Experimental Study On Ultrasonic Assisted Laser Brazing Diamond Abrasive Grains

In recent years,diamond tools have been widely used in industrial production for their excellent performance.Improving the efficiency of diamond tool preparation and improving the performance of diamond tools has always been the focus of attention of scholars and manufacturers.The high-temperature brazing diamond tool has a long preparation period,the brazed workpiece is limited by the size of the vacuum furnace,and the diamond abrasive grains are exposed to high temperature for a long time,which is prone to thermal damage.Laser brazing uses a laser as a heat source to achieve an interfacial chemical bond between the Ni-Cr brazing alloy and the diamond abrasive grains.It has the characteristics of controllability,high heating efficiency,small heat affected zone and flexibility.Therefore,this paper uses a new fiber laser to laser braze experiment of diamond abrasive grains and Ni-Cr brazing alloy,and introduces ultrasonic waves into the laser brazing process to carry out ultrasonic-assisted laser brazing diamond abrasive grains experiment.Firstly,using Ni-Cr brazing alloy,the fiber laser brazing diamond abrasive grains process experiment is carried out.The influence of process parameters such as laser power and welding speed on the quality of laser brazed weld formation was investigated by means of microscope,and the key parameters were optimized by response surface methodology.The results show that the laser power and welding speed have a great influence on the melting degree of Ni-Cr brazing alloy and diamond thermal damage.The optimum process parameters are as follows:The laser power is 690 W?770 W,the welding speed is 0.9 mm/s?1.6 mm/s,and the defocusing is+18 mm.The weld appearance under the optimum process parameters is well formed,and the Ni-Cr brazing alloy spreads and climbs on the diamond surface.The surface of the diamond abrasive grain is complete.Secondly,the experimental research on ultrasonic assisted laser brazing and laser brazing diamond abrasive grains was carried out.Scan electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD)were used to study the interface microstructure and composition of Ni-Cr brazing alloy and diamond abrasive grains,and analyze the application of ultrasonic wave to the brazing interface.The results show that the diamond abrasive grains and the Ni-Cr brazing alloy have better infiltration and stronger bonding.The elements such as C and Cr are interdifused at the interface between the diamond abrasive grains and the Ni-Cr brazing alloy,and the thickness of the diffusion layer is 7 ?m-8 ?m.During the laser brazing,the interface between the diamond abrasive grains and the Ni-Cr brazing alloy forms Cr3C2 compound,while the ultrasonic assisted laser brazing forms the Cr3C2 and Cr7C3 compounds.This indicates that the diamond abrasive grains form an interfacial chemical bond with the Ni-Cr brazing alloy during laser brazing,and the ultrasonic assisted effect has a certain promoting effect on the interfacial reaction process.Raman spectroscopy revealed that there was no graphitization on the surface of the diamond after laser brazing.Finally,the combination of Ni-Cr brazing alloy and steel substrate interface under laser brazing process was studied by means of metallographic microscope,microhardness tester and energy-dispersive X-ray spectroscopy.The results show that the interface between Ni-Cr brazing alloy and steel substrate is tight,and there are no defects such as pores and cracks,which form an interface chemical bond.Moreover,the hardness of the Ni-Cr brazing alloy zone,the transition zone of the substrate,and the substrate zone are gradient transitions.This gradient change is beneficial to improve the bonding quality and performance of the interface between the Ni-Cr brazing alloy and the steel substrate.