A review is provided, which first considers low-temperature diffusion bonding with silver nanomaterials as filler materials via thermal sintering for microelectronic applications, and then other recent innovations in low-temperature joining are discussed. The theoretical background and transition of applications from micro to nanoparticle (NP) pastes based on joining using silver filler materials and nanojoining mechanisms are elucidated. The mechanical and electrical properties of sintered silver nanomaterial joints at low temperatures are discussed in terms of the key influencing factors, such as porosity and coverage of substrates, parameters for the sintering processes, and the size and shape of nanomaterials. Further, the use of sintered silver nanomaterials for printable electronics and as robust surface-enhanced Raman spectroscopy substrates by exploiting their optical properties is also considered. Other low-temperature nanojoining strategies such as optical welding of silver nanowires (NWs) through a plasmonic heating effect by visible light irradiation, ultrafast laser nanojoining, and ion-activated joining of silver NPs using ionic solvents are also summarized. In addition, pressure-driven joining of silver NWs with large plastic deformation and self-joining of gold or silver NWs via oriented attachment of clean and activated surfaces are summarized. Finally, at the end of this review, the future outlook for joining applications with silver nanomaterials is explored.
Laser welds were made in three dual-phase (DP) alloys with ultimate tensile strengths ranging from 450-980 MPa and varying microstructures to investigate effects of heat input on heat affected zone (HAZ) softening. To compare the total heat transferred into the HAZ of all the welds, heat input was normalized using the Rosenthal Equation. It was found that HAZ softening experienced in a DP steel was a function of both martensite content and heat input. Maximum HAZ softening was proportional to the martensite content, and the heat input controlled the completion of softening. Material softening was normalized by martensite content, which showed that the contribution of martensite to material hardness from the three materials is the same; however the materials had different transformation kinetics.
Evaluating the impact performance of resistance spot welded joints in advanced high strength steels (AHSS) is critical for their continued integration into the automotive architecture. The effect of strain rate on the joint strength and failure mode is an important consideration in the design of welded structures. Recent results suggest that the failure mode is dependent upon the strength, chemistry, and processing of AHSS. Current literature, however, does not explain the effects of weld microstructure and a comprehensive comparison has yet to be conducted. The present study details the fracture paths within the joint microstructure of spot welded AHSS, including dual phase (DP), transformation induced plasticity (TRIP) and ferritic-bainitic (FB), in comparison to new high strength low alloy steels. Quasi-static and impact tests were conducted using a universal tensile tester and an instrumented drop tower respectively. Results for elongation, failure load and energy absorption for each material are presented. Failure modes were detailed by observing weld fracture surfaces. In addition, cross-sections of partially fractured weldments were examined to detail fracture paths during static loading. Correlations between the fracture path and mechanical properties were developed using observed microstructures in the fusion zone and heat affected zone. Results showed that good impact performance was obtained in DP780 and TRIP780 grades in relation to DP600, 590R and conventional high strength low alloy.
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