In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical resea...In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical research, the plasma actuator is placed downstream of the trailing edge of the film cooling hole and a phenomenological model is employed to provide the electric field generated by it, resulting in the body forces. Our results show that as the plasma actuation strength grows larger, under the downward effect of the plasma actuation, the jet trajectory near the cooling hole stays closer to the wall and the recirculation region observably reduces in size. Meanwhile, the momentum injection effect of the plasma actuation also actively alters the distributions of the velocity components downstream of the cooling hole. Consequently, the influence of the plasma actuation strength on the Reynolds stress downstream of the cooling hole is remarkable. Furthermore, the plasma actuation weakens the strength of the kidney shaped vortex and prevents the jet from lifting off the wall. Therefore, with the increase of the strength of the plasma actuation, the coolant core stays closer to the wall and tends to split into two distinct regions. So the centerline film cooling efficiency is enhanced, and it is increased by 55% at most when the plasma actuation strength is 10.展开更多
A novel co-sputtering method that combined magnetron sputtering (MS) with ion beam sputtering (IBS) was used to fabricate CuCr alloy films without breaking vacuum after depositing diffusion barrier with IBS. Different...A novel co-sputtering method that combined magnetron sputtering (MS) with ion beam sputtering (IBS) was used to fabricate CuCr alloy films without breaking vacuum after depositing diffusion barrier with IBS. Different bombardment energies were used to improve the comprehensive properties of Cu alloy film. The results indicated that the effects of diffusion barriers and bombardment energy on adhesive strength could be evaluated by a rolling contact fatigue adhesion test. Diffusion barrier can enhance the adhesive strength, and the adhesion of CuCr/CrN was higher than that of CuCr/TiN. When bombarding energy was higher, the adhesive strength of CuCr/TiN films was higher due to the broader transition zone.展开更多
Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method. A lower slope of the initial elastic segment of the curve of X-ray measure...Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method. A lower slope of the initial elastic segment of the curve of X-ray measured stress versus applied strain results from incomplete elastic strain transferred from the substrate to the film due to insufficiently strong interface cohesion. So the slope of the initial elastic segment of the X-ray stress （or X-ray strain directly） of the film against the substrate applied strain may be used to measure the film-substrate cohesive strength. The yield strength of the attached copper film is much higher than that of the bulk material and varies linearly with the inverse of the film thickness.展开更多
A novel test structure to characterize the fracture strength of MEMS(Micro-electro-Mechanical Systems)thin films is presented.The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and t...A novel test structure to characterize the fracture strength of MEMS(Micro-electro-Mechanical Systems)thin films is presented.The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and test specimen.The test structure is capable of producing large displacement and stresswhile keeping a relatively low temperature gradient across the test specimen.A voltage is applied across the beams of the chevron-shaped actuator,producing thermal expansion force to fracture the test specimen.Actuator deflection is computed based on elastic analysis of structures.To verify the test structure,simulations have been implemented using COMSOL Multiphysics.A 620μmlong,410μm wide,10μm thick test structure produced stress of 7.1 GPawhile the applied voltage is 5 V.The results indicate that the test structure is suitable for in-situ measurement of the fracture strength of MEMS thin films.展开更多
The fraction of TiN/Si3N4 in the cross section was observed with scanning electric microscope （SEM）, and residual stresses of TiN coated on the surface of Si3N4 ceramic were measured with X-ray diffraction （XRD）.T...The fraction of TiN/Si3N4 in the cross section was observed with scanning electric microscope （SEM）, and residual stresses of TiN coated on the surface of Si3N4 ceramic were measured with X-ray diffraction （XRD）.The hardness of TiN film was measured, and bonding strength of TiN film coated on Si3N4 substrate was measured by scratching method. The formed mechanism of residual stress and the failure mechanism of the bonding interface in the film were analyzed, and the adhesion mechanism of TiN film was investigated preliminarily. The results show that residual stresses of TiN film are all behaved as compressive stress, and TiN film is represented smoothly with brittle fracture, which is closely bonded with Si3N4 substrate. TiN film has high hardness and bonding strength of about 500 MPa, which could satisfy usage requests of the surface of cutting Si3N4 ceramic.展开更多
Large advancement has been made in understanding the nucleation and growth of chemical vapor deposition （CVD） diamond, but the adhesion of CVD diamond to substrates is poor and there is no good method for quantitati...Large advancement has been made in understanding the nucleation and growth of chemical vapor deposition （CVD） diamond, but the adhesion of CVD diamond to substrates is poor and there is no good method for quantitative evaluation of the adhesive strength. The blister test is a potentially powerful tool for characterizing the mechanical properties of diamond films. In this test, pressure was applied on a thin membrane and the out-of-plane deflection of the membrane center was measured. The Young＇s modulus, residual stress, and adhesive strength were simultaneously determined using the load-deflection behavior of a membrane. The free-standing window sample of diamond thin films was fabricated by means of photolithography and anisotropic wet etching. The research indicates that the adhesive strength of diamond thin films is 4.28±0.37 J/m^2. This method uses a simple apparatus, and the fabrication of samples is very easy.展开更多
The cantilever bending test,particularly monitored by an acoustic emission technique, was adopted to measure the tensile and interfacial adhesive strengths of the HCD ion plated fine TiN film on pure Ti substrate.The ...The cantilever bending test,particularly monitored by an acoustic emission technique, was adopted to measure the tensile and interfacial adhesive strengths of the HCD ion plated fine TiN film on pure Ti substrate.The behaviors of film damaging were found to be characterized by:an internal tensile stress which exceeded its tensile strength for TiN facing upward,and a shearing stress along film substrate interface which exceeded its adhesive strength for TiN facing downward.The measured tensile and adhcsive strengths are 603 and 242 MPa respectively.展开更多
文摘In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical research, the plasma actuator is placed downstream of the trailing edge of the film cooling hole and a phenomenological model is employed to provide the electric field generated by it, resulting in the body forces. Our results show that as the plasma actuation strength grows larger, under the downward effect of the plasma actuation, the jet trajectory near the cooling hole stays closer to the wall and the recirculation region observably reduces in size. Meanwhile, the momentum injection effect of the plasma actuation also actively alters the distributions of the velocity components downstream of the cooling hole. Consequently, the influence of the plasma actuation strength on the Reynolds stress downstream of the cooling hole is remarkable. Furthermore, the plasma actuation weakens the strength of the kidney shaped vortex and prevents the jet from lifting off the wall. Therefore, with the increase of the strength of the plasma actuation, the coolant core stays closer to the wall and tends to split into two distinct regions. So the centerline film cooling efficiency is enhanced, and it is increased by 55% at most when the plasma actuation strength is 10.
