Joining of stainless-steel specimens with nanostructured Al/Ni foils

Abstract

We describe the joining of stainless-steel specimens at room temperature using free-standing Al/Ni foils as local heat sources for melting AuSn solder layers. The foils contain many nanoscale layers of Al and Ni that react exothermically, generating a self-propagating reaction. The heats, velocities, and products of the reactions are described, and the microstructure and the mechanical properties of the resulting joints are characterized. Increasing the foil thickness, and thereby increasing the total heat released, can improve the strength of the joints until foil thickness reaches 40 μm. For thicker foils, the shear strength is almost constant at 48 MPa, compared to 38 MPa for conventional solder joints. The higher strength is due to finer microstructures in the solder layers of reactive joints. A numerical study of heat transfer during reactive joining and experimental results suggest that the solder layers need to melt completely and remain molten for at least 0.5 ms to form a strong joint.

Characterization and Application of Al/Ni Reactive Multilayers in Exploding Foils

“…Heat release, peak temperature and predicted premixing thickness are listed in Table 1. The total thermal effects calculated from the DSC data are close to the values in references [19,20]. The exotherm of the samples was reduced continuously with decreasing bilayer thickness, which should be ascribed to a larger volume fraction of premixing.…”

“…The peak temperature rose slightly with increasing bilayer spacing, from 231.7 °C to 256.9 °C for the first peak for example, which suggested that longer diffusion distances were indispensable for the Al and Ni atoms to interdiffuse and fully react. The heat released can be used to figure out the premixing thickness, according to the following equation [19]:…”

Prediction and characterization of heat-affected zone formation in tin-bismuth alloys due to nickel-aluminum multilayer foil reaction

“…Wang et al, 3 which studied similar foils, the thickness of the intermixed layer was determined to be 2.3 nm.…”

“…[10][11][12][13][14][15][16][17][18][19][20] By comparison, fewer investigations have been undertaken to develop applications for the RMFs. [1][2][3][4][5][6][7] Little is understood regarding the effect of RMFs on neighboring materials (such as a substrate) and the relationship between heat transport in the bulk material and its consequential effect on the microstructure evolution of the ensemble. (Throughout this work, the word "substrate" refers to the bulk Sn-Bi alloy to which the multilayer is bonded through reaction.…”

“…[1][2][3][4][5][6][7] These materials utilize alternating submicron layers of reacting elements to generate heat. The alternating layers provide short diffusion lengths for mixing of the reactive elements to occur.…”