Journal of Materials Engineering and Performance最新文献

A corrosion inhibition study of mild steel in 1 M sulfamic acid was conducted using grape seed extract (GSE) as a possible green inhibitor. Electrochemical techniques were adopted to measure the corrosion rate in both the absence and presence of the GSE. Conditions were standardized to obtain optimum inhibition efficiency by varying the concentration of inhibitor and temperature. The kinetic parameters were calculated using the Arrhenius equation. Surface analysis was conducted by scanning electron microscope (SEM) and atomic force microscope (AFM) techniques. A suitable mechanism was proposed for the corrosion inhibition process. Grape seed extract showed a maximum efficiency of 65%, with a concentration of 0.24 g/L at 303 K from potentiodynamic polarization (PDP) studies. With the increase in temperature, the efficiency decreased, resulting in the GSE inhibitor’s physical adsorption. Surface morphology studies supported the adsorption of GSE on mild steel. GSE acted as an efficient green inhibitor with environmental benefits.

The present study deals with the development and characterization of Mo-35Ti-10Si and Mo-35Ti-10Si-2B (wt.%) alloy for ultra-high temperature applications beyond the temperature limit of existing super alloys. The microstructural characterization using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron back scattered diffraction (EBSD), x-ray diffraction (XRD) revealed that the Mo-35Ti-10Si-2B alloy was consisted of three phases, namely, (Mo, Ti)_ss, (Mo, Ti)₅SiB₂ and (Ti, Mo)₅Si₃; whereas, Mo-35Ti-10Si alloy was found to be consisting of (Mo, Ti)ss, and (Mo,Ti)₃Si phases. Since quantification of boron is difficult by EDS, Particle Induced Gamma-ray Emission (PIGE), a nuclear reaction analysis technique was used for chemical composition analysis of boron. The oxidation behavior of the Mo-35Ti-10Si-2B alloy in the temperature regime of 825-1250 °C was studied in detail and compared with boron-free Mo-35Ti-10Si alloy. Mo-35Ti-10Si-2B alloy exhibited superior oxidation behavior at intermediate temperatures of 825 °C, and excellent oxidation resistance at higher temperatures between 1000 and 1250 °C due to the formation of the protective borosilica and double oxide layers (TiO₂ and duplex borosilica-TiO₂), respectively. High-temperature oxidation mechanisms were discussed using detailed microstructural cross section analysis of the oxidized alloy samples. The micro-mechanical behavior of constitutive phases of the Mo-35Ti-10Si-2B alloy were studied by microhardness, nano-indentation and micropillar compression testing. The micropillar compression of (Mo, Ti)_ss phase showed fairly ductile behavior with the evidence of activation of dislocation in the form of slip lines revealed through the post-deformation fractography. Deformation studies of (Mo, Ti)₅SiB₂ and (Ti, Mo)₅Si₃ phases were also carried out which showed large strain bursts indicating possibility of activation of dislocation activities even at room temperatures imparting low level of ductility.

EN-GJS-400-15U nodular cast iron intended to be used as load-bearing element in long-term geological disposal canisters containing spent nuclear fuel in Finland and Sweden was studied for static strain aging (SSA). Tensile test specimens manufactured from the nodular cast iron were pre-strained to 1%, 2% and 3% nominal plastic strains. The pre-strained specimens were aged at different temperatures ranging from room temperature to 400 °C for varying times. The aged specimens were tested with conventional tensile testing using constant cross-head speed of 0.016 mm/s. Additionally, four specimens were studied with digital image correlation (DIC) during the tensile testing to obtain full-field strain measurements. SSA resulted in elevated pronounced yield point in all the conditions, while the as-received material showed continuous yielding behavior. SSA reduced the elongation to fracture. DIC tests showed more localized yielding behavior in the SSA specimens. Over-aging effect was observed at 400 °C where increasing pre-strain did not increase the yield stress more. For 1-day aging time, the highest yield stress increment was found after aging at 200°C. The yield stress of the material was almost identical after aging in 100°C and 200°C.

The work presented in this paper focuses on modeling the welding process to develop a numerical model able to perform a good prediction of welding distortions. The model is developed for a butt welded joint using S235 steel as the base metal and an electrode (AWS E6013) as the filler metal. To assess accuracy, numerical and experimental results are compared. The present work makes it possible to identify the main factors influencing the accuracy of the numerical model, which must be taken into account to obtain satisfactory results. To carry out this analysis, the effect of the mechanical properties of deposited metal and the effect of the deposition process were taken into account. The effect of the variation of the mechanical properties of the filler metal on the distortions is illustrated. The model was developed by using APDL language, and the birth and death technique is used to model the deposition process. Distortion results obtained by numerical models approach properly the experimental measurement. Further analysis of the numerical data reveals considerable fluctuation of the obtained results by modifying the models used to describe the plastic behavior and the work hardening process. Regarding this strong correlation, numerical modeling of the welding process needs a vigilant identification of the work hardening mode appropriate for the used materials.

