materials. The microstructure consisted of fine alpha-beta two phase structure with massive alpha phase at grain boundaries (GB). The highest fatigue strength at 107 cycles, 60 kgf/mm2, was obtained for the compacts HIP'ed at 850°C, which was equal to that reported for Ti-6A1-4V compacts produced by the same method. However, the fatigue ratio at 107 cycles was lower and the scatter of the fatigue data was larger. The examination of the fatigue crack initiation sites by the precision sectioning method revealed that the lower fatigue life was related to the fracture along GBα boundary. The fatigue crack initiation sites were always in the interior of the specimens. Independent of the stress level, the initiation site was located at about the same depth(100200μm) below the surface, indicating maximum zone of tensile stress in these regions.
