Research On Micro-structure And Properties Of Laser-cladding Of Boron High Entropy Alloy

The multi-element high-entropy alloy is based on the atomic ratio,high mixing entropy of the alloy design concept developed.Unlike traditional single or two principal alloys,high entropy alloys are typically composed of five or more main elements.Due to the high entropy effect,the formation of simple face-centered cubic?FCC?or body-centered cubic?BCC?solid solution,no or a small amount of intermetallic compounds appeared.Compared with the traditional alloy,high entropy alloy has great research prospects.At present,high entropy alloys are usually prepared by traditional casting methods.For high entropy alloy coatings,especially those boron-containing high entropy alloy coating are less studied.In order to obtain high-performance coating,the FeCoNiCrAlxCu0.7Si0.1By?x =0.3,2.3;y=0.15,0.3,0.6?and the FeCoNiCrAl_xCu_0.7Si_0.1B_0.3?x=0.7,1.0,1.2,1.5,1.8?high entropy alloy coating were prepared on the surface of Q235 substrate by laser cladding.Optical metallographic microscope?OM?,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,energy dispersive spectrometer?EDS?,microhardness and other equipment were used to study the effect of boron element content,Al content and preparation process on the microstructure and mechanical properties of boron-containing high entropy alloy.The experimental results show that the FeCoNiCrAl0..3Cu0.7Si0.1Bx coating consists of a simple FCC phase;The FeCoNiCrAl2..3Cu0.7Si0.1Bx coating consists of a simple BCC,No significant secondary phase precipitates were appeared.With the increase of Boron content,the content of Cr element in the dendrites gradually increased,and the Cr content in the intergranular region decreased gradually,and the segregation of the coating increased.The solid solubility of the boron element in the FCC structure is more than the solid solubility in the BCC structure.Boron elements should not be added too much,in the coating by adding excessive Boron element will cause serious component segregation,interdependent tissue increased thickening,and the coating toughness greatly deteriorated.The results of this study show that:the application of laser cladding boron high entropy alloy with the boron element of the relative composition of the addition is not more than 0.3.The FeCoNiCrAl_xCu_0.7Si_0.1B_0.3?X = 0.7,1.0,1.2,1.5,1.8?high entropy alloy coating has a simple crystal structure.When the relative composition of Al element is x ? 0.7,the coating is a simple FCC solid solution.When the relative composition of the Al element is x = 1.0,the coat-ing is FCC + BCC double phase structure.Boron element can significantly delay the transition from FCC phase to BCC phase.When the relative composition of the Al element is x ? 1.2,the coating is mainly BCC solid solution,FCC phase basically disappeared.When the addition of the Al element relative to the composition of x ? 1.5,the coating between the dendrites separated a small amount of lamellar similar precipitates.The increase of Al content can change the phase structure of the coating,and can significantly improve the hardness of the coating,but the fracture toughness will be worse.When the content of Al is x = 1.2,the coating is a singlephase BCC solid solution,and the microstructure is small,and the comprehensive performance of the coating is the best.After a series of temperature gradient annealing,the dendritic structure of the coated dendrites is gradually fused,and a small amount of the precipitates are dissolved at high temperature and the crystal structure of the coating does not change.In general,the hardness of the alloy coating decreased slightly after annealing,and the fracture toughness was improved.The high-entropy alloy coating was prepared by the laser rapid solidification technique and the block was prepared by vacuum melting technology with the same compositiont,the highentropy alloy coating prepared by laser solidification technology has significantly inhibited the precipitation of boride in the coating.Whether it is microhardness or fracture toughness,the coating is higher than the block,showing the rapid solidification of laser technology in the preparation of high entropy alloy superiority.Under the premise of ensuring the combination of coating and matrix,with the increase of scanning speed,the microstructure becomes more small,and the hardness and fracture toughness of the coating are improved.Addition of an appropriate amount of Mn and Mo elements in the high entropy alloy coating resulted in the formation of FCC phase,and no obvious precipitated phase formed in the coating,showing good fracture toughness.After adding Mn and Mo elements in the coating and removing the Cu element,the coating was annealed at 1200 ?,and the hardness decreased by only 3%,which showed great high temperature stability.