Tribocor 532N — a new material for environments involving wear and corrosion

Abstract

Tribocor 532 is an alloy having the composition Nb-30%Ti-20%W 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 Nb-Wrich matrix. The reaction produces a surface hardness in excess of low binder content hard metals ( e.g WC-4.5%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 and temperatures are far less than for common wear grades of cemented tungsten carbide. Excelent resistance to stress corrosion cracking has also been found in tensile and bend test samples evaluated in chloride and alkaline environments.