Progressive induction hardening is an in-line steel heat treatment method commonly used to surface harden powertrain components. It produces a martensitic case layer with a sharp transition zone to the base material. This rapid process will induce large residual stresses, where a compressive state in the case layer will shift to a tensile state in the transition zone. For fatigue performance, it is important to quantify the magnitude and distribution of these stresses, and moreover how they depend on material and processing parameters. In this work, x-ray diffraction in combination with a layer removal method is used for efficient and robust quantification of the subsurface stress state, which combines electropolishing with either turning or milling. Characterization is done on C45E steel samples that were progressively induction hardened using either a fast or slow (27.5 or 5 mm/s, respectively) scanning speed. The results show that although the hardening procedures will meet arbitrary requirements on surface hardness, case depth and microstructure, the subsurface tensile stress peak magnitude is doubled when using a fast scanning speed. However, the near-surface compressive residual stresses are comparable. In addition, the subsurface tensile residual stress peak is compared with the on-surface tensile stresses in the fade-out zone.

The generation of residual stresses by grinding process on the surface for a soft material results in poor performance and diminished life. Ball end magnetorheological finishing (BEMRF) process is a recently developed process that is effectively used for fine figuring and polishing of a variety of magnetic and non-magnetic materials. In this paper, grinding-induced residual stresses are addressed, and an attempt is made to relieve these residual stresses while achieving high surface finish using chemical assisted ball end magnetorheological finishing (CA-BEMRF) process. The impact of various CA-BEMRF variables on percentage surface roughness reduction and percentage reduction in residual stresses are discussed statistically and graphically. Residual stresses of workpiece surfaces have been measured by using portable x-ray residual stress analyzer. Scanning electron microscopy (SEM) of the finished workpiece before and after CA-BEMRF process is carried out to assess the effects of magnetizing current, tool rotation and working gap on surface topography of machined surface. It has been observed that reduction in residual stress is achieved along with high surface finish on aluminum workpiece surface using CA-BEMRF technique. Significant process parameters affecting the residual stresses and surface roughness during polishing of workpiece are obtained using analysis of variance (ANOVA) and F-test. The optimization problem for maximum percentage reduction in surface roughness and maximum percentage reduction in residual stress is formulated as multiobjective, multivariable, nonlinear optimization problem. Maximum percentage surface roughness reduction and minimum residual stress has been found at magnetizing current 2.3A, rotational speed of tool 550 rpm and working gap of 0.5 mm. Confirmatory experimental tests have been conducted and results obtained were found very close to the predicted outcome.

The microstructure, mechanical properties and residual stress of dissimilar AA3105/ AA2024 friction stir welds have been investigated. The formation of voids was observed at high rotational speeds and low transverse speeds due to the high weld heat input and abnormal stirring. The precipitate fragmentation was noticeable at higher tool rotational speed. The highest hardness was obtained at the AA2024 side of the joints due to the presence of precipitates. The results showed that the welding transverse speed has more effect on UTS than the rotational speed. Tensile residual stresses were found at the AA2024-T6 side and the welding line; while residual stresses at the AA3105 side were compressive.

Autofrettage processes allow engineers to reduce the thickness of thick-walled cylinders or components in high-pressure applications without sacrificing strength, life, or safety. However, during the autofrettage process, residual stresses will be generated due to plastic deformation. The complex tube material behavior is dominated by the Bauschinger effect. A better understanding and accurate prediction of the residual stress field is critical, which will enable better piping design strategies to minimize deformation and stresses under operating conditions. This study aims to predict and analyze residual stresses resulting from hydraulic re-autofrettage of a swage-autofrettaged thick-walled cylinder by computer modeling. A case study was performed on a thick-walled cylinder of A723 alloy with a radial interference of 2.5%. In order to investigate the effect of the chosen material constitutive representation, results based on the true material constitutive model were compared with the simplified prevalent material model of bi-linear kinematic strain hardening. Computer implementation for the true material was via a user-developed subroutine that incorporates the complex Bauschinger effect. The results indicate that an accurate material constitutive representation is crucial for better and more accurate prediction and understanding of residual stresses induced by autofrettage processes. Computer modeling based on the true material constitutive representation will likely prove to be a powerful tool for the design of autofrettage processes in general and thick-walled cylinders in particular.

In the present study, directional and spatial variations in the mechanical properties are calculated in two nuclear-grade materials. In practice, multiple ASTM standard specimens are tested to measure mechanical properties of any material. The variations obtained in the properties during the tests are generally neglected assuming such variations are due to experimental uncertainties. However, such variations may indicate some degree of anisotropy and spatial inhomogeneity in the material due to component fabrication. In the present study, multiple miniaturized tensile specimens are tested. These specimen materials are taken across the thickness and at different geometrical locations in the two manufactured nuclear-grade components. The experimental load versus displacement data of all the specimens are then used to evaluate stress-strain data and cohesive zone parameters. These parameters are determined for each tested specimen separately to gather variations over the geometries of the components. Subsequently, TPB specimens are analyzed employing these parameters to calculate variations in fracture initiation toughness over the geometry. The key findings of the present work include higher strengths in circumferential direction in comparison to the longitudinal direction for SA333 Gr6 steel. A new equation is developed to correlate the material toughness with the fracture toughness with a proportionality constant of 2.7778 for low-alloy carbon steels. The study showed that directional and spatial variations in J_ini are less pronounced in 20MnMoNi55 compared to SA333Gr6 materials. This finding is crucial for safety analyses in nuclear components and indicates that this methodology can be applied more widely across different materials.