Visco-Elastic Properties of Semi-Solid Alloys

Oscillation and creep experiments have been performed with Semi-Solid Material (SSM) AlSi7 with 35% solid fraction to investigate the early visco-elastic properties after shearing of the material in a Searle Rheometer. The preparation of the SSM has been done in situ using a standard procedure to guarantee for all experiments the same initial properties of the material. First, oscillation experiments at low amplitude allowed to study the evolution of material structure with time. Subsequently, creep experiments have been performed changing the resting period based on previous results. Creep experiments are characterized by exposing the material to a sudden increase of shear stress. The resolution in time has been 0.01 seconds, which allows observing the dynamics of the development of visco-elastic properties.The material exhibits viscoelastic properties that are becoming more pronounced with longer resting time. This is in accordance with previous experiments where the ratio between elastic and viscous properties increases with increasing resting time. The development of the elastic properties follows the increase of the yield stress due to the creation of an internal structure of the material, which starts immediately after stopping shearing. The investigation of the short-term response of SSM can be particularly relevant for industrial practice, where material deformation during die filling is very fast and the material flow does not take place in steady-state condition.

Coercimeter for non-destructive control of solid alloys

The widespread use of solid-alloy tools in modern engineering makes it necessary to ensure and maintain quality in the process of their production. The use of hard alloy plates of inadequate quality results in the instability of the mechanical processing and, as a consequence, the quality of the processed products in the batch is reduced. Heterogeneity of structure and properties is a significant disadvantage of products of cermet solid alloys as a product of powder metallurgy. They must therefore be subject to 100 per cent quality control. Today, various methods are used in order to control the physical and mechanical properties of products, such as hardness and microhardness of the surface and surface layer. Non-destructive control methods, one of which is a magnetic method based on measurement of the coercive force of an article, are of high priority and potential. A coercimeter instrument is proposed to implement this method. This research gives a description of the principle of its work, the functions performed by individual nodes, their electrical circuits and possibilities.

Dissimilar Metal Solution from Solid Alloys as Observed for Steels and Nickel‐Based Alloys in the Presence of Lead‐Based Liquid Alloys or Liquid Tin

The solution of elements from metallic alloys is analyzed, notably the initial stage characterized by solution in proportion to the alloy composition and subsequent selective leaching of alloying elements. For the latter stage of the process, characteristic features of the originating depletion zone are derived for different formation mechanisms. The results are compared with observations for steels and nickel-based alloys after exposure to lead-based liquid alloys or liquid tin, and, where possible, the prevailing mechanism is identified. Furthermore, the influence of dissolved oxygen and formation of intermetallic compounds are addressed.

Analytic Binary Alloy Volume–Concentration Relations and the Deviation from Zen’s Law

Alloys expand or contract as concentrations change, and the resulting relationship between atomic volume and alloy content is an important property of the solid. While a well-known approximation posits that the atomic volume varies linearly with concentration (Zen’s law), the actual variation is more complicated. Here we use the apparent size of the solute (solvent) atom and the elasticity to derive explicit analytical expressions for the atomic volume of binary solid alloys. Two approximations, continuum and terminal, are proposed. Deviations from Zen’s law are studied for 22 binary alloy systems.

Triaxial Compression on Semi-solid Alloys

Multi-axial compression of the mushy zone occurs in various pressurized casting processes. Here, we present a drained triaxial compression apparatus for semi-solid alloys that allow liquid to be drawn into or expelled from the sample in response to isotropic or triaxial compression. The rig is used to measure the pressure-dependent flow stress and volumetric response during isothermal triaxial compression of globular semi-solid Al-15 wt pct Cu at 70 to 85 vol pct solid. Analysis of the stress paths and the stress–volume data show that the combination of the solid fraction and mean effective pressure determines whether the material undergoes shear-induced dilation or contraction. The results are compared with the critical state soil mechanics (CSSM) framework and the similarities and differences in behavior between equiaxed semi-solid alloys and soils are discussed.

Поверхностно-излучающий квантово-каскадный лазер с кольцевым резонатором

The results of studies of quantum-cascade laser with a surface emission through a grating formed in the layers of the top cladding of the waveguide by ion beam milling are presented. The active region of the QCL heterostructure was formed based on a heteropair of In0.53Ga0.47As / Al0.48In0.52As solid alloys with two-phonon resonance design. It is shown that lasing at room temperature close to 7.9 µm is demonstrated for a laser with a ring diameter of 191 µm. The mode spacing corresponds to whispering gallery modes.

Theory of Inhomogeneous Short Range Order and Calphad Modeling. Part 6. Order-Disorder Transformations in Alloys

Formalism of Theory of Inhomogeneous Short Range Order (TISR) is extendedto describe Order–Disorder transformations in solid alloys. The result is a naturalintegration of Short and Long Range Order description in the framework of thesame theory.The equations of Cluster Site Approximation (CSA) are deduced directly fromthe equations of TISR. Formalism and interpretation of CSA are simplified andclarified.