Research On Preparation And Ultrasonic Propagation Behavior Of Cu-W/SiC Graded Materials

Graded materials are a class of functional materials with regular gradual changes in composition,structure,and performance.They possess strong designability and service advantages under extreme conditions,and are widely used in the engineering field.The performance of graded materials shows an inseparable connection with their structural parameters,and therefore the development of a high-efficiency and high-precision non-destructive testing technology for structural parameters becomes an urgent problem in the development,production,and application of graded materials.Ultrasonic non-destructive testing has advantages over other non-destructive methods,including low cost,harmless to the human body and the surrounding environment,etc.As the consequence,the application of ultrasonic propagation theory on non-destructive testing in graded materials is quite essential.However,the non-uniformly distributed scatterers lead complex,the scattering behavior of ultrasonic waves in the graded layers.When the structure of the interlayer interface changes variously,the reflection and transmission of ultrasonic waves would be different,which increases the difficulty of extracting ultrasonic feature quantities.In this dissertation,based on the results of experiments and finite element simulations,the correlation between the propagation velocity and attenuation of ultrasonic waves in composites and the microstructure of composites was established;different forms of interlayer interface models were constructed,and finite element simulation method was adopted to analyze the reflection and transmission of ultrasonic waves at the clear and fuzzy interfaces between graded layers,then the ultrasonic propagation behavior in graded materials was discussed.On this basis,the calculation formula suitable for the ultrasonic reflection coefficient spectra of graded materials was derived,and the ultrasonic experiment on simultaneous determination of layer thicknesses in graded materials was also carried out.Spark plasma sintering was used to prepare Cu-W/Si C composites and graded materials,and the influence of sintering temperature,sintering pressure,and holding time on the density and microstructure of Cu-W/Si C composites was studied.The results showed that the optimum processing parameters are 950 ~oC-40 MPa-15 min.The minimum density of Cu-W/Si C composites with the different W/Si C contents reaches 98.7%,with no obvious pores,and the W/Si C particles are evenly dispersed in the Cu matrix.Due to the weak interface bonding between W,Si C and Cu,the fracture modes of Cu-W/Si C composites are the shedding of W,Si C particles from the Cu matrix,and the ductile fracture of the Cu matrix.There is no obvious interlayer interface in the Cu-W/Si C graded material.The layer thicknesses are controlled accurately with the 1%-2.3%errors.Due to the small difference in the thermal expansion coefficient of graded layers of the Cu-W/Si C graded material,the bending deformation of the graded material is small,and the height difference of line profiles is about 10μm.Based on the experiment and the finite element simulation results,the propagation behavior of ultrasonic waves in Cu-W/Si C composites was studied.The results showed the acoustic attenuation coefficient and ultrasonic frequency of Cu-W,Cu-Si C,and Cu-W/Si C composites satisfy the power function change form(α=Af ~n).When the ultrasonic frequency is low,the acoustic attenuation coefficients of Cu-W and Cu-Si C composite materials increase with the increase of W and Si C content;when the ultrasonic frequency is high,they first increase then decrease with the increase of W and Si C content,the maximum value is obtained when the W content is30 vol%and the Si C content is 20 vol%,respectively.According to the particle scattering theory,the attenuation of ultrasonic waves caused by the independent scattering of particles and the interaction between particles in the composites were quantitatively analyzed.The result showed that the attenuation of the interaction between particles of Cu-W composites is positive,while the opposite is true for Cu-Si C and Cu-W/Si C composites.This is because the scatterings of ultrasonic waves by W and Si C particles are mainly in the opposite and same direction respectively as propagation directions of the incident ultrasonic waves.The scatter waves of former are easier to dissipate in the Cu-W composites,while the scatter waves of latter are superimposed on each other to form new"incident ultrasonic waves",which are difficult to dissipate in Cu-Si C and Cu-W/Si C composites.Since the W particles in the Cu-W/Si C composites will change the propagation direction of scattered waves of the Si C particles,and the scattered wave is easily dissipated in the composite material,the acoustic attenuation coefficient of the Cu-W/Si C composites is much greater than that of Cu-W and Cu-Si C composites.W content and particle size have little effect on the sound velocity of Cu-W composites.The sound velocity of Cu-Si C and Cu-W/Si C composites is mainly determined by the content of Si C,which changes with the content of Si C in the form of a quadratic function.The propagation behavior of ultrasonic waves in Cu-W/Si C graded materials was studied by finite element simulation.The results showed that the ultrasonic waves are reflected and transmitted at the clear interface between the graded layers.Different from the clear interfaces of W/Cu and Cu/Si C,the reflected waves of the clear interfaces of 80W-20Cu/80Cu-20W and 80Cu-20Si C/80Si C-20Cu are affected by the scattered waves in the graded layers.There is no reflection of ultrasonic waves at the fuzzy interface of 90Cu-10W/70Cu-30W and 90Cu-10Si C/70Cu-30Si C,and the propagation of ultrasonic waves is not affected by the fuzzy interfaces.The propagation of ultrasonic waves in Cu-W and Cu-Si C gradient materials is affected by the scattering of particles in the graded layers and the reflection and transmission at the clear interface between the graded layers.Based on the ultrasonic propagation behavior in graded materials,the mathematical expression of the ultrasonic reflection coefficient spectra in graded material was derived and the functional relationship between the ultrasonic reflection coefficient and the layer thickness was established.The sensitivity analysis of the ultrasonic reflection coefficient spectra to the layer thickness was also carried out.The result showed that the ultrasonic reflection coefficient spectra are big sensitivity to the layer thicknesses,and meanwhile the solution of the inverse problem is stable.The particle swarm optimization algorithm was further introduced to fit and optimize the ultrasonic reflection coefficient spectrum for inverting the layer thicknesses.A 15MHz ultrasonic probe was used to determinate the layer thicknesses of three-layered Cu-W/Si C graded materials simultaneously.The relative errors of the measured layer thicknesses are+4.74%,-5.44%,and+2.27%,respectively.The convergence of the layer thicknesses was also analyzed,and the result showed that the objective function has only a minimum value within the selected parameter range,and shows good convergence.Therefore,the feasibility and effectiveness of simultaneous determination of layer thicknesses in graded materials are successfully verified.