Effect of Solution-ECAP-Aging Treatment on the Microstructure and Properties of TB8 Titanium Alloy

The microstructure and mechanical properties of the TB8 titanium alloy were controlled by a secondary processing technology of solution-equal channel angular pressing(ECAP)-aging treatment,which combined strong plastic deformation with heat treatment. The effects of ECAP and heat treatment on the microstructure and properties of the titanium alloy were systematically investigated by optical microscopy(OM), scanning electron microscopy(SEM), hardness tests, and tensile property analysis. The results indicate that the metallographic structure without ECAP treatment is mainly equiaxed β-phase, while that after ECAP treatment is equiaxed β-phase with grain fragmentation, slip bands, and new small grains. After 850 ℃ solutionECAP-520 ℃ aging treatment, the titanium alloy has the smallest grain size, while the directionality of tissue growth along the ECAP direction is the most apparent. Under the same solution-aging conditions, the hardness of the titanium alloy increases from 431.5 to 531.2 HV compared to that without ECAP treatment, i e, increases by 23.11%, and the tensile strength increases from 1 045.30 to 1 176.25 MPa, i e, increases by 12.5%.

Variant selection of nanocrystalline a phase in metastableβTB8 titanium alloy via electric pulse treatment

In this paper,the metastableβTB8 titanium alloy with nanocrystallineαphase is achieved by electric pulse treatment.The morphology evolution and variant selection of nanocrystallineαphase in metastableβTB8titanium alloy were investigated by using scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and transmission electron microscope(TEM)analysis.The results indicated that the morphologies of the nanocrystallineαphase were mainly triangular clusters and needle-like at the pressure of 0 MPa.With increasing pressure from 20 to 50 MPa,the volume fraction of needlelikeαphase decreased,and a large amount of V-shapedαphase formed in the interior ofβgrains.Based on the EBSD data,the parentβphase was reconstructed by MTEX software.In the interior of theβgrains,12 variants can form for the samples electric pulse treated at 0 and20 MPa,while only 3 and 6 variants can form for the samples electric pulse treated at 30 and 50 MPa.In the grain boundary of theβgrains,one or more grain boundaryαvariants can be generated for the samples electric pulse treated at different pressures as long as one of the neighborβgrains follows the Burgers orientation relationship.

Microstructure and texture evolution of TB8 titanium alloys during hot compression

In this study, microstructure and texture evolution of TB8 titanium alloys during hot deformation were investigated by using electron back-scattered diffraction(EBSD) analysis. The results showed that dynamic recrystallization(DRX) behavior of TB8 titanium alloys was drastically sensitive to the strain. As the true strain raised from 0.2 to 0.8, the degree of DRX gradually increased. The nucleation mechanism of recrystallization was observed, including discontinuous dynamic recrystallization(DDRX) resulting from the bulging of original boundaries. Furthermore, continuous dynamic recrystallization(CDRX) occurred because of the transformation of low-angle grain boundaries(LAGBs) to high-angle grain boundaries(HAGBs) in the interior of the original deformed grains. The texture evolution of TB8 titanium alloy during hot deformation process was analyzed in detail, and five texture components were observed,including{001}h100 i,{011}h100 i,{112}h110 i,{111}h110 i, and {111}h112 i. As the true strain increased,deformation textures were gradually weakened due to an increase in the volume fraction of DRX grains. When the true strain was 0.8, the main texture components consisted of the recrystallization texture components of the{001}h100 i and {011}h100 i textures.

Rolling reduction-dependent deformation mechanisms and tensile properties in aβtitanium alloy

This work investigated the dependence of deformation mechanisms and mechanical properties on cold rolling reductions of the metastable TB8 titanium alloy.Results shown that the crystal orientation of the matrix changes with the increasing level of reduction,leading to the activation of complex deformation mechanisms in the matrix.When the rolling reduction is 10%,the deformation mechanisms are dominated by dislocations and{332}<113>deformation twins.As the reductions increase to 20%-50%,the secondary deformation twinning(SDT)is triggered in primary deformation twins besides the primary kink band is activated.Meanwhile,the secondary kink bands and{332}<113>twins have be observed in the primary kink bands.When the reduction reaches to 60%,the deformation mechanisms are dominated by dislocations and deformation twins.Furthermore,the matrix refined by crisscrossing among the twins,kink bands and other deformation mechanisms during cold rolling,which shortens the dislocation mean free path and then affects the strength and shape of the alloy.The dynamic Hall-Petch effect and the interaction between multi-scale deformed structures control the work hardening behavior of the alloy.