Abstract
Tensile properties of Ti-6Al-4V titanium alloy, sintered by a new process (sintering, phase transformation, and dehydrogenation of titanium hydride compacts, termed HSPT process), were investigated to determine how the sintering pores influence the tensile strength and ductility. It was found that the ductility in the sintered alloy is severely affected by the size of the largest pore, referred here as extreme-sized pore, even when the average volume fraction of porosity is nearly constant between a large number of samples. It is shown that the rapid decrease in ductility, with an increase in the extreme pore size, is caused by strain localization around the extreme-sized pore and early crack initiation. This crack initiation leads to fracture of the plane containing the pore thereby limiting the extent of uniform plastic strain that can be attained before fracture. Interestingly, the strength properties are, however, found to be independent of the size of the extreme-sized pore. The results are explained on the basis of stress concentration and strain localization around the extreme-sized pores. The work also reveals that if the extreme-sized pores are eliminated, PM Ti-6Al-4V alloy with high strength (~1100 MPa) and good ductility (~12 pct), which is easily comparable to a wrought Ti-6Al-4V alloy, can be achieved even at oxygen levels up to 0.4 wt pct.
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Acknowledgments
The authors duly acknowledge a financial grant from the U.S. Department of Energy, Innovative Manufacturing Initiative (DEEE0005761), through the Advanced Manufacturing Office and the Office of Energy Efficiency and Renewable Energy. The initial raw powders were supplied by Ametek Specialty Metal Products, PA. We also thank James Paramore and Pei Sun for their help in the experimental work.
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Kumar, P., Ravi Chandran, K.S., Cao, F. et al. The Nature of Tensile Ductility as Controlled by Extreme-Sized Pores in Powder Metallurgy Ti-6Al-4V Alloy. Metall Mater Trans A 47, 2150–2161 (2016). https://doi.org/10.1007/s11661-016-3419-5
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DOI: https://doi.org/10.1007/s11661-016-3419-5