Production and characterization of high temperature corrosion resistant materials.

Operating temperatures of the current Nickel and Cobalt-base superalloys used in industrial applications, energy production and transportation are getting closer to their limits (~1200 degree Celcius). Thus, there is a search for new metallic structural materials that can be utilized in high temperature as well as corrosive environments. Because of their melting temperatures above 2000 degree Celcius, refractory metals can be considered as candidate materials for the next generation high temperature alloys. However, in environments such as air, refractory metals and their alloys cannot develop protective oxide layers. The objective of this study has been the production and characterization of refractory metal-based materials that are resistant to air oxidation at temperatures above 1000 degree Celcius.In this study, production of binary and ternary Niobium alloys by the Vacuum Arc Melting (VAM) method was made by using both bulk and powder raw materials. Alloys produced from powders had better homogeneity even in ?as-cast? condition. Effects of alloying elements like Cr, Mo and Ti on alloy microstructure and oxidation behavior were investigated through extensive characterization studies conducted by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Oxidation resistances of the produced alloys were moderate and depended on the multi-phase structures of the alloys. For long-term use at high temperatures alloys will require some form of coatings. Boronizing, as a method of surface modification was applied to pure refractory metals Nb and Mo and found to increase their oxidation resistance. As future work on this Thesis work, investigation of the effect of heat-treatment on alloy microstructure and development of oxidation-resistant coatings are considered.