Study On The Fabrication And Heat Treatment Of TiBw/Ti60 Composites With A Network Microstructure

TiBw/Ti60 composites were fabricated by hot-pressing sintering method based on the system of large and spherical Ti60 powders and fine TiB2 powders. TiB whiskers were distributed by a uniform network microstructure in the composites by adjusting the milling and sintering parameters. Thermodynamic analysis was used to confirm the possibility of reaction system within the blended powders between Ti60 and TiB2, the microstructure of TiBw/Ti60 composites was studied with XRD and SEM analysis. The room and high temperature mechanical properties were tested. Finally, the composites were heat treated. The effects of heat treatment on the microstructure and mechanical propertirs were investigated.5vol.%, 8vol.% and 12vol.%TiBw/Ti60 composites with a network microstructure were fabricated , respectively. XRD result reveals that the TiB2 powders were fully reacted at 1200oC, when the titanium matrix composites were sintered at 1300oC, SEM analysis reveals that: the sintered composites get high relative density, the microstructure of Ti60 matrix contains equiaxedαphase and near-equiaxedαphase, TiB is a rod whisker with the cross-section of Non-equilateral hexagon, which likes a dowel growing toward the inside of Ti60 particles. It is important to connect the matrix. When the volume fraction of TiBw increased, the size of TiBw obviously changed. It was also found that "sand-grey" layers were formed in the network reinforcement systems and the shape of TiBw became very thin. When the volume fraction of TiBw reached 12vol.%, which is bad for the mechanical property of TMCs.In order to get better mechanical property, the heat treatment contains two steps: quenching and aging. The temperature and time of quenching were 1020oC and 30 minutes, respectively. The temperature of aging was 450 oC, 550 oC and 650oC, the time of aging was 2.5, 6 and 8 hours, respectively. The result shows that: firstly, because ofβphase turned into Martersite phase, the contrast ofβphase has obviously changed after the quenching process. Otherwise, some primaryαphase turned intoβphase, so the width ofβphase became wider. Secondly, with the increase of temperature and time of aging process, the trend of Martersite decomposition is gradually evident, so the plastic is gradually increased. At a low temperature, there remains some Martersite left, which has high brittleness; At 550oC, the Martersite phase will turn into fine (α+βphases) mixed microstructure; but at a high temperature, the generated (α+βphases) mixed microstructure will be coarsed. So the strength first increased and thereafter decreased.