# Oscillating Laser Welding of TC4-304SS Dissimilar Joints: Regulating Microstructure and Mechanical Properties via Cu, Mo, and Nb Interlayers

## TL;DR

This paper explores using Cu, Mo, and Nb interlayers in laser welding to improve the strength of titanium-steel joints by reducing brittle compounds.

## Contribution

The study introduces Mo and Nb interlayers as effective solutions to enhance mechanical properties in Ti-steel dissimilar welding.

## Key findings

- Mo-interlayer joints showed 31% higher shear strength compared to direct welding.
- Fracture transitioned from brittle IMC layers to interlayer-TC4 interfaces with Mo and Nb.
- Cu interlayer promoted TiFe2 and TiCu4 phases, while Mo/Nb inhibited Ti-Fe IMCs.

## Abstract

This study investigated the use of oscillating laser welding with Cu, Mo, and Nb interlayers to mitigate the issue of brittle intermetallic compound (IMC) formation in titanium-steel dissimilar welding for TC4/304SS lap joints. This study systematically examined the influence of interlayer type on joining mechanisms, microstructure, and mechanical properties. Results indicated that direct welding produced Ti-Fe IMCs (TiFe phase) through fusion, resulting in a thick brittle layer. The Cu interlayer facilitated fusion welding while promoting the formation of TiFe2 and TiCu4 phases. Mo and Nb interlayers, through fusion-brazing and brazing mechanisms, respectively, inhibited Ti-Fe IMCs by generating Fe-Mo/Nb IMCs and (Ti, Mo/Nb) solid solutions. Mechanical testing indicated that Mo-interlayer joints exhibited the highest shear strength at 1129.53 N, representing a 31% increase relative to direct joining. This was followed by Nb at 1004.4 N, Cu at 871.6 N, and direct welding at 859.13 N. Fracture transitioned from brittle IMC layers in Cu and direct welding to interfaces between interlayers and TC4 in Mo and Nb systems. This study presents Mo/Nb interlayers as the most effective choice for high-strength Ti-steel joints, providing insights for the selection of interlayers in engineering applications.