2018 Fiscal Year Research-status Report
Development of a strong and ductile Ti-based bulk multi-gradients material utilizing friction stir powder surface processing technique and phase transformation theory
| Project/Area Number |
18K14027
|
|---|
| Research Institution | Osaka University |
|---|
Principal Investigator |
劉 恢弘 大阪大学, 接合科学研究所, 助教 (40748943)
|
|---|
| Project Period (FY) |
2018-04-01 – 2020-03-31
|
| Keywords | Ti / Multi-gradients material / Friction stir processing / Phase transformation |
|---|
| Outline of Annual Research Achievements |
In this study, we utilized friction stir processing to ultra-refine and alloying both-surfaces of alpha-type Ti to develop a novel bulk Ti-based multi-gradients material (MGM). Through proper heat treatments, this MGM is expected to simultaneously possess multi-gradients, thus having a great potential to be strong and ductile due to strong surfaces and ductile core, respectively. A beta-type Ti-alloy (Ti-15-3) sheet of 1.5 mm thick was lap-joined on an alpha-type Ti sheet by friction stir processing under an optimal condition with a rotation speed of 250 rpm, a travel speed of 100 mm/min and a plunge length of 1.9 mm using a WC-based-alloy tool with a shoulder diameter of 12 mm, a probe diameter of 6 mm and a probe length of 1.8 mm. The same processing was also conducted on the other surface of the alpha-type Ti sheet to fabricate a Ti-based plate with beta-phase surfaces and alpha-phase core. The transverse cross section of the fabricated plate was carefully inspected and no defect was visible throughout the cross section, suggesting that the sound weld was achieved between the alpha-Ti and beta-Ti-alloy sheets. Moreover, ultrafine- and coarse-grained microstructures were identified in the surface and core regions, respectively. These results indicated that a bulk Ti-based MGM was successfully fabricated, in which ultrafine-grained beta-phase, ultrafine-grained (beta+alpha)-phase, and coarse-grained alpha-phase microstructures were produced in the top surfaces, subsurfaces, and core of the plate, respectively.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The objective of this study is to develop a novel bulk Ti-based multi-gradients material (MGM) utilizing the friction stir processing technique and phase transformation theory. In the last year, a beta-type Ti-alloy sheet with a thickness of 1.5 mm was lap-joined on an alpha-type Ti sheet by friction stir processing at an optimal processing condition with a plunge length of 1.9 mm using a WC-based-alloy tool with a probe length of 1.8 mm. The same processing was conducted on the other side of the alpha-type Ti sheet so that a Ti-based plate with beta-phase surfaces and alpha-phase core was obtained. The results showed that a bulk Ti-based MGM with the absence of defects, contaminations and porosities was successfully fabricated, in which ultrafine-grained beta-phase, ultrafine-grained (beta+alpha)-phase, and coarse-grained alpha-phase microstructures were obtained in the top surfaces, subsurfaces, and core of the plate, respectively. However, the most appropriate heat treatment has still not been conducted on the fabricated plate to induce the desired phase transformation in order to achieve the best combination of strength and ductility in the plate as planned. Therefore, based on the above views, we consider that the study is progressing rather smoothly.
|
| Strategy for Future Research Activity |
In the last year, a novel bulk Ti-based multi-gradients material (MGM), in which ultrafine-grained beta-phase, ultrafine-grained (beta+alpha)-phase, and coarse-grained alpha-phase microstructures were obtained in the top surfaces, subsurfaces, and core of the plate, respectively, had been successfully fabricated. For the next step, the heat treatment will be conducted and optimized on the fabricated plate in order to induce the desired phase transformation in the beta phases. The microstructure of the fabricated plates with and without heat treatment will be systematically inspected by optical microscopy, X-ray diffraction, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. Mechanical properties including hardness distribution, tensile properties and fatigue properties of the fabricated plates are planned to be evaluated. Furthermore, deformation mechanism of the optimized bulk MGM will be systematically investigated by in-situ SEM/EBSD observation during tensile deformation. The obtained findings might not only assist to develop a novel strong and ductile Ti-based bulk MGM for structural applications, but also provide an innovative strategy to develop desired gradient materials utilizing the friction stir processing principle and phase transformation theory.
|
Research Products
(28 results)
