The experimental stress–strain data from isothermal hot compression tests, in a wide range of temperatures (1123–1523
K) and strain rates (10
−3–10
2
s
−1), were employed to develop constitutive ...equations in a Ti-modified austenitic stainless steel. The effects of temperature and strain rate on deformation behaviors were represented by Zener-Holloman parameter in an exponent type equation. The influence of strain was incorporated in the constitutive analysis by considering the effect of strain on material constants. The constitutive equation (considering the compensation of strain) could precisely predict the flow stress only at 0.1 and 1
s
−1 strain rates. A modified constitutive equation (incorporating both the strain and strain rate compensation), on the other hand, could predict the flow stress throughout the entire temperatures and strain rates range except at 1123
K in 10 and 100
s
−1. The breakdown of the constitutive equation at these processing conditions is possibly due to adiabatic temperature rise during high strain rate deformation.
The experimental stress–strain data from isothermal hot compression tests over a wide range of temperatures (1073–1473K), strains (0.1–0.5) and strain rates (0.001–1s−1) were employed to formulate a ...suitable constitutive model to predict the elevated-temperature deformation behaviour in a Ti-modified austenitic stainless steel (alloy D9). It was observed that the Johnson–Cook (JC) model in its original form is inadequate to provide good description of flow behaviour of alloy D9 in the above hot working domain. This has been attributed to the inadequacy of the JC model to incorporate the coupled effects of strain and temperature and of strain rate and temperature. A modified constitutive model based on the Zerilli–Armstrong model has been proposed for considering the effects of thermal softening, strain rate hardening and isotropic hardening as well as the coupled effects of temperature and strain and of strain rate and temperature on flow stress. The proposed modified constitutive model could predict the elevated-temperature flow behaviour of alloy D9 over the specified hot working domain of alloy D9 with good correlation and generalization.
Deformation twinning is known to be one of the reasons that cause texture transition (copper type to brass type) in single phase fcc materials and is studied extensively. The role of deformation ...twinning in two phase materials is an area yet to be explored. Similarly in two phase materials, the effect of one phase on the texture evolution of the other phase is not well understood. In this work, a combination of experiments and modelling are used to address their effects on texture evolution in duplex stainless steels. The material is cold rolled to 80% thickness reduction and texture evolution is studied at various strain levels. These are compared with a series of crystal plasticity simulations using the Taylor model and grain interaction based LAMEL model which was extended to a two phase material. Deformation twinning in austenite is incorporated by predominant twin reorientation (PTR) scheme. It is observed that only by accounting for the strong local interactions between the phases, the correct textures are predicted. The texture transition from {001}〈110〉 to {112}〈110〉 orientation observed in ferrite at higher strain levels is attributed to deformation twinning in austenite. A number of simulations with ideal orientations observed in fcc and bcc materials are performed to assess the role of one phase on texture evolution of the other. It is concluded that experimental observations are also required to comment on the dominant phase during texture evolution.
Duplex stainless steels (DSS) are characterised by vivid phase morphology and crystallographic textures. The typical microstructure consists of elongated phases (along rolling direction, RD) stacked ...alternatively along the normal direction (ND). In this study, uni-axial testing in multiple macroscopic directions is used to explore the anisotropic evolution of work hardening. Crystal plasticity simulations are used to gain insights into the same. The compressive stress and work hardening of samples loaded in the transverse direction (TD) are observed to be higher than those loaded in the RD and ND. Austenite and ferrite developed 110 and 111 parallel to the loading direction type fibre textures during uni-axial compression. The weak austenite texture behaves similarly to its single-phase counterparts regarding reorientation. The plastic anisotropy evolution is aided by the strong ferrite texture, which deviates from its single-phase behaviour. When loaded along TD compared to other directions, microstructural characterisation revealed the formation of deformation twins in austenite and lower effective slip length of both the phases.
Controlled near plane strain deformation was imposed on a super duplex stainless steel. Subsequent characterization involved extensive microtexture measurements, and measurements of general corrosion ...and corrosion behavior (and nature of the passive film) of the individual phases. The general corrosion was controlled by the corrosion performance of the austenite phase, and corresponding microtextural developments. Corrosion resistance in the austenite phase, as well as the general corrosion, improved until a true strain of 0.26 and then dropped. Enhanced corrosion resistance coincided with slip band formation and generation of low-angle boundaries. Beyond a strain of 0.26, shear bands and associated lattice curvatures plus high-angle boundaries led to a clear degradation in the corrosion behavior.
▶ Constitutive analysis of various austenitic stainless steels was performed. ▶ The materials show strain hardening, strain rate hardening and thermal softening. ▶ They show coupled effect of ...temperature and strain, and temperature and strain rate. ▶ The modified Zerilli-Armstrong (MZA) model has been applied to predict flow stress. ▶ MZA model could predict the elevated temperature flow behaviour of the materials.
High temperature flow behaviour of various grades of austenitic stainless steels viz. 304L, 304, 304 (as-cast), 316L and 15Cr–15Ni–Ti modified austenitic stainless steels (alloy D9) were analyzed by performing isothermal hot compression tests in a wide range of temperatures (1073
K to 1473
K for 304L, 304, 304 (as-cast), 316L and 1123
K to 1523
K for alloy D9) and strain rates (0.001–1
s
−1). It has been observed that all these materials show strain hardening, strain rate hardening, thermal softening, coupled effect of temperature and strain, and temperature and strain rate on flow stress in the hot working domain. The modified Zerilli–Armstrong (MZA) model which considers the above significant effects on flow stress has been applied to predict the flow behaviour of these materials. The material constants of the MZA model for each material have been evaluated and subsequently applied to predict the flow stress. It has been demonstrated that the MZA model could adequately represent the elevated temperature flow behaviour of these materials over the entire ranges of strain, strain rate and temperature.
