| Transition metal nitrides(TMN,TM = Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W)have been widely used in the field of aerospace,biomedical science,microelectronic devices,automotive industries due to their high hardness,electrical conductivity,good wear and corrosion resistance,thermal and chemical stability,diffusion barrier and biocompatibility.In these applications,the electrical and wear properties of the films are of utmost importance.It is very crucial,therefore,to improve these properties.It has been reported that incorporate another transition metal changes electrical conductivity and wear resistance of TMN films.However,there are still having problems that remain to be resolved:1.The incorporation of transition metals.(1)How does the structure of TMN films evolve during alloying process? Is the formation of a solid solution structure,or a multi-phase mixed structure? Different researchers obtain different results.(2)What is the relationship between the electrical conductivity of TMN films and incorporation of another transition metal into them? We cannot draw any definite conclusions on the basis of previous studies.(3)What is the mechanism of improvement in wear resistance of TMN films? It has found that the introduction of the second metal element can improve the wear property,but the mechanism is different.Some people believe that H3/E2 value plays the decisive role,but others believe that it is attributed to the generation of oxides.2.The incorporation of silver.(1)For the incorporation of Ag into transition metal nitrides,at present,people just focus on the content of Ag which is less than 30%,while the effect of high content of Ag incorporation on the structure and properties of thin films are rarely reported.(2)Compared with the introduction of transition metal,what is the difference of Ag incorporation on the evolution of film structure and the improvement of properties?According to the problems above,we prepared Hf-Ta-N and Hf-Ag-N films with different contents via magnetron sputtering.The structure of the films was characterized using the Gracing Incident X-ray Diffraction(XRD),Raman spectrometer,and high-resolution transmission electron microscope(HRTEM).X-ray photoelectron spectroscopy(XPS)and Energy dispersive X-ray spectrometry(EDS)were used for measuring Ta and Ag contents.The electrical property has been tested using a Hall-effect measurement system.The wear property has been studied by Scanning Electron Microscope,optical microscope,nanoindentation,Dektak3 surface profiler and a ball-on-disk tribometer.The conclusions as follows:1.The Hf-Ta-N solid solution films possess rock-salt structure with x(x = Ta/(Hf +Ta +N))in the range of 0-1.The electrical conductivity of HfN film is remarkably improved by incorporating proper amount of Ta into it,which is due to the increase of electron concentration.This investigation suggests that Hf-Ta-N film with x = 0.03 has the highest electrical conductivity(8.3×105 Sm-1),which is 1.7 and 5.2 times of the electrical conductivity of HfN(4.9×105 Sm-1)and TaN(1.6×105 Sm-1)films,respectively.The wear rate and friction coefficient of HfN films are significantly decreased by the incorporation of Ta,due to the increase in H/E and H3/E2 ratios caused by the effect of solid solution hardening.This investigation suggests that Hf-Ta-N films with x = 0.37 has the lowest wear rate(1.2×10-6 mm3/Nm)and the smallest friction coefficient(0.50),which are only 10% and 77% of those of HfN film(11.6×10-6 mm3/Nm,0.65),and 49% and 91% of those of TaN film(2.5×10-6 mm3/Nm,0.55),respectively.2.With the increase of Ag content(x,x = Ag/(Hf +Ag +N)),Hf-Ag-N films have two stages of structural evolution:(i)when 0 ? x < 0.039,the film is a solid solution of rock salt structure.(ii)When 0.039 ? x ? 1,the films are solid solution and rich-Ag two-phase coexistence structure.The incorporation of Ag can also improve the electrical conductivity and wear properties of HfN film.In this paper,we found that as x increases from 0 to 1,the film electrical conductivity continues increases from 3.22×105 Sm-1 to 33.1×105 Sm-1,which is due to the increase in electron concentration.The wear properties were optimal when x = 0.171.Compared with pure HfN(16.7×10-6 mm3/Nm,0.65),the wear rate(0.54×10-6 mm3/Nm)and friction coefficient(0.38)decreased by 96.8% and 38.7%,due to the increase in H3/E2 ratios caused by the effect of solid solution hardening and low shear modulus of Ag.These results show that alloying is an effective way to improve the electrical conductivity and wear properties of transition metal nitrides.Compared with the Hf-Ta-N films,the strcture of Hf-Ag-N films exhibited from a solid solution to a two phase mixed structure.The electrical conductivity is remarkably improved,which is due to Ag has more electron concentration than Ta.The good wear properties of Hf N films by the incorporation of Ag,due to the increase in H3/E2 ratio caused by the effect of solid solution hardening and low shear strength of Ag. |
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