Phase-evolution in high entropy alloys: Role of synthesis route

Synthesis route can have a significant influence on the process of phase-choice and -evolution in High Entropy Alloys (HEAs). With the objective of instituting awareness, this communication on the foundation of phase diagrams, adopted using the CALPHAD approach, attempts at describing and deciphering the cause for such gradation.     

Effect of heavy cryo-rolling on the evolution of microstructure and texture during annealing of equiatomic CoCrFeMnNi high entropy alloy

The effect of cryo-rolling on the evolution of microstructure and texture during annealing was investigated in equiatomic CoCrFeMnNi high entropy alloy. For this purpose the alloy was cold- and cryo-rolled to 90% reduction in thickness followed by annealing at temperatures ranging from 700 °C to 1200 °C. The two alloys showed the development of predominantly brass type deformation texture consistent with profuse nano-twin formation reported in this alloy. The cryo-rolled material showed significantly finer grain size after different annealing treatments as compared to the cold-rolled alloy. This could be attributed to finer microstructure in the cryo-rolled material providing greater number of available sites for nucleation. The recrystallization texture of cold- and cryo-rolled materials showed the presence of similar texture components indicating that cryo-rolling had limited effect on the formation of annealing texture. The volume fractions of different texture components did not reveal significant dependence on the annealing temperature. The evolution of texture could be explained on the basis of absence of strong preferential nucleation and growth during annealing.     

First-principles calculations and experimental studies of Sn-Zn alloys as negative electrode materials for lithium-ion batteries

The physical characters and electrochemical properties of various phases in a Sn-Zn electrode,such as formation energy,plateau potential,specific capacity,as well as volume expansion,were calculated by the first-principles plane-wave pseudo-potential method based on the density functional theory.Sn-Zn films were also deposited on copper foils by an electroless plating technique.The actual composition and chemical characters were explored by scanning electron microscopy (SEM),X-ray diffraction (XRD),plasma atomic emission spectrometry (ICP),and constant current charge/discharge measurements (CC).The results show that separation phases with tin and zinc including a small quantity of Cu6Sn5 phase were obtained,the initial lithium insertion capacity of the Sn-Zn film was 661 mAh/g,and obvious potential plateaus of about 0.4 V and 0.7 V were displayed,which is in accordance with the results of theoretical calculations.The capacity of the Sn-Zn film decreased seriously with the increase of cycle number.     

X-ray photoemission spectrum, electronic structure, and magnetism of UCu2Si2

The room temperature X-ray photoemission spectrum of the ferromagnetic compound UCu₂Si₂ (T_C = 100 K) was measured using an Al K_α source. Related theoretical spectra were computed from densities of electronic states obtained in the local density approximation (LDA), the generalized gradient approximation (GGA), and using the GGA + U method. The calculated spectrum is in a good agreement with the experimental one. The spin polarized calculations based on the GGA + U approach as well as GGA/LSDA with orbital polarization (OP) corrections taken into account provide values of the total magnetic moment in reasonable agreement with the experimental values ranging between 1.6 and 2.0 μ_B/U atom.     

Effect of the primary heat treatment on the bond formation in cold welding of aluminum and steel by cold forging

Cold forging enables the manufacturing of high strength monolithic components. When used as joining technology it can also be extended to an enabler of multi-material product design. The contact conditions at the interface between the components during the cold forging process play a crucial role. The joining of two billets of steel and aluminum is investigated by a finite element analysis with regard to the material distribution and the effect of a primary heat treatment of both materials. These parameters affect the surface enlargement and the contact normal stress which are decisive parameters for the formation of a sound bond between aluminum and the hardly cold weldable steel. The experimental results present the effect of a primary heat treatment on the bond formation. Microscopic analyses of the bond formation allow a deeper insight into the bonding mechanism. Thus, the results lead to process design guidelines for cold welding by cold forging.     

不同相组成铸态Mg-xLi-1Al合金的阻尼性能(英文)

采用真空熔炼法制备三种不同相态的Mg-xLi-1Al三元合金,并使用光学显微镜、X射线衍射分析及动态力学分析仪研究其显微组织及阻尼性能。结果表明:由于锂含量的增加,合金的相结构发生转变且出现新的阻尼机制,其中BCC结构的出现使阻尼性能显著提高,同时弹性模量的减小也使临界应变振幅值降低。两相共存状态的合金随温度变化表现出较高的阻尼现象,并在低温与高温区均出现两个较为明显的峰值,其中低温区的P1峰是位错阻尼峰,高温区的P2峰是晶界阻尼峰。     

The effect of titanium surface treatment on the interfacial strength of titanium – Thermoplastic composite joints

Co-consolidated titanium – carbon fibre reinforced thermoplastic composite hybrid joints show potential for application in aerospace structures. The strength of the interface between the titanium and the thermoplastic composite is crucial for the strength of the entire hybrid joint. Application of a surface treatment on the titanium is an effective way to improve this interfacial strength. This paper evaluates the effect of several titanium surface treatments on the interfacial strength between titanium and carbon fibre reinforced polyetheretherketone (PEEK) or polyetherketoneketone (PEKK). Furthermore, the underlying bonding mechanisms, activated by these surface treatments, are studied. The research result shows that the grit blasted titanium – carbon fibre reinforced PEKK interface outperforms the other interfaces.     

Laser cutting of triangular blanks from thick aluminum foam plate: Thermal stress analysis and morphology

Laser cutting of triangle blank from aluminum foam is carried out. Thermal stress field in the cutting section is predicted using ABAQUS finite element code in line with the experimental conditions. Laser cutting experiments are carried out prior to the model study to determine the optimum cutting parameters for the quality cuts. Temperature predictions are compared with thermocouple data obtained from the experiment. Morphological and metallurgical changes in the cut section are examined using optical and scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction. It is found that von Mises attains high values along the circumference of the cut edges at the onset of cooling cycle initiation. Laser cut edges are free from defects and asperities; however, locally distributed few dross attachments take place at the kerf exit.