Microstructure and Mechanical Property Correlation Between Rotary Friction Welded Nitinol–Nitinol Joints

Ateekh Ur Rehman,Mahesh Kumar Talari,Hisham Al-Khalefah,Nagumothu Kishore Babu,Yusuf Siraj Usmani

doi:10.3389/fmats.2021.726383

Ateekh Ur Rehman, Mahesh Kumar Talari + Show 3 more

Open Access

https://doi.org/10.3389/fmats.2021.726383

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Abstract

In the present study, a rotary friction process was used to join nitinol in a similar welding combination. Macro- and microstructure characteristics of the weld zone were compared with adjacent zones and the base metal. The hardness and tensile properties of the joints were evaluated, and the results were discussed in relation to the weld microstructure. The weld macrostructure revealed a uniform flash around the circumference of the weld. The optical microstructure of the welded sample revealed fine recrystallized grains at the weld interface due to heavy deformation followed by dynamic recrystallization. The phase transformation behavior of the base metal and welded samples was studied by using a differential scanning calorimeter (DSC). The drift in phase transformation temperatures after rotary friction welding may be attributed to fine grain formation at the weld interface. Friction welded samples exhibited improved yield strength and hardness values compared to the base metal due to grain refinement at the weld interface.

Highlights

Nitinol (NiTi) alloys exhibit unique functional properties of superelasticity and the shape memory effect
The weld interface exhibited a higher hardness value (325 HV) than the base metal (306–312 HV) and thermomechanically affected zone (TMAZ) and heat-affected zone (HAZ) (313–315 HV). This could be attributed to the fine recrystallized grains present at the weld interface due to heavy deformation followed by dynamic recrystallization
The nitinol–nitinol similar welds produced using the rotary friction welding process have been analyzed for weld macroand microstructures, grain size, and mechanical properties

Summary

Introduction

Nitinol (NiTi) alloys exhibit unique functional properties of superelasticity and the shape memory effect. These alloys have excellent strength, ductility, corrosion resistance, and biocompatibility properties Because of such a distinctive combination of properties, NiTi finds uses ranging all the way from space to biomedical applications. It is believed that a novel NiTi spring tire on the wheels would prolong rover’s life, as these tires can withstand the treacherous surface of Mars as compared to pneumatic ones (Padula et al, 2019). Biomedical applications utilize both of the NiTi properties—superplastic and the shape memory effect—in devices such as stone retrieval basket, Simon nitinol inferior vena cava filter (Kapoor, 2017)

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