Microstructure and mechanical properties evolution of heat treated Ti65 alloy fabricated by laser deposition manufacturing
Ti65 alloy samples prepared by laser deposition manufacturing technology(LDM)were treated by annealing,solution+aging heat treatment.The internal relationship between the microstructure,element distribution and tensile strength of the samples was comprehensively analyzed.The conclusions are as follows:the α lamellar structure is dominant in all of the Ti65 samples,including as deposited,annealed and solution+aged.The lamellar length-width ratio decreases with the increase of the maximum heat treatment temperature.Transformed β(βT)was found in solution+aging treated samples.The silicide was observed by TEM and its size increases with the increase of heat treatment temperature.The samples heat treated at 850℃for 2 h followed by air cooling(AC)show the best tensile properties at both room temperature and 650℃among the 5 group samples.For samples heat treated at 980℃,Nb,Ta,W and other elements are enriched in β phase,α laminar is not solid solution strengthened enough,while the size of silicide increases,the three factors result in the lowest plasticity and the lowest yield/tensile strength difference at room temperature,and high plasticity but insufficient strength at high temperature.The enrichment of Zr,Nb,Ta,W and other elements in the silicide weakens the solid solution strengthening effect of the above β-stable elements on the α and β phases,promotes the precipitation of more silicides,resulting in a relatively low yield strength and plasticity of the alloy.After the silicide is coarsened and enriched,the plastic damage is more significant.
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