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

Effect of three heat treatments and two cooling ways on the microstructures and tensile properties of IMI834 titanium alloy were studied. An optical microscope was used to analyze the evolution of the microstructures of the alloy. The Image-Pro Plus v5.1 (IPP) and Nano Measure image analysis software were used to calculate the size of equiaxed alpha phase (alpha(p)) and secondary alpha ( alpha(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 alloy in the different cooling ways was analyzed using SEM. The distribution of second phase was analyzed by TEM. The results show that in the double annealing test, with the increase of the first annealing temperature, the content and the size of ap gradually decrease, but as clusters increase; the strength of IMI834 alloy first increases and then decreases. The elongation and reduction of area do not change significantly. When the first annealing temperature is 1020 degrees C, the strength of IMI834 titanium alloy reaches the highest under the two test conditions of rapid cooling and slow cooling and the strength of the sample under rapid cooling is higher than that under 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 beta phase between the ap and as 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 alpha/ beta boundaries is the reason for the different morphologies.