The mechanical properties of Ti-6Al-4V-XCu (1, 4 and 10 wt% Cu) alloys were examined. The castings for each alloy were made in a centrifugal titanium casting machine. Two shapes of specimens were used: a dumbbell (20 mm gauge length x 2.8 mm diameter) for mechanical property studies, and a flat slab (2 mm x 10 mm x 10 mm) for metallography, microhardness determination and X-ray diffractometry. Tensile strength, yield strength, modulus of elasticity, elongation and microhardness were evaluated. After tensile testing, the fracture surfaces were observed using scanning electron microscopy. The tensile strengths of the quaternary alloys decreased from 1016 MPa for the 1% Cu alloy to 387 MPa for the 10% Cu alloy. Elongation decreased with an increase in the copper content. The 1% Cu alloy exhibited elongation similar to Ti-6Al-4V without copper (3.0%). The results also indicated that the copper additions increased the bulk hardness of the quaternary alloy. In particular, the 10% Cu alloy had the highest hardness and underwent the most brittle fracture. The mechanical properties of cast Ti-6Al-4V alloy with 1 and 4% Cu were well within the values for existing dental casting non-precious alloys.
Author's Note: All compositions are given in atomic percent unless otherwise indicated.The kinetics and mechanisms of oxidelayer formation on Ti-Al-X alloys, specifically have been studied. The activation energies for the oxide formation of each of the alloys used in this work were determined, and the values obtained were compared with those obtained by other researchers for identical alloys.
The oxidation behavior of TiAl 3 was investigated. The studies were carried out using thermogravimetric analysis (TGA) in the temperature range from 1123 to 1273 K in a 1 atm pure oxygen environment. Samples were analyzed using the X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion X-ray analysis techniques. The oxidation product was determined to be Al 2 O 3 over the temperature range of the investigation. The parabolic-rate constant for TiAl 3 was deduced and compared with those for Ti, TiAl, and Ti 3 Al. The electronprobe microanalysis technique was used to obtain concentration profiles for O, Al, and Ti in the oxide layer and the matrix alloy. The parabolicrate data were used to calculate the diffusivities of oxygen at various temperatures. The activation energy for diffusion was determined to be 337.66 kJ/mol, while the frequency factor (D 0 ) was 167.2 ϫ 10 Ϫ4 m 2 /s.
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