2020 Fiscal Year Research-status Report
Dissimilar friction welding of titanium alloy and stainless steel and its welding principle elucidation for spinal fixation application
| Project/Area Number |
20K05169
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| Research Institution | Osaka University |
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Principal Investigator |
劉 恢弘 大阪大学, 接合科学研究所, 准教授 (40748943)
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | Friction welding / Titanium alloy / Stainless steel / Microstructural / Mechanical properties |
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| Outline of Annual Research Achievements |
Ti-6Al-4V alloy (Ti64) and SUS316L stainless steel rods of 10 mm in diameter were dissimilarly friction welded. The relationship between the processing conditions, weld interface microstructure and its evolution, and mechanical properties of the fabricated joints were systematically investigated in order to obtain a sound dissimilar Ti64/SUS316L joint. The results show that the increased friction pressure unexpectedly decreased the welding temperature, which effectively suppressed the formation of the thick intermetallic compound layers at the weld interface that was supposed to be beneficial for the joint strength improvement. However, high shear strain rate and high temperature rising rate occurred between the faying surfaces caused a formation of the hard and brittle Ti64/SUS316L mechanically mixed layers at the weld interface, which significantly deteriorated the joint quality. Based on the above findings, rotation speed reduction and liquid CO2 cooling were accordingly utilized to reduce the shear strain rate and the temperature increasing rate. As a result, the formation of the harmful mechanically mixed layers was effectively suppressed at the weld interface, and a high-quality dissimilar Ti64/SUS316L friction welded joint was successfully fabricated.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
This study aims to elucidate the welding principle for the friction welding of Ti64 and SUS316L and fabricate a sound dissimilar Ti64/SUS316L joint. In the last year, Ti64 and SUS316L rods with the diameter of 10 mm were subjected to the friction welding under various processing parameters. The interface microstructure, microstructural evolution, and mechanical properties of the obtained joints were carefully examined. We found that even though the increased friction pressure acted to effectively lower the welding temperature hence to significantly suppress the brittle intermetallic compound layer formation, the harmful Ti64/SUS316L mechanically mixed layers were generated at the weld interface due to the high shear strain rate and high temperature rising rate between the faying surfaces, that remarkably deteriorated the joint quality. Rotation speed reduction and external cooling were accordingly adopted, which effectively suppressed the mechanically mixed layer formation and successfully improved the joint quality. Based on the above results, we consider that the study is progressing rather smoothly.
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| Strategy for Future Research Activity |
In the last year, we have conducted friction welding on Ti64 and SUS316L rods and carefully investigated the relationship between the processing parameters, interface microstructure and its evolution, and mechanical properties of the fabricated joints. We found that the formation of the harmful Ti64/SUS316L mechanically mixed layers, which closely correlated to the joint quality, was attributed to the high shear strain rate and high temperature rising rate between the faying surfaces and successfully improved the joint quality through suppressing the harmful mechanically mixed layer formation via a series of corresponding parameter optimizations. For the next step, the thermal cycles and material deformation behaviors at the weld interface during friction welding under different processing conditions will be discussed via experimental and simulation methods, so that the processing parameters, temperature/strain/strain-rate evolution, and microstructure/mechanical properties of the joints could be comprehensively analyzed, allowing the welding principle for the friction welding of Ti64 and SUS316L possible to be clarified. Based on the obtained findings, we will further optimize the processing parameters, trying to further improve the joint quality using simpler and easier welding procedures.
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