Preparation And Performance Investigation Of Fe-based Laser Cladding Coating

With the rapid development of modern industry,the mechanical properties of Q235 steel should be improved to meet the higher requirement of enginnering structural components under complex service conditions.Under the service conditions of corrosion,friction,wear and fatigue,the crack is usually originated from the surface of structural component,resulting in the failure.Amorphous alloys have attracted much attention due to their high strength,high wear resistance and excellent corrosion resistance.However,The limited glass forming ability（GFA）and room temperature brittleness hinder their practical application.It has been proved that fabricating coatings of amorphous alloy on the surface of structural componet can solve the problems of limited GFA and intrisinic brittleness and thus has great application potentiality for the enginnering fields such as the coal mining,ships and aerospace.It is worth noting that the crystalline phase,pores and cracks often appears in laser cladding coating,which may deteriorate the service performance of the coating.To overcome the above mentioned problems,the Fe₄₈Cr₁₅Mo₁₄Y₂B₆C₁₅ with high GFA and Fe₇₈Si₁₃B₉amorphous alloy with low GFA were selected as conating materials in this theis,then the effects of element addition and powder preparation method on the microstructures and performances of coatings were systematacially investigated.The main contents and achievements obtained are included as following aspects:（1）The Fe_48+xCr₁₅Mo_14-xC₁₅B₆Y₂ alloy powders were prepared by gas atomization method,and the Fe-based alloy coatings were fabricated by laser cladding technology.The effects of Mo content on the microstructure,microhardness and corrosion resistance behavior of the laser cladding coatings were systematically studied.The results show that with decreasing Mo content,the number of crack coating decreases,but the GFA of the powders is significantly decreased.The coating forms a good metallurgical bond with the substrate and is mainly composed of crystal phasesα-Fe,M₂₃（B,C）₆,M₂（B,C）,M₃（B,C）and Fe Mo metal compounds.The microstructure of the coating is composed of cellular crystal,columnar crystal,equiaxed crystal and plane crystal.The average hardness of the coating is about 1050 HV_0.2.Appropriate reduction of Mo content in the alloy is beneficial to reduce the mismatch of mechanical properties between the coating and the substrate,as well as increase the corrosion resistance of the coating.When the content of Mo is 6.5 at.%,the corrosion potential（-0.344 V）and corrosion current density(2.927×10^-6 A·cm^-2)of the coating are improved compared to those of the substrate,showing a better corrosion resistance.（2）The(Fe₇₈Si₁₃B₉)_100-xCr_x alloy powders were prepared by gas atomization method,and the Fe-based alloy coatings were prepared by laser cladding technology.The effects of Cr content on the microstructure,microhardness and corrosion behavior of the laser cladding coatings were studied.The results show that the coating consists of a single-structureα-Fe phase.Furthermore,the coating forms a good metallurgical bond with the matrix of Q235 steel and no obvious crack are defected.With the addition of Cr element,the cross-sectional structure of the coating is dendritic and planar.When the Cr content is 12 at.%,the average microhardness of the coating is about 700 HV_0.1,and the coating exhibits the optimal corrosion resistance with a corrosion potential of-0.339 V,a corrosion a current density of 5.566×10^-7 A·cm^-2 and a pitting potential of0.959 V.（3）The(Fe₇₈Si₁₃B₉)_100-xCr_x amorphous powders were prepared by mechanical crushing method,and the Fe-based alloy coatings were fabricated by laser cladding technology.The effects of Cr content on the microstructure,microhardness and corrosion behavior of the laser cladding coatings were systematically studied.The results show that the coating forms a good metallurgical bond with the substrate and thre crack is barely observed.The phase structure of the coating is mainly composed of singleα-Fe phase,which exhibits dendritic state.With the increase of Cr content,the microhardness of the coating increases and the maximum hardness can reach 800HV_0.1.When the Cr content is 12 at.%,the coating exhibits the best corrosion behavior with a corrosion potential of-0.316 V,a corrosion current density of 2.993×10^-7 A·cm^-2 and a pitting potential are of 0.347 V.