Effect of degassing treatment on microstructure and mechanical properties of P/M Ti-6Al-4V

The effect of the degassing treatment on the microstructure and the mechanical properties of prealloyed PREP Ti-6Al-4V powder was investigated. An optimized hot degassing condition, heating up to 500deg C, then 2 h holding in vacuum, was determined from the quantitative analysis of the extracted gases as a function of temperature and time. The principal gases extracted by the hot degassing treatment were H2O and H2. To understand the effects of the extracted gases on the mechanical properties, cold degassing, i.e. evacuation at room temperature, was also performed and compared with the hot degassed condition after HIP consolidation. All static and dynamic mechanical properties of the cold degassed compacts were equivalent to the hot degassed compacts except the area reduction. These observations were attributed to high solubility of hydrogen and oxygen in the titanium alloys. In the cold degassed compact, micropores were aligned at prior powder particle boundaries and a hydride phase was precipitated at alpha/beta phase boundaries. Due to the rare occurence of these inhomogeneities, the mechanical properties were, however, not affected. (orig.)