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Porosity, Microstructure, and Mechanical Properties of Ti-6Al-4V Alloy Parts Fabricated by Powder Compact Forging
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Web End = MINGTU JIA, DELIANG ZHANG, JIAMIAO LIANG, and BRIAN GABBITAS
Ti-6Al-4V alloy powders produced using a hydrogenationdehydrogenation process and a gas atomization process, respectively, were rapidly consolidated into near-net-shaped parts by powder compact forging. The porosity, microstructure, and tensile mechanical properties of specimens cut from regions at dierent distances from the side surfaces of the forged parts were examined. The regions near the side surfaces contained a fraction of pores due to the circumferential tensile strain arising during the powder compact forging process, and the porosity level decreased rapidly to zero with increasing the distance from the side surface. The forged parts had a fully lamellar structure with the a + b colony sizes and a lamella thickness changing little with the distance from the side surface. The specimens cut from the regions near the side surfaces had a lower yield strength and tensile strength. The correlation of porosity with the yield strength of the specimens suggested that the reduction of load bearing areas due to the porosity and unbonded or weakly bonded interparticle boundaries was not the only reason for the lower strength, and the stress concentration at the pores and associated with their geometry also played an important role in this. It is likely that the eect of stress concentration on yield strength reduction of the forged part increases with oxygen content. The HallPetch relationship of the yield strength and the average a lamella thickness suggested that the strength of the fully dense and fully consolidated forged parts was increased by oxygen solution strengthening.
DOI: 10.1007/s11661-017-3965-5 The Minerals, Metals & Materials Society and ASM International 2017
I. INTRODUCTION
TITANIUM and titanium alloys are widely used in aerospace, chemical, automobile, and biomedical industries due to their high specic strength, high fracture toughness, excellent corrosion resistance, and good biocompatibility.[16] However, the range of applications of titanium alloys can be much wider and the amount of usage can be much higher than the current level of around 100,000 tons per annum,[7] if the costs of titanium and titanium alloy mill products and shaped parts are signicantly reduced. In order to reduce the costs of shaped...