Equiaxed Treatment And Hot Deformation Of TC11 Titanium Alloy

Mechanical properties and processing capacity of theα+βtitanium alloy greatly depend on its microstructure. So, it is necessary to establish the effect of hot working and heat treatment processing parameters on microstructure and properties by deformation and heat treatment. Firstly, equiaxed microstructure could be produced by treatments including hot compression and duplex anneal. Then, high temperature compression with various processing parameters on the TC11 titanium with equiaxed microstructure was tested in the temperature range 900¹060°C and strain rate range 0.001¹0 s^-1 on the Gleeble^-1500D simulator. On the basis of stress data, the constitutive equations were constructed in theα+βphase region andβphase region, respectively; and thermal processing maps and an index evaluating deformation capacity were obtained too. Finally, the superplastic tensile tests were done to further evaluate deformation capacity. Meanwhile, electron microstructures were analysed by optical microscopy,scanning electron microscopy,transmission electron microscopy and electon back-scattered diffraction.Uniform equiaxed microstructure was obtained by the deformation at 995℃followed water-quenching and the duplex anneal of 995℃2 h FC+920℃4h FC+570℃6h AC, and the grain size was about 9μm. The strength was enhanced from 830MPa to 1190MPa, yield strength from 590 MPa to 1130 MPa, and the relative elongation can reach 13.7% from 1.6% at room temperature for the TC11 titanium alloy with equiaxed microstructure.The high temperature compression of TC11 titanium alloy with equiaxed microstructure shows that all of the stress-strain curves exhibited a peak stress followed by moderate flow softening and steady-state flow in theα+βphase region resulted from dynamic recrystallization and recovery together with the work-hardening effects. However, no flow softening but steady-state flow after a peak stress in theβphase region. The flow stress decreases gradually with the increase of temperature and the decrease of strain rate. At high strain rates(>1s^-1), especially 10 s^-1, the flow curves display discontinuous yield in bothα+βphase region andβphase region. As seen from microstructure analysis, the microstructures after deformation remain basically unchanged at the temperature belove 920℃, while originalαphase transforms transformedβphase as deformed or heated, and originalαphase does mostly transformedβphase at 980℃(below the beta transus temperature nearly 30℃). The microstructure of discontinuous yield displays local high temperature characteristics. The best available technology deformation parameters are 920⁹60℃and 0.001⁰.1s^-1 by thermal processing maps and superplasticity tensile analysis.