Effect of aging temperature on α-phase characteristics,mechanical properties and corrosion behavior of Ti-35Nb-5Ta-7Zr alloy
Effect of aging temperature on the quantity,size and distribution characteristics of α-phase,mechanical properties,and corrosion behavior of Ti-35Nb-5Ta-7Zr alloy was studied using X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nanoindentation,and electrochemical testing.The results show that after aging at 400-450 ℃,a large amount of needle like α-phase preferentially precipitates at grain boundaries,and then it transforms into a network structure as the temperature increases.After aging treatment above 500 ℃,the α-phase further grows and exhibits triangular characteristics with uniform distribution.The strength and elastic modulus of the alloy show a trend of first increasing and then decreasing with the increase of aging temperature,reaching a peak at 450 ℃,and the elongation gradually increases with the increase of aging temperature.It can be seen that the changes in the alloy strength,plasticity and elastic modulus with aging temperature are closely related to the quantity,size and distribution characteristics of α-phase.As the aging temperature increases,the corrosion resistance of the Ti-35Nb-5Ta-7Zr alloy in simulated body fluid shows a trend of first decreasing and then increasing.Analysis shows that during aging at 400-450 ℃,needle likeα-phase rich in Ti but less Nb and Zr precipitates at grain boundaries and within the grains,due to the potential difference between them and the matrix,more galvanic batteries are formed,so the increase in the number of needle like α-phase leads to the decrease in corrosion resistance of the alloy.When the aging temperature exceeds 500 ℃,the α-phase uniformly precipitates at grain boundaries and within the grains,reducing the tendency for local corrosion,promoting the formation of a uniform passivation film,and improving corrosion resistance of the alloy.
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