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

oleh: Chuan-Sheng Kao, Leu-Wen Tsay, Shan-Bo Wang, Ren-Kae Shiue

Format: Article
Diterbitkan: MDPI AG 2019-10-01

Deskripsi

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&#8722;15&#8722;3 alloy was vacuum brazed with a clad Ti&#8722;35Ni&#8722;25Nb foil. The brazed zone consisted of a Ti<sub>2</sub>Ni intermetallic compound in a (&#946;-Ti,Nb)-rich matrix for specimen brazing at 1000 &#176;C/600 s. Raising brazing temperature and time resulted in the Ti<sub>2</sub>Ni dissolving into the (&#946;-Ti,Nb)-rich matrix. For the specimen brazing at 1100 &#176;C/600s, Ti<sub>2</sub>Ni could only be observed at the grain boundaries of the (&#946;-Ti,Nb)-rich matrix. After further raising it to 1200 &#176;C/600 s, the Ti<sub>2</sub>Ni intermetallic compound was all dissolved into the (&#946;-Ti,Nb)-rich phase. The average shear strength was significantly raised from 140 (1000 &#176;C/600 s) to 620 MPa (1100 &#176;C/3600 s). Crack initiation/propagation in the brittle Ti<sub>2</sub>Ni compound with the cleavage fractograph were changed into the Ti&#8722;15&#8722;3 base metal with a ductile dimple fractograph. The advantage of using Nb in the TiNiNb filler foil was its ability to stabilize &#946;-Ti, and most of the Ni in the braze alloy was dissolved into the &#946;-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.