Ni-Cr-W-C系合金の不純Heガス中における高温腐食挙動

Abstract

Influence of the minor alloy constituents such as Al, Mn and Si on the hot corrosion behavior of Ni-20Cr-20W-0.07C alloy was studied in 99.995% helium gas at 1 000°C, comparing with that behavior of commercial Ni-base superalloys (Hastelloy X and Inconel 617).The low oxidizing potential in the impure helium gas usually causes selective oxidation of these elements and the growth of oxide whiskers on the surface of specimen at elevated temperature.The intergranular attack was caused by selective oxidation of Al, Si and Mn. The spalling of oxide film was restrained by addition of Mn and Si, providing tough spinel type oxide film on the surface and ‘Keyes’ on the oxide-matrix interface respectively.The amount and the morphology of the oxide whiskers depended on Si and Mn content. More than 0.29% of Si content without Mn always caused the growth of rather thinner whiskers with smooth surface, and the whiskers analyzed by electron diffraction patterns and EPMA to be Cr2O3 containing Si. Mn addition changed the whiskers to thicker ones of spinel type oxide (MnCr2O1) with rough surface.On the basis of these results, the optimum content of Al, Mn and Si to minimize the growth of whiskers, the intergranular attack and the spalling of oxide film was discussed.