摘要
利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、纳米压痕以及电化学测试等研究了时效温度对Ti-35Nb-5Ta-7Zr合金α相的数量、尺寸与分布特征以及力学性能和腐蚀行为的影响.结果表明:在400～450℃时效处理后,大量针状α相优先在晶界位置析出,并随温度升高呈网状结构;在超过500℃时效处理后,α相进一步长大,呈三角特征且分布均匀.合金的强度与弹性模量随时效温度升高呈现先升高再降低的趋势,在450 ℃时达到峰值,断后伸长率随时效温度升高逐渐提高.由此可见,合金强度、塑性与弹性模量随时效温度的变化与α相数量、尺寸和分布特征密切相关.随着时效温度的升高,Ti-35Nb-5Ta-7Zr合金在模拟体液中的耐蚀性呈现先降低后升高的趋势.分析可知,400～450 ℃时效时,富Ti而少Nb、Zr的针状α相在晶界与晶内析出,因其与基体存在电位差形成原电池,故针状α相数量增加导致耐蚀性降低;时效温度超过500 ℃时,α相在晶界与晶内均匀析出,降低了局部腐蚀倾向,促进均匀钝化膜的形成而提升耐蚀性.
Abstract
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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