In-Situ Preparation and Structural Properties of MAX Phase Composite Coatings on Copper Alloys
MAX phases demonstrate good electrical conductivity,high strength and elastic modulus,superior oxidation resistance,as well as strong resistance to damage due to their remarkable combination of ceramic and metallic properties.Therefore,MAX-Cu composite coatings is one of research idea to increase the wear resistance of copper alloys without great sacrifice of electrical conductivity.This will enable them to meet the working conditions of electromagnetic railgun and other applications.To address the high cost of MAX-phase powder and the susceptibility of MAX-phase to oxidation and decomposition during the coating preparation process,we suggest the in-situ preparation of MAX-phase through atmospheric plasma spraying.This paper explored the preparation process and structural property characterization of in-situ MAX-Cu composite coatings.The research results provided new technical routes and re-search ideas for the application of MAX phase in coatings.Two powder combinations,Ti-Al-TiC and Ti-Al-C,were prepared using powder proportioning granulation and sintering.Ti-Al-TiC and Ti-Al-C composite coatings were then prepared on the surface of Cu sub-strate using atmospheric plasma spraying technique.MAX phase was in situ generated during the preparation process.The samples un-derwent heat treatment at 600,700 and 800 ℃ using a vacuum furnace to increase the content of MAX phases.X-ray diffraction(XRD)was performed using a Rigaku Ultima Ⅳ instrument with a copper source(Cu Kα radiation,k=0.15406 nm)and a scanning speed of 10(°)·min-1 to characterize the phase composition of the samples.The physical phase composition of the samples was deter-mined by analyzing them with XRD using a Rigaku Ultima Ⅳ instrument.The microhardness of the samples was analyzed using an MH-5LD microhardness tester with load of 5 N and holding time of 20 s.The microhardness was characterized by calculating the aver-age value of ten selected points.The bonding strength of the coating was tested using the tensile test method with a WDW-5E electronic tensile tester.The electrical conductivity of the samples was tested using a precision resistance tester(RK2514N,unit:10-6 Ω).Dur-ing the spraying process,Ar was ionized to produce high temperatures that cause the powder to melt quickly.The powder exited the ionization zone and rapidly cools upon reaching the substrate.The reaction time was short,resulting in insufficient reaction and the for-mation of additional(Ti,Al)C and TixAly phases,as well as residual TiC,Ti,and Al phases.Ti-Al-TiC system composite coatings ex-hibited weaker oxidation compared to Ti-Al-C system composite coatings doped with Cu,suggesting that TiC provided protection to Cu against oxidation.MAX-Cu composite coatings,prepared by heat treatment of the elements,diffused with each other,enhancing the content of MAX phases,such as Ti2AlC.Ti-Al-C system composite coatings had the best effect of mutual solubility of the elements af-ter heat treatment and the highest hardness of HV05 687.1.The results of the bonding strength test experiments showed that the bonding force after spraying was greater than 20 MPa,indicating good coating bonding force.The overall conductivity of the experimental speci-mens was all over 70％IACS,which had a good electrical conductivity.After annealing at 800 ℃,all samples containing Ti-Al-C pow-ders exhibited higher electrical conductivity,measuring 92.29％IACS.Thus,it could be inferred that:(1)Ti2AlC phase was generat-ed in situ in the coating after plasma spraying using Ti-Al-TiC system and Ti-Al-C system granulated powders.The coating products un-derwent further reaction after vacuum heat treatment at temperature of 600～800 ℃,resulting in an increase in the content of Ti2AlC phase with the increase in temperature.(2)After heat treatment at different temperatures,MTiCCu0.2 coating had the fewest holes and the densest coating.However,there were still a small number of unmelted particles,and the degree of powder melting was not as good as that of MCu0.2 coating.(3)The hardness of the sprayed coatings increased gradually after heat treatment.The average hardness value of MCu0.2 reached a maximum of HVo5 687.1 after heat treatment at 800 ℃.Ti-Al-C system coatings exhibited higher hardness than Ti-Al-TiC system coatings.(4)The bonding strength of the samples was good.Ti-Al-TiC system exhibited better bonding strength than Ti-Al-C system coating.Additionally,the bonding strength of the coatings improved after Cu doping.(5)All samples exhibited good elec-trical conductivity,with values above 70％IACS.MCu0.2 sample reached a maximum conductivity of 92.29％IACS after heat treatment at 800 ℃.This study examined the use of plasma spraying technology to achieve MAX phase composite coatings prepared in situ,and provided a new technical idea for the development of conductive wear-resistant coatings on the surface of copper alloys.Future work should focus on optimizing the coating structure and comprehensive performance characterization.
MAX phasesin-situ preparationcomposite coatingsconductivity
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