Microstructural Evolution and Mechanical Properties of Ti Alloy/Stainless Steel Lap Joints during Cold Metal Transfer Te
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JMEPEG https://doi.org/10.1007/s11665-020-05053-9
Microstructural Evolution and Mechanical Properties of Ti Alloy/Stainless Steel Lap Joints during Cold Metal Transfer Technique with CuSi3 Filler Wire Gang Li, Shengyu Xu, Xiaofeng Lu, Xiaolei Zhu, Jufeng Song, and Yupeng Guo (Submitted May 12, 2020; in revised form July 12, 2020) Joining of dissimilar titanium (Ti) alloy to stainless steel is a very significant challenge during conventional fusion welding. In this study, cold metal transfer (CMT) technique is developed for lap joining of Ti alloy to stainless steel with CuSi3 filler wire. The microstructure evolution, mechanical properties and fracture mechanism of Ti alloy/stainless steel joints are investigated. When low heat input is applied, many fine spherical particles are distributed in the fusion zone, which are indicated as iron-rich phase in the Cu matrix. With an increase in the heat input, the particles become irregular and coarser in the fusion zone, inferring as Fe-Si-Ti ternary phase and Fe2Ti phase. Since the fractions of the melted Ti alloy and stainless steel increase, the reaction of Ti with Fe and Si becomes more intense and Fe-Si-Ti ternary phase and Fe2Ti phase thus appear in the fusion zone. The shear strength of the lap joints decreases with an increase in the heat input. There are two fracture modes in the lap joints, suggesting different fracture mechanisms. The fracture path of the joints is along the Ti-Cu interface under low heat input. The brittle Ti-Cu intermetallics are observed on the fracture surface, indicating that the shear strength and fracture feature of the joints are associated with the compound layer. The fracture failure of the lap joints occurs in the fusion zone under large heat input. The Fe-Si-Ti ternary phase and Fe2Ti phase have detrimental effects on the joint strength, resulting in a brittle fracture in the fusion zone. Keywords
cold metal transfer, mechanical properties, microstructure, the interface, Ti alloy/stainless steel lap joints
1. Introduction The composite components composed of titanium (Ti) alloy and stainless steel can fully utilize the two materials to complement each other in performance and economic advantages. So, they have been widely used in aerospace, automotive and electrical power industry. However, it is very difficult to produce a reliable Ti alloy/stainless steel joint because of metallurgical incompatibility, the formation of inevitable intermetallic compounds (IMCs) and cracking. Direct joining has been proved to form brittle Fe2Ti and FeTi phases in the joints, which seriously deteriorate the mechanical properties (Ref 1, 2). Joining of Ti alloy to stainless steel is a very significant challenge until now. In recent years, scientists have developed extensive methods to reduce the growth of IMC layer in Ti alloy/stainless steel joints. Zakipour et al. (Ref 3) reported transient liquid phase bonding of 316L and Ti-6Al-4V using pure Cu interlayer with different thicknesses. Kundu et al. (Ref 4) investigated diffusion bonding of 17-4 precipit
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