Research On Co-based Coating On The Surface Of Titanium Alloy By Laser Cladding

Laser cladding is an advanced superficial modification technology which uses a defocused laser beam to melt powder onto the surface of metal and its alloys, and forms a coating with high hardness and good thermal stability which has metallurgical bond with the substrate. Nowadays, it is gradually applied to industrial production. Titanium alloys are widely used in national defense and military, aerospace, chemical, petrochemical, and medical engineering owing to their excellent performance. However, the application of titanium alloys is restricted due to their low hardness, poor wear resistance and inflammable in high temperature and speed. Therefore, improving surface properties of titanium alloys by laser cladding is becoming a new popular trend of research.In order to improve the surface hardness and wear resistance of titanium alloys, this research clad the CoCrW cobalt-based alloys on the surface of TA15alloy by laser beam in single track laser cladding and multi-track-joined laser cladding respectively under the optimal process parameters. Then analyze the results by metallographic, XRD, SEM, EPMA, hardness measurement, and wear resistance measurement.The CoCrW cobalt-based alloys laser cladding experiment results show that the metallurgical combination is achieved between the coating and the substrate. The cladding layer is fine with the rapid solidification microstructure. There is typical dentrite in cladding zone. The main phases of the coating are y-Co, CrCo and a little of a-Ti, with the distribution of TiC, Cr23C6, Cr5Si3, NiSi2, NiC, WCi-x, etc. The hardness of the coating is1180HV in average, which is three times higher than that of the substrate. Particularly, the hardness changes smoothly from the surface to the substrate. The wear resistance of the laser cladding layer is obviously enhanced that the average wear rate of the coating is1/14that of the substrate.The CoCrW cobalt-based alloys laser cladding experiment results in which B element content presents gradient change show that the metallurgical combinations are also achieved between the coating and the substrate. TiB2and WB are added on the composition of produced phase of the cladding layer whose content increase with the increasing of B element content. The hardness of the cladding layer is obviously enhanced. The coating’s highest average hardness is about1200HV when the element content of B is0.08%(wt) The multi-track-joined laser cladding experiment results show that the cladding layer has the rapid solidification microstructure essentially. The organization of unaffected part of the multi-track-joined laser cladding layer is similar to the single track laser layer. The bonding interface of overlapping area is wider and the plane crystal which is growing vertically of the interface in the single track one has no directionality there. Affected by the overlapping heat, the organization is coarsening. The kinds of phase in the coating are the same with the single track laser layer besides the contents of a-Ti■> TiC■> T1B2increased. The hardness is obviously enhanced. The trend of the longitudinal hardness is similar to the single one with the different hardness in different tracks. So the transverse hardness has a cyclical distribution. However, crackle occurs on some samples’bonding interface and overlapping area, which is different from the single track cladding layer.