Preparation Of Super-hard Ta-(Me)-C/a-C Nano-composite Films And Study On Tribological Behavior

Transition metal carbides ceramic films show extremely high ductility transition temperature(0.5?T_m),and the hardness-toughness trade-off effect limit its application as a mechanical components.In this context,taking TaC as the research object,preparing binary TaC_x nanocomposite films with different C content,alloying W to construct miscible ternary Ta-W-C film,and incorporating softness metal Ag to construct immiscible TaC-Ag composite film by magnetron sputtering system,aiming to design and obtain super-hard,high-toughness and wear-resistant protective coating.The TaC_x films prepared under different graphite target powers have different structures.As the graphite power increases,the film changes from Ta₂C and Ta mixed phase to FCC-TaC structure.The TaC110 film obtains super hard(42.8 GPa)and high toughness(3.40 MPa?m^1/2,H/E>0.11).The TaC50 film dominated by graphitized carbon and part of the oxide tribological layer on the friction interface exhibits the lowest friction(COF?0.18)and wear rate(1.44?10^-6 mm³/N?m).The incorporation of W atoms induces the structure of ternary Ta_1-xW_xC_y film transforms from single-phase solid solution to a nanocomposite structure with a-C wrapped Ta(W)C grains.Under the synergistic effect of solid solution strengthening and interface strengthening,the Ta_0.69W_0.31C_0.75 film simultaneously obtains super hard(43.9 GPa),high fracture toughness(3.95 MPa?m^1/2),the lowest friction coefficient(0.28)and wear rate(1.12?10^-6mm³/N?m).For the TaC-Ag composite films,with increasing the Ag power,the solid solution transformes to Ta(Ag)C/Ag/a-C three-phase coexistence structure.The TaC-Ag8 film achieves ultra-high hardness(49 GPa)and enhanced toughness(2.2 MPa?m^1/2),also exhibits strong anti-friction(COF of 0.25)and wear resistance(wear rate of 3.5?10^-6mm³/N?m).Under the lubrication of low shear strength Ag clusters,Ag Ta O₃ and graphitized carbon,the TaC-Ag30 film obtains the lowest COF,but low load carrying capacity and rapid loss of Ag element lead to the highest wear rate.There is no linear relationship between the fracture toughness and H/E in nanocomposite films due to the amorphous carbon(a-C)deflects and suppresses the propagation of the cracks.The friction performance of Ta-(Me)-C/a-C composite film does not completely depend on its mechanical properties,when the self-lubricating phase(graphitized carbon,metal oxide,etc.)dominates friction.