Dissimilar laser welding of NiTi to Ti6Al4V via Zr interlayer

ABSTRACT

The ability to integrate multiple distinct properties into a single structure is the driving force behind the development of NiTi to Ti6Al4V dissimilar joints. However, differences in thermophysical properties and the subsequent development of brittle Ti₂Ni and Ni₃Ti intermetallic compounds (IMCs) make fusion welding of these alloys rather challenging. The solidification of brittle IMC causes cracking upon solidification and a significant reduction on the joint mechanical properties. In this study, two strategies were used concurrently to reduce the formation of brittle IMC: zirconium (Zr) interlayer was introduced alongside with the laser beam being offset to the Ti6Al4V side. The influence on microstructural evolution was investigated using various characterization techniques. Scanning electron microscopy aided by energy dispersive spectroscopy and micro-X-ray diffraction supported by Rietveld refinement revealed that the volume fraction of the Ti₂Ni brittle phase was drastically reduced from 90 to 9%, leading to improvements on the joint mechanical performance. A joint with a lower hardness of 392 HV was obtained, compared to 515 HV for the conventional NiTi/Ti6Al4V joint. The strength and ductility of the Zr-interlayered joint were improved to 320 MPa and 1.7%, respectively, compared to 148 MPa and 0.8% for the Zr-free joint.

KEYWORDS:

• Laser
• welding
• NiTi
• Ti6AL4V
• intermetallic
• rietveld
• microstructure
• interlayer

Acknowledgements

JPO acknowledges Fundação para a Ciência e Tecnologia (FCT) for its financial support through the project UIDB/00667/2020 (UNIDEMI). JPO acknowledges the funding of CENIMAT/i3N by national funds through the FCT-Fundação para a Ciência e a Tecnologia, I.P., within the scope of Multiannual Financing of R&D Units, reference UIDB/50025/2020-2023.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/10426914.2022.2089897.

Additional information

Funding

This work was supported by Natural Science Foundation of China [No. 52175292], Science and Technology Project of Sichuan Province [No. 2020ZDZX0015, 2021YFG0053] and GuangDong Basic and Applied Basic Research Foundation [2021B1515140048].