Vacuum Brazing Ti–15–3 with a TiNiNb Braze Alloy

Kao Kao,Tsay Tsay,Shiue Shiue,Wang Wang

doi:10.3390/met9101085

Abstract

Among all types of brazing fillers, Ti-based fillers show satisfactory joint strengths in brazing titanium alloys. However, the major concern in using such fillers is the formation of Cu/Ni/Ti intermetallic compound(s) in the joint. In this study, a Ti–15–3 alloy was vacuum brazed with a clad Ti–35Ni–25Nb foil. The brazed zone consisted of a Ti2Ni intermetallic compound in a (β-Ti,Nb)-rich matrix for specimen brazing at 1000 °C/600 s. Raising brazing temperature and time resulted in the Ti2Ni dissolving into the (β-Ti,Nb)-rich matrix. For the specimen brazing at 1100 °C/600s, Ti2Ni could only be observed at the grain boundaries of the (β-Ti,Nb)-rich matrix. After further raising it to 1200 °C/600 s, the Ti2Ni intermetallic compound was all dissolved into the (β-Ti,Nb)-rich phase. The average shear strength was significantly raised from 140 (1000 °C/600 s) to 620 MPa (1100 °C/3600 s). Crack initiation/propagation in the brittle Ti2Ni compound with the cleavage fractograph were changed into the Ti–15–3 base metal with a ductile dimple fractograph. The advantage of using Nb in the TiNiNb filler foil was its ability to stabilize β-Ti, and most of the Ni in the braze alloy was dissolved into the β-Ti matrix. The brazed joint could be free of any intermetallic phases with a proper brazing cycle applied, and the joint was suitable for a few harsh applications, e.g., repeated stresses and impact loadings.

Highlights

The joining of titanium and its alloys is important in the industry, because joining technology is a fundamental process of manufacturing [1,2]
The brazed zone consisted of a Ti2 Ni intermetallic compound in the (β-Ti,Nb)-rich matrix for the specimen brazing at 1000 ◦ C/600 s
Raising the brazing time/temperature resulted in the dissolution of the Ti2 Ni intermetallic compound into the (β-Ti,Nb)-rich matrix

Summary

Introduction

The joining of titanium and its alloys is important in the industry, because joining technology is a fundamental process of manufacturing [1,2]. The similar/dissimilar joining of Ti and its alloys has been widely evaluated in the literature for many applications [3,4,5,6,7,8,9]. Simoes proposed a dissimilar joining of titanium alloys as well as many advanced ceramics, and they produced components with extraordinary and unique properties for the automotive and aerospace industries [10]. Welding and brazing are two alternative approaches of the metallurgical bonding of Ti alloys [12]. For certain applications such as the manufacturing of heat exchangers and dissimilar joining, brazing is more appropriate than welding [12].

Methods

Results

Conclusion