| Magnetostrictive materials have important applications in transducers,actuators and sensors.In recent years,magnetostrictive electromagnetic ultrasonic guided wave detection,as a new non-destructive testing technology,has shown a great application prospect in defect detection and service monitoring of long-distance transportation pipelines,railway rails and bridge chains by virtue of its technical characteristics of single point installation and long-distance detection.As a core sensitive unit,magnetostrictive material has a crucial influence on the performance of electromagnetic ultrasonic guided wave sensor.However,there are many practical problems.The magnetostrictive coefficient of traditional magnetostrictive materials is small,the giant magnetostrictive materials of Tb-Dy-Fe alloy cannot be prepared into thin sheets,and the Fe-Ga rolled plates with thickness greater than 0.3 mm cannot meet the requirements of the cambered special-shaped components detection.In order to solve the problems encountered in the use of magnetostrictive materials in ultrasonic guided wave detection,this work aims to explore the preparation of fine-grained,large magnetostrictive,bendable Fe-Ga alloy sheetss as well as attaching the Fe-Ga(Al)alloy coatings on 316L stainless steel substrates.The microstructure,texture and magnetic properties of the thin strips and coatings were studied respectively.At the same time,the application of Fe-Ga(Al)alloy sheet and coating in ultrasonic wave detection and torque sensor were investigated.The obtained results of this work were as follow:The alloy sheets of(Fe83Gai7)99.9(NbC)0.1 with a thickness of 0.06?0.15 mm were prepared by warm rolling from the Goss-oriented sheets with a thickness of 0.3 mm.The influence of heat treatment on texture and magnetic properties was studied.After annealing at 1200? for 2 h,the microstructure of the sheet was uniform and the average grain size was about 80?m,forming a {100}<001>cubic texture.The saturation magnetostriction was 147 ppm with a elongation of 4.4%.Two kinds of alloy powders of Fe83Ga17 and Fe81Alig were prepared by gas atomization and the Fe-Ga(Al)alloy coatings with different thicknesses were prepared by high velocity oxyfuel spraying.The magnetostriction of the as-deposited Fe83Ga17 alloy coating reached 34.5 ppm.The main combination mode between the coating and the substrate was mechanical bonding.During the heat treatment process,the cooling rate had an effect on the phase structure of the coating The quenching made the coating keep in a single A2 phase structure,and the magnetostriction reached 46 ppm.However,the furnance cooling induced the phase transformation from the A2 phase to the A2+DO3 phase,resulting in a decrease of magnetostriction.The experimental device of exciting and receiving SH ultrasonic guided wave was designed by using(Fe83Ga17)99.9(NbC)0.1 alloy sheet and the ultrasonic wave sensing properties of sheets in different states were studied.The Fe-Ga alloy sheet had good guided wave sensing properties.The experimental device for exciting and receiving the L mode and T mode ultrasonic guided wave was designed by using the Fe-Ga(Al)alloy coatings sprayed on 316L stainless steel pipe.The group velocity dispersion curves were obtained by numerical calculation according to the material and geometric parameters of the pipeline,and the ultrasonic waveguide excitation frequency was selected as 180 kHz.It was found that the echo signal of the detected defect increased with the enhancement of the applied bias magnetic field,which was related to corresponding magnetic field H33 of the d33 of the coating.When the applied bias magnetic field was larger than H33,the excitation magnetic field would work in a large region of d33,and the coating exhibited good guided wave properties.The intensity of the L mode ultrasonic guided wave echo signal detected in the annealed Fe81Al19 alloy coating was higher than that in the as-deposited coating,which was correlated to the high strain sensitivity(d?/dH)corresponding to the annealed coating.Based on the inverse magnetostrictive effect,the exploration of the Fe-Ga alloy sheet on the torque sensor was investigated.The loading torque and the output voltage had a good linear relationship,which shows Fe-Ga alloy have a good prospect applied in the field of torque sensor. |
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