Investigation on microstructure and compressive strength of brazing porous nickel to copper and stainless steel

This paper investigates the effects of brazing temperatures on the microstructure and compressive strength for brazing porous nickel (Ni) to copper and stainless steel 304 using VZ2250 as the brazing filler metal (BFM). A high vacuum furnace is used to braze the samples. Three (3) different brazing process parameters (680 degrees C/5 min, 710 degrees C /5 min, and 740 degrees C/5 min) were set with a heating rate and cooling rate of 10 degrees C/min, respectively. The characteristics of the joint interface have been investigated to evaluate the performance of the brazed samples by use of scanning electron microscope (SEM), energy-dispersive X-Ray spectroscope (EDS), X-Ray diffractometer (XRD), and Instron Universal Testing machine (for compressive strength testing). The data obtained has been quantitively analyzed to confirm the diffusion of the BFM during the brazing process. It has been found that the diffusion process resulted in an increase in the rigidity of the porous Ni. The compressive strength tests for the brazed Cu/Porous Ni/SS304 joint showed that the maximum compressive strength can be achieved for brazing at 680 degrees C/5 min. The highest compressive strength value has been justified by quantitative analysis of the microstructural data. It has been proved that the VZ2250 BFM effectively diffused into the porous Ni at the brazing temperature of 680 degrees C; brittle phases (Cu3P and Cu6Sn5) were detected at the brazed Interface 1, whereas MnNi3 phase was observed at the brazed Interface 2.