Micro Structure And Mechanical Properties Of Laser-coated Co/Ti₃SiC₂ Composite Coating On TC4 Alloy

Titanium and its alloys are widely used in marine,chemical,aerospace and medical fields because of their high specific modulus,good corrosion resistance,high specific strength and good biocompatibility.Among them,Ti6A14V alloy has been gotten much more attention.However,its low hardness and poor wear resistance limit its application as a tribological specimen.Laser cladding is a common surface modification technology,and Ti3SiC2 is a typical representative of MAX-phase ceramic solid lubricating materials.It has been widely concerned by researchers.because of its unique ternary layered structure and excellent self-lubricating performance.At present,there are few researches on metal-based Ti3SiC2 Composite coating with Co powder on Ti6A14V surface,and its tribological properties at medium and high temperature have not been analyzed.In view of this,four different powder systems(wt%)of pure Co(N1),Co+2%Ti3SiC2(N2),Co+5%Ti3SiC2(N3),Co+8%Ti3SiC2(N4)were used as raw materials,and the self-lubricating composite coating was successfully prepared by laser cladding on Ti6A14V surface with multiple times.Hardness of coating was tested by HX-1000TM/LCD digital microscope hardness tester,and microstructure and phase composition of coating were analyzed by X-ray diffraction(XRD),scanning electron microscope(SEM)and energy dispersive X-ray analysis(EDS).HT-1000 high temperature ball-and-disc friction and wear tester was used to test friction coefficient of substrate and coating,and assisted by probe-type wear mark measuring instrument to measure volume wear of substrate and coating after wear.At the same time,other powder systems:Co+5%Ti2SiC2+10%Cu(N5),Co+5%Ti3SiC2+10%Cu(N6)were also coated,and then compared with the reference coating(N3).Their microstructure,phase,tribological properties and wear mechanism were also analyzed.The results show that the main phases of N1 coating are y-Co solid solution,CoTi,CoTi2 intermetallic compound,and the main phases of N2,N3 and N4 coatings are y-Co solid solution,CoTi,CoTi2,TiC,TisSi3 with residual Ti3SiC2 ceramic phase and Co2Ti4O new hard ceramic phase.The microhardness values of N1,N2,N3 and N4 are 676.86HV0.5,712.01HV0.5,811.39 HV0.5 and 753.58HV0.5,respectively.With the increase of Ti3SiC2 content,the hardness of the coating increases at first and then decreases.Co0.52Cu0.48,Cu-Ti intermetallic compounds Cu3Ti,Ti2Cu3 and CuTi were also found after adding copper powder,and so as Cu-Ti-Al intermetallic compound Ti(Cu,Al)2,solid solution(Cu,Si),carbide SiC and unreacted residual Cu metal,etc.Average microhardness of N5 and N6 coatings is 608.75HV0.5 and 710.51HV0.5,respectively.At 25℃,the friction coefficients of Ti6A14V alloy,N1 pure Co coating,N2,N3 and N4 coatings are 0.5,0.5,0.58,0.55 and 0.43 respectively.The wear mechanism of substrate and pure Co coating is mainly:abrasive wear and plastic deformation;The wear mechanisms of N2,N3 and N4 are mainly abrasive wear,plastic deformation and hard phase shedding.When the test temperature is 300℃,the friction coefficient of each coating is lower than that of the substrate under the same conditions.The wear mechanisms at 300℃ are abrasive wear,adhesive wear,plastic deformation and oxidation wear.N3 and N4 show plastic deformation,delamination and oxidation wear.At 600℃,the friction coefficients of substrate,N1,N2,N3 and N4 coatings are 0.46,0.56,0.41,0.48 and 0.62,respectively.The substrate exhibits the wear mechanism of plastic deformation and oxidation wear at 600℃.While the Co/Ti3SiC2 coatings show hard phase shedding,adhesion wear and oxidation wear.The average friction coefficients of N5 and N6 coatings at 25℃ are 0.14 and 0.20 respectively,which are greatly reduced compared with N3 reference coating,and the wear resistance of N5 and N6 coatings is significantly improved.The average friction coefficients of N5 and N6 copper-containing composite coatings at 300℃are 0.347 and 0.258,respectively.The addition of copper powder makes better anti-friction effect for N5 and N6 coatings.At 300℃,N5 coating shows adhesion wear,oxidation wear and oxide film peeling.While N6 coating shows plastic deformation and oxidation wear.The wear mechanism of N5 coating at 600℃ is mainly:slight abrasive wear,plastic deformation and oxidation wear;while N6 coating shows the wear mechanism of adhesive wear,slight abrasive wear and oxidation wear at the same condition.