Studies Of Fabrication And Properties Of Laser Cladded CrCoNi Medium Entropy Alloy

Multi-principal-element alloy is a new alloy design strategy in metallurgy research.It breaks through the limitations of traditional alloy design concepts on the types of alloy systems and provides a broad space for the development of new materials with excellent properties,which attracts people's attention.Among them,the CrCoNi medium entropy alloy is a novel alloy derived from the CrCoNi Fe Mn alloy system,which has become one of the most attractively cryogenic materials for its exceptional cryogenic damage-tolerance.However,most of its researches focus on bulk materials,and the preparation methods are limited to casting and sintering,which limits its application.Laser cladding technology is an advanced method of surface repair and modification,having been proven that it can effectively suppress phase segregation in multicomponent alloys and make the structure uniform and dense.At the same time,laser cladded coating has low dilution rate and good metallurgical combination with substrate.All in all,laser cladding technology is an effective method to coat multi-principal-element alloy,which can reduce costs and broaden its application.In this paper,the CrCoNi medium entropy alloy coating is successfully fabricated on 9Ni steel by laser cladding and studied in detail.The process parameters are optimized by orthogonal method.The structure of coating is uniform and dense and the dilution rate is small and coating is well bonded with substrate.The coating forms a single FCC phase and mainly with a columnar crystal structure.As its corrosion properties,we have studied the electrochemical corrosion behavior of laser cladded CrCoNi coating in 3.5wt.%Na Cl solution and 0.5mol/L H₂SO₄ solution,which both show good corrosion resistance.The mainly corrosion forms in both test environment are local corrosion,and Cr plays an important role in preventing pitting corrosion.In 3.5wt.%Na Cl solution,the main component of passive film is Cr(OH)₃,and its stability is greatly affected by Cl^-.In 0.5mol/L H₂SO₄ solution,its E_corr is positive and the passive film formed at open circuit potential behaves as a dielectric,which indicates that it can hardly corrode in sulfuric acid solution.As its mechanical properties,annealing can effectively improve its microhardness,and the microhardness range after heat treatment is approximately 240-280HV.In terms of tensile property testing,due to dislocations and twins introduced by rapid cooling,its tensile properties at room temperature can compare with fully recrystallized cast samples whose grain size are smaller than one order of magnitude.As it has relatively large grain size,its tensile properties improved relatively inapparent at low temperatures.In terms of impact performance,the impact energy of the coating increases with decreasing temperature,and no ductile-brittle transition occurs.