| Based on the characteristics of tungsten material and the technical advantages of HIPAC,the structure and properties of nanocrystalline W thin films with wide thickness range and tungsten films low nitrogen doping deposited by HIPAC technology were systematically studied for the potential future applications in three fields cover integrated circuit metal interconnection,surface strengthening of key components and PEMFC metal bipolar plate protection.Firstly,the microstructure and properties of W films on a wide thickness range deposited by HIPAC technology were investigated.The results show that the surface of the W film deposited by HIPAC presents a"Nanoridge"structure.The surface roughness decreases with the decrease of the film thickness and tends to be stable.?-W phase is found in the 67 nm and50 nm W films.The microstructure analysis of the W films with thickness above 95 nm shows that the lattice constant is not significantly dependent on the film thickness,and the residual compressive stress decreases step by step with the increase of the film thickness.The 95 nm W films have the smallest average grain size(?15.7 nm)and microstrain(?0.124%),and the average grain size and microstrain of the other W films are similar:?85 nm and?0.5%,respectively.The resistivity of W film increases monotonically with the decrease of film thickness,and the increase range is obviously larger.The 1300 nm W film has the highest hardness(?18 GPa),and the rest of the thickness W film hardness is about 15 GPa.The microstrain in W film decreases with the increase of annealing temperature,but the average grain size is not dependent on the annealing temperature.The metastable?-W phase in the 50nm W film changes to?-W during annealing at 500?700?,resulting in a significant decrease in electrical resistivity.In addition,tungsten oxide nanowires were formed on the surface of annealed W films.Secondly,the microstructure and properties of N-doped W nanocrystalline films deposited by HIPAC technology were investigated.The results show that the average grain size decreases by 70.7%and the lattice constant,microscopic strain and residual compressive stress increase by 0.67%,70.2%and 152%,respectively,with?5.4 at.%N atom doping.In addition,the surface morphology of the W(N)film changes from"Nanoridge"to"Dimple",the cross section of the film changes from uniform and slender columnar crystal to featureless structure,and the preferred orientation of the film changes from(110)to(222).Due to the synergistic effect of fine grain strengthening,solution strengthening,dispersion strengthening and higher residual compressive stress,the hardness of W(N)films is increased by 93.5%and toughness enhances.The creep degree of W(N)films decreases by 190%,and the creep deformation mechanism changes from dislocation slip to grain boundary slip.After annealing at 700?,the W(N)films obtained the ultrahigh hardness up to?50 GPa,and the toughness is also enhanced.However,the mechanical properties of W(N)films weaken significantly after annealing at 900?.Finally,the feasibility of protecting PEMFC metal bipolar plate with nanocrystalline W film deposited by HIPAC technology was investigated.The results show that the Ti protected by W film is more suitable for the bipolar plate on the anode side of PEMFC,and the protection efficiency of W film for Ti is up to 99.67%.The charge transfer resistance of W/Ti is three orders of magnitude higher than that of Ti matrix after W/Ti is immersed in corrosion solution for 48 h.It was found by accident that the electrochemical oxidized W/Ti had excellent capacitance performance,the specific area capacitance reached 50.23 mF·cm-2,but the capacitance retention rate was only 82%after 5000 cycles. |
PDF Full Text Request