Effect of Holding Time on the Microstructure of Mg-3Si-1.70Sn Alloy during Semisolid Isothermal Heat Treatment

The microstructural evolution behavior of Mg-3Si-1.70Sn alloys during semisolid isothermal heat treatment was investigated by optical microscopy observations in the present study. With the holding time increasing, the grains evolve to be more spheroidal and 15min is adequate for the alloy to be spheroidized, after this coarsening begins to happen. The amount of the liquid islands inside α-Mg grains decreases and that of the liquid phase at the grain boundaries increases with the prolonged holding time. Moreover, the morphology of eutectic Mg2Si phases changes from the Chinese script and/or long-fiber shape to short fiber or spherical shapes during semisolid isothermal heat treatment, which can be attributed to the Rayleigh shape instability.

The Degradation of Microstructure of AlCu4Ni2Mg Aluminium Alloy after Prolonged Annealing at Elevated Temperature

The influence of long term annealing on microstructure of Al-Cu4-Ni2-Mg aluminum alloy was investigated. The castings were subjected to T6 heat treatment followed by annealing at 523 K and 623 K for 100, 150, 300, 500 and 750 hours. The soaking time and temperature was adjusted by corresponding to real service conditions of the elements of an aircraft and motor engines from investigated alloys. Microstructural examination of the alloy was carried out with optical microscope, as well as scaning and transmissiom electron microscopes. The result of microscopic analysis showed that applied heat treatment caused an increasing in the particles of hardening (θ’-Al2Cu) phase size. The significant growth of the length and changing the value of shape factor of hardening phase precipitations was observed. The phenomenon of the increase in size and change in shape of precipitations of hardening phases continually change with the prolonged holding time at high temperature. The microstructure degradation is connected to a decrease of mechanical properties of alloy, confirmed by the result of tensile tests.

Microstructure Evolution and Softening Processes Occurring during Annealing of Hot Deformed Ni-30Fe Austenite

The current work investigates the microstructure evolution and softening processes that take place during annealing of an austenitic Ni-30Fe model alloy subjected to hot deformation in the dynamic recrystallization (DRX) regime. The substructure of the deformed matrix grains largely comprised organized microband arrays, though that of the DRX grains consisted of more random, complex subgrain/cell arrangements. This substructure disparity was also reflected by the distinct difference in the mechanism of post-deformation softening taking place during annealing of the deformed matrix and DRX grains. In the former, the recrystallization process took place through nucleation and growth of new grains fully replacing the deformed structure, as expected for the classical static recrystallization (SRX). The corresponding texture was essentially random, in contrast to that of the DRX grains dominated by low Taylor factor components. The microbands originally present within the deformed matrix grains displayed some tendency to disintegrate during annealing, nonetheless, they remained largely preserved even at prolonged holding times. During annealing of the fully DRX microstructure, a novel softening mechanism was revealed. The initial post-dynamic softening stage involved rapid growth of the dynamically formed nuclei and migration of the mobile boundaries in correspondence with the well-established metadynamic recrystallization (MDRX) mechanism. However, in contrast to the deformed matrix, SRX was not observed and the sub-boundaries within DRX grains rapidly disintegrated through dislocation climb and dislocation annihilation, which led to the formation of dislocation-free grains already at short holding times. Consequently, the DRX texture initially became slightly weakened and then remained largely preserved throughout the annealing process.

Effect of MgO Coating on the Hydration Resistance of MgO-CaO Clinkers

To overcome the disadvantage of MgO-CaO refractories, as the poor hydration resistance, MgO coating on the MgO-CaO clinker was fabricated by carbothermal reduction MgO with carbon as reduction agent and then the oxidation of Mg vapor. Effect of processing parameters (such as carbon source, reaction temperature and holding time) on the hydration resistance of MgO-CaO clinkers were investigated by hydration resistance test and SEM. The results indicated that the hydration resistance of treated MgO-CaO clinkers was improved when carbon black was used as reduction agent due to easy reaction with MgO than the graphite and coke. The high reaction temperature among 1450~1600°C and prolonged holding time within 4 h resulted in improvement of the hydration resistance of treated MgO-CaO clinker. Deposition mechanism of MgO coating on the MgO-CaO clinker was discussed.

