(Fe,Co,Ni)-B-based Amorphous Alloys Issued From A Cluster-based Model And Their Laser Cladding On 45 Steel Surface

Amorphous alloys have high strength,hardness,good wear resistance and corrosion resistance,etc.,but the amorphous state usually requires strict control of the alloy composition range as well as a high cooling rate(105 K/s).In general,most of the binary or ternary amorphous alloys can only form thin strip-shaped products with a thickness of micrometers.The three-dimensional size is far below to the standard of bulk materials,thus limiting the amorphous alloy applications.Laser cladding is one of the important technical means for rapid surface processing.It is essentially a complex physical metallurgical process characterized by rapid heating and cooling away from equilibrium.In the past,a large amount of hard materials was used as the cladding material,and the non-uniformity of composition and microstructure as the main disadvantages needs to be overcome.The use of amorphous alloy as the cladding material]brings at least two advantages:First,the amorphous alloy can provide uniform composition and structure,and both the powder and the strip state are beneficial to the control of cladding process;Secondly,(Fe,Co,Ni)-B based amorphous alloy can be used to prepare alloy coatings on a large area of most metal substrates.For the coating’s good wear-reducing and wear-resistance properties,the development and preparation of amorphous cladding alloys have received extensive attention in the field of surface engineering technology.This paper attempts to study the amorphous alloys cladding behavior of the of 3d transition metal(Fe,Co,Ni)and metalloid(B,Si)systems.The(Fe,Co,Ni)-B binary alloy were analyzed by cluster-plus-glue-atom model and the optimal glass forming ability composition was obtained.A series of components had been tested on 45 steel substrates by a CO2 laser source.In the Fe-B-Si system,the effects of the cladding materials in the crystalline and amorphous states were compared,and the amorphous powders were proved to have more excellent cladding properties.The multi-component Co-based amorphous alloy composition with high amorphous forming ability were laser-clad on the surface of 45 steel,and cladding layers with different amorphous contents were obtained under different processes.None of the obtained cladding layers contained amorphous after replacing part of the Co element with the Ni element.The results are as follows:(1)Based on the theory of the cluster-plus-glue-atom model,the local structures of the amorphous phase-related phases of Fe-B,Co-B and Ni-B amorphous alloy systems were analyzed.According to the selection principle of clusters,the amorphous correlation clusters of Fe-B,Co-B and Ni-B binary alloy systems are:[Fe-Fe]2],[B-Fe9]and[B-B2Fe8];[Co-Co12],[B-Co9],[B-B2Co8]and[Ni-Ni12],[B-Ni6]and[B-B2Ni8].According to the 24-electron rule and the cluster-resonance condition,the corresponding cluster formulas are verified.The ideal amorphous clusters corresponding to the stable liquid are[B-B2Fe8]Fe,[B-Co9]B and[B-Ni9]B.(2)Different compositions of Fe-B-Si amorphous alloys were subjected to laser cladding tests on 45 steel surfaces.Crystalline and amorphous composite powders were prepared by ball milling broken method and grinding spinning ribbon method.respectively,from the master alloy Fe79.73B8.86Si11.41.The composite powder of Fe79.73B8.86Si11.41 has high thermal stability with values of Tm and T1 are 1417 K and 1448 K,and the values of Tg and Trg(Trg=Tg/Trg)are 729.43 K and 0.503,respectively.The values of T8,Tm and T1 for Fe75B15Si10 are 838 K.1402 K and 1474 K,respectively.Phases of the powders,microstructure and properties of the clad layer were analyzed.The results show that the cladding performance of the amorphous composite powder is superior to that of the crystalline composite powder under the same cladding energy condition.No porosity and cracks on the surface and inside of the cladding layer acquired from amorphous composite powder are observed.Comparing the cladding effects of Fe-B-Si amorphous alloys with different compositions,it is known that the quality of the cladding layer obtained by the amorphous powder of Fe79.73B8.86Si11.41 is superior to other components.By comparing the hardness and wear resistance of the cladding layer,the Fe75B15Si10 coating has a higher B content and better hardness and wear resistance than the Fe79.73B8.86Si11.41 coating.(3)Co-based amorphous composite coatings were produced by laser cladding on the 45 medium steel substrate.The composition was found with the best glass forming ability in the previous experiment,that can form a bulk metallic glass with a diameter of 4 mm.Results show that the coatings are mainly composed of three different zones.One zone is clad layer consisting of the Co2B equiaxed dendrite dispersed in the amorphous matrix.The second is transition zone containing dendritic and columnar Co2B phase and intergranular Co3B phase.The third is interface bonding zone composed of α’-(Co,Fe)phase distributed in the α-(Co,Fe)matrix.As the laser power increases,the volume fraction of amorphous in the surface area increases significantly,and the wear resistance and wear reduction gradually increase.When the laser power reaches 4.0 kW,the cladding layer has the highest amorphous content and the smallest wear volume.Compared with the cladding coating formed by the ternary Fe-based amorphous alloy,the hardness and wear resistance of the Co-based cladding layer are greatly improved.(4)Four glass-forming alloys Co55.1Ni6.1B26.2Si7.8Ta4.8,Co49.0Ni12.2B26.2Si7.8Ta4.8,Co42.8Ni18.4B26.2Si7.8Ta4 8 and Co36.8Ni24.4B26.2Si7.8Ta4.8 obtained by replacing Co atoms with Ni have been laser-clad on 45 steel substrate.In contrary to the quaternary case,none of the layers content the amorphous phase and the clad layers are characterized by a matrix of α-(Fe,Co,Ni)solid solution plus CoB,Co3B and Co3Ta types of precipitates.The cladding layer are divided into four regions:near-surface dendrites.α-(Fe,Co,Ni)solid solution plus dispersed particles in the middle zone,columnar bonding zone,and heat affected area that consists of martensite.The hardness gradually decreases with increasing Ni content,and the maximum hardness occurs in the middle zone.Both the friction coefficient and wear volume are minimized in the alloying contenting 12.2%Ni.Compared with the previous cobalt-based quaternary alloy Co61.2B26.2Si7.8Ta4.8,the addition of the Ni element reduces the glass forming ability as well as hardness and wear resistance of the clad layers.