Calculation of the Surface Segregation of Cu-0.3 at. pct Au Alloy

1. IntroductionIt is now clearly known that the surface modification of materials by ion-direct implantation andatomic maing etc. has been extensively used inindustry[1]. In the field of surface modification of materials, an importal question is how to force impurity atoms to be enriched at suface Iapers, particularlyat the first surface layer. Evidentlys if the impurityatoms in materials are segregating species this aimIlilght be eajsily attained.If a material is pure metal, such as Cu, stu…     

Distortion Regions near the Grain Boundary and Their Effects on Nanocrystalline Materials

1. IntroductionGrain boundaries are the most common extendeddefects in crystalline materials. They strongly affect,and to a great extent control, the physical and mechanical properties of materials. In nanocrystallinematerials, the fraction of atoms locating at grainboundaries becomes so large that the material can beregarded as a two-phase system consisting of a boundary component and a crystalline component. Many ofthe properties of nanocrystalline materials are influenced by the grain bound…     

Universality and Specificity of Fractal Dimension of Fractured Surfaces in Materials

1. IntroductionSince Mandelbrot et al.11] showed .that fracturedsurfaCes are fractals in nature and that the fractaldimension of fractured surfaCes correlates well withthe toughness of ~erials. Many authors have doneexperimellts on this probleml2,3]. Now, it is generally accepted that the fractured surface is a fractalwith self-affine property if the applied stress is ModeI loading. Several years later, Bouchaud et al.14] reported thst the rouglmess index of the fractured surfaces would be …     

Dislocation Model and Morphology Simulation of bcc fcc Martensitic Transformation

By using molecular dynamics computer simulation at atomic level, the effects of single dislocation and dipole dislocations on nucleation and growth of martensitic transformation have been studied. It was found that only the location of tension or compression stress fields of the dislocations are favorable for martensite nucleation in NiAl alloy and the dislocations can move to accommodate partly the transformation strain during the nucleation and growth of martensite. Combined with the molecular dynamics simulation, a two dimensional simulation for martensite morphology based on a dislocation model has been performed. Many factors related to martensitic transformation were considered, such as supercooling, interface energy, shear strain, normal strain and hydrostatic pressure. Different morphologies of martensites, similar to lath, lenticular, thin plate, couple-plate and lenticular couple-plate martensites observed in Fe-C and Fe-Ni-C alloys, were obtained.     

Modeling of Solidification Microstructures Based on Fully Coupling of Macro-transport Phenomena with Cellular Automata

This paper has attempted to simulate the microstructure formation based on fully coupling of temperature field, concentration field and velocity field with micro-kinetics. The authors presented a new way, which is the combination of FDM and cellular automata (CAFD) to visualize the microstructure formation of the thin complex superalloy turbine blades cast by the vacuum investment process. The distribution, orientation and mechanism of the heterogeneous nucleation, the growth kinetics of dendrites and the columnar to equiaxed transition (CET) are considered. Capitalizing on these simulating schemes, the comprehensive influence of key process variables on the scale and uniformity of grains has been investigated quantitatively. The simulated grain size and morphology agree well with the experimental results.     

A Study on Crystal Defects in Epitaxial GaN Film by High-Order Weak-Beam Electron Microscopy

Various crystal defects in epitaxial GaN film were studied by high-order bright-field and dark-field electron microscopy. The results revealed that the film is composed of small grains in nano-meter scale. Distinct shapes of the grain boundaries and a great number of threading dislocations were shown in the experimental g/3g weak-beam images. Diffraction contrast analysis verified that the majority of threading dislocations is 1/3<11 0> edge dislocation. A unique (11 0) planar defect was observed in the specimen. The defect was identified to have a similar structure to the incipient 1/3[11 0] edge dislocation.     

Environmental and internal hydrogen embrittlement of a directionally solidified Ni-rich Ni3AI intermetallics

The influence of tensile orientation, test environments and internal hydrogen contents on the room temperature tensile properties of a directionally solidified Ni₃Al alloy was investigated. The specimens parallel to the growth direction exhibited a good ductility and little susceptibility to test environment. The values of elongation in vacuum, air and H₂ are 39.7%, 39.2% and 29.7%, respectively. Also, a transgranular fracture mode was observed in the specimens. However, the specimens perpendicular to the growth direction exhibited lower ductility, much more sensitivity to test environment and intergranular fracture mode. The elongation values in vacuum, air and H₂ are 13.7%, 10.3% and 3.3%, respectively. The results indicate that the cohesive strength of grain boundaries in the alloy is low and they are more susceptible to test environment than are grain interiors. In addition, only a slight embrittlement of the internal hydrogen was found in the specimens parallel to the growth direction.     

Temperature fluctuation/hot pressing synthesis of Ti3SiC2

A novel temperature fluctuation synthesis and simultaneous densification process for the preparation of Ti₃SiC₂ was developed. The advantages of this novel method include low synthesis temperature, short reaction time and simultaneous densification. The microstructure and room temperature mechanical properties of the Ti₃SiC₂ synthesized using this method were investigated. The result demonstrated that the Ti₃SiC₂ ceramic consisted of mainly laminated grains. It was found, with the aid of computer simulated crystallite shape, that the laminated Ti₃SiC₂ grains were composed of thin hexagonal plates. These laminated grains characterized the Ti₃SiC₂, and were responsible for the mechanical properties of the polycrystalline Ti₃SiC₂ ceramic. The measured flexural strength and the fracture toughness were 470 ± 26 MPa and 7.0 ± 0.2 MPa·m^1/2, respectively. The high toughness was attributed to the contribution of crack deflection, crack bridging, delaminating and grain pull-out of laminated Ti₃SiC₂.     

Pure mechanical wear loss measurement in corrosive wear

The method for the measurement of the pure mechanical wear loss for 321 stainless steel, 1045 steel and pure iron in the study of the synergy between corrosion and wear was studied. The methods studied included the measurement in distilled water, by cathodic protection and by adding inhibitor KI, and all were compared with the wear loss in air. The experiment showed that the pure mechanical wear losses and friction coefficients obtained by the three methods were close to each other and can be used to calculate the various wear components in the study of the interaction of corrosion and wear, but the measurements in distilled water for pure iron and 1045 steel are not recommended due to their corrosion