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• Transient quenching experiment was carried out by multiple water-impinging jets. • Hydrodynamic phenomena of quenching by multiple jets was discussed. • Effectiveness of quenching parameters was analyzed on local average heat flux. • Characteristic of maximum heat flux at stagnation and upwash point was studied. • Effect of the quenching parameters was studied on average heat transfer. Experiments have been conducted to analyze quenching of a hot rotary hollow cylinder by one and two rows of water-impinging jets. Sub-cooled water jets (Δ T sub = 45 –85 K) with flow rate 8006 to 36,738 impinged on hollow cylinder with rotation speed 10 to 70 rpm at various initial wall superheat temperatures from 250 to 600 ° C. Jet-to-jet and jet-to-surface spacing varied between 4 to 10 d and 1.5 to 7 d respectively and angular position of impinging jets were tested from 0 to 135 °. Effectiveness of the defined parameters on stagnation point's local average heat flux was found lower in the film and nucleate boiling compare to transition boiling regime where rotation speed had the highest impact. Characteristic of maximum heat flux (MHF) at stagnation point and upwash flow point were analyzed based on surface heat flux, time and temperature corresponding to MHF. Same maximum heat flux levels were captured in the both points which reveals importance of the flow behavior at the upwash flow point. The effectiveness of the parameters to improve average heat transfer was studied based on cooling area of each water-impinging jet in the multiple configurations. Higher average heat transfer was obtained by increasing flow rate and subcooling temperature and lower initial wall superheat temperature corresponding to onset of transition boiling regime. [ABSTRACT FROM AUTHOR]

In this study, a two-dimensional linear transition inverse heat conduction problem (IHCP) was solved using the Generalized Minimal Residual Method (GMRES) in quenching process by water jets. The inverse solution method was validated by set of artificial data and solution sensitivity analysis was done on data noise level, regularization parameter, cell size, etc. An experimental study has been carried out on quenching a rotary hollow cylinder by one row of subcooled water jets. The inverse solution approach enabled prediction of surface temperature and heat flux distribution of test specimen in the quenching experiments by using measured internal specimen temperature. Three different boiling curves were defined in the quenching process of a rotary cylinder. Result obtained by the inverse solution showed clear footprint of rotation in surface temperature and heat flux on each revolution of cylinder and temperature variation damping from quenching surface toward interior of specimen. [ABSTRACT FROM AUTHOR]

Insights from a detailed investigation into the anisotropic strain hardening, tension/compression yield asymmetry, and evolution of crystallographic texture of rolled WE43 rare earth magnesium alloy during quasi-static tension and compression at room temperature are presented in this paper. It is seen that WE43 exhibits monotonically falling normalized strain hardening rates during both tension and compression in multiple loading directions, which is unusual for Mg alloys. Moreover, the difference in strain hardening in tension and compression subsequent to initial yield is observed to be very small and, as a result, the tension/compression asymmetry is not pronounced. Nevertheless, crystallographic texture evolves substantially, where crystals before deformation oriented with their crystallographic c -axis parallel with the normal direction (ND) and slightly tilted towards the rolling direction (RD) of the plate reorient their c -axis nearly parallel to the compression direction for every testing direction. Amount of deformation twinning in WE43 with plastic strain is quantified here for the first time and correlated with the above-described aspects of plastic deformation and texture evolution. In doing so, we confirm that the 10 1 ¯ 2 1 ¯ 011 twin is the preferred extension twin in WE43 just like in many Mg alloys. Besides, we find a substantial activity of another c -axis extension twinning mode 11 2 ¯ 1 1 ¯ 1 ¯ 26 in WE43, which is another unusual observation for Mg alloys. Activity of the c -axis contraction twins was found to be negligible. The falling strain hardening rates in WE43 are rationalized here to be a consequence of: (1) modest texture hardening because the activation stress for pyramidal slip systems is similar in magnitude to those of basal and prismatic slip systems, (2) small Hall-Petch-like hardening effect due to extension twinning because of their transmissivity to slip and rapid growth, and (3) negligible Hall-Petch-like hardening effect due to contraction twinning because of their small activity. [ABSTRACT FROM AUTHOR]

