Fundamental Studies On Fabrication Method Of Embedded Heat Flux Gauge By Laser Micro-cladding

Heat flux is a key factor affecting the service life of durable components in aerospace vehicles.The thin-film heat flux gauges have been widely used in the field of heat flux measurement due to their advantages of small size,high measurement accuracy and fast response speed.However,the traditional manufacturing methods for thin-film heat flux gauge mainly use thin-film technologies such as magnetron sputtering,photolithography technique,and evaporation deposition,which are complex,requiring masks and expensive equipment,especially difficult to fabricate on the surface of large-size or curved components.These reasons have restricted the development of heat flux measurement.Therefore,this dissertation proposes to fabricate the embedded heat flux gauge by the micro-pen direct writing and laser micro-cladding for the first time,which provides a novel idea for maskless,high-efficiency fabrication.First,the fabrication method of polyimide(PI)dielectric layer by micro-pen direct writing and thermal curing process was studied.The physical model of direct writing PI dielectric layer was established by studying the direct writing parameters and thermal curing process for PI material precursor solution.The results showed that when the thickness of the liquid film in direct writing is less than 200?m,the PI dielectric layer is relatively smooth.After testing,the bonding strength of PI film with the substrate can reach 10.7 MPa and it can be used in the environment below 300°C.Secondly,the fabrication method of the embedded PI thermal resistance layer was studied.The best parameter ranges of laser etching were determined through experiments,and the thermal resistance layer grooves with a depth of 320?m were etched on the aluminum alloy substrate.The micro-pen direct writing was used to fill the grooves full in order to fabricate the thermal resistance layer.The results showed that the thermal resistance paste mixed with soluble PI powder and polyamide acid solution has the best filling effect.Then,the process parameters of fabricating the thermopile by micro-pen direct writing and laser micro-cladding were optimized by orthogonal experiments.The results showed that when the viscosity of the electronic paste is constant,the main factors affecting the line width of the direct writing are the inner diameter of the micro-pen and the driving air pressure,and the main factors affecting the thicknesses of the direct writing are the inner diameter of the micro-pen and the direct writing speed.The effect of the laser processing parameters on the line widths and thicknesses of the thermopile in laser micro-cladding was studied systematically.The results showed that the line width of laser sintering increases with the increase of the input laser energy and decreases with the scanning speed;and the thickness of film layer is mainly determined by the thickness of preset film,which was not much affected by the laser processing parameters.Within the range of optimized laser processing parameters,silver thermopile and silver pads were fabricated with high quality.After testing,the volume resistivity of the fabricated silver metal layer can be 13.1×10^-8?·m,and the bonding strength with the substrate can be 8MPa.The silver pads showed good solderability during the soldering process of solder Sn62Pb36Ag2.Next,through the thermogravimetric-differential thermal analysis and scanning electron microscopy(SEM)analysis of the electronic paste before and after laser processing,the mechanisms of laser micro-cladded electronic paste were studied.During the period of laser action,the organic phase in the electronic paste volatilizes and burns,the adhesive phase softens and flows to bond with the substrate.Then the metal particles agglomerate into particle clusters and contact with each other to form a conductive network.The higher the input laser energy,the bonding strength were better among the agglomeration of metal particles.Finally,based on the above process study,the embedded heat flux gauge samples were fabricated with the thermoelectric performance calibration.The structure and graphics of the heat flux gauge were designed by theoretical analysis and simulation calculations,and the fabrication process and common failures of the embedded heat flux gauge were analyzed.The fabricated heat flux gauges were calibrated by the comparative calibration method,and the calibration results showed that the output linearity of the heat flux gauge was good enough and the sensitivity of the silver-platinum heat flux gauge was 6.30×10^-1?V/(W/m²),which was obvious higher than the heat flux gauges fabricated by thin film technology.In summary,the direct writing by laser micro-cladding method in this dissertation opens up a fast,maskless manufacturing method of heat flux gauge fabrication.In addition,this technology can also be applied to manufacture the functional layer or packaging layer of other thick film devices and has broad industrial application prospect.