Development Of Electro-explosion Spraying Apparatus For Tube Internal Wall And Process Test Of Preparation Of Ti₃SiC₂ Coating

With the rapid development of industry and manufacture,the requirements of inner wall coatings for small-caliber pipes are becoming higher and higher,which include wear resistance,corrosion resistance,high temperature resistance,etc.Conventional thermal spraying methods,such as flame spraying,plasma spraying,and arc spraying,are only for the preparation of inner wall coatings for large-caliber pipes,and cannot meet the needs for the preparation of inner wall coatings for small-caliber pipes.Electro-explosive spraying has become a new type of thermal spraying method at present:the high-voltage pulse is used to release charge for the sprayed material,and Ohmic heating generated by large current to achieve explosion at the same time.The substrate collides to form a coating.The outstanding advantage for this method is the small size of the device,which can be used to prepare the inner wall coating of small-caliber long pipes.This thesis designed and produced a set of continuous electric explosion spray test equipment for the inner wall of small-caliber long pipes.The equipment is mainly composed of five parts:the loading rod transfer device,the loading rod rotation positioning device,the entire tubular electric explosion gun,the substrate positioning device,and the programmable controller?PLC?device.The principle is that the high-voltage transformer charges the energy storage capacitor.When the capacitor is discharged,the voltage is introduced to the high-voltage electrode side through a high-voltage conductive tube.At this time,a high-voltage electric field is formed between the high-voltage electrode and the ground electrode.Then the loading rod conveying device sends the loading rods into the high-voltage electric field in sequence.At this time,a large pulse current generated due to a gas discharge is introduced into the spray powder,and it is ohmically heated to instantly melt and expand to cause an explosion.The generated shock wave sprays molten particles onto the surface of the tubular workpiece at high speed to form a coating.The entire process can accurately control the capacitor charging,the transfer of the carrier rod,the horizontal and circumferential movement of the substrate through the PLC control system to achieve the overlap of the coating.With the above equipment,Ti₃SiC₂ ceramic powder of different particle sizes and600 mesh graphite powder were selected for electro-explosive spraying test under the condition of the initial voltage of 11kV,13kV and 15kV to study the influence of charging voltage,powder particle size and graphite powder mixing ratio on coating formation.The results show that when the particle size is 500 mesh,the voltage is 15k V,and the proportion of graphite powder is 10%,the energy deposition value of the electric explosion process is the largest.It is about 14?m to form a metallurgical bonding coating.In all the experiments,the oscilloscope collected two representative curren t and voltage waveform modes:smooth oscillation and sudden change.According to the analysis,the conductivity of the powder directly affects the value of the deposition energy inside the powder,and then affects the quality of the coating.Finally,the performance of the dense and smooth coating produced by electric explosion was analyzed.The bonding strength test of the coating was carried out by the cemented dual tensile method.The breakage type was that of the adhesive layer.The bonding strength was greater than the adhesive strength.In the two tests,the average bonding strength of the coating was greater than 37MPa The bonding strength requirements of the layer;further determined by the XRD diffraction pattern of the coating surface,the effective coating surface material formed is a composite coating composed of Ti₃SiC₂ and TiC;the microhardness test of the coating cross section shows The Vickers hardness of the section was 260HV.Based on the above analysis,it is confirmed that the coating formed by the electric explosion spray test of this device has good performance and reaches the industrial use standard.