Predicting the Thermodynamic Ideal Glass Transition Temperature in Glass-Forming Liquids

The Kauzmann temperature TK is a lower limit of glass transition temperature, and is known as the ideal thermodynamic glass transition temperature. A supercooled liquid will condense into glass before TK. Studying the ideal glass transition temperature is beneficial to understanding the essence of glass transition in glass-forming liquids. The Kauzmann temperature TK values are predicted in 38 kinds of glass-forming liquids. In order to acquire the accurate predicted TK by using a new deduced equation, we obtained the best fitting parameters of the deduced equation with the high coefficient of determination (R2 = 0.966). In addition, the coefficients of two reported relations are replaced by the best fitting parameters to obtain the accurate predicted TK, which makes the R2 values increase from 0.685 and 0.861 to 0.970 and 0.969, respectively. Three relations with the best fitting parameters are applied to obtain the accurate predicted TK values

The Influence of Grain Boundaries on Crystal Structure and Tensile Mechanical Properties of Al_0.1CoCrFeNi High-Entropy Alloys Studied by Molecular Dynamics Method

The mechanical properties of high-entropy alloys are superior to those of traditional alloys. However, the key problem of finding a strengthening mechanism is still challenging. In this work, the molecular dynamics method is used to calculate the tensile properties of face-centered cubic Al0.1CoCrFeNi high-entropy alloys containing Σ3 grain boundaries and without grain boundary. The atomic model was established by the melting rapid cooling method, then stretched by the static drawing method. The common neighbor analysis and dislocation extraction algorithm are used to analyze the crystal evolution mechanism of Σ3 grain boundaries to improve the material properties of high-entropy alloys during the tensile test. The results show that compared with the mechanical properties Al0.1CoCrFeNi high-entropy alloys without grain boundary, the yield strength and Young’s modulus of a high-entropy alloy containing Σ3 grain boundary are obviously larger than that of high-entropy alloys without grain boundary. Dislocation type includes mainly 1/6 Shockley partial dislocations, a small account of 1/6 Stair-rod, 1/2perfect dislocation, and 1/3 Hirth dislocations. The mechanical properties of high-entropy alloys are improved by dislocation entanglement and accumulation near the grain boundary

Evolution of Microstructure and Mechanical Properties of the CoFeNiMnMox High-Entropy Alloys

In this study, the microstructure evolution and mechanical properties of CoFeNiMnMox high-entropy alloy after adding Mo were investigated. With the increase in Mo content, Mo atoms occupied lattice sites and the microstructure changed from hypoeutectic of primary FCC-phase to Laves phase particles of FCC-phase, and Vickers microhardness increased steadily from 193 to 357. The yield strength increased from 187 MPa when the Mo content was 0.25 to 537 MPa when the Mo content was 1.0. The microstructure formation can be explained by atomic size difference δ and parameter ΔχA. δ ≥ 3.87% and ΔχA ≥ 5.24% criterion is proposed to better predict the microstructure formation of the coexistence of (FCC + Laves) phases

Crystallization Kinetics of the Fe₆₈Nb₆B₂₃Mo₃ Glassy Ribbons Studied by Differential Scanning Calorimetry

Fe-based metallic glass has wide industrial application due to its unique mechanical behavior and magnetic properties. In the present work, the non-isothermal crystallization kinetics in Fe68Nb6B23Mo3 glassy alloys were investigated by differential scanning calorimeter (DSC). The results indicate that both the glass transformation and crystallization process display an obvious kinetic effect. The activation energy is calculated using Kissinger’s method and Ozawar’s method. The activation energy for Tg (glass transition temperatures), Tx (crystallization initiation temperatures) and Tp (crystallization peak temperatures) calculated from Kissinger equation, is 308 ± 4, 342 ± 5 and 310 ± 7 kJ mol−1, respectively. The activation energy for Tg, Tx and Tp calculated from Ozawa equation is 322 ± 3, 356 ± 5 and 325 ± 7 kJ mol−1, respectively. With the increase of the crystallization volume fraction x, the Avrami exponent n(x) first decreases and then increases. At the preliminary step, 0 x n(x) n(x) decreases from 2.5 to 1.5, indicating that this stage is controlled by the growth of small particles with a decreasing nucleation rate

Comparing the formation, properties and structure between Fe20Co20Ni20Cr20(P0.45B0.2C0.35)20 high-entropy metallic glass and the predecessor Fe75Cr5P9B4C7 metallic glass

In present work, formation, properties and local structure features between novel Fe20Co20Ni20Cr20(P0.45B0.2C0.35)20 high-entropy metallic glass (HEMG) and the predecessor Fe75Cr5P9B4C7 metallic glass (MG) were thoroughly characterized by experiments and ab-initio molecular dynamics (AIMD) simulation. Compared with predecessor MG, the HEMG possesses a higher thermal stability of supercooled liquid with wider supercooled liquid region of 57 K, superior corrosion resistance with higher corrosion potential, lower corrosion and passive current density along with wider passive region in 3 wt.% NaCl solution. Additionally, the HEMG possesses a paramagnetic feature with low magnetization of only 9.38 emu·g−1, while predecessor MG possesses a good soft-magnetic property with a high saturation magnetization of 115.16 emu·g−1. The corresponding local structure differences deriving from AIMD simulation exhibit that the HEMG possesses a higher content of icosahedra-like structures (with bond pair indexes (BPIs) of 1551, 1541 and 1431) and Voronoi polyhedra (VPs) with relative smaller coordination numbers (8, 9, 11, 12 and 13), lower content of crystal-type structures (with BPIs of 1421, 1422, 1441 and 1661) and VPs with larger coordination numbers (15 and 16) compared with predecessor MG. These results show that the formation, properties and local structures can be visibly changed after present high-entropy alloying by similar solvent elements Co, Ni and Cr equiatomic substitution of Fe in predecessor MG. Additionally, both alloys possess dominant VPs with coordination numbers from 12 to 15 and good ductility without fracture as bent by 180°

Influence of interstitial carbon content on the microstructure, mechanical and electrochemical corrosion properties of CoFeNiMn multi-principal component alloys

In this study, the effects of carbon content on the microstructural evolution as well as compression and electrochemical corrosion properties of CoFeNiMn multi-principal component alloys (MPCAs) were investigated. A series of (Co25Fe25Ni25Mn25)100−xCx (x = 4, 5, 6, 7, 8) alloys were prepared by vacuum arc melting. Increasing carbon content, the structure transits from a single face-centered-cubic (FCC) phase into a mixed structure containing FCC phase and M23C6 carbides. The yield strength and hardness of the (Co25Fe25Ni25Mn25)100−xCx alloys were enhanced by increasing carbon content, which in turn decreases the ductility. The alloys containing eutectic carbides had a good combination of high yield strength (880 MPa), high fracture strength (2773 MPa), and large fracture strain (47%). Electrochemical measurements indicated that carbon content evidently affects the corrosion resistance of (Co25Fe25Ni25Mn25)100−xCx alloys in 3.5 wt% NaCl solution. Their corrosion resistance initially increases and then decreases with increasing carbon content. The increase in M23C6 carbides can accelerate pitting corrosion and degenerate their corrosion resistance. These findings not only provide comprehensive understanding of the carbon-alloyed behavior in FCC-type MPCAs but also show their potential engineering application as high-performance structural materials