| 研究実績の概要 |
A beta Ti-alloy (Ti-15V-3Cr-3Sn-3Al) sheet was lap-joined to an alpha pure-Ti sheet by friction stir processing (FSP). The same processing was also performed on the opposite side of the pure-Ti sheet. The transverse cross section of the specimen was subjected to a microstructural analysis using OM, XRD, EBSD and EDS. The tensile test was conducted to evaluate the mechanical properties. An ultrafine-grained beta-phase microstructure with a high LAGB ratio and a low texture intensity, an ultrafine-grained alpha-phase microstructure with a high LAGB ratio and a high texture intensity, an ultrafine-grained alpha-phase microstructure with a low LAGB ratio and a low texture intensity, and a coarse-grained alpha-phase microstructure with a high LAGB ratio and a low texture intensity were generated in sequence from the specimen surface to the core. The tensile results show that the specimen has a quite high tensile strength of ~716 MPa, which is slightly lower than that of the beta Ti alloy but much higher than that of the alpha pure Ti, and a large elongation of ~0.46 which is much larger than those of both beta Ti alloy and alpha pure Ti. A novel strong and ductile Ti-based bulk multi-gradients material, containing grain sizes, grain boundary characteristics, chemical compositions, and phase constitutions gradients, was thus successfully fabricated in the present study. This work not only develops a novel strong and ductile Ti-based bulk multi-gradients material, but also provides a new strategy to develop other high-performance gradient materials utilizing FSP technique.
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