Preparation Technology And Microstructure&Properties Of AlCoCrCuFeNiTi High-Entropy Alloy Coatings By Laser Cladding

AlCoCrCuFeNiTi high-entropy alloy coatings were prepared by laser cladding on Q235 steel substrate surface,the laser processing parameters were optimized by orthogonal experiments.The micro structure of the samples which prepared by laser cladding were examined through optical microscopy,scanning electron microscopy,transmission electron microscopy and X-ray diffraction;the microhardness,wear resistance,corrosion resistance were measured by micro/Vickers hardness tester,abrasive wear testing machine and electrochemical workstation.The results show that,the optimal parameters of preparation AlCoCrCuFeNiTi high-entropy alloy coatings on Q235 steel substrate surface by laser cladding were as follows:laser power =2500W,scanning speed =3 mm/s,cladding powder thickness=1.0 mm,spot diameter =4.0 mm.AlCoCrCuFeNiTi high-entropy alloys mainly consists of cladding zone,bounding zone,heat affected zone and substrate.The cladding layer and the substrate with good combination;under the rapid heating and cooling effect,the cladding zone mainly composed of equiaxed grains,dendrites,columnar crystal,and there distribution of the spherical nanoparticles and"Plum-like" particles etc.Al₂CoxCrCuFeNiTi high-entropy alloy coatings easy appeared crack during process,mainly due to the presence of residual stresses in the cladding layer.Cracks can be suppressed by adding an appropriate amount of Si element into cladding powder.EDS analysis shows that,AlCoCrCuFeNiTi high-entropy alloy coating composition exists segregation,but the degree was small.AlCoCrCuFeNiTi high-entropy alloy coatings with a simple structure due to high-entropy effect,as FCC,BCC structure and Laves phase.Ni element and Ti element promoted the BCC structure formation,and inhibit the FCC structure formation to some extent,the increase of Co element content promote the emergence of FCC structure,and inhibit BCC structure to some extent.The surface hardness of Al₂CoCrCuFeNixTi high-entropy alloys up to 968 HV,under the effect of the laser rapid heating and rapid cooling,the microstructure is extremely small and dense,which provide a guarantee to obtain high hardness,in addition,the differences of atomic radius make more serious crystal lattice distortion,and enhance the solid solution strengthening effect.With the increases of Ni content,the hardness showed an increasing trend.The maximum surface hardness of Al₂CoxCrCuFeNiTi high-entropy alloy laser cladding layers reach up to 1050 HV,which about as 5 times as Q235 steel.The large number of the solid solution in alloys produce a strong solid solution strengthening effect;the fine spherical particles also play a dispersion strengthening effect.With the increasing of Co content,the surface hardness of alloys showed a decreased trend.The reason is that:the hardness of FCC crystal structure is lower,while the hardness of BCC crystal structure is higher.Al₂CoCrCuFeNiTix high-entropy alloy laser cladding layers with high hardness,the maximum value of 988 HV,which about as 4.5 times as Q235 steel 4.5 times.Large atomic radius of Ti elements produce lattice distortion,solid solution strengthening effect is obvious;the fine"plum-like" particles precipitation between equiaxed grains and tiny spherical particles play a dispersion strengthening effects,which make the high-entropy alloy coatings with high hardness.The relative wear resistance of AlCoCrCuFeNiTi high-entropy alloy coatings greatly improved compared to Q235 Steel.With the increase of Ni content,the relative wear resistance of Al₂CoCrCuFeNixTi high-entropy alloy coatings first increased and then decreased.The reason is that:the hardness of the alloy contribution on wear resistance,while the ductility also affects the wear resistance.Ni0.0,Nio.5 and Ni1.0 alloys has a certain hardness,but also has a certain degree of ductility,so wear is relatively higher,while the brittleness of Ni1.5 and Ni2.0 alloys are higher,making the relative resistance reduced compared with Ni1.0 alloy.With the increase of Co element content,the relative wear resistance of Al₂CoxCrCuFeNiTi high-entropy alloy coatings showed a decreasing trend.Compared to Q235 steel,the corrosion current density?Icorr?of AlCoCrCuFeNiTi high-entropy alloy coatings in 1 mol/L NaOH solution,3.5%NaCl solution,0.5 mol/L H2SO₄ solution,0.5 mol/L HCl solution and 0.5 mol/L HNO3 solution is reduced,the corrosion potential?Ecorr?shift toward positive direction except for a few alloys.Description high-entropy alloy coatings can play a protective role for Q235 steel.The reason is that:high-entropy alloy coating structure,element characteristics,high-entropy alloy coating surface state and the passive film formed on the surface coating are different degrees impact on the corrosion resistance.All Al₂CoCrCuFeNiTix,high-entropy alloy coatings in 0.5 mol/L H2SO₄ solution appear secondary passivation except Ti1.0 alloy coating.With the extension potential time,failure occurs on passivation film weak parts,when the Cu2+in coatings encounters S2-inH2SO₄ solution will be react,and generate Cu2S,then formation secondary passivation.Circular polarization curve show that,AlCoCrCuFeNiTi high-entropy alloy coatings no pitting in 3.5%NaCl solution and 0.5 mol/L H2SO₄ solution.Al₂CoCrCuFeNixTi and Al₂CoxCrCuFeNiTi high entropy alloy coatings appear pitting in 0.5 mol/L HCl solution;Al₂CoCrCuFeNixTi high-entropy alloy coatings appear pitting in 0.5 mol/L HNO3 solution.Al₂CoxCrCuFeNiTi high-entropy alloy coatings appear pitting in 1 mol/L NaOH solution.