Effect of Cr, Hf and temperature on interface reaction between nickel melt and silicon oxide core
Effects of Cr, Al and Hf, varied from 0–32 wt.%, 1–7.5 wt.% and 0.3–1.5 wt.% respectively, on reactions between nickel base alloy melt and silicon oxide core were investigated in this paper. Role of temperature also was studied. Morphology and structures of reaction products were analyzed by scanning electron microscope (SEM) with the energy dispersive spectrometry (EDS) and the X-ray diffraction (XRD) technique. Amount of alumina in interface increased with Cr level, and formed a layer with thickness up to several microns in alloy of 32 wt.% Cr, and 1 wt.% Al. Reaction products in alloy without Hf were mainly alumina, while in alloy with Hf were mainly hafnium oxides and alumina. More hafnium oxides were formed in alloy with 1.5 wt.%Hf and 9 wt.% Cr, while more alumina formed in alloy with 0.3 wt.%Hf and 15 wt.%Cr, a double layer of reaction products formed at the temperature of 1540 °C, which were composed of a hafnium oxide layer near the metal and a alumina layer above it. The result shows that Cr, Hf levels in the alloy and reaction temperature have the effect of accelerating interface reaction.