| The effect of the degassing treatment before HIPing on the microstructures and the mechanical properties were investigated using prealloyed PREP Ti-6Al-4V powder. Degassing condition was determined from the quantitative analysis of the extracted gases as a function of temperature and time. The determined degassing condition is heating up to 500℃ and then holding 2 hours in vacuum. The principal gases extracted by the treatment were H₂O and H₂. The compacts produced with cold degassing and HIPing exhibited slightly improved strength due to oxygen embrittlement with similar ductility and reduction of area to the cold degassed compacts. Dynamic properties, like fatigue strength, fracture toughness, fatigue crack propagation rate, were also not decreased compared to hot degassed compact. It was interpreted due to the high solubility of gas elements into the titanium matrix. Pores were, however, existed at prior powder particle boundaries due to dissolution of the adsorbed gases into the matrix in the cold degassed compact. The oxygen entered with powder particles located at α/βphase boundaries, and the hydrogen formed titanium hydride phase inside of the a phase. |
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