Nitriding of Sintered VT1-0 Titanium Alloy

Abstract

Components produced 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 of a sintered VT1-0 titanium alloy at atmospheric (105 Pa) and reduced (1 Pa) nitrogen pressure at 800, 850, and 900°C for 5, 10, and 20 h versus a wrought titanium alloy of the same composition. The study employed 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 alone and from a mixture of titanium and titanium hydride powders was studied in comparison with wrought titanium. Under the nitriding parameters in question, the weight gain of all samples was described by a parabolic law and the weight gain of the sintered samples was higher than that of the wrought ones. The kinetic parameters of nitriding for the sintered and wrought VT1-0 titanium alloys were determined for the first time in the test temperature–time and gas dynamic conditions. Changes in the surface and near-surface layers depending on metal porosity were shown. After nitriding, the surface microhardness of the sintered titanium was lower than that of the wrought titanium samples because of porosity, and the strengthened surface layer was thicker. The nitride film formed on the sintered titanium alloy was thinner and less distorted than that on the wrought titanium alloy. The results can be used to develop nitriding conditions for sintered VT1-0 titanium products.