Co-based metallic glasses (MGs) are a new class of soft magnetic materials, which have promising application value in high-frequency fields due to their high magnetic permeability and low coercivity. However, these kinds of MGs have poor glass-formation ability (GFA) and relatively low saturated magnetic flux density, so their application scope is limited. The atomic size of metalloid elements <i>M</i> (B, C, Si, and P) is small, which can easily enter the gap between atoms, and there is a relatively large negative enthalpy of mixing between metalloid elements and metal elements. Therefore, alloying with metalloid elements <i>M</i> is an effective method to improve the GFA while maintaining superior soft magnetic properties for Co-based MGs. In this paper, the formation process of Co₇₂Y₃B₁₅<i>M</i>₁₀ (<i>M</i>=B, C, Si, P) MGs was simulated by <i>ab initio</i> molecular dynamics (AIMD) methods, and the effects of the addition of metalloid elements <i>M</i> (C, Si, P) on the GFA and magnetic properties of Co-Y-B MGs have been investigated. It is devoted to analyzing the relationship between local atomic structures and properties from different perspectives at the atomic level.<br>According to the results of the characterization parameters of local atomic structures (pair distribution function, coordination numbers, chemical short-range order, Voronoi polyhedron index, local five-fold symmetry, and mean square displacement), it is found that the GFA of the four alloys is different due to their different local atomic structures. Co₇₂Y₃B₁₅C₁₀ and Co₇₂Y₃B₁₅P₁₀ alloys possess a higher fraction of prism structures, and the solute segregation between B/C-C and B/P-P atoms is weak, resulting in the higher atomic diffusivity in the supercooled state (1100 K), and hence weaken the GFA of the alloys. The Co₇₂Y₃B₁₅Si₁₀ alloy has a higher fraction of icosahedral-like structures, the stronger attraction between Co-Si atoms and solute segregation between B/Si-Si atoms reduce the atomic diffusivity in the supercooled state, whilst improving the thermal stability of alloy melts, stability of the local atomic structures, and the degree of five-fold symmetry, thereby increasing the GFA. Based on the analysis of the local atomic structures, it is speculated that the addition of Si is beneficial for enhancing the GFA, while the addition of C or P will reduce the GFA, that is, the GFA of the four alloys decreases in the order of Co₇₂Y₃B₁₅Si₁₀ > Co₇₂Y₃B₂₅ > Co₇₂Y₃B₁₅P₁₀ > Co₇₂Y₃B₁₅C₁₀. In terms of magnetic properties, with metalloid elements <i>M</i> addition, the total magnetic moment of Co₇₂Y₃B₁₅<i>M</i>₁₀ (<i>M</i>=B, C, Si, P) alloys decreases as follows Co₇₂Y₃B₂₅ > Co₇₂Y₃B₁₅Si₁₀ > Co₇₂Y₃B₁₅C₁₀ > Co₇₂Y₃B₁₅P₁₀. The stronger p-d orbital hybridization between Co-Si atoms enhances the ferromagnetic exchange interaction, leading to the total magnetic moment less affected by Si addition.

The primary carbide in high carbon chromium bearing steels, which arises from solute segregation during non-equilibrium solidification, is one of the key factors affecting the mechanical properties and performance of the related components. In this work, the effects of carbide forming element diffusion, primary austenite grain size, and the cooling rate on solute segregation and carbide precipitation during the solidification of an Fe–C binary alloy were studied by the phase-field method coupled with a thermodynamic database. It was clarified that increasing the ratio of solute diffusivity in solid and liquid, refining the grain size of primary austenite to lower than a critical value, and increasing the cooling rate can reduce the solute segregation and precipitation of primary carbide at late solidification. Two characteristic parameters were introduced to quantitatively evaluate the solute segregation during solidification including the phase fraction threshold of primary austenite when the solute concentration in liquid reaches the eutectic composition, and the maximum segregation ratio. Both parameters can be well-correlated to the ratio of solute diffusivity in solid and liquid, the grain size of primary austenite, and the cooling rate, which provides potential ways to control the solute segregation and precipitation of primary carbide in bearing steels.