电磁场对激光熔覆镍基涂层组织性能的影响

Effect of Electromagnetic Field on Microstructure Properties of Laser Cladding Nickel-based Coatings

目的研究稳态磁场作用下不同类型及大小的电场对激光熔覆Ni基涂层组织性能的影响,从偏析的角度对电磁场的影响进行研究。方法电磁场采用大小和方向相同的稳态磁场,以及不同大小的交流电场(AC)和直流电场(DC),在45钢表面采用电磁场辅助激光熔覆技术制备致密的Ni60涂层。采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、往复式摩擦磨损试验机等手段检测涂层的元素偏析和组织性能。结果电磁场对熔池产生的搅拌作用会加速熔覆层的传热与传质,从而减少CrB、Ni_(2)B等物质的生成,减少熔覆层宏微观偏析,其中交流电场(AC)试样组的偏析程度低于电流相同的直流电场(DC)试样组。在摩擦磨损实验中,AC200试样具有最低的平均摩擦因数(0.323),磨损量也在整组试样中最低,比未添加电磁场的试样低39.3%。AC200试样具有最高的自腐蚀电位(−185 mV)、最低的自腐蚀电流密度(6.01μA/cm^(2)),其抗腐蚀性能在整组试样中最佳。AC试样的性能优于对应电流的DC试样。结论电磁场辅助激光熔覆可以明显减少涂层的宏微观偏析,从而提高涂层的性能,在AC200条件下制备的涂层的耐磨损性能和抗腐蚀性能最佳。

Laser cladding technology is an environmentally friendly surface modification technology,which has the characteristics of high precision,small heat input,dense structure of prepared parts,etc.In this process,different kinds of metal powders can be covered by high power laser melting to the substrate surface to obtain different properties.It has great development potential in parts repair,surface strengthening and other aspects,but some scholars have found that in the process of laser cladding,due to the segregation of elements in the melt pool,the surface performance of the coating will be reduced and even defects such as cracks and pores will appear.The aim of this work is to study the effect of electromagnetic field on the microstructure and properties of the laser cladding Ni-based coating on 45 steel by adding an electromagnetic field to the laser cladding process.In the experiment,a steady-state magnetic field with a size of 80 mT and a downward direction was used.At the same time,alternating current and direct current of different sizes were applied to the 45 steel matrix during processing.The alternating current frequency was 5 Hz,and the current size was 100 A,200 A,and 300 A,respectively.A coaxial laser cladding device(TFL-H6000)was used for multi-channel laser cladding,the bonding rate was 30%,the protective gas was Ar gas,and the laser cladding process parameters were selected as power 1800 W,scanning speed 5 mm/s,and powder delivery capacity 4 g/s.Six samples were prepared.And after polishing,metallographic corrosion was carried out with mixed reagents(anhydrous ethanol,FeCl3,concentrated hydrochloric acid).A metallographic microscope(JSM-6360LV),a scanning electron microscope(JSM-6510LV),and an X-ray diffractometer(D/MAX-2500PC)were used to observe and analyze the microstructure,phases,and elements of the cladding layer.The friction and wear properties of the cladding layer were measured with a reciprocating friction and wear tester(HRS-2M),and electrochemical experiments were carried out on an electrochemical workstation.The stirring effect of the electromagnetic field on the melt pool would change the growth and distribution of the microstructure of the cladding layer and accelerate the heat and mass transfer of the cladding layer,thus reducing the formation of CrB,Ni_(2)B and other substances and reducing the macro and micro segregation of the cladding layer.Among them,the segregation degree of the AC electric field(AC)sample group was lower than that of the DC sample group with the same current size.The AC200 sample had the least segregation,and the AC200 sample had the least wear amount and the best wear resistance in the friction and wear test.The self-corrosion potential of the coatings prepared with the aid of electromagnetic field was significantly higher than that of the non-electromagnetic field coating,and the current density was lower than that of the non-electromagnetic field coating.The AC200 sample had the highest self-corrosion potential of−185 mV and the lowest self-corrosion current density of 6.01μA/cm^(2),and its corrosion resistance was the best for the whole group of samples.It is found that the corrosion resistance of coating increased first and then decreased with the increase of AC and DC current,and the performance of AC sample was better than that of DC sample with corresponding current.The electromagnetic field assisted laser cladding can significantly reduce the macro and micro segregation of the coating and improve the performance of the coating,and the coating prepared under AC200 conditions has the best performance.