Microstructure simulation of rapidly solidified ASP30 high-speed steel particles by gas atomization

In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element （CAFE） model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions （UDFs） to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also inves- tigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy （SEM）. The experimental re- suits showed that four major types ofmicrostructures were formed： dendritic, equiaxed, mixed, and multi-droplet microstructures. The simu- lated results and the available experimental data are in good agreement.

First principles application for mechanical properties of Ti-doped W particles enhanced U matrix composite

The stability, bonding, work of adhesion and electronic structure of the U/W interface with and without Ti were investigated by first principles to explore the me- chanical properties of W particles enhanced U-Ti alloy matrix composite as a construction material. The calculated results indicate that the preferable orientation of the U/W interfacial structure is （001）U/（110）w crystallographic plane, Ti atoms originating from U slab are prone to diffuse into W slab through the interface, and additional Ti in U matrix is the stronger adhesion to W, with an ideal work of adhesion of 6.93 J.m-2 for U-Ti/W interface, relative to the value of 6.72 J.m-2 for clean U/W interface. The stronger adhesion performance is due to the increase in valence electron hybridization for U-Ti/W compared with U/W interface, as evidenced by the characteristic of the local density of states for the interfacial atoms.

Mechanical properties of U-0.95 mass fraction of Ti alloy quenching and aging treatment:a first principles study

First principles plane wave pseudopotential method was executed to calculate the mechanical properties with respect to the uranium-0.95 mass fraction of titanium （U-0.95 mass fraction of Ti） alloy for quenching and aging, including the elastic modulus, the value of shear modulus to bulk modulus （G/B） and the ideal tensile strength. The further research has also been done about the crack mechanism through Griffith rupture energy. These results show that the elastic moduli are 195.1 GPa for quenching orthorhombic ~ phase and 201.8 GPa for aging formed Guinier-Preston （G.P） zones, while G/B values are 0.67 and 0.56, respectively. With the phase change of uranium-titanium （U-Ti） alloy via the quenching treatment, the ideal tensile strength is diverse and distinct with dif- ferent crystal orientations of the anisotropic ~ phase. Comparison of quenching and short time aging treatment, both of the strength and toughness trend to improve slightly. Further analysis about electronic density of states （DOS） in the electronic scale indicates that the strength increases continuously while toughness decreases with the aging proceeding. The equilibrium structure appears in overaging process, as a result of decomposition of metastable quenching 7 phase. Thereby the strength and toughness trend to decrease slightly. Finally, the ideal fracture energies of G.P zones and overaging structure are obtained within the framework of Griffith fracture theory, which are 4.67 J/m2 and 3.83 J/m2, respectively. These results theoretically demonstrate strengthening effect of quenching and aging heat treatment on U-Ti alloy.

Interface reaction of high-strength low-alloy steel with Al-43.4Zn-1.6Si(wt.%)metallic coating

The microstructure,elemental distribution,phase composition,and thickness of intermetallic layers between high-strength low-alloy steel(H420)/mild carbon steel(DC51)and Al–43.4Zn–1.6Si(wt.%)(galvalume,GL)alloy were comparatively investigated.The experimental results reveal that the interfacial reaction layer was composed of Fe2Al5,Fe4Al13,and Al8Fe2Si intermetallic compounds.Moreover,the growth curves of the Fe2Al5 and Fe4Al13 intermetallic layers fit the parabolic law well,and the total thickness of the intermetallic layers of H420+GL was almost the same as that of DC51+GL.However,the thickness of the Fe2Al5 layer in H420+GL was thinner than that in DC51+GL.In addition,first-principle calculations were performed to explore the effect of Mn on the growth of the Fe2Al5 intermetallic phase,and the results indicate that Mn substitution in Fe2Al5 removes electronic charge from the Al atoms,thus decreasing the thickness of the Fe2Al5 interface layer.