Performance of Oxygen-Carbon Co-cementation Coating on Titanium Alloy

The Ti6Al4V alloy specimens were planished, polished, cleaned by ethyl-alcohol with ultrasonic, and dried. Then, the treated specimens were put into a special equipment for oxygen-carbon co-cementation. The X-ray diffractometer (XRD), scanning electron microscope (SEM), energy disperse spectroscope (EDS), HV hardness tester, and universal material testing machine were used to analyze the phase, microstructure, composition, hardness, frictional wear, and mechanical properties of the co-cemented layer. XRD results show that TiC and TiO_x phases appear in the co-cemented layer. The microstructure of the original Ti6Al4V alloy specimen is changed by the oxygen-carbon co-cementation. The microstructure of the co-cemented layer is obviously different from that of Ti6Al4V alloy specimens after carburization treatment, oxygen permeation treatment, and treatment under CO₂ atmosphere. EDS results show that the content of C and O elements changes gradually. The surface hardness of the co-cemented layer is 3.8 times higher than that of the substrate, and the hardness of the co-cemented layer also changes gradually. The oxygen-carbon co-cementation changes the adhesive wear and friction state of the original specimen. Only slight friction trace occurs on the surface of the co-cemented specimen and no wear appears. The wear amount of the co-cemented specimen is 3.5% of that of the original specimen, and the friction coefficient is about 30% of that of the original specimen. In the tensile fracture process, the outer surface of the co-cemented specimen peels off to a certain extent, and the surface is covered by cracks, resulting in the slightly decreased strength of the specimen. The elongation and the reduction of area are comparable to those of the original specimen. After oxygen-carbon co-cementation of Ti6Al4V alloy, the surface hardness of the specimen is improved, the wear rate and friction coefficient are reduced, and the mechanical properties of the specimens basically remain.