Study On Mechanical Property Of Films By Nanoscale Dynamic Load Test Technology

Diversified films have been widely used in the fields of national defense,automobile,communication,aviation and so on.The size of thin film materials is small.And surface and interface exist in the thin film materials.Hence thin film materials have unique properties that are different from bulk materials.Owning to the particularity of the preparation technology and the service condition,study on the macroscopic failure process and the relationship between the micro structure and the damage mechanism of the multi thin film has great significance.In addition,achieve quantitative detection for the mechanical properties of thin film materials based on nano scale mechanical testing method also has great significance.In this paper,in view of the special structure of the nanometer scale multiple thin film,pure Cu metal film,(Fe-Co-Ni)x(Ti-Zr-Al)100-x high entropy alloy film,TiN ceramic thin film that were widely used in micro electro mechanical systems were prepared by magnetron sputtering technique.The mechanical properties of multi thin film under the condition of dynamic service were explored by using the combination of micro nano dynamic loading technique and nanoindentation method.Quasi-static loading method,partial unloading method and continuous testing method of nanoindentation on the accuracy of the hardness and elastic modulus of thin films with different thickness was contrasted.It is found that continuous testing method is more applicable for thin films testing.In order to obtain the stress free samples used in the test and improve the accuracy of the calculation results,we have the film bracket independently designed.By adjusting element content of Fe-Co-Ni in the(Fe-Co-Ni)x(Ti-Zr-Al)100-x non equal molar ratio high entropy alloy thin film,polycrystalline FCC solid solution film with different content of amorphous and different size of nanocrystalline were prepared.From microstructure of alloy thin films,it is found that with the increase of element content of Fe-Co-Ni,the size of the nanocrystals in the films will be larger.And the oxidation resistance of the films will be better.Dynamic loading test and nano impact test were employed to test the fatigue property of the films,it is found that dynamic loading method is more suitable for the quantitative characterization of fatigue life of thin film materials.The initial contact stiffness of the thin films is 16.81μN/nm,16.82μN/nm and 16.89μN/nm respectively,when the content of x is 5,10 and 15.In the process of dynamic loading,the value of stiffness will drop in the time point of fatigue failure,consequently the number of circle loading can be defined as the fatigue life of thin films.In order to explore the influence of the difference of films and substrate materials on the mechanical properties of thin film materials.The typical Cu/Si films of soft film and hard substrate were prepared.By adjusting the thickness of the film,it is found that the residual compressive stress in the thin film decreases with the increase of the thickness.When the film thickness reaches to 2000Nm,compressive stress becomes tensile stress.And the value of stress is 0.301 GPa.By using dynamic load test and molecular dynamics simulation,the cyclic deformation of the soft films and hard substrate materials under dynamic loading were analyzed from the perspective of atoms/molecules.The initial stiffness of Cu thin films is 15μN/nm,and the value of stiffness drops to 9μN/nm when the fatigue failure of the film occurred.The failure mode is crack and delamination.In the process of dynamic indentation test,with the increase of indenter radius,the deformation range of the film will be larger,and the damage accumulation will also be larger.With the increase of loading speed,the elastic limit of the plastic deformation of Cu thin film also increases,thus accelerating fatigue failure.For the sake of research the influence of film thickness,film thickness and loading conditions on the fatigue life of the films,nano scale dynamic load test and finite element simulation were used to investigate the TiN/Si thin films.The initial stiffness of TiN thin film is 20μN/nm,which is larger than the contact stiffness of soft films.The main fatigue failure modes of the films are delamination and spalling.The increase of average load and amplitude of load can enlarge the plastic deformation of the material,lead to stress concentration and reduce the fatigue life of the film.Based on statistical theory,and have the results of dynamic load test fitted.Finally the model as Nf 569.730+ 0.037·T-1.376·f-28.830p0-16.632pm-0.539v + 5.067S for film fatigue life prediction was built.Factors such as film thickness,contact stiffness,load frequency and so on are contained in the model.So the model is suitable for the structure of soft film/hard substrate and hard film/soft substrate.It provides a new method for quantitative detection of cyclic loading times of fatigue failure(Nf).The Sig.value of regression analysis was used to test the model.It is found that the error of the model is less than 5%.Consequently this model can be used to quantitatively predict the fatigue life of thin film materials.