Kinetics of Lamellar Decomposition Reactions in U-Nb Alloys

Discontinuous precipitation (DP) and discontinuous coarsening (DC) reactions have been observed in numerous alloy systems [1]. DP has been observed in the U-Nb system [2, 3, 4, 5]. The U-Nb phase diagram (Fig. 1) exhibits a continuous γ-BCC solid solution at high temperatures and a two-phase mixture of a-orthorhombic and γ-BCC below the 647°C monotectoid isotherm. The DP reaction occurs during continuous cooling and isothermal aging over 300-647°C. No metallographic evidence of a DC reaction in U-Nb has been published, although this is suggested from x-ray observations of distinct changes in the Nb content of the γ phase upon prolonged holding after the DP reaction [2, 3, 6]. This study will provide direct evidence for a DC reaction. Discontinuous and other aging reactions [7] are undesirable in U-Nb alloys, since they degrade corrosion resistance [5], ductility [8], and the shape-memory effect [9]. Hence, an improved understanding of the kinetics of these discontinuous phase transformations in U-Nb alloys is of practical interest.

Graphite Morphology Evolution during Melt Holding of Ductile Iron

Evolution processes of graphite morphology in ductile iron were investigated by quenching specimens during a long time holding of iron melt in a Ar atmosphere. Results show that spheroidal graphite is only observed at the early stage of melt holding. There are no evident changes in morphology of spheroidal graphite with increasing holding time up to 180 min. Subsequently chunky graphite precipitates directly after holding for 240 min as spheroidizing ability (Mg residual and RE residual) is insufficient. The number and size of eutectic chunky graphite cells increase with prolonged holding time. It should be noted that vermicular graphite forms around eutectic chunky graphite cells after holding for 360 min. When holding time reaches 420 min, graphite morphology is flake-like together with some chunky graphite. The graphite morphology in ductile iron changes from spherical to chunky, then chunky to vermicular, finally to flake with an increase in melt holding time. Both spheroidizing ability and numbers of effective nucleus decrease with prolonged holding time of melt, which affect graphite morphology.

Eco-Friendly Grain Refinement for A3003 Alloy

Eco-friendly grain refinement of A3003 alloy was studied by addition of non-toxic Al-Ti alloy because of toxic-fluorine in Al-Ti-B alloys which used as a representative grain refiner for aluminum and its alloys. TiAl3 phase in Al-Ti alloy bring to decrease grain size of A3003 alloy. But, grain growth occurred with prolonged holding time due to the solution of Ti into aluminum matrix. In contrast, lasting grain refinement of A3003 alloy was occurred in graphite crucible. It can be mentioned that carbon comes from graphite crucible was combined with Ti solute in aluminum melt and then TiC acts as a heterogeneous nucleation for A3003 alloy.

Disruption and reassociation of casein micelles during high pressure treatment: influence of whey proteins

In the study presented in this article, the influence of added α-lactalbumin and β-lactoglobulin on the changes that occur in casein micelles at 250 and 300 MPa were investigated by in-situ measurement of light transmission. Light transmission of a serum protein-free casein micelle suspension initially increased with increasing treatment time, indicating disruption of micelles, but prolonged holding of micelles at high pressure partially reversed HP-induced increases in light transmission, suggesting reformation of micellar particles of colloidal dimensions. The presence of α-la and/or β-lg did not influence the rate and extent of micellar disruption and the rate and extent of reformation of casein particles. These data indicate that reformation of casein particles during prolonged HP treatment occurs as a result of a solvent-mediated association of the micellar fragments. During the final stages of reformation, κ-casein, with or without denatured whey proteins attached, associates on the surface of the reformed particle to provide steric stabilisation.