Influence Of Phase Morphology Research Articles

Influence of phase morphology, static recrystallization, and crystallographic texture on room temperature tensile properties of Ti–6Al–4V alloy: Comparison between post-tested equiaxed, bimodal, and lamellar microstructures

The influence of phase fractions, morphology, recrystallization, and crystallographic texture on the room temperature uniaxial tensile properties were investigated in a Ti–6Al–4V (Ti-64) alloy. The hot rolled and annealed Ti-64 alloy was heat treated to generate three different microstructures (equiaxed, bimodal, and lamellar) with varying volume fractions and dimensions of constituent phases (equiaxed primary α, transformed α laths, and β laths). The tested tensile specimens were characterized using techniques such as electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and X-Ray diffraction-based bulk texture analysis to determine the deformation mechanism of the alloy. Among three different microstructures, the equiaxed microstructure (α/β-900/950-FC) exhibited a superior strength-toughness combination, while the lamellar microstructure (β-1050-AC) displayed poor tensile properties. The bimodal microstructure (α/β-900/950-AC) showed intermediate tensile properties. Recrystallized α grains and their connectivity promoted an extended steady-state flow during deformation and ductile fracture. The bimodal microstructure work hardened faster as compared to the other two microstructures. TEM investigation on the post-tested microstructures showed that events such as dislocation multiplication and dislocation-dislocation interactions, formation of slip bands across the α grains, multiple slip and dislocation pile-ups contribute to hardening mechanisms during deformation. Whereas, slip transfer across α/α boundary and breaking of β laths are the events of softening mechanisms. The slip transfer across two adjacent α grains happens when the misalignment between grains is less than 10°. Equiaxed microstructures exhibited maximum slip transfer due to interconnected primary α grains. Bimodal microstructures (α/β-900/950-AC) exhibited slip transfer when a higher fraction of interconnected primary α is present in the microstructure. In contrast, the lamellar microstructure showed no evidence of slip transfer. The prism slip is the dominant active slip system in the equiaxed and bimodal microstructures. However, the lamellar microstructure with no primary α showed only the prismatic <c+a> and pyramidal <a> slip activities.

Observing the On-Site Generation of Excitons and Charges by Low-Temperature Spectroscopy.

Understanding the relation between phase morphology and physical processes in polymer blends is the key to the fabrication of reproducible and reliable polymer optoelectronic devices. In this work, taking the advantage of low-temperature spectroscopy, we have observed the on-site generation of excitons and long-lived charges in different phase morphology polymer/fullerene blends. Probing at 10K, the photo-generated species are localized to where they are generated. We found that the generation of excitons and long-lived charges is highly influenced by the local molecular phase morphology. We further demonstrated that although the influence of phase morphology is localized to the place that excitons and long-lived charges are generated, this influence can persist over sub-millisecond timescales. Thus, we believe that the fate of excitons and long-lived charges is determined by the location at which they are generated, which can in turn be controlled precisely by molecular phase morphology.

Influence of phase morphology on the rheology and thermal conductivity of HDPE/PA6 immiscible blends with alumina whiskers

The thermal conductivity (TC) of HDPE/PA6/alumina whisker composites was measured as a function of the whisker amount and HDPE/PA6 ratio and related to their composite morphology and rheological properties. The preparation of the composites, in two extrusion steps, encouraged filler localization in the HDPE phase. The addition of the whiskers produced a morphological refinement in composites with 60/40 and 50/50 HDPE/PA6 ratios, resulting in a sea-island morphology with smaller domains of polyamide (dispersed phase). For the 40/60 HDPE/PA6 ratio, a sea-island microstructure with dispersed polyethylene domains filled with alumina was observed. The best TC data was measured in composites with a 50/50 HDPE/PA6 ratio, which was associated with an increase in the effective filler amount in the host phase, in agreement with the rheological data. Induced flow at low shears produced an increase in TC, which was associated with conductive network strengthening for the 40/60 and 60/40 HDPE/PA6 ratios.

Computational analysis of nonlinear creep of polyphase aggregates: Influence of phase morphology

AbstractThe constitutive laws of polyphase aggregates dominantly depend on the operative deformation mechanisms, phase morphology and modes, and environmental conditions. Each of these factors has the potential to dramatically affect bulk mechanical properties as well as the local stress and strain rate distributions. To focus on the effects of phase morphology, we have developed a rigorous multiscale approach based on asymptotic expansion homogenization. The proposed methodology has two fundamental goals: (1) accurately predict bulk behavior in aggregates by explicitly taking into account phase morphology and (2) calculate detailed distributions of strain rates, stresses, and viscosities in heterogeneous materials. The methodology is able to consider general nonlinear phase constitutive laws that relate strain rates to stresses, temperature, and other factors such as water fugacity and grain size. We demonstrate the approach by analyzing power law creep of computer‐generated and natural polyphase systems and benchmarking the results against analytical solutions. As an outcome of this analysis, we find that the approximation of an aggregate as a power law material is reasonable for isotropic, homogeneous phase distributions but breaks down significantly with high degrees of phase organization. We also present distributions in strain rate, stress, and viscosity for different applied loading conditions. Results exhibit areas of high internal stresses and substantial localization. We describe and provide a freely available software package supporting these calculations.

