| Amorphous alloy,called metallic glass,is widely used in aerospace,medical,electric power and other fields.The service environment is diverse and complex,which puts forward higher requirements for its quality and performance.The main bottleneck restricting the improvement of quality and performance of amorphous alloys is the preparation technology and the ability of amorphous formation.However,the amorphous structure characteristics and formation law are still unclear,and the study of the amorphous structure characteristics and formation law of elemental metals is one of the important ways to explore this problem.Iron is widely used in various fields of industrial production because of its rich natural resources,good ductility and excellent conductivity.There are many ways to prepare Fe-base amorphous alloy,among which the laser cladding coating can realize metallurgical bonding with the substrate,thus improving the coating quality and enhancing the stability of the coating.In this paper,molecular dynamics with reactive force field were carried out to simulate the preparation process of iron amorphous coatings,to quantitatively study the bonding behaviors of contact interface as well as the quality and structure of coatings,and to reveal the diffusion mechanisms of contact interface and formation behaviors of coatings structures.The main contents and results of the thesis can be summarized as follows:With the increase of cooling rate/melting temperature/preheating temperature,the internal stress of coating layer decreases,the number of atomic diffusion at the interface increases,the atomic diffusion travel increases,and the interface bonding area becomes thicker,The bonding quality of coating and substrate is improved.In the case of amorphous substrate,with the increase of preheating temperature,the number of interfacial atomic diffusion increases,the internal stress of coating layer is small,which improves the metallurgical bonding quality of coating and substrate,and enhances the stability of coating.When the structure of the amorphous substrate is quantified,it is found that the preheating promotes the formation of amorphous structure of the coating compared with the state of room temperature.In the radial distribution function analysis of the coating,it is found that the first peak splitting of the radial distribution function indicates the formation of a crystalline structure,while the second peak splitting of the radial distribution function indicates the formation of an amorphous structure.By analyzing the local structure of Voronoi polyhedron,it is found that the crystalline structure is composed of body-centered cubic structure,and the amorphous structure is composed of several deformed icosahedrons and a few standard icosahedrons.By quantifying the structure,it is found that the number of amorphous structures increases and the number of crystalline structures decreases with the increase of preheating temperature.With the increase of cooling rate,the number of amorphous and crystalline structures did not change greatly.With the increase of melting temperature,high melting temperature promoted the formation of amorphous structure.By tracing the formation process of local amorphous atomic clusters in the iron cladding layer/substrate,it is found that the formation process of atomic clusters is mainly as follows:(1)chain formation process,in the initial stage of cooling,atoms are connected into short bond chains,the number is small and the distribution is relatively scattered;(2)In the nucleation process,the bond chains become longer and more,interweave disordered in space,and gather into larger volume clusters;(3)In the process of cluster densification,the surrounding atoms move to the center atoms greatly,the clusters become smaller and denser,and irregular amorphous clusters are produced;(4)Cluster stabilization process,the atoms in the cluster undergo spatial fine-tuning,irregular clusters become standard icosahedral clusters. |
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