Microstructural evolution of Cu/W nano-multilayers filler metal during thermal treatment

Copper/Tungsten (Cu/W) nano-multilayers show potential for application as novel low-temperature brazing filler metals. Therefore, researchers are interested in understanding phase stability and microstructural evolution of the nano-multilayers during thermal treatment. A repetition of 50 alternating nanolayers of Cu and W with individual thicknesses of 10 nm were prepared by magnetron-sputtering on silicon substrates. The structural evolution of Cu/W nano-multilayers (NMLs) within the temperature range 400 & DEG;C-800 & DEG;C was monitored using real-time in-situ XRD, SEM, TEM, SAXS, DSC and in-house XRD system. The results showed that the melting point of Cu/W nano-multilayers determined using DSC was 793.694 & DEG;C was remarkably lower than the melting point of bulk Cu(1083 & DEG;C) and W (3140 & DEG;C). After annealing at 400 & DEG;C for 30 min, the surface of the NMLs exhibited more copper grains, with significant coarsening of the copper grains. The layered structure of the Cu/W NMLs was unaffected after annealed at 400 & DEG;C. When annealed at 600 & DEG;C for 30 min, some Cu particles migrated into the W layers along the internal interface leading to cracks which partially collapsed the original stratified structure. The nano-multilayered structure was completely destroyed when annealed at 800 & DEG;C. Further, the in-situ XRD results showed that the copper grains grew substantially, while the tungsten size remained unchanged with increasing temperature.