| In this work,the effects of solid solution treatment temperature,cooling rate after solution treatment and aging temperature on microstructure and mechanical properties of a wrought Ti2AlNb alloy were investigated.Besides,enironmental adaptability of the Ti2AlNb alloy was studied.The main results are as follows:The effect of different solution temperature on microstructure and mechanical properties of the TAN-2 alloy(Ti-22Al-24Nb-0.5Mo,at.%)was studied.It was found that the B2 phase exhibits good plasticity at room temperature.The coarse O phase was formed during solution process,which made the order degree of B2 phase decrease and the plasticity of B2 phase increase.For this reason,the TAN-2 alloy exhibited better elongation at room temperature.However,when the specimens with a2+B2 were tested at 650?,elongation decreased and this was attributed to the fine O phase particles precipitating from the B2 phase.Then the effect of solution temperature on microstructure and mechanical properties of the TAN-2 alloy under identical aging treatment was studied.It was found that the yield strength increased with the increase of solution temperature at room temperature as well as 650?.The effect of cooling rate on the microstructure and tensile properties of TAN-2 alloy was studied.It was found that the coarse O phase lath was only precipitated during furnace cooling.There was little change in the microstructure obtained by furnace cooling in the process of aging treatment.There were a large number of fine O phase laths precipitated in the process of aging treatment in the specimens cooled after air cooling,oil quenching and water quenching.The volume percentage of ?2 phase reduced and the volume percentage of BCC based phase increased with the increase of cooling rate.The disordered P phase was formed in the process of furnace cooling.The ordered B2 phase was obtained after oil quenching.When the cooling rate increased from furnace cooling to air cooling,the strength obviously increased and the elongation decreased at room temperature and 650?.When the cooling rate continued to increase,the strength had a slight increase at room temperature and 650?.The effect of aging treatment on microstructure and mechanical properties of the TAN-2 alloy was studied.For TAN-2 alloy,We evaluated its microstructural parameters and tested its mechanical properties.The results indicated that when the aging temperature increased,the length and width of O phase lath increased obviously and the volume fraction of O phase increased slightly.Besides,the acicular ?2 phase became finer and the width of O/?2 phase and edge O phase gradually increased with the increase of aging temperature.The strength and elongation of TAN-2 alloy increased with the increase of aging temperature at room temperature as well as at 650?.The tensile and fracture behavior of TAN-2 alloy with three types of microstructure were investigated in the temperature range between 25 ? and 650?.The O+BCC microstructure(basketweave microstructure)possesses an elongation maximum at 500? and its drop at 650? has been attributed to dynamic strain aging as suggested by previous investigators.However,the elongation of the specimens with ?2+O+BCC microstructure increased with the increase of test temperature.We found no elongation drop at 650? in the ?2+O+BCC microstructure,which indicated that the elongation drop at 650?caused not by dynamic strain aging,but by the variation in microstructure.The ?2+B2 microstructure has the highest room temperature elongation(?f>18%)and the cause of the elongation drop at 650? is suggested to be the fine O phase precipitates from the B2 phase.The specimens of TAN-2 alloy were exposed in the temperature range 650?750? for time up to 150h,in order to study the oxidation resistance of TAN-2 alloy and the damage of exposure to mechanical properties.It was found that the average oxidation rate increased with the increase of exposure temperature.At the same exposure temperature,the average oxidation rate was the highest at the beginning.After exposure for 50h at 650?and 700?,the average oxidation rate was basically constant,but it was actually accelerated after exposure for 100h at 750?,which was caused by change of the proportion of the oxides in the oxide layer.After exposure at high temperature,the strength changed little,but the elongation reduced significantly.The main cause of the reduction of elongation is the brittle layer.The secondary reason is the change of microstructure during exposure.After exposure at 650? for 100h,the yield strength of TAN-2 alloy was basically unchanged and the elongation of TAN-2 alloy remained above 3%,which showed that TAN-2 alloy had a good environmental adaptability. |
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