NITRIDING OF SINTERED VТ1-0 TITANIUM ALLOY

Abstract

Products from sintered titanium alloys are increasingly used in mechanical engineering, but need to be protected for operation in corrosive environments because of porosity. Nitriding is one of the effective protection methods. The objective  of the study was to analyze the nitriding kinetics for a sintered VT1-0 titanium alloy at atmospheric (10⁵ Pa) and reduced (1 Pa) nitrogen pressure at 800, 850, and 900 °С for 5, 10, and 20 h in comparison with a deformed titanium alloy of the same composition. The study used discrete gravimetry, hardness measurement, optical and electronic metallography, profilometry, and X-ray diffraction. The nitriding kinetics of the VT1-0 titanium alloy sintered from titanium powder and from a mixture of titanium and titanium hydride powders was studied in comparison with deformed titanium. Under given nitriding parameters, the weight gain of all samples is described by a parabolic law and the weight gain of the sintered samples is higher than that of the deformed ones. The kinetic parameters of nitriding for the sintered and deformed VT1-0 titanium alloy were determined for the first time in the test temperature-time and gas-dynamic conditions. Changes in the surface and the near-surface layers depending on porosity of the metal are shown. After nitriding, the surface microhardness of sintered titanium is lower than that of the deformed titanium samples because of porosity, and the hardened surface layer is larger. The nitride film formed on the sintered titanium is thinner and less distorted than on the deformed titanium alloy. The results can be used to develop nitriding conditions for sintered VT1-0 titanium products.