Effect Of Thermal Action On Microstructure And Properties Of Ti-14Al-10Nb Alloy

In order to improve the high-temperature service performance and formability of Ti-14Al-10Nb alloy.In this paper,the deformation parameters of the alloy were optimized based on isothermal hot compression test.According to the processing map of the alloy with different deformation parameters,learned about the appropriate processing range and instability.In accordance with the solution and aging heat treatment process,the effect of thermal action on the microstructure of as casted and as forged alloys was discussed respectively,the influence of microstructure evolve for the mechanical properties and the tensile fracture mechanism were analyzed,determined relationships between phase parameters and mechanical properties.The main research work was as follows:The flow stress of Ti-14Al-10Nb alloy was sensitive to the change of deformation temperature and strain rate.The flow stress of the alloy decreases with the deformation temperature rised,while the strain rate was contrary.Discontinuous yielding features arised at the large strain rate(>0.1s^-1).The high-temperature constitutive equation of Ti-14Al-10Nb alloy was constructed using hyperbolic sine Arrhenius equation that can better predict the change of flow stress with deformation parameters.The calculation of model parameters with different strains showed that the average error between the calculated value and the measured value of flow stress were less than 10%.It proved that the prediction accuracy of constitutive equation was high.On the basis of the DMM theory proposed by Prasad,the processing map of Ti-14Al-10Nb alloy was established and that can be safely implemented in the following areas:the temperature of 995℃～1050℃and 1065℃～1100℃,the strain rate of 0.01～0.1s^-1.The destabilizing effect of alloy happened to low temperature and high strain rate.The microstructure of as cast Ti-14Al-10Nb alloy were composed ofα₂phase（acicular）andβphase.With the rised of solution temperature cause that the content and thickness ofα₂phase decrease accordingly.The solution temperature has a great influence on the mechanical properties of the alloy.The content and thickness ofα₂phase decreased accordingly with the increased of solution temperature.The solution temperature has great effect on the mechanical properties of the alloy.The strength of the alloy increased,the plasticity and the wear resistance decreased with the ascended of solution temperature.The tensile strength of the alloy was 1139 MPa which was 25.3%higher than that of the as cast alloy at 900℃,however its tenacity deteriorated sharply with the impact of solution strengthening,at this time its elongation was only 1.5%.Microstructure evolution played a key role.The microstructure of as forged Ti-14Al-10Nb alloy consisted ofα₂phase（equiaxed）andβphase.Equiaxedα₂phase content gradually decreases with the solution temperature went up.The tensile strength of the alloy reached the maximum（1220MPa）,but its elongation was only 4.8%at 700℃.The tensile strength and ductility of the alloy were improved for the solution temperature continues to rised.The microstructure of the alloy turned into slender needle shape alone with solution and aging treatment.The varies of aging temperature and time has tremendous influence on the tensile properties of as forged Ti-14Al-10Nb alloy.The strength and toughness match was well at the 800℃/1h×AC+500℃/8h×AC.At this point,the tensile strength of the alloy reached 1127MPa,and the elongation reached 10.7%.