FACTORS AFFECTING ISOTHERMAL SOLIDIFICATI ON DURING TRANSIENT LIQUID PHASE-BRAZING OF NICKEL

The effects of base metal grain size and quenching method form the bra zing temperature on isothermal so cation during TLP-brazing with Ni-11 mass%P filler metal were investigated. Single crystal, coarse-grained and fine-grained nickel base metals were brazed at 1423 K for various holding times, and the test specimens were then air-cooled, oil-quenc hed or water-quenched. Scanning electron microscopy and element analys is revealed that the eutectic width produced in air-cooled and in oil- quenched samples were smaller than that in the water-quenched specimen s. This difference in eutectic width was due to different solidificati on modes occurring during cooling from the brazing temperature. The eu tectic width decreased linearly with the square-root of the brazing ti me in single crystal, coarse-grained and fine-grained nickel base meta ls. The completion time for isothermal solidification decreased in the order of single crystal, coarse-grained and fine-grained base metals. The difference in isothermal solidification rates produced when brazi ng the different base metals could be explained qualitatively by the i nfluence of base metal grain boundaries on the apparent mean diffusion coefficient of phosphorus in solid nickel.