Effect of phase morphology and interfacial strength on barrier properties of high density polyethylene/polyamide 6 membranes

AbstractA barrier and resistance membrane consisting of alternating layers of high‐density polyethylene (HDPE) and polyamide 6 (PA6) was prepared by microlayered coextrusion. The influence of phase morphology, number of layers, and compatibilizer (CP) content of HDPE/PA6‐microlayered membranes on their gas barrier and water resistance properties were characterized using a scanning electron microscopy, gas in permeability, and water absorption tests. The results suggest that this special‐layered structure led to significant improvement of gas barrier and water resistance properties, compared with conventional membranes. In addition, the barrier and resistance properties of microlayered membranes were obviously enhanced with increased number of layers and CP content. An optimal number of layers and CP content were determined for the improved barrier and resistance properties. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers

Duplex Stainless Steel Microstructural Developments as Model Microstructures for Hot Ductility Investigations

Duplex stainless steels (DSS) are alloys made of ferrite and austenite, with a proportion of each phase around 50%. Their main advantage in comparison with other austenitic and ferritic stainless steels is the attractive combination of high strength and corrosion resistance together with good formability and weldability. Unfortunately, DSS often present a poor hot workability. This phenomenon can stem from different factors associated to the balance of the phases, the nature of the interface, the distribution, size and shape of the second phase, and possibly also from difference in rheology between ferrite and austenite. In order to determine the specific influence of phase morphology on the hot-workability of DSS, two austenite morphologies (E: Equiaxed and W: Widmanstätten) with very similar phase ratio have been generated using appropriate heat treatments. It was checked that the latter treatments generate stable microstructures so that subsequent hot mechanical tests are performed on the microstructures of interest. One microstructure consists of a ferritic matrix with austenitic equiaxed islands while the other microstructure is composed of a ferritic matrix with Widmanstätten austenite. The latter morphology corresponds to the morphology observed in as-cast slabs.

Influence of phase morphology on the sliding wear of polyethylene blends filled with carbon nanofibers

AbstractIn this work, phase separation in carbon nanofiber (CNF) composites with a blend of ultrahigh molecular weight polyethylene (UHMWPE)/high‐density polyethylene (HDPE) was revealed, and its effects on tribological properties were investigated. Results from morphological analysis by optical and scanning electron microscopy indicated two distinct microstructures: a dispersed UHMWPE phase and a continuous microstructure containing HDPE and CNFs. The addition of CNFs into the UHMWPE/HDPE blend induced a decreased steady‐state torque indicative of a decreased dissolution and improved processability. Because CNFs predominantly resided into the HDPE phase, neat HDPE, a HDPE/CNF composite, and neat UHMWPE samples were also prepared for comparison. Wear results, determined by a pin‐on‐disk apparatus, showed that both initial run‐in and steady‐state wear rates of the UHMWPE/HDPE/CNF nanocomposites were reduced with an increasing concentration of CNFs. The wear resistance of the UHMWPE/HDPE blend was more strongly influenced than neat HDPE by the addition of CNFs, which may have been affected by a reduced dissolution and improved interfacial interaction between the two phases. Results from this study suggested that HDPE may not be appropriate for processing UHMWPE composites, as CNFs reside in the HDPE phase, and HDPE diminishes the wear resistance of the material. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Al–Al2O3 Composites with Interpenetrating Network Structures: Composite Modulus Estimation

The effective Young's moduli of co‐continuous Al–Al2O3 composites over the 5–97 vol% Al2O3 composition range were experimentally measured and compared with theoretical composite modulus values predicted using the methods of Ravichandran, Tuchinskii, Hashin‐Shtrikman, and the effective medium approximation (EMA). The influence of phase morphology and the modulus ratio (E1/E2) of the constituent phases on the resulting experimental and calculated Young's modulus is discussed. For two‐phased co‐continuous composites with a modulus ratio greater than 5, the EMA, with an appropriate microstructural shape factor, was the most consistent method for approximating the composite Young's modulus over the entire composition range.

Influence of Phase Morphology and Deformation Mode on the Behaviour during Hot Working of a Two-Ductile Phase Composite

Influence of Phase Morphology and Deformation Mode on the Behaviour during Hot Working of a Two-Ductile Phase Composite