Study On High Temperature Uneven Plasticity Deformation Behavior Of Ti-48Al-2Cr-2Nb Alloy

TiAl-based alloys are widely used because of their excellent high temperature properties,creep resistance and light weight,but there still have many shortcomings in practical applications,such as low molding,hot processing is difficult and so on.The lamellar tissue of the original crude cast is thinning by cyclic heat treatment.The finite element simulation of high temperature compression process of original cast microstructure Ti-48Al-2Cr-2Nb alloy,microstructure after three tempering in a biphasic zone and fine lamellar structure after four tempering in two phase+solid solution treatment was carried out respectively.And high temperature compression experiments were also conducted.The calculation of critical damage factor of Ti-48Al-2Cr-2Nb alloy with small slice structure obtained by heat treatment based on Cockroft-Lathem criterion,the main conclusions obtained are as follows:The cast microstructure with grain size of 1200?m was refined through the rapid heating-cooling cycle heat treatment process,and the small layer of grain with a grain size of about 250?m was obtained,the hardness value increased from 250HV_0.5.5 to280HV_0.5.The finite element simulation results of the deformation process of Ti-48Al-2Cr-2Nb alloy under 1050?,0.01s^-11 in different tissue states show that:The strain maxima are mainly distributed in large deformation zones,the stress and damage maximum are distributed in the free deformation zone.The most uniform distribution of strain,stress and damage was found in the microstructure,the strain,stress field and damage distribution of cast microstructure are the most inhomogeneous.The maximum damage in the free deformation zone of the cast microstructure reaches 2.87 when the deformation is 60%,and the maximum damage in the free deformation area of small lamella tissue was 0.47.The recrystallization degree of the alloys with different microstructure States after deformation is large deformation zone>free deformation zone>difficult deformation zone,the recrystallization in the deformation zone of the thin film structure obtained by heat treatment is most sufficient.The strain field,stress field and damage distribution of the alloy with small lamellar structure are the most uniform at high temperature and low strain rate(1200?,0.001s^-1),the maximum damage in the free deformation zone is only 0.37when the deformation is 60%,the strain field,stress field and damage distribution are not uniform at low temperature and high strain rate(1100?,0.1 s^-1),the maximum damage in free deformation zone reaches 3.32,the alloy is sensitive to the deformation temperature and strain rate,the reduction of strain rate and the rise of deformation temperature are beneficial to the uniformity of deformation and damage reduction of the alloy.The recrystallization degree of microstructures in different deformation zones of small lamellar alloys varies greatly when they are deformed at low temperature and high strain rate.The recrystallization of the deformed zone is more complete when it is deformed at high temperature and low strain rate,the reduction of strain rate and the rise of deformation temperature is conducive to the reduction of non-uniform microstructure distribution in the deformation areas of Ti-48Al-2Cr-2Nb alloy,and promote the complete recrystallization of tissues in various deformation zones.The critical damage factor of Ti-48Al-2Cr-2Nb alloy with small sheet structure under different thermal deformation parameters is calculated based on the Cockroft-Lathem criterion and the microscopic organization was verified.The results show that the critical damage factor varies from 0.205 to 1.817,the critical damage factor ranges from 0.205 to 0.214 at high temperature and low strain rate(1200?,0.001s^-1),the critical damage factor ranges from 1.736 to 1.817 at low temperature and high strain rate(1100?,0.1s^-1).