Effect of Water Vapor on the Oxidation Behavior of the Eutectic High‐Temperature Alloy Mo‐20Si‐52.8Ti

Abstract

Herein, the effect of water vapor on the oxidation resistance of the alloy Mo‐20Si‐52.8Ti (at%) is investigated. The alloy is oxidized in dry, wet, as well as in in situ changing atmospheres at 1100 °C. The oxidation kinetics changes from nearly parabolic to linear if water vapor is present in oxidizing atmosphere. Under all conditions, the oxide scales consist of an outer TiO2 and a TiO2SiO2 duplex layer underneath. In wet atmosphere, the thicknesses of the two regions substantially increase indicating a severe ingress of water vapor. The inferior oxidation resistance in wet environment is primarily rationalized by the fast diffusion of H2O through SiO2.

Materials properties characterization in the most extreme environments

“…205 To simulate reentry conditions, including thermal shock resistance, less expensive oxyacetylene torch tests [206][207][208] and more expensive arc jet tests in a temperature range between 1373 K (simulating hypersonic flights at Mach 6) and beyond 2273 K are carried out; [201][202][203] see Figure 3d representing a test of a ZrB 2 /SiC-based composite, coated with Mo-Si-B, tested at NASA's HyMETS test facility. 209 However, as many of these materials are considered to form a protective silica scale, investigations under water vapor have additionally been carried out, 210,211 which clearly demonstrate (detrimental) accelerated scale growth under wet conditions. An interesting novel method for mechanical testing superimposed with wet air and sodium chloride (i.e., SCC) was exemplified recently for Ti alloys at elevated temperatures (723 K).…”