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摘要:
Microstructure and phase transformation of Ti46Al8Nb0.5B0.2C alloy have been investigated. X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that as-cast and hot isostatic pressing (HIP) alloy mainly composed of gamma and alpha(2) phase have fully lamellar microstructure with point-like or ribbon-like TiB2 distributing in lamellar colony or at grain boundary. The mean size of lamellar colony is about 150 and 450 mu m for as-cast and HIP alloy, respectively. The lamellar spacing is about 550 and 600 nm for as-cast and HIP alloy, respectively. It has been found that cooling rates and quenching temperatures have significant effect on phase transformation of Ti46Al8Nb0.5B0.2C alloy. When the alloy is treated at 1380 degrees C for 1 h and cooled from alpha domain, water cooling leads to complete alpha -> alpha(2) transformation, oil cooling leads to predominant alpha -> alpha(2) and part alpha -> gamma(m) transformation, air cooling leads to alpha -> alpha + gamma(p2) -> L(alpha + gamma) -> L(alpha(2) + gamma) transformation, and furnace cooling leads to alpha -> alpha + gamma(p3) -> L(alpha + gamma) -> L(alpha(2) + gamma) transformation. However, when the alloy is treated at 1400 degrees C for 1 h and cooled from a domain, water cooling leads to predominant alpha -> alpha(2) and part alpha -> alpha + gamma(p4) -> gamma(n) transformation, oil cooling leads to alpha -> alpha + gamma(p5) -> gamma(m) transformation, air cooling leads to alpha -> alpha + gamma(p6) -> L(alpha + gamma) -> L(alpha(2) + gamma) transformation, and furnace cooling leads to alpha -> alpha + gamma(p7) -> L(alpha + gamma) -> L(alpha(2) + gamma) transformation. Microstructural evolution of the alloy during various heat treatments has been examined and the phase transformation mechanisms have been elucidated. Based on the experimental observation, schematic CCT diagrams for the alloy have been given.
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JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY
ISSN: 1005-0302
年份: 2012
期: 5
卷: 28
页码: 453-460
1 0 . 9 0 0
JCR@2022
ESI学科: MATERIALS SCIENCE;
JCR分区:1
中科院分区:3