This paper reports the enhancement of long-term oxidation of copper at room temperature by a graphene coating. Previous studies showed that graphene is an effective anticorrosion barrier against ...short-term thermal and electrochemical oxidation of metals. Here, we show that a graphene coating can, on the contrary, accelerate long-term oxidation of an underlying copper substrate in ambient atmosphere at room temperature. After 6 months of exposure in air, both Raman spectroscopy and energy-dispersive X-ray spectroscopy indicated that graphene-coated copper foil had a higher degree of oxidation than uncoated foil, although X-ray photoelectron spectroscopy showed that the surface concentration of Cu2+ was higher for the uncoated sample. In addition, we observed that the oxidation of graphene-coated copper foil was not homogeneous and occurred within micrometer-sized domains. The corrosion enhancement effect of graphene was attributed to its ability to promote electrochemical corrosion of copper.
Type 316LN stainless steel (SS) weld joints are widely used in several high temperature applications. The variations of creep properties across the microstructurally heterogeneous regions of 316LN SS ...weld joint such as base metal, weld metal and heat affected zone (HAZ) have been evaluated using Small Punch Creep (SPC) technique at 923K. Both the SPC rupture and deformation behaviors were investigated. The creep strength gradient across 316LN SS weld joint showed a smooth increasing trend from base metal to weld metal. However, the trend of the rupture life for weld metal shifted with change in load level. The SPC deformations of various regions of weld joint have been analyzed according to the equation,δ=δ0+δT(1−e−κt)+δ̇st+δ3eϕ(t−tr). The variations of transient, secondary and tertiary creep parameters were determined across the weld joint. The master curve for transient creep deflection was obtained for various regions of weld joint.
This paper reports a systematic investigation of Hastelloy-X (Hast-X) structures built by Laser Directed Energy Deposition in as-built and post heat-treated conditions. The optical microscopy shows ...microstructures with fine dendrites in as-built condition due to higher cooling rate during deposition, while recrystallized equiaxed grains are observed after post heat-treatment (at 1177 °C) due to recrystallization. X-ray diffraction studies reveal nickel γ-matrix with variation in crystallite size and a peak shift after post heat-treatment, primarily due to change in surface residual stress. Surface topography reveals the reduction in average roughness with post heat-treatment. Further, the maximum compressive residual stress of 350 MPa and maximum tensile residual stress of 252 MPa are observed at the surfaces of post heat-treated and as-built samples, respectively. The average micro-hardness changed from 239 HV1.96N to 208 HV1.96N after post heat-treatment. Single Cycle Ball Indentation studies indicated increase in energy storage capacity by a factor of 1.55 after post heat-treatment. Automated Ball Indentation studies quantify yield strength and ultimate strength as 478 MPa and 765 MPa in as-built samples, while 393 MPa and 630 MPa in post heat-treated samples, respectively. Further, crack propagation studies indicate an improvement in the fatigue life after post heat-treatment, while the specific wear rate increased by a factor of 1.72 with increased delamination in heat-treated samples. Thus, post heat-treatment of Hast-X samples changes the material properties significantly.
•Post heat-treatment of Laser Directed Energy Deposited Hastelloy-X structures.•Dendritic microstructure with fine crystallites observed in as-built samples.•Homogenized microstructure and surface compressive stress after heat-treatment.•Improved fatigue behavior, energy storage and ductility after heat-treatment.
Automated ball indentation (ABI) tests were conducted across the 316LN stainless steel (SS) weld joints at 298 K, and 823 K. Zone wise tensile properties of 316LN SS weld joints such as weld metal, ...heat affected zone (HAZ), and base metal region are evaluated in this work. Uniaxial tensile tests were conducted to assess the effect of welding processes on the tensile properties. The weld joints were initially fabricated using arc based and laser based welding processes. The variations of tensile properties such as yield strength, ultimate tensile strength and strain hardening component values across the heterogeneous microstructure zones of the weld joints were evaluated. The correspondence between the microstructure variations and the tensile properties have been studied. The variations in grain size, secondary dendrite arm spacing (SDAS) and δ-ferrite content are found to be the primary cause of tensile strength variation across the weld joints. The gradient in tensile strength across the weld joints was higher at 298 K than at 823 K which was attributed to the microstructural changes at higher temperature causing material softening. It was noticed that the 316LN stainless steel weld joint made by hybrid laser MIG welding exhibited the highest values of strength and ductility among all the weld joints. It was attributed to the combined effect of higher δ-ferrite content and finer SDAS values. Therefore, the HLM welding process is recommended for welding of 316LN stainless steel components from the point of view of better tensile properties.
