Interfacial behavior of a thermoelectric film bonded to a graded substrate

To improve the thermoelectric converting performance in applications such as power generation,reutilization of heat energy,refrigeration,and ultrasensitive sensors in scramjet engines,a thermoelectric film/substrate system is widely designed and applied,whose interfacial behavior dominates the strength and service life of thermoelectric devices.Herein,a theoretical model of a thermoelectric film bonded to a graded substrate is proposed.The interfacial shear stress,the normal stress in the thermoelectric film,and the stress intensity factors affected by various material and geometric parameters are comprehensively studied.It is found that adjusting the inhomogeneity parameter of the graded substrate,thermal conductivity,and current density of the thermoelectric film can reduce the risk of interfacial failure of the thermoelectric film/graded substrate system.Selecting a stiffer and thicker thermoelectric film is advantageous to the reliability of the thermoelectric film/graded substrate system.The results should be of great guiding significance for the present and upcoming applications of thermoelectric materials in various fields.

Investigation of Two-Dimensional Ultrasonic Surface Burnishing Process on 7075-T6 Aluminum

A novel two-dimensional ultrasonic surface burnishing process(2D-USBP)is proposed.7075-T6 aluminum samples are processed by a custom-designed 2D-USBP setup.Parameter optimization of 2D-USBP is conducted to determine the best processing strategy of 7075-T6 aluminum.A uniform design method is utilized to optimize the 2D-USBP process.U〔3(133)and 4(72)tables are established to conduct parameter optimization.Burnishing depth,spindle speed,and feed rate are taken as the control parameters.The surface roughness and Vickers hardness are taken as the evaluation indicators.It establishes the active control models for surface quality.Dry wear tests are conducted to compare the wear-resistance of the 2D-USBP treated sample and the original sample.Results show that the machining quality of 2D-USBP is best under 0.24 mm burnishing depth,5000 r/min spindle speed,and 25 mm/min feed rate.The surface roughness of the sample is reduced from 2517.758 to 50.878 nm,and the hardness of the sample surface is improved from 167 to 252 HV.Under the lower load,the wear mechanism of the 2D-USBP treated sample is mainly abrasive wear accompanied by delamination wear,while the wear mechanism of the original sample is mainly delamination wear.Under the higher load,the accumulation of frictional heat on the sample surface transforms the wear mechanisms of the original and the 2D-USBP treated samples into thermal wear.