Homogeneous dispersion of reinforcement particles within a matrix is of paramount importance for achieving high quality metal-matrix composite (MMC) materials. This paper develops a protocol for quantitative evaluation of particle size and dispersion in MMC microstructures. The protocol is based on statistical analysis of features in micrographs and embedding the information into a suitably defined microstructure homogeneity metric ( H -metric) and a particle size distribution metric. Every micrograph undergoes the K -means clustering algorithm for accurate separation of phases before it is used in calculation of the metrics. Finally, the protocol relies on analysis of variance to verify the meaningfulness of results. The protocol is applied to study homogeneity and particle size distribution in MMCs consisting of Cu-matrix with 20 vol.%-SiC The composites were processed using high pressure torsion and double torsion to a different number of torsional turns. During processing, particles fragment and form clusters of fragments. As straining continues, the clusters of fragments disperse in the matrix. A decrease and then increase of the H -metric demonstrate that the metric can pick up these processes occurring in the microstructure. The analysis reveals a strong correlation between the particle dispersion homogeneity and particle size distribution. The protocol developed herein can facilitate the design of MMCs with superior properties through engineering optimal homogeneity and particle size distributions in function of process variables. [ABSTRACT FROM AUTHOR]

In this work, carbon nanotubes (CNTs) reinforced aluminum (Al) matrix composites are synthesized using Bc equal-channel angular extrusion (ECAP) route and their mechanical behavior is examined under compression and shear deformation. The results show that at room temperature, eight ECAP passes are necessary to achieve the density of the composite where the effect of CNTs in enhancing the mechanical properties become significant. Samples of pure Al are also processed under the same ECAP conditions, and their properties are further examined to facilitate the comparison. The well-densified composites with only 2 vol.% of CNTs exhibit an approximately 30% increase in yield strength compared to the pure Al samples. Microstructure data in terms of porosity volume fraction, crystallite size, and dislocation density, along with the residual lattice strain measurements, are used to explain the observed improvements in strength. As measured by X-ray diffraction (XRD), higher levels of dislocation density, smaller crystallite sizes, and larger residual lattice strains are present in Al-CNT than in pure Al samples. Finally, fractographic analysis using scanning electron microscopy is performed revealing that the fracture surfaces of the composite exhibit a more brittle behavior than pure Al samples. [ABSTRACT FROM AUTHOR]

In this work, 2 vol% carbon nanotubes (CNTs) reinforced aluminum (Al) matrix composites of superior microstructural homogeneity are successfully synthesized using Bc equal-channel angular extrusion (ECAP) route. The key step in arriving at high level of homogeneous distribution of CNTs within Al was preparation of the powder using simultaneous attrition milling and ultra-sonication processes. Microstructure as revealed by electron microscopy and absence of Vickers hardness gradients across the material demonstrate that the material reached the homogeneous state in terms of CNT distribution, porosity distribution, and grain structure after eight ECAP passes. To facilitate comparison of microstructure and hardness, samples of Al were processed under the same ECAP conditions. Significantly, the composite containing only 2 vol% exhibits 20% increase in hardness relative to the Al samples. [ABSTRACT FROM AUTHOR]

In this work, metal-matrix composites of commercially pure copper (Cu) and silicon carbide (SiC) are synthesized by standard high-pressure torsion (HPT) and novel high-pressure-double-torsion (HPDT) processes of severe plastic deformation (SPD). Based on detailed microstructural examinations, it is found that significant homogeneity of fine particle distribution as well as weakness of crystallographic texture can be obtained in the composites fabricated using these processes. The most homogeneous particle distribution is obtained in the material processed under HPDT, which imposes the highest strain levels. Crystallographic texture in the composite is found to be weaker than in monolithic Cu processed under the same processing conditions. The randomization of texture in the composites is linked to the homogenization of the particle distribution. [ABSTRACT FROM AUTHOR]

