Effect of Cr and Al alloying on the oxidation resistance of a Ti5Si3-incorporated MoSiBTiC alloy

Xi Nan,Nobuaki Sekido,Tomotaka Hatakeyama,Kyosuke Yoshimi,Shuntaro Ida

doi:10.1515/htmp-2021-0024

Abstract

Abstract The effects of adding Cr and Al on the oxidation behavior of a Ti5Si3-incorporated MoSiBTiC alloy (46Mo–28Ti–14Si–6C–6B, at%) were investigated at 800 and 1,100°C. The addition of Cr and Al largely improved the oxidation resistance of the MoSiBTiC alloy at 800°C due to the formation of Cr2(MoO4)3 and Al2(MoO4)3 in the oxide scales. These protective molybdates mainly formed on the molybdenum solid solution (Moss) and Mo3Si phases that show poor oxidation resistance in the Cr- and Al-free alloy and consequently increased the oxidation resistance of the alloys. However, accelerated oxidation occurred on the 10Al alloy after the long-term oxidation test, suggesting that the formed oxide scale has limited protection ability. At 1,100°C, the addition of Cr and Al also enhanced the oxidation resistance to some extent by forming Cr2O3 and Al2O3 in the oxide scales.

Highlights

Molybdenum–silicon–boron (Mo–Si–B) alloys are promising ultra-high temperature structural materials for heat engines because of their high melting point and impressive creep strength above 1,150°C [1,2,3,4,5]
In the present study, varying amounts of Cr and Al were added to the Ti5Si3-incorporated MoSiBTiC alloy, and the oxidation performance was evaluated by analyzing oxidation kinetic curves and oxide scales formed at different temperatures, aiming to provide insights for the alloy design of advanced MoSiBTiC alloys for ultra-high temperature applications
It can be concluded that the addition of Cr and Al to the base alloy contributed to the formation of protective molybdates upon molybdenum solid solution (Moss) and Mo3Si phases, which suppressed the inward diffusion of oxygen and increased the oxidation resistance of the entire alloy

Summary

Introduction

Molybdenum–silicon–boron (Mo–Si–B) alloys are promising ultra-high temperature structural materials for heat engines because of their high melting point and impressive creep strength above 1,150°C [1,2,3,4,5]. It is well known that Cr and Al are beneficial alloying elements for improving oxidation resistance by forming protective Cr2O3 and Al2O3 layers. Oxidation resistance of Cr and Al-added MoSiBTiC alloys 205 the presence of the Al2O3 scale on the surface at high temperature [16,17,18,19]. Zhao et al reported that adding Al or Cr into Mo–Ti–Si–B alloy (35Mo–35Ti–20Si–10B) yielded better intermediate-temperature oxidation resistance [20]. In the present study, varying amounts of Cr and Al were added to the Ti5Si3-incorporated MoSiBTiC alloy, and the oxidation performance was evaluated by analyzing oxidation kinetic curves and oxide scales formed at different temperatures, aiming to provide insights for the alloy design of advanced MoSiBTiC alloys for ultra-high temperature applications

Experimental procedures

Microstructure

Conclusion