Fabrication And Properties Of Reactive Plasma Sprayed TiCN Based Muti-scale Composite Coatings

In this paper,Ti-graphite composite powders were obtained by spray dried of micron-sized Ti powders and graphite.Cr and Mo powders were mixed with Ti-graphite powders for spraying.The multi-scale TiCN based composite coatings?TiCN-Cr and TiCN-Mo?were fabricated by using reaction plasma spraying method under the reaction gas consition of N₂.The unique structure may contribute to reduce the stress of nano-TiCN coating to solve the inverse problem of nano-coating hardness and toughness.The obtainted coating with good toughness and strength can meet the anti-wear performance under high load conditions.The effects of the addition of Cr and Mo on the microstructure and properties?hardness,toughness,bonding strength,friction and wear resistance?of TiCN coating were studied.With the Cr addition,the TiCN-Cr composite coating was composed of mainly TiC_0.7N_0.3 and metal Cr,with minor phase of Cr_0.5Ti_0.5N and Ti₃O.The reaction was complete and there was no unreacted Ti.With the Mo addition,the TiCN-Mo composite coating consisted of mainly TiC_0.7N_0.3.3 and metal Mo,with minor TiC_0.2N_0.8.8 and MoC₂.In addition,the presence of Ti-C,Ti-N,C-N,Cr-Ti,Cr-Cr,Mo-C,Mo-Mo and other bonding bonds was confirmed by XPS analysis.The TiCN based composite ceramics showed a crossing feature with laminated TiCN phase and metal Cr?Mo?,and the density of the two composite coatings were significantly higher than that of the pure TiCN coating.For the TiCN-Cr composite coatings,the porosity of the coating decreased at first and then increases and the average value of microhardness increased firstly and then decreased with the increase of the Cr content.With the addition of 10 wt.%Cr,the porosity is 3.57%.The microhardness reaches the maximum value(1309 HV_0.2)with the Cr content increasing to 20 wt.%.Compared with the original TiCN coating,the density of the TiCN based composite coating was also increased with Mo addition.With increasing of the Mo content,the microhardness of the coating increased firstly and then decreased.When the Mo content is 20 wt.%,the microhardness of the composite coating reached 1460.7 HV_0.2.The toughness of the coating with the addition of Cr is improved through the indentation of TiCN-Cr composite coating and TiCN coating.Although the microhardness of the coating decreased after adding Cr?Mo?,it is still high enough to meet the general required working conditions.The bonding strength of TiCN coating was 21.25 MPa,which was obtained by the tensile test,and it was obviously increased when Cr and Mo were added.When the Cr content was 20 wt.%,the bonding strength of coating was the highest?24.67 MPa?.When the Mo content is 20 wt.%,the bonding strength of the coating was as high as 29.84 MPa.It can be observed from microstructure of the tensile test that the fracture occurs inside the coating.In such a case,the critical bonding strength was the cohesive bond strength of the coating.And the bonding strength between the coating and the matrix was higher than this value.The wear resistance of TiCN-Cr coating was better than that of TiCN coating,while the wear resistance of TiCN-Mo composite coating was less than that of TiCN coating.Although the TiCN coating showed lower friction coefficient under the same test conditions,the TiCN-Cr composite coating exhibited less mass loss.The wear mechanism of the composite coatings were mainly abrasive wear and adhesive wear,accompanied with the oxidation wear.