| The working environment of the structural parts of high speed train,the key parts of railway turnout and the metal mold parts are very poor,wear,corrosion,fatigue and complex loads,resulting in premature failure of these key components,reducing the overall life of the equipment.The preparation of intermetallic compound coating by laser cladding on the surface of metal material is a promising method.The difference of the coefficient of expansion between the laser cladding coating and the substrate,so that the cladding layer contains a large number of residual stress,and then produce cracks.Invar alloy because of its special Fe and Ni ratio on the microstructure of special effects,the expansion coefficient of the material was significantly lower.This paper is based on invar effect materials,preparation of cladding coating by laser cladding technology,and Research on the microstructure and properties of cladding layer.Laser cladding Fe-36 Ni Invar alloy coating was fabricated on the surface of 45 steel by a diode laser.Based on the orthogonal experiment,the effect of process parameters on cracking and wear resistance in laser cladding layers was investigated,including laser power,powder feed rate,scanning speed,overlapping rate,etc.The Fe-Ni-Al(Ti)composite coating was prepared by laser cladding on the basis of orthogonal experiment.The miccrostructure of the coating was analyzed with optical microscope,scaning electron microscopy(SEM),x-ray diffraction(XRD)and energy disperse spectroscopy(EDS).The microhardness and wear resistance were examined by hardness tester,abrading machines and multi-functional tester for material surface.The results indicated that all those parameters have significant effects on the cracking and wear resistance of laser cladding layers.And the parameter of laser power has impact on cracking and hardness.It is found that the cladding layers shows the lowest crack rate and Cladding layer surface has highest wear resistance as the laser power is 1400 W with powder feed rate of 25 g/min,scanning speed of 270 mm/min,overlapping rate of 45%.Fe-Ni-Al alloy cladding coating is smooth,uniform and dense.The main phases in cladding zone are AlNi,Al0.9Ni1.1,?-Fe and ?-Fe.With the increase of Al content,coating invar effect is gradually destroyed;When the content of Al is 4%,the cladding coating with small number of cracks and high wear resistance can be obtained.The wear loss of laser cladding Fe-Ni-Al alloy coating(multi lap)was 0.0189 g,the wear resistance of the coating is 4.6 times that of the substrate 45 steel,which greatly improves the wear resistance of the material.Preparation of Fe-Ni-Ti composite coating by laser cladding.The results show that the invar effect can effectively reduce the cracks in the laser cladding coating and can refine grain,eliminate pores.The main phases in cladding zone are ?-[Fe?Ni],Fe0.64Ni0.36 and Fe3Ni2.With the gradual increase of Ti content,the ?-Fe gradually transformed into alpha ?-Fe,and theNi3 Ti metal compound and TiC formation in the cladding layer.When the content of Ti is 6%,the coating with less cracks and high wear resistance can be obtained,At this time,the microhardness of the cladding layer is 508.9HV0.2,which is 2.2 times of the substrate material;The multi lap laser cladding with 45% lap ratio,the wear resistance is 8 times of the substrate,effectively improve the overall wear resistance of the material. |
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