Growth mechanisms and properties of carburized layers with a certain extent of surface oxidation on TA1 and TC21 alloys during the process of conventional solid pack carburizing

The carburized layers were grown on the surfaces of α titanium alloy TA1 and α+ β titanium alloy TC21 during pack carburizing at temperatures of 950-1050 o C for various holding time. The constituent phases, surface morphologies and cross-sectional microstructures of carburized layers were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscopy. The results showed that the carburized layer of TA1 alloy was composed of a top zone with TiC embedded in α-Ti phase and a bottom diffusion zone of oxygen rich α-Ti phase, while the carburized layer of TC21 alloy was almost comprised by a diffusion zone of α-Ti phase except for a very thin zone of TiC+Ti 3 AlC 2 underneath TiO film. The thickness of carburized layer increased with carburized temperature rising for TA1 alloy, but it decreased for TC21 alloy. The growth mechanisms of the carburized layers on TA1 and TC21 alloys were elaborated in terms of surface oxidation, diffusion of oxygen element, diffusion path of carbon element, phase transformation from α-Ti to β-Ti, and distribution of alloying elements. When compared with untreated TA1 and TC21 alloys, the carburized titanium alloys allowed for a significantly improved wear resistance.