Erosive Effects of Various Pure and Combustion-Generated Gases on Metals. Part II.

Abstract : This study continues the experimental investigation of the thermal and chemical erosion characteristics of steel alloys which were begun under Contract DAAG46-72-C-0078. The high pressure (approx. 3 kbars) and high temperature (approx. 3000 K) environment to which the steel specimens are subjected is produced by a ballistic compressor and by a solid propellant combustor. Equilibrium thermochemical calculations of the possible reactions indicate that the most probable reaction products are oxides, nitrides, carbides, and carbonyls, in that order. The cause of surface cracks was found to be thermal and not relatable to the degree and severity of erosion. Erosion tests of the pure metals used as alloying elements revealed that molybdenum has the highest erosion resistance, followed by nickel. There is no evidence that alloying elements alter the chemical interaction between oxygen and iron. SEM studies revealed that when an accumulation of oxide scale occurs with successive firings, oxidation and thermal protection is provided. It is hypothesized that as long as steel remains below its solidus temperature, the primary erosion mechanism is the reaction of combustion gases with the steel surface to form scales and the subsequent carrying-away of the scales by the high speed flow.