| As a new kind of alloy material,metallic glass ribbons(MGRs)have been widely used in the fields of power electronics,communication technology and distribution transformer,etc.The main method used in industrial production of MGRs is the singleroll method.However,the limitation of this method has caused surface pits,scratches and other defects,which seriously affect its service performance.Laser repairing is a technology which mainly uses the instantaneous thermal effect of laser beam to melt the material,fills the surface defects with the molten material and then freezes,making the surface flat.For this purpose,it is attempted to repair the surface defects of MGRs via nanosecond laser and the following research work is mainly carried out:Firstly,nanosecond laser was used to irradiate Zr-based MGRs in air environment,and the surface morphology was characterized by optical microscope.The experimental results showed that the surface defects of ribbons were not obviously repaired and the surface was seriously ablated.On this basis,laser irradiation under argon atmosphere was further carried out and the influence of laser parameters such as laser power,scanning speed,overlap rate and number of irradiations on the surface repairing effect was studied in argon atmosphere.The scanning electron and laser confocal microscope were used to characterize the surface morphology and the roughness of ribbon surface,illustrating the evolution process and mechanism of surface morphology.At the same time,the optimum parameters of laser repairing ribbon surface defects were obtained.Based on the above research,the mechanical properties of laser repairing ribbon surface in argon atmosphere were compared and analyzed.The indentation and scratch characteristics of the ribbon surface were measured by nanoindentation instrument and scratch tester.The test results showed that the hardness of repaired surface decreased,and the maximum hardness value had decreased by 1.75 GPa.Under the scratch load of300 m N,the friction coefficient of ribbon surface was increased from 0.45 to 0.53,the scratch width was increased by 4μm,the scratch damage resistance and wear performance of ribbon surface were decreased.Then,the surface of Zr-based MGR irradiated by nanosecond laser in nitrogen atmosphere was investigated.The influence of parameters such as laser power,overlap rate,scanning speed and number of irradiations on the ribbon surface morphology was tested,and the corresponding surface roughness was characterized.At the same time,X-ray diffractometer(XRD)was used to characterize three different repaired surfaces,the results indicated that nitriding reaction occurred when the surface defects of the MGR were repaired under nitrogen atmosphere.Further,the mechanical properties of laser repairing ribbon surface in nitrogen atmosphere were investigated.The indentation and scratching properties of irradiated surface were respectively tested and the experimental results showed that the hardness of repaired ribbon surface is improved.According to the results of XRD characterization,the nitriding layer formed on the surface is the main reason for the enhancement of hardness.Under the scratch load of 300 m N,the scratch width decreased from 12.50μm to 10.3-11.6μm,and the friction coefficient decreased by 0.18.In conclusion,the surface defects of MGRs can be repaired by nanosecond laser irradiation.In this paper,the evolution of different laser parameters on the surface topography was studied to achieve the control of ribbon surface quality,and through the change of processing method and gas atmosphere,the hardness and wear resistance performance of the repaired surface can be controlled and its application field would be expanded.The nanosecond laser repairing proposed in this paper has the advantages of non-contact and easily controlling,which provides a technical means for the surface defect repairing of metallic glass ribbons. |
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