13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Figure 3 Microstructures of prior β phase observed by TEM and the electron diffraction patterns. Figure 4 Schematic illustration to explain the change in microstructure with the duplex treatment. If the aging temperature was increased beyond 803 K, the decomposition of prior β phase proceeded and the hardness showed a decline tendency. The yield and tensile strengths obeyed the hardness of prior β phase (Fig. 6). Namely, the static strengths were improved by STQ treatment, and they were further increased by the subsequent short-time aging. The highest static strengths were achieved by STA treatment (aging temperature: 803 K), and their improvement rates were 46 % and 28 %, respectively. The interesting point was found on the change in ductility. The reduction in area was increased by STQ treatment in spite of the great increase in the static strengths. This improvement will result from the strain-induced transformation of metastable β phase under tensile loading [3, 10]. Through the subsequent short-time aging, the ductility slightly decreased because a part of metastable β phase was decomposed. Nevertheless, the reduction in area was higher than that of the untreated material. As mentioned above, STA treatment greatly improved the static strengths without reduction in ductility.
RkJQdWJsaXNoZXIy MjM0NDE=