Shearing Effects on the Phase Coarsening of Binary Mixtures Using the Active Model B

The phase separation of a two-dimensional active binary mixture is studied under the action of an applied shear through numerical simulations. It is highlighted how the strength of the external flow modifies the initial shape of growing domains. The activity is responsible for the formation of isolated droplets which affect both the coarsening dynamics and the morphology of the system. The characteristic dimensions of domains along the flow and the shear direction are modulated in time by oscillations whose amplitudes are reduced when the activity increases. This induces a broadening of the distribution functions of domain lengths with respect to the passive case due to the presence of dispersed droplets of different sizes.

Creep Damage Repair of a Nickel-Based Single Crystal Superalloy Based on Heat Treatment

Taking nickel-based single crystal superalloy DD6 as the research object, different degrees of creep damage were prefabricated by creep interruption tests, and then the creep damage was repaired by the restoration heat treatment system of solid solution heat treatment and two-stage aging heat treatment. The results show that with the creep time increasing, the alloy underwent microstructure evolution including γ′ phase coarsening, N-type rafting and de-rafting. After the restoration heat treatment, the coarse rafted γ′ phase of creep damaged specimens dissolved, precipitated, grew up, and became cubic again. Except for the specimens with creep interruption of 100 h, the γ′ phase can basically achieve the same arrangement as the γ′ phase of the original sample. The comparison of the secondary creep test shows that the steady-state creep stage of the test piece after the restoration heat treatment is relatively increased, and the total creep life can reach the same level as the primary creep life. The high temperature creep properties of the tested alloy are basically recovered, and the restoration heat treatment effect is good.

Modeling and Simulation of the Phase Coarsening Process for Cocontinuous Polymer Blends

Among different phase structures in immiscible polymer blends, the cocontinuous phase structure is considered to be advantageous for load transfer and achieving good mechanical properties. Due to the presence of an interpenetrating interface, phase coarsening naturally occurs during melt processing of cocontinuous polymer blends, and harness of the coarsening kinetics is important for structural control. Existing models for phase coarsening are mostly founded on the basis of scaling or dimensional analysis while computational models embodying more realistic phase geometries are demanded. In this paper, we present a two-step computational approach for prediction of the coarsening kinetics. First, a phase-field transport equation is solved to establish an initial phase geometry. Second, a moving-boundary flow model is implemented to solve the hydrodynamic problem. Case studies are presented both in 2D and in 3D domains. An empirical model on the basis of fractional calculus is also proposed to fit the computational results. Once verified by experimental data, this approach can provide an integrated tool for assisting in the processing of cocontinuous polymer blends where phase coarsening is of concern.

Modeling and Simulation of the Process for the Generation of Gradient Porous Structures From Immiscible Polymer Blends

There has been growing interest in integrating gradient porous structures into synthetic materials like polymers. One particular method for making gradient porous polymers is nonisothermal annealing of co-continuous phase structures of immiscible polymer blends under well-defined thermal boundary conditions. In this paper, we report a method to simulate this nonisothermal phase coarsening process for the generation of gradient-phase structures by the combined implementation of phase-field transport and momentum transport. Specifically, a phase-field equation is solved first to obtain a phase structure with phase size comparable with that of the blend to be annealed. This phase structure is then used as an initial geometry in a two-phase moving-interface flow simulation to gauge into the phase structure coarsening process. Several case studies were performed, and the results show that the controllable generation of gradient-phase structures can be enabled by well-designed geometry and thermal boundary conditions. Using 2D simulations, different types of gradient-phase structures experimentally observed were predicted. With increasing power in computation, the capability of 3D simulation may be unveiled for a more accurate prediction of the nonisothermal phase coarsening process and may ultimately evolve into a useful tool for the design and processing of gradient porous polymers.

Effect of Aging Treatment on Microstructural Evolution of Rapidly Solidified Eutectic Sn-Pb Alloy Powders

The microstructural stability of rapidly solidified eutectic Sn–Pb alloy solder powders was investigated through aging at room temperature (25 °C) and temperatures of 40 °C–120 °C. The coarsening behavior of the Pb-rich phase both at room and elevated temperatures was observed. The evident coarsening of the Pb-rich phase was detected upon storage after 40 days. At elevated temperatures, a similar sequence of Pb-rich phase coarsening was observed; however, it occurred substantially more quickly. Pb-rich coarsening rate kinetics at different temperatures were estimated using the Arrhenius equation. The apparent activation energy was 45.53 ± 4.23 KJ/mol, which indicates that grain boundary diffusion is a crucial mass transport mechanism controlling Pb-rich phase coarsening under annealing.