Nanocrystalline AA 6061 alloy reinforced with alumina (0, 4, 8, and 12 wt%) in amorphised state composite powder was synthesised by mechanical alloying and consolidated by the conventional powder ...metallurgy route. The as-milled and as-sintered (573 K and 673 K) nanocomposites were characterised by XRD and TEM. The peaks corresponding to fine alumina were not observed by XRD patterns due to amorphisation. HRTEM confirmed the presence of amorphised alumina observed in Al lattice fringes. The crystallite size, lattice strain, deformation stress, and strain energy density of the AA 6061 matrix were determined precisely from the first five most intensive reflections of XRD using simple Williamson-Hall models (uniform deformation model, uniform stress deformation model, and uniform energy density deformation model). The uniform energy density deformation model was the best fit and most realistic model for mechanically alloyed powders. This model showed the more anisotropic nature of the ball milled powders. The XRD peaks of as-milled powder samples demonstrated a considerable broadening with percentage of reinforcement due to grain refinement and lattice distortions during same milling time (40 h). The as-sintered (673 K) unreinforced AA 6061 matrix crystallite size from well fitted uniform energy density deformation model was 98 nm. The as-milled and as-sintered (673 K) nanocrystallite matrix sizes for 12 wt% Al2O3 well fitted by the uniform energy density deformation model were 38 nm and 77 nm respectively, indicating that the fine Al2O3 pinned the matrix grain boundary and prevented grain growth during sintering. The lattice parameter of Al matrix in as-milled and as-sintered conditions was also studied.
The aim of the study was to describe imaging characteristics and detection rates of phenotypic features in macular telangiectasia type-2 (MacTel) on multicolor (MC), blue reflectance (BR), green ...reflectance (GR), infrared reflectance (IR), and fundus autofluorescence (FAF) and to evaluate sensitivity, specificity, and predictive values across modalities.
In this monocentric observational study, 282 eyes of 148 patients with MacTel underwent color fundus photograph, MC, BR, GR, IR, FAF, spectral-domain optical coherence tomography (SD-OCT), OCT-angiography (OCT-A), and fundus fluorescein angiography (FFA). Grading was done by two graders qualitatively and quantitatively for the presence of the following prespecified MacTel findings crystals, right-angle vessels (RAVs), plaques, subretinal neovascularization (SRNV), and MacTel area. Across each imaging modality, the detection rate of RAVs and SRNV was compared with reference standard OCT-A (RAVs and SRNV) and FFA (SRNV), whereas that of plaques was compared with reference standard SD-OCT.
MC identified overall MacTel characteristics in 92.7% of eyes. Regarding the presence, number, and quadrants of RAVs and the presence and number of crystals, MC and GR had superior detection rates as well as the highest sensitivity and negative predictive value. Retinal plaques were better detected using FAF (97%), followed by MC (88%). In proliferative MacTel, SRNV was identified in 86% and 79% of eyes on MC and IR, respectively. While BR clearly delineated MacTel area in 100% eyes, FAF was able to ascertain a larger area of involvement in proliferative MacTel.
The findings demonstrate the ability of MC, its component channels, and FAF to describe MacTel characteristics qualitatively and quantitatively.
This paper discusses the application of artificial neural network modeling in austenitic stainless steels research, including: (i) correlation between chemical composition, process variables and flow ...stress of austenitic stainless steels under hot compression; (ii) constitutive flow behavior of type AISI 304L stainless steel during hot torsion; (iii) microstructural evolution during dynamic recrystallization of alloy D9; (iv) correlation between chemical composition and tensile properties of alloy D9. Multilayer perceptron based feed-forward networks have been trained by comprehensive in-house datasets. Very good performances of the neural networks are achieved. Various effects are modeled, among which are: (i) influence of alloy composition and processing parameters on flow behavior of austenitic stainless steels; (ii) effect of strain rate on torsional flow behavior of 304L stainless steel; (iii) combined influence of temperature and strain on dynamic recrystallization behavior of alloy D9. The simulated results are found to be consistent with the metallurgical trends. Finally, the issue of neural network's “black box” approach to modeling is addressed.
Hastelloy-X is a nickel-based superalloy predominantly using in engine combustion zone parts of gas turbines. Micro-holes are drilling to the surface of these parts for air-cooling passageways to ...improve part-life by reducing thermal fatigue. Laser, micro-electric discharge machining (
µ
EDM), and micro electrochemical machining (
µ
ECM) are the major processes for creating holes in superalloys. Yet, if used individually, these techniques could end up with faulty holes. The sequential application of multiple drilling methods for hole-making will eliminate the defects. In this work, micro-holes have drilled on Hastelloy-X by using a laser in sequence with
μ
EDM and laser in sequence with
μ
ECM. Holes produced by these two-hybrid approaches are later compared for productivity and quality features. Both form and productivity factors have been estimated, and optimal input combinations for each response have been identified from the mean analysis. The Pareto-Analysis of Variance has been used to determine the critical factors for each response. A detailed characterization study has been done to ensure the surface integrity of the holes. It has been found that micro-holes formed by sequential laser processing with
μ
EDM improve the responses compared to the individual
μ
EDM outputs. A similar improvement has also observed in laser combined with
µ
ECM holes concerning individual
µ
ECM. Both results collectively indicated that the novel sequential laser approach with
µ
EDM is more efficient than the sequential application of laser with the
µ
ECM. This study provides clear guidance for the sequential micro-drilling of Hastelloy-X using numerous non-traditional drilling approaches.
