Effect of Heat Treatment Temperature on Microstructure and Impact Performance of TC18 Titanium Alloy
TC18 titanium alloy bars were heat treated at different temperatures,and then cooled in the fur-nace.The effects of heat treatment temperature on the microstructure,phase composition,impact perfor-mance and impact fracture micromorphology of the alloy were analyzed by optical microscope,scanning e-lectron microscope,X-ray diffractometer and impact tester.The results show that the size,distribution and morphology of α phase in TC18 titanium alloy have different degrees of change after heat treatment at dif-ferent temperatures.In the process of increasing the heat treatment temperature,the large block α phase gradually disappears,the long strip α phase becomes finer,and more fine needle α phase precipitates.The microstructure of the alloy after heat treatment at different temperatures and furnace cooling forms α phase and β phase,and with the increase of heat treatment temperature,the diffraction peak intensity of some α phase and β phase increases.The equiaxed and strip-shaped α phase can make the crack propagation path smoother,while the needle α phase and β phase can disperse the stress of the alloy when it is impacted and avoid brittle fracture caused by stress concentration.The impact performance of the alloy gradually decrea-ses with the increase of heat treatment temperature.When the heat treatment temperature is 835℃ ,the al-loy has the best impact performance with an impact absorption energy of 46 J and an impact toughness of 57 J/cm2.When the heat treatment temperature is low(835℃ and 855℃ ),the impact fracture micromor-phology of the alloy is mainly characterized by large dimples,which contain a large number of small dim-ples.When the heat treatment temperature is high(875℃ and 895℃ ),the fracture dimple size becomes smaller,tearing edges appear,and the void size increases.
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