基金the Natural Science Foundation of China for its financial support under the granted No.59931010.
文摘A novel co-sputtering method that combined magnetron sputtering (MS) with ion beam sputtering (IBS) was used to fabricate CuCr alloy films without breaking vacuum after depositing diffusion barrier with IBS. Different bombardment energies were used to improve the comprehensive properties of Cu alloy film. The results indicated that the effects of diffusion barriers and bombardment energy on adhesive strength could be evaluated by a rolling contact fatigue adhesion test. Diffusion barrier can enhance the adhesive strength, and the adhesion of CuCr/CrN was higher than that of CuCr/TiN. When bombarding energy was higher, the adhesive strength of CuCr/TiN films was higher due to the broader transition zone.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No. 2004CB619302)the National Natural Science Foundation of China (Grant No. 51071098)
文摘Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method. A lower slope of the initial elastic segment of the curve of X-ray measured stress versus applied strain results from incomplete elastic strain transferred from the substrate to the film due to insufficiently strong interface cohesion. So the slope of the initial elastic segment of the X-ray stress （or X-ray strain directly） of the film against the substrate applied strain may be used to measure the film-substrate cohesive strength. The yield strength of the attached copper film is much higher than that of the bulk material and varies linearly with the inverse of the film thickness.
基金supported by the National High Technology Program of P. R. China under Grant No. 2015AA042604
文摘A novel test structure to characterize the fracture strength of MEMS(Micro-electro-Mechanical Systems)thin films is presented.The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and test specimen.The test structure is capable of producing large displacement and stresswhile keeping a relatively low temperature gradient across the test specimen.A voltage is applied across the beams of the chevron-shaped actuator,producing thermal expansion force to fracture the test specimen.Actuator deflection is computed based on elastic analysis of structures.To verify the test structure,simulations have been implemented using COMSOL Multiphysics.A 620μmlong,410μm wide,10μm thick test structure produced stress of 7.1 GPawhile the applied voltage is 5 V.The results indicate that the test structure is suitable for in-situ measurement of the fracture strength of MEMS thin films.
文摘The fraction of TiN/Si3N4 in the cross section was observed with scanning electric microscope （SEM）, and residual stresses of TiN coated on the surface of Si3N4 ceramic were measured with X-ray diffraction （XRD）.The hardness of TiN film was measured, and bonding strength of TiN film coated on Si3N4 substrate was measured by scratching method. The formed mechanism of residual stress and the failure mechanism of the bonding interface in the film were analyzed, and the adhesion mechanism of TiN film was investigated preliminarily. The results show that residual stresses of TiN film are all behaved as compressive stress, and TiN film is represented smoothly with brittle fracture, which is closely bonded with Si3N4 substrate. TiN film has high hardness and bonding strength of about 500 MPa, which could satisfy usage requests of the surface of cutting Si3N4 ceramic.
文摘Large advancement has been made in understanding the nucleation and growth of chemical vapor deposition （CVD） diamond, but the adhesion of CVD diamond to substrates is poor and there is no good method for quantitative evaluation of the adhesive strength. The blister test is a potentially powerful tool for characterizing the mechanical properties of diamond films. In this test, pressure was applied on a thin membrane and the out-of-plane deflection of the membrane center was measured. The Young＇s modulus, residual stress, and adhesive strength were simultaneously determined using the load-deflection behavior of a membrane. The free-standing window sample of diamond thin films was fabricated by means of photolithography and anisotropic wet etching. The research indicates that the adhesive strength of diamond thin films is 4.28±0.37 J/m^2. This method uses a simple apparatus, and the fabrication of samples is very easy.
文摘The cantilever bending test,particularly monitored by an acoustic emission technique, was adopted to measure the tensile and interfacial adhesive strengths of the HCD ion plated fine TiN film on pure Ti substrate.The behaviors of film damaging were found to be characterized by:an internal tensile stress which exceeded its tensile strength for TiN facing upward,and a shearing stress along film substrate interface which exceeded its adhesive strength for TiN facing downward.The measured tensile and adhcsive strengths are 603 and 242 MPa respectively.
