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采用电磁冷坩埚定向凝固技术制备了成分为Ti-47Al-2Cr-2Nb的合金铸锭,定向凝固后的显微组织为α2+γ全片层结构。在0.4~1.2mm/min的抽拉速率范围内,随着抽拉速率的增加,片层间距减小,柱状晶与生长方向的夹角增大。随着温度升高,合金的拉伸强度有所下降,但由于细化片层界面对切变应力变形的阻碍作用,合金的高温拉伸强度会随着抽拉速率的增加而提高。通过对抽拉速率为1.0mm/min试样的拉伸强度与温度的拟合,得到了拉伸强度和温度之间的函数关系。随着抽拉速率的增加,Ti-47Al-2Cr-2Nb合金的持久寿命明显升高,对于抽拉速率为1.2mm/min试样的持久性能测试表明,其持久寿命最长,达到了48h。持久试样的断口形貌表明,其断裂的主要方式是伴随着少量延性断裂的脆性解理断裂。最后根据时间-温度模型,分别采用Larson-Miller和Manson-Haferd参数法建立了定向凝固Ti-47Al-2Cr-2Nb合金的持久强度预测函数模型,预测的理论值与试验结果吻合度较高。
The alloy ingot with the composition of Ti-47Al-2Cr-2Nb was prepared by directional solidification technology of electromagnetic cold crucible. The microstructure after directional solidification was α2 + γ full lamellar structure. With the drawing rate of 0.4 ~ 1.2mm / min, the interlamellar spacing decreases with the increase of the drawing rate, and the angle between the columnar grains and the growth direction increases. With the increase of temperature, the tensile strength of the alloy decreased, but the tensile strength of the alloy increased with the increase of the drawing rate due to the obstruction of the thinning layer interface to the shear stress deformation. The relationship between tensile strength and temperature was obtained by fitting the tensile strength and temperature of the sample with the pull rate of 1.0 mm / min. With the increase of drawing speed, the life expectancy of Ti-47Al-2Cr-2Nb alloy increased obviously. The long-term durability test of 1.2mm / min pull-out rate showed the longest lasting life of 48h. The rupture morphology of the long-lasting specimens shows that the main mode of rupture is the brittle cleavage fracture accompanied by a small amount of ductile fracture. Finally, according to the time-temperature model, the Lugson-Miller and Manson-Haferd parameters were respectively used to establish the predictive function model of the strength of the directional solidification Ti-47Al-2Cr-2Nb alloy. The predicted theoretical values are in good agreement with the experimental results.