•Type 316LN stainless steel weld joints were fabricated by fusion, advanced laser and hybrid-laser welding techniques.•The variations of tensile properties across the different zones in the fabricated weld joints were obtained at 298and 823 K.•The automated ball indentation (ABI) and Uni-axial tensile testing methods were utilised to evaluate the tensile properties.•Influence of secondary dendrite arm spacing and amount of delta ferrite content on the tensile properties are presented.•The 316LN stainless steel weld joint exhibiting the highest strength and ductility is identified.
We present a methodology for Bayesian analysis of software quality. We cast our research in the broader context of constructing a causal framework that can include process, product, and other diverse ...sources of information regarding fault introduction during the software development process. In this paper, we discuss the aspect of relating internal product metrics to external quality metrics. Specifically, we build a Bayesian network (BN) model to relate object-oriented software metrics to software fault content and fault proneness. Assuming that the relationship can be described as a generalized linear model, we derive parametric functional forms for the target node conditional distributions in the BN. These functional forms are shown to be able to represent linear, Poisson, and binomial logistic regression. The models are empirically evaluated using a public domain data set from a software subsystem. The results show that our approach produces statistically significant estimations and that our overall modeling method performs no worse than existing techniques.
•Laser Directed Energy Deposited Hastelloy-X in as-built and heat-treated conditions.•Fine dendrites with segregations and carbide precipitation in as-built condition.•Recrystallized equiaxed grains ...in heat-treated condition.•Strength and ABI hardness decreased with an increase in test temperature.•Yield strength of heat-treated samples are close to conventional samples.
The microstructure and elevated temperature mechanical properties of Hastelloy-X (Hast-X) bulk structures built using Laser Directed Energy Deposition (LDED) based Additive Manufacturing is investigated in as-built (AB) and heat-treated (HT) conditions. Microscopic analysis show the presence of fine cellular and dendritic growth in AB samples and recrystallized and coarsened equiaxed grains in HT samples. The AB samples revealed random grain orientation with slightly preferred texture along the< 100 >plane, unlike in the HT samples. Further, the AB samples revealed the elemental segregation of Mo, Si and C and precipitation of Mo-rich carbides, which are absent in the HT samples. Micro tensile test results at ambient temperature showed excellent agreement with the mechanical properties obtained from automated ball indentation (ABI) tests of LDED built Hast-X in AB condition. Subsequently, ABI tests are used to evaluate the mechanical properties in AB and HT conditions from ambient temperature to 873 K. It is observed that the strength and ABI hardness decreased with increase in test temperature, while the strain hardening exponent and uniform ductility showed an opposite trend. The yield strength (YS) of AB sample is higher than conventional sample, while YS of HT sample is similar to the YS of conventionally processed wrought Hast-X taken from literature at all test temperatures. Further, the indentation size and material pile up around the indentation also increased with heat-treatment and increase in the test temperature. This study paves a way towards the successful deployment of LDED built Hast-X for various applications in hostile conditions.
We study the spectral properties of positive absolutely minimum attaining operators defined on infinite dimensional complex Hilbert spaces and using this we derive a characterization theorem for such ...type of operators. We construct several examples and discuss some of the properties of this class. Also, we extend this characterization theorem for general absolutely minimum attaining operators by means of the polar decomposition theorem.
To evaluate the diagnostic capability of optical coherence tomography (Stratus OCT 3) for early glaucoma in Asian Indian eyes.
Cross-sectional observational study.
Two groups of patients (early ...glaucoma and normal) who satisfied the inclusion and exclusion criteria were included. Early glaucoma was diagnosed in presence of open angles, characteristic glaucomatous optic disc changes correlating with the visual field on automated perimetry (visual field defect fulfilling at least 2 of Anderson and Patella's 3 criteria with mean deviation > or = -6 dB). Normals had visual acuity > or =20/30, intraocular pressure <22 mmHg with normal optic disc and fields and no ocular abnormality.
All patients underwent complete ophthalmic evaluation including visual field examination (24-2/30-2 SITA standard program) and imaging with Stratus OCT 3.
Sensitivity, specificity, positive and negative predictive values, area under the receiving operating characteristic curve and likelihood ratios were calculated for various Stratus OCT 3 parameters.
Seventy-two eyes (72 patients) with early glaucoma and 96 eyes (96 normal subjects) were analyzed. The inferior maximum parameter had the best combination of sensitivity and specificity, 75% (95% confidence interval CI, 70.2-79.8%) and 89.6% (95% CI, 82.6-96.6%), respectively. The 6-o'clock parameter had a sensitivity of 61.1% (95% CI, 52.3-69.9) and specificity of 99% (95% CI, 95-100); for an assumed prevalence of 5%, the positive and negative predictive values were 75% and 98%, respectively. The positive likelihood ratio for the 6-o'clock parameter (P<5%) in early glaucoma was 61.
Optical coherence tomography has moderate sensitivity with high specificity for the diagnosis of early glaucoma and may have a potential role in screening.
PDF
