TRIBOCOR 532N — A new material for environments involving wear and corrosion

Abstract

TRIBOCOR 532/sup */ is an alloy having the composition Nb-30Ti-20W which is produced by the conventional melting techniques used for other refractory metal alloys. The cast alloy is highly fabricable and can be readily formed into various and complex part shapes by cold working, machining, and welding methods. Surface nitriding of the finished shape produces a structure of coherent, hard nitrided phases dispersed in a refractory metal alloy matrix (TRIBOCOR 532N). During nitriding, titanium nitride forms preferentially and grows as platelets within the grains of the base metal alloy. As the metal matrix adjacent to the platelets becomes depleted in titanium, niobium enters into the reaction, resulting in a final structure of complex nitrides in a niobium-tungsten rich matrix. The reaction produces a surface hardness in excess of low binder content hard metals (e.g., WC-4.5 pct Co). The depth of hardness and the gradient from the surface to the core metal can be varied over considerable limits with different nitriding treatments. The corrosion resistance of TRIBOCOR 532N has been found to be outstanding in a number of different corrosive media, including hydrochloric, nitric, phosphoric, and sulfuric acids, and chloride solutions. The corrosion rates over a wide range of concentrations andmore » temperatures are far less than for common wear grades of cemented tungsten carbide. Excellent resistance to stress corrosion cracking has also been found in tensile and bend test samples evaluated in chloride and alkaline environments.« less