Ultrasonic Welding of Nickel with Coarse and Ultrafine Grained Structures

Elvina Shayakhmetova,Ayrat Nazarov,Mariya Murzinova

doi:10.3390/met11111800

Elvina Shayakhmetova, Ayrat Nazarov + Show 1 more

Open Access

https://doi.org/10.3390/met11111800

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Journal: Metals	Publication Date: Nov 9, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: Institute of Metal Superplasticity Problems

Abstract

Solid state joints of samples of coarse-grained (CG) and ultrafine-grained (UFG) nickel have been obtained for the first time using spot ultrasonic welding (USW). The UFG structure in disk-shaped samples was processed by means of high-pressure torsion (HPT). On the basis of lap shear tests, the optimal values of the clamping force resulting in the highest values of the joint strength are determined. The microstructures in the weld joints obtained at optimal parameters of USW are characterized by scanning electron microscopy. It is shown that during ultrasonic welding of coarse-grained nickel, a thin layer with an UFG microstructure is formed near the weld surfaces. The bulks of sheets retain the CG microstructure, but a significant dislocation activity is observed in these regions. During USW of samples having an UFG initial microstructure, significant grain growth occurs. Fine grains are observed only along the welding interface. An average lap shear strength of 97 MPa was obtained by welding the UFG samples, which was approximately 40% higher than the strength of samples processed by welding coarse-grained sheets (70 MPa). It is concluded that higher strength weld joints can be obtained by using sheets with the UFG structure as compared to the CG sheets.

Highlights

Ultrasonic welding (USW) of metals is a relatively new technology capable of joining metallic foils, thin sheets and wires [1,2,3,4,5]
Spot USW has developed into a mature technology, which is widely used in electrical, automotive, medical, aerospace, and other industries [4,5]
The present paper aims at a detailed elucidation of the role of the UFG state of nickel in the evolution of its microstructure during USW, determination of the strength of the joints of UFG sheets obtained by USW, and a comparison of the results to the welding characteristics of nickel in the coarse-grained state

Summary

Introduction

Ultrasonic welding (USW) of metals is a relatively new technology capable of joining metallic foils, thin sheets and wires [1,2,3,4,5]. USW is based on the use of the energy of mechanical vibrations generated in materials to be welded by a welding tool of an oscillatory system that performs reciprocating movements with an ultrasonic frequency, normally in the range of 19–25 kHz. Unlike the welding of plastics, when the vibrations occur normally to the joining interface, metals are ultrasonically welded by vibrations parallel to the interface. Unlike the welding of plastics, when the vibrations occur normally to the joining interface, metals are ultrasonically welded by vibrations parallel to the interface These vibrations cause the friction of surfaces to be welded, destruction of oxide layers, and the heating and plastic deformation of materials in the welding area followed by their bonding [4]. Diffusion is believed to play a considerable role in the joining process too [2,5]

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