| Thermomechanical treatment is a kind of strengthening method which combines plastic processing and heat treatment.This combination method of comprehensive utilization of thermomechanical strengthening and heat treatment strengthening will make the material obtain a good match of high strength,high toughness and high plasticity which cannot be obtained by a single strengthening method.On the one hand,it is beneficial to simplify the production process,improve the economic benefits;on the other hand,it can meet the increasing demand Long performance requirements.With the rapid development of the aerospace industry,components in aircraft industry should own excellent comprehensive properties with strength,plasticity and thermal strength to meet complicate conditions.It is the main research direction of this subject that whether we can get good microstructure and comprehensive properties through thermomechanical treatment.In this paper,TC17 titanium alloy,which is widely used in the aerospace industry,is taken as the research object.The isothermal compression test of TC17 titanium alloy is carried out by using a thermal simulator.The microstructure of the deformed alloy is observed using an optical microscope?OM?,scanning electron microscope?SEM?and back scattering electron microscope?EBSD?.The thermal deformation behavior of TC17 alloy with initial?lamellar structure under different processing parameters is studied,the dynamic material model?DMM?is used to construct the hot processing map of the alloy.The analysis of the processing map is combined with the structure,and the hot working property is studied deeply and the optimal hot working parameters are worked out.Furthermore,the relationship between the microstructure evolution and mechanical properties of TC17 alloy was explored.The main conclusions are as follows:In the process of high-temperature hot deformation,TC17 alloy shows two kinds of different rheological softening phenomena.In the?+?two-phase region,the continuous softening behavior occurs at a high strain rate and low strain rate.In the?single-phase region,after the rheological stress reaches the peak value,it rapidly reduces to a stable value,and in the high strain rate,it shows obvious discontinuous yield phenomenon,followed by oscillation,and At low strain rate,the effect of true strain on the flow stress is very small,showing a stable flow pattern,and the peak stress increases with the decrease of deformation temperature and the increase of strain rate.According to the calculated thermal deformation activation,the deformation activation energy decreases from 670.1 to 370.1 kj·mol-1 with the increase of strain in the?+?two-phase region,and the deformation mechanism is globularization.In the?single-phase region,the activation energy of deformation decreased from 301.4to 239.3 k J·mol-1 with the increase of strain.At a high strain rate,the main deformation mechanism is dynamic recovery.It is?dynamic recrystallization at a low strain rate,Based on the analysis of the hot processing map,the strain has a significant effect on the instability map of TC17 alloy.When the true strain increases from 0.3 to 0.7,the instability region in the instability map increases with it,and the increase of the instability region means that the processing region of titanium alloy becomes narrower.The optimal processing parameters(deformation temperature is 860?,strain rate is 10-1s-1)can be obtained from the power dissipation map.At this time,the peak power dissipation reaches 0.5,which is the ideal hot processing areaTC17 titanium alloy will be aged at different temperatures after high-temperature deformation in the?phase region.The results show that the main feature of microstructure evolution is the coarsening of the?-phase,and the coarsening degree increases with the increase of the aging temperature.The result shows that the tensile strength of TC17 titanium alloy increases with the increase of?-lamellar thickness,while the plasticity shows the opposite trend.The impact toughness increases with the increase of?-lamella thickness.Further study shows that there is a linear relationship between tensile properties and impact toughness and?-lamella thickness.That is to say,under the conditions of this experiment,the strength and toughness of TC17 alloy can be adjusted in the range of 540??630?.Thermomechanical treatment can effectively improve the comprehensive properties of TC17 alloy.The strengthening effect mainly comes from the precipitation of?phase in the aging process.The fracture analysis shows that?-lamella plays an important role in the process of crack growth inhibition.The?-lamella can be used as an effective control unit for the plastic toughness of TC17alloy. |
PDF Full Text Request