Using finite element and polycrystalline plasticity modeling, we explore the influence of die design and material behavior on the extrusion of bimetallic tubes. Three distinctly different extrusion designs are introduced and evaluated based on a range of macroscopic and microstructural criteria: die and punch stress, interface roughness, peak forming loads, and strain and crystallographic texture heterogeneities across the tube thickness. We find that an extrusion die design proposed here that differs from the conventional one is better for reduction of peak forming load satisfying objectives of the traditional design. However, when the design is more constrained and considerations of strain and microstructural heterogeneities and gradients are made part of the design criteria, we show that one die design promotes such gradients while the other minimizes them. In all three designs, large disparities in flow stress and hardening rate (>3 times) lead to larger interfacial strain gradients. These findings provide basic die designs that can be used to evaluate the degree and locations of strain and texture gradients across the tube thickness. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the effect of the ram speed was investigated on the final microstructure and mechanical properties of the Al–SiCp composites through the hot extrusion process. The extrusion process was conducted at 550°C by applying different ram speeds in the range of 0.2–4mms−1. Optical image microscopy (OIM) results showed that by applying the higher value of ram speed, a microstructure can be obtained including oriented SiC particles in the Al matrix. Finite element analysis (FEA) was also utilized to examine the velocity components values at different ram speeds during the extrusion process. The differences in spacing between particle chains at the edge and center of the extruded samples were minimum at ram speed 2mms−1. The mechanical properties of the final products were examined by the means of uni-axial tensile and Vickers micro-hardness tests. The tensile test results showed that the highest values of ultimate tensile and yield stresses were obtained at the ram speed 2mms−1. There is a good agreement between the change in the microstructure and the hardness values gradient through the longitudinal cross-section. [Copyright &y& Elsevier]

Abstract: In the present study, torsion extrusion (TE) process was compared with conventional forward extrusion (FE) process as a severe plastic deformation (SPD) method. To simulate the above-mentioned processes, finite element analysis (FEA) was carried out using three-dimensional finite element analysis ABAQUS/Explicit simulation. It was shown that the load requirement for the TE is lower than that for the FE. Calculation of the equivalent stress also showed that a lower stress magnitude was imposed during the TE. The maximum principal stresses on the surface of the specimen indicate that more compressive stresses can be expected during plastic deformation using the TE. Calculation of the equivalent plastic strains by the FEA proved that higher strain values can be obtained by the TE. The strain distribution of the TE sample at the final stage of the extrusion showed a smoother strain gradient in comparison with the sample produced by the FE. Higher values of ultimate tensile strength and lower values of ductility were also obtained for the TE samples. To evaluate the results of the tensile tests, the Kocks and Mecking model was utilized. [Copyright &y& Elsevier]

This work adapts a recently developed multi-level constitutive model for polycrystalline metals that deform by a combination of elasticity, crystallographic slip, and deformation twinning to interpret the deformation behavior of alloy WE43 as a function of strain rate. The model involves a two-level homogenization scheme. First, to relate the grain level to the level of a polycrystalline aggregate, a Taylor-type model is used. Second, to relate the aggregate level response at each finite element (FE) integration point to the macro-level, an implicit FE approach is employed. The model features a dislocation-based hardening law governing the activation stress at the slip and twin system level, taking into account the effects of temperature and strain rate through thermally-activated recovery, dislocation debris formation, and slip-twin interactions. The twinning model employs a composite grain approach for multiple twin variants and considers double twinning. The alloy is tested in simple compression and tension at a quasi-static deformation rate and in compression under high strain rates at room temperature. Microstructure evolution of the alloy is characterized using electron backscattered diffraction and neutron diffraction. Taking the measured initial texture as inputs, it is shown that the model successfully captures mechanical responses, twinning, and texture evolution using a single set of hardening parameters, which are associated with the thermally activated rate law for dislocation density across strain rates. The model internally adjusts relative amounts of active deformation modes based on evolution of slip and twin resistances during the imposed loadings to predict the deformation characteristics. We observe that WE43 exhibits much higher strain-hardening rates under high strain rate deformation than under quasi-static deformation. The observation is rationalized as primarily originating from the pronounced activation of twins and especially contraction and double twins during high strain rate deformation. These twins are effective in strain hardening of the alloy through the texture and barrier hardening effects. • A multi-level grain-to-polycrystalline aggregate-to-macro-level model, T-CPFE, is adapted for modeling of WE43. • EBSD, neutron diffraction, and mechanical testing data are used to calibrate and validate the model. • Anisotropy in mechanical response induced by microstructural evolution is predicted. • Role of deformation modes on the mechanical behavior and texture evolution is discussed. • Formation of contraction twins is identified to increase the rate of strain hardening under high strain rate deformation. [ABSTRACT FROM AUTHOR]

An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. Using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclic mechanical test data applied in different AM build directions. It is demonstrated that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates. [ABSTRACT FROM AUTHOR]