The effect of aluminum and boron addition on the oxidation behavior of alloys from the niobium-chromium-silicon system
Nickel based superalloys have been developed to perform substantially in industry however as technology develops, the need and desire to increase service temperatures to improve efficiency and performance is pushing the capabilities of these alloys. These aspired requirements entail the research and development of new structural materials that surpass the abilities of nickel alloys. Research in Nb-based alloys is underway as Nb alloys have shown to be a promising alternative with similar density but higher melting temperatures than the Ni alloys. However, because Nb has poor oxidation properties extensive studies are necessary to develop an alloy that can perform as highly as the Ni alloys in industry. This study will focus on the effect of Al and B on oxidation resistance by subjecting five alloys from the Nb-Cr-Si system to isothermal static and cyclic conditions. Oxidation in air for 24 hours at temperatures ranging from 700°C to 1400°C has been conducted on alloys with composition of Nb-30Cr-10Si, Nb-30Cr-10Si-5Al, Nb-30Cr-10Si-10Al, Nb-30Cr-10Si-5B, and Nb-30Cr-10Si-10B (at%). The weight gain per unit area as a function of temperature was determined and samples were analyzed using SEM, EDS, XRD, and x-ray mapping. Better oxidation resistance was observed in the low temperature range in the Nb-30Cr-10Si and in alloys with boron additions. At higher temperatures, the 5Al and boron additions were beneficial to the oxidation response of the alloys. Complete oxidation occurred in all the alloys at 900°C except in the 10B alloy. The 10Al addition was detrimental at all temperatures. Alloys with boron addition yielded better oxide adherence compared to the Nb-30Cr-10Si and aluminum alloys. Cyclic oxidation for 168 hours was also performed which resulted in spalling of the oxides and limited amounts of metal left.
Esparza, Nydia Judit, "The effect of aluminum and boron addition on the oxidation behavior of alloys from the niobium-chromium-silicon system" (2012). ETD Collection for University of Texas, El Paso. AAI1512566.