The hot deformation characteristics of the Ti-5.7Al-2.1Sn-3.9Zr-2Mo-0.1Si(Ti-6242S)alloy with an acicular starting microstructure were analyzed using processing map.The uniaxial hot compression tests were performed at...The hot deformation characteristics of the Ti-5.7Al-2.1Sn-3.9Zr-2Mo-0.1Si(Ti-6242S)alloy with an acicular starting microstructure were analyzed using processing map.The uniaxial hot compression tests were performed at temperatures ranging from 850 to 1000℃and at strain rates of 0.001-1 s-1.The developed processing map was used to determine the safe and unsafe deformation conditions of the alloy in association with the microstructural evolution by SEM and OM.It was recognized that the flow stress revealed differences in flow softening behavior by deformation at 1000℃compared to the lower deformation temperatures,which was attributed to microstructural changes.The processing map developed for typical strain of 0.7 in two-phase field exhibited high efficiency value of power dissipation of about 55%at 950℃and 0.001 s-1,basically due to extensive globularization.An increase in strain rate and a decrease in temperature resulted in a decrease in globularization ofαlamellae,whileαlamellar kinking increased.Eventually,the instability domain of flow behavior was identified in the temperature range of 850-900℃and at the strain rate higher than 0.01 s-1 reflecting the flow localization and adiabatic shear banding.By considering the power efficiency domains and the microstructural observations,the deformation in the temperature range of 950-1000℃and strain rate range of 0.001-0.01 s-1 was desirable leading to high efficiencies.It was realized that(950℃,0.001 s-1)was the optimum deformation condition for the alloy.展开更多
The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature.The rate of coars...The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature.The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations.For the CS route, an increase in liquid fraction resulted in faster coarsening.A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate.The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014.Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries.This could be the result of pinning or of the liquid film impeding diffusion at the boundary.展开更多
文摘The hot deformation characteristics of the Ti-5.7Al-2.1Sn-3.9Zr-2Mo-0.1Si(Ti-6242S)alloy with an acicular starting microstructure were analyzed using processing map.The uniaxial hot compression tests were performed at temperatures ranging from 850 to 1000℃and at strain rates of 0.001-1 s-1.The developed processing map was used to determine the safe and unsafe deformation conditions of the alloy in association with the microstructural evolution by SEM and OM.It was recognized that the flow stress revealed differences in flow softening behavior by deformation at 1000℃compared to the lower deformation temperatures,which was attributed to microstructural changes.The processing map developed for typical strain of 0.7 in two-phase field exhibited high efficiency value of power dissipation of about 55%at 950℃and 0.001 s-1,basically due to extensive globularization.An increase in strain rate and a decrease in temperature resulted in a decrease in globularization ofαlamellae,whileαlamellar kinking increased.Eventually,the instability domain of flow behavior was identified in the temperature range of 850-900℃and at the strain rate higher than 0.01 s-1 reflecting the flow localization and adiabatic shear banding.By considering the power efficiency domains and the microstructural observations,the deformation in the temperature range of 950-1000℃and strain rate range of 0.001-0.01 s-1 was desirable leading to high efficiencies.It was realized that(950℃,0.001 s-1)was the optimum deformation condition for the alloy.
基金the UK Engineering and Physical Sciences Research Council (EPSRC Grant GR/M89096) and the University of Leicester for financial support
文摘The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature.The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations.For the CS route, an increase in liquid fraction resulted in faster coarsening.A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate.The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014.Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries.This could be the result of pinning or of the liquid film impeding diffusion at the boundary.
