Ping Ren

Structure Stability and Mechanical Property of Y 2 O 3 Thin Films Deposited by Reactive Magnetron Sputtering

Y2O3 has a great application potential at reaction barrier coating of high-temperature composites due to its high thermodynamic stability and high melting point, and the phase structure stability at high temperature and structure dependent mechanical property are key parameters for this application. Y2O3 thin films were deposited on silicon (100) wafers by DC magnetron sputtering with various oxygen partial pressure and substrate bias, and then vacuum annealing at 1000°C was performed to investigate the phase structure stability. The microstructure, stress and hardness of as-deposited and annealed Y2O3 thin films were explored by X-ray diffraction, transmission electron microscope, and nanoindenter. The result showed that as-60 bias voltage was applied to substrate, cubic-c phase formed regardless of variation of oxygen partial pressure, and the cubic-c phase remains stability and crystallinity became better after annealing at 1000 °C.In addition, the hardness and modulus also just had minor changes as a function of oxygen partial pressure. As oxygen partial pressure was kept at 0.043 Pa, phase transition from cubic-c to monoclinic-b phase took place with increasing substrate bias, accompanying by the increment of hardness and modulus, and 1000 °Chigh-temperature annealing resulted in that as-deposited monoclinic-b phase transforms to cubic-c phase.

Deposition and Characterization of Reactive Magnetron Sputtered Tungsten Carbide Films

Tungsten carbide thin films were deposited on silicon (100) substrates by DC reactive magnetron sputtering using CH4 as a carbon source. The microstructure, compressive stress, hardness and tribological behaviors showed great dependences on the rates of CH4 flow (FCH4). Increasing the FCH4 from 2 to 5 sccm, the film exhibited a phase transition from hexagonal-W2C to cubic-WC1-x. Further increasing the FCH4 larger than 10sccm, the film presented amorphous state. As the FCH4 increased, the Raman revealed that the films showed a graphitization trend, meanwhile, the surface of the films became smoother and smoother. The hardness of tungsten carbide films first increased, and then decreased after reaching the maximum 38.5GPa (FCH4=10 sccm). While the sample deposited at 15 sccm obtained the lowest wear rate (2.17×10-6 mm3/Nm) and low coefficient of friction (CoF, 0.24) and still maintained a high hardness of 32.1 GPa. The lowest wear rate could be ascribed to the highest ratio of H3/E2.

Deposition and Characterization of C-NbN/NbCN Multilayers on Si(100) Substrates

The cubic-NbN/NbCN multilayers with modulation periodicity (Λ) ranging from 4.2 to 39.1 nm were deposited on Si (100) substrate by reactive magnetron sputtering in a mixture of Ar and N2 gases. The Λ dependent structural, mechanical and tribological properties for resulting c-NbN/NbCN multilayers were explored. As Λ varied from 4.2 to 39.1 nm, all the films exhibited an obvious modulated structure. Increasing the Λ, the Nb (C,N)(111) peak in XRD gradually shifted to bigger angles and the peak intensity of NbN(111) became stronger. The stress for all multilayers was compressive ranging in between the stress for both NbN and NbCN single layers, and the stress value was stable with increasing Λ. The NbN layer was beneficial to relaxing the compressive stress which induced by NbCN layer. In addition, as Λ increases, the hardness (H) first increased, and then decreased after reaching a maximum value. The obvious enhancement in hardness for multilayers was observed, whose maximum value approaches 43.3 GPa when Λ = 8.4 nm, 37% larger than that obtained by the rule of mixture value. The friction coefficient values of NbN/NbCNmultilayers ranging between 0.34 and 0.4 were much lower than that of NbN monolayer but higher than that of NbCN monolayer were.

Microstructure, Mechanical and Tribological Properties of NbN/Ni Coatings

The NbN/Ni coatings were deposited by co-sputtering on Si (100) substrates. The structure, hardness and tribological properties were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscopy (SEM), nanoindentation test and ball-on-disc tribometer. XRD revealed that the NbN/Ni coatings exhibited a NaCl-type NbN structure but no sign of any nickel phase. For the coatings with various nickel powers ranged from 20 W to 40 W, the shrinkage of the lattice parameter of NbN indicated that Ni atoms might be incorporated into the NbN lattice with a substitution of Nb atoms by the smaller Ni atoms. Further increasing of Ni powers, the degree of crystallinity of the coatings became worse. The NbN coating doped with a certan power of Ni (40 W) exhibited the best degree of crystallinity among all samples. It also displayed a maximum microhardness of 25 GPa combined with a better resistance to plastic deformation, which could attribute to the grain refinement and the solid solution strengthening. Tribilogical properties of NbN/Ni coatings were also found to be depentent on nickel powers significantly. For the pure NbN coating, the coefficient of friction (CoF) was 0.7 approximately, while it decreased to 0.54 when the power of Ni increased to 40 W. Simultaneously, the wear resistance of the NbN/Ni coatings was improved due to the spontaneous oxidation of the wear track surfaces caused by the addition of a certain amount of nickel to the niobium nitride coatings.

Preparation and Microstructure, Mechanical, Tribological Properties of Niobium Carbide Films

Niobium carbide films was deposited by direct current reactive magnetron sputtering on Si (001) substrates in discharging a mixture of CH4/Ar gas. The effects of growth temperature (Ts) and methane flow rate (FCH4) on the phase structure, composition, mechanical and tribological properties for NbCx films were explored. For the film grown at FCH4=6 sccm, a phase transition from cubic-NbC phase to hexagonal-Nb2C phases occurred with increasing the Ts; In contrast, when the film deposited at FCH4=16 sccm, only the cubic-NbC phase was observed at different Ts. The surface of all the films became rough with increasing the Ts. In addition, when the Ts increased from RT to 600 °C, the films exhibited the compressive stress and kept rising. While as the Ts > 600 °C, the stress partially relaxed both at FCH4=6 sccm and FCH4=16 sccm. The hardness (H) for sample grown at FCH4=6 sccm first increased up to a maximum value, and then decreased with increasing the Ts. And the films grown at FCH4=16 sccm kept decreasing with the maximum super-hard value of the filmsof 40.5 GPa at FCH4=6 sccm and 600 °C. The friction coefficient for the film obtained at FCH4=16 sccm was lower than that at FCH4=6 sccm, which might be due to the presence more carbon in the film grown at FCH4=16 sccm.