Boronizing of the silicide coating on a multicomponent Nb–Ti–Si based alloy as protection against corrosion at high temperatures

In this work, the preparation, high temperature oxidation and hot corrosion behavior of multilayered composite coatings prepared on Nb–Ti–Si based alloy have been reported. By boronizing of the Si–Y co-deposition silicide coating, part of (Nb,X)Si ₂ layer was transformed into (Nb,X)B ₂ by a replacement reaction between the active B atom and (Nb,X)Si ₂ . Isothermal oxidation resistance tests showed that the as-prepared coating can provide good oxidation resistance both at an intermediate temperature of 850 °C and a high oxidation temperature of 1250 °C. The oxidation kinetics of the coating followed the parabolic law at both temperatures. After 100 h of exposure at 850 and 1250 °C, the mass gains are 1.35 and 4.05 mg/cm ² respectively. The good oxidation resistance of the composite coating should be attributed to the formation of the dense glass-like scale. At 900 °C, the Na ₂ SO ₄ -25 wt% NaCl molten salts can cause a serious damage to the composite coating which showed a big mass gain and a thick corroded scale after hot corrosion for 100 h.