热处理对IMI834钛合金组织及拉伸性能的影响

Effect of Heat Treatment on the Microstructure and Tensile Properties of IMI834 Titanium Alloy

摘要:

研究了三种热处理制度和两种冷却方式对IMI834钛合金组织及拉伸性能的影响。采用光学显微镜分析了不同热处理制度对合金显微组织的影响；使用Image-Pro Plus v5.1(IPP)和Nano Measuer图像分析软件,统计了组织中初生等轴α相(α_p)及次生α相(α_s)集束等的尺寸；使用原位SEM拉伸并结合EBSD分析技术,原位观察合金的变形行为,并对变形前后的晶体取向进行了表征；采用扫描电子显微镜,表征了不同冷却方式下材料的断口形貌特征,并借助TEM分析了组织中第二相分布情况。结果表明：在双重退火试验中,随着第一重退火温度的升高,IMI834合金初生α相含量及尺寸逐渐降低,次生α相集束尺寸逐渐增加；随着第一重退火温度的升高,IMI834合金强度逐渐上升随后下降,延伸率及断面收缩率无明显变化,当第一重退火温度为1020℃时,IMI834钛合金在快冷和慢冷两种试验条件下强度均达到最高,快冷强度高出慢冷约50MPa；α_p/α_s界面间β相的存在,能够保证晶界两侧在几何协调性因子较低的条件下仍能够进行滑移传递；快冷条件下试样断口的准解离形貌为椭球状或多边形状,而慢冷条件下其为长条形,α/β相界面第二相的析出差异是导致两种试样中准解离形貌不同的原因。

Abstract:

The effects of three heat treatment regimes and two cooling ways on the microstructure and tensile properties of IMI834 titanium alloy were studied. An optical microscope was used to analyze the evolution of the microstructure of the alloys in different heat treatment states; Image-Pro Plus v5.1 (IPP) and Nano Measuer image analysis software were used to calculate the size of equiaxed α phase (α_p) and secondary α(α_s) clusters in the microstructure; The crystal orientation and the deformation behavior of the alloy in situ before and after deformation were characterized using in-situ SEM tensile test and EBSD technology. The fracture morphology of the material in the different cooling speeds was analyzed using scanning electron microscope.The distribution of second phase was analyzed by TEM. The results show that:in the double annealed test,with the increase of the first annealed temperature,the content and the size of α_pgradually decreased,but the secondary α clusters increased.With the increase of the first annealed temperature, the strength of IMI834 alloy first increased and then decreased. The elongation and reduction of area did not change significantly.When the first annealed temperature is 1020℃, the strength of IMI834 titanium alloy reaches the highest under the two test conditions of sample heat treatment (rapid cooling) and block heat treatment (slow cooling).The strength of the sample heat treatment (rapid cooling) is higher than that of the block heat treatment (slow cooling) by about 50 MPa; In the early deformation stage of IMI834 alloy, the crystal rotation angle of fast cooling is generally higher than that of slow cooling;The existence of the β phase between the α_pand α_s can ensure that the slip transfer can still be carried out under low geometric compatibility factor; The quasi-cleavage facets of the fracture surface under fast cooling conditions is ellipsoidal or polygonal, and under slow cooling conditions, it is elongated. The difference of the distribution of second phase in the α/β bounderies is the reason for the different morphologies.