Simultaneous intermetallics suppression and residual-stress relaxation of heat-resistant Nb-interlayer-inserted Ti-6Al-4V/Si3N4 joints via one-step transient liquid phase bonding and brazing. (10th March 2023)

• Record Type: Journal Article
• Authors: Ong, Fei Shen; Tobe, Hirobumi; Sato, Eiichi
• Is Part Of: Journal of materials science & technology. Volume 139(2023)
• Page Start: 79
• Page End: 91
• Publication Date: 2023-03-10
• Subjects: Transient liquid phase bonding -- Brazing -- Ceramics -- Residual stress -- Finite element analysis; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2022.08.023
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: One-step bonding of Ti-6Al-4V/Nb/Si3 N4 joints by simultaneous transient liquid phase bonding and brazing. Suppression of intermetallics in Ti-6Al-4V/Nb side of joints by transient liquid phase bonding. Tailoring of filler's thickness for sound interfacial bonding in Nb/Si3 N4 side of joints. Enhancement of residual-stress relaxation with highly ductile Ag-rich filler. Elevated temperature strength of joints determined by tradeoff between stress relaxation and filler's weakening. Abstract: This work has successfully proposed a solution to produce robust Nb-interlayer-inserted Ti-6Al-4V/Si3 N4 joints optimized for a maximum operating temperature of 873 K; transient liquid phase bonding (TLPB) of Ti-6Al-4V/Nb side was carried out with Cu and Ni fillers to suppress brittle intermetallic compounds (IMCs), whereas brazing of Nb/Si3 N4 side was performed using a highly ductile Ti-added Ag-rich filler for effective residual-stress relaxation. A sound yet simple one-step bonding process incorporating simultaneous TLPB and brazing was achieved with a relatively short holding time of 10 min at 1213 K. TLPB of Ti-6Al-4V/Nb side with Cu and Ni foils of 2-µm-thick each as a laminated filler suppressed brittle Ti-based IMCs and developed a homogenized microstructure consisting mainly of (α + β)-Ti via isothermal solidification. Meanwhile, brazing of Nb/Si3 N4 side with 100-µm-thick SILVER-ABA filler (92.75Ag-5Cu-1Al-1.25Ti mass%) foil enhanced interfacial bonding with sufficient total Ti content and accommodated residual stress better than conventional eutectic Ag-Cu-based fillers, and it was verified by finite element analysis with consideration of materials' temperature-dependent elasto-plastic properties. All joints with a bonding area of 10 mm × 10 mm were tested via symmetrical four-point bending from room temperature (RT) to 873 K fractured from Nb/Si3 N4 side. When re-heating the joints from RT to 673 K, fracture initiation gradually shifted from Si3 N4 towards interfacial-compounds/Si3 N4 interface and bending strengths maintained ∼220 MPa as weakening of SILVER-ABA filler was compensated by residual-stress relaxation in Si3 N4 . When tested at 873 K, joints fractured mainly across the Ag-rich solid solution in a ductile manner and bending strength degraded by ∼20% to 171 MPa as weakening of SILVER-ABA filler dominated. Graphical abstract: Image, graphical abstract