Effect of Bonding Temperature on Microstructure and Mechanical Properties of 304L/Zircaloy‐4 Diffusion‐Bonded Joints with Ni/Ta Hybrid Interlayer

Abstract

Diffusion bonding of stainless steel 304 L and zircaloy‐4 (Zr‐4) in solid state is conducted using Ni and Ta as the hybrid interlayer at the bonding temperature of 850−1000 °C for the bonding time of 30 min under the bonding pressure of 6 MPa in vacuum. The effect of the bonding temperature on the microstructure and the mechanical properties of the joints is investigated. The microstructure analysis is conducted by a scanning electron microscope, energy dispersive spectroscopy, and X‐ray diffraction. The mechanical properties of the joints are measured by a shear test and microhardness test. The results show that Ni3Ta intermetallic compounds are formed at the Ni/Ta interface, and the solid solution of Zr and Ta appears at the Ta/Zr‐4 interface. In the meantime, the maximum shear strength reaches 194 MPa and the highest hardness value across the interface of joints is 356 HV in the Ni3Ta layer.

Microstructure and Mechanical Properties of Zr‐4 Alloy and 316 Stainless Steel Diffusion Bonding Joint Using Nb/Ni Composite Interlayer

“…Until now, alternative interlayer materials in the bonding of Zr alloys and SS have been reported including Ti, [ 19 ] Cu, [ 20 ] Al, [ 21 ] Ta, [ 22 ] Ni, [ 23 ] Ag/Ti, [ 24 ] Ta/Ni, [ 25 ] Ti/Ni, [ 26 ] etc. Among the mentioned interlayers, Ni interlayer has good metallurgical compatibility with SS and plasticity which could effectively eliminate residual stresses.…”

“…Z. Wang et al. [ 25 ] and V. Srikanth et al. [ 26 ] used Ta/Ni and Ti/Ni interlayers to join Zr‐4 and SS‐304 L, respectively.…”

Microstructure and Mechanical Properties of Vacuum Diffusion Bonded Zr-4 Alloy Joint

“…Therefore, the development of a reliable technique to join Zr alloys is indispensable to its engineering applications. To date, many scientists have focused on zirconium alloy welding technology, which includes vacuum electron beam welding (EBW), tungsten inert gas welding (TIG), pulsed laser welding (LBW), and pressure resistance welding (RPW) [12][13][14][15][16]. J.G.…”

“…Moreover, the long-period crevice corrosion tendency of the brazed Zr-4 alloy joint would be increased owing to the incomplete penetration structure [17]. Additionally, the metallurgical transformation is facile to occur in the heat-affected zones, resulting in the formation of intermetallic compounds and the reduced performance of joints [16,18]. The EBW [12] and TIG [15] methods are successfully employed to weld Zr-4 alloy and stainless steel, but the molten and heat-affected zones have an irreversible negative impact on the mechanical performance of the internal fuel core [19].…”

“…The diffusion zone at the bonded joint has a large thickness value of 700 µm, which is conducive to buffering the difference of mechanical properties between the two materials and improving the bonding performance of the joint. Additionally, the Ni and Ta as the hybrid interlayer, which was employed to prevent the formation of brittle Zr(Fe, Cr) 2 and Zr 2 (Fe, Ni), was also used to bond Zr-4 alloy to 304 L stainless steel at 850-1000 • C [16]. The shear strength of the bonded joint first increases and then decreases with the increase of the bonding temperature, and the maximum shear strength of 194 MPa was obtained at 950 • C. Until now, there are few studies on the diffusion bonding of zirconium alloy itself, so the microstructure and properties of the self-diffusion bonded joints of zirconium alloys still need further study.…”