Elastic moduli and tensile and physical properties of heat-treated and quenched powder metallurgical Ti-6Al-4V alloy
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I.
INTRODUCTION
A M O N G the commercial titanium alloys, Ti-6AI-4V is the most widely used. The alloy consists primarily of two phases: hexagonal close-packed (hcp) alpha and bodycentered cubic (bcc) beta. Depending upon heat treatment and quenching (HTQ), the beta phase may be replaced by soft alpha" martensite or by hard alpha' martensite. The tensile properties of the alloy are a function of the phase volume ratio and the composition of the phases, which can be controlled by heat treatment. Several physical properties of the alloy, such as specific heat, Debye temperature, and velocity of sound, can be derived from the elastic constants. The elastic constants are not only important for the understanding of the physical nature of a material but also for its design and performance, e.g., in aerospace application. Elastic constants are generally insensitive to heat treatment, deformation, and microstructure. However, the Ti-6A1-4V alloy behaves differently in this respect because of the phase transformation(s) in the beta phase. Modulus variation is also caused by texture, [~}oxygen concentration [2] and precipitate phases produced by certain heat treatments. [3] Several investigations [4'~,61 have described the effects of heat treatment, but a separation from the effects of texture and oxygen has not been made. Heat treatment itself has a significant effect on the alloy's elastic modulus and damping. {7] The effects of oxygen on modulus and strength have been previously reported [2,~,41and will not be discussed here. The objective of this work is to report the variation of the elastic moduli and the tensile and physical properties of Ti-6A1-4V as a function of the microstructures obtained by quenching from heat-treatment temperatures Y.T. LEE, formerly Research Associate, Institute for Materials Research, German Aerospace Research Establishment, is Head, Department of Materials Research, Korea Institute of Machinery and Metals, 66, Sangnam-dong, Changwon, Korea. M. PETERS, Senior Scientist, is with the Institute for Materials Research, German Aerospace Research Establishment, D-5000 Cologne 90, Federal Republic of Germany. G. WELSCH, Associate Professor, is with the Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106. Manuscript submitted April 2, 1990. METALLURGICALTRANSACTIONSA
between 600 ~ and 1200 ~ To eliminate texture effects, sintered compacts were used. To eliminate oxygen as a variable, compacts with identical oxygen concentration of 0.24 wt pct were selected. The authors are aware that this oxygen level is higher than typically reported for this alloy. The influence of oxygen on properties has been reported previously. [4] II.
EXPERIMENTS
Specimens of the Ti-6A1-4V alloy were made by the blended elemental powder metallurgy (BE/PM) process. ts] The chemical composition in weight percent is 6.1A1, 4.1V, 0.240, 0.1Na, 0.1C1, 0.03Fe, 0.02C, 0.01N, and balance Ti. The density of the alloy was measured according to ASTM B 328-73. tg] The measured density
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