Alloy

About: Alloy is a research topic. Over the lifetime, 171884 publications have been published within this topic receiving 1719420 citations. The topic is also known as: alloys.

Evidence of a Glass-Liquid Transition in a Gold-Germanium-Silicon Alloy

Abstract: Gold‐rich (73–81 at.% Au) alloys of gold–germanium–silicon were “splat” cooled to an amorphous solid form. Thermal and rheological evidence of a glass‐liquid transition in the Au0.77Ge0.136Si0.094 alloy is reported. The transition was manifested thermally by an abrupt rise of 5.5 cal/g‐atom·°K in specific heat, Cp, as the alloy was heated from 285° to 297°K. Just above 297°K, Cp starts to fall with increasing T on a reasonable extrapolation of the high‐temperature Cp–T relation of the liquid alloy. This thermal behavior could be repeated on the same sample after it had been carried through the transition and chilled again. The apparent glass‐transition temperature was increased by 1°–3° by increasing the heating rate by a factor of 16. The viscosity η of the amorphous alloy increases rapidly with falling temperature from 0.9 × 109 P at 305°K to 1.4 × 1013 P at 285°K and is described by the equation: η = 0.52 exp [136 / (T − 241.3)] P. The steady isothermal viscosity is independent of stress over the range...

Novel hexagonal structure and ultrahigh strength of magnesium solid solution in the Mg–Zn–Y system

Abstract: A magnesium (Mg) solid solution with a long periodic hexagonal structure was found in a Mg97Zn1Y2 (at.%) alloy in a bulk form prepared by warm extrusion of atomized powders at 573 K. The novel structure has an ABACAB-type six layered packing with lattice parameters of a = 0.322 nm and c = 3 × 0.521 nm. The Mg solid solution has fine grain sizes of 100 to 150 nm and contains 0.78 at.% Zn and 1.82 at.% Y. In addition, cubic Mg24Y5 particles with a size of about 7 nm are dispersed at small volume fractions of less than 10% in the Mg matrix. The specific density (ρ) of the extruded bulk Mg–Zn–Y alloy was 1.84 Mg/m3. The tensile yield strength (σy) and elongation (δ) are 610 MPa and 5%, respectively, at room temperature, and the specific yield strength defined by the ratio of σy to ρ is as high as 3.3 × 105 Nm/kg. High σy values exceeding 400 MPa are also maintained at temperatures up to 473 K. It is noticed that the σy levels are 2.5 to 5 times higher than those for conventional high-strength type Mg-based alloys. The Mg-based alloy also exhibits a high-strain-rate superplasticity with large δ of 700 to 800% at high strain rates of 0.1 to 0.2 s−1 and 623 K. The excellent mechanical properties are due to the combination of the fine grain size, new long periodic hexagonal solid solution containing Y and Zn, and dispersion of fine Mg24Y5 particles. The new Mg-based alloy is expected to be used in many fields.

Structure Determination of Mg5Si6 Particles in Al by Dynamic Electron Diffraction Studies

Abstract: Precipitation hardening, in which small particles inhibit the movement of dislocations to strengthen a metal, has long been used to improve mechanical strength, especially of aluminum alloys. The small size of precipitates and the many possible variants of the orientation relation have made their structural determination difficult. Small precipitates in commercial aluminum-magnesium-silicon alloys play a crucial role in increasing the mechanical strength of these alloys. The composition and structure of the β” phase in an aluminum-magnesium-silicon alloy, which occur as precipitates (typically 4 nanometers by 4 nanometers by 50 nanometers) and are associated with a particularly strong increase in mechanical strength, were determined. Element analysis indicates that the composition is Mg 5 Si 6 . A rough structure model was obtained from exit waves reconstructed from high-resolution electron microscopy images. The structure was refined with electron nanodiffraction data (overall R value of 3.1 percent) with the use of a recently developed least squares refinement procedure in which dynamic diffraction is fully taken into account.