Papers by Keyword: Microstructural Analysis

Abstract: This study investigates the deformation behaviour of the CM247LC superalloy through a combination of physical experimentation and computational analysis. High temperature deformation was conducted at 600°C, 800°C, and 1000°C with a strain rate of 0.001 s⁻¹ and 50% of deformation. This research integrates microstructural analysis and mathematical equations to enhance understanding of the alloy's response under varying conditions. The findings reveal that at 600°C, the superalloy exhibits high flow stress and significant ultimate strength due to limited dynamic recovery (DRV) and restricted dynamic recrystallization (DRX). The increase in yield strength from 708 MPa at 600°C to 814 MPa at 800°C is attributed to effective precipitation strengthening from the γ' phases, corroborated by FEM simulations that show higher average yield strength values ranging from 875 MPa to 900 MPa at 800°C. Microstructural analysis indicates the role of finely dispersed carbides at lower temperatures and their coarsening at higher temperatures, which affects the material's strain-hardening behaviour and softening mechanisms. While physical simulations provide empirical data on mechanical properties and microstructural changes, FEM simulations predict stress-strain distributions and identify potential instability regions.

Abstract: This study investigates the Mg-6.5Zn-7.24Sn-1.22Ca alloy, focusing on its microstructural evolution, corrosion resistance, and mechanical performance under varying thermal and mechanical treatments. The alloy was cast under an argon environment, homogenized at 400°C for 18 hours, and hot rolled at 400°C with a 15% thickness reduction. Microstructural analysis through XRD, SEM-EDS, and optical microscopy revealed grain refinement, phase redistribution, and reduced porosity after rolling. Corrosion behavior in 3.5% NaCl solution, assessed via electrochemical techniques and weight loss measurements, indicated superior corrosion resistance in the homogenized condition due to reduced micro-galvanic coupling. Rolling, however, increased corrosion susceptibility due to strain-induced defects. High-temperature ( 200°C- 350°C ) tensile tests at strain rates of 10-4 and 5×10-4 s-1 demonstrated that tensile strength decreases with temperature, driven by dynamic recrystallization and grain boundary sliding. Strain rate variations revealed increased tensile strength at higher rates due to enhanced dislocation density and strain hardening. These findings highlight the interplay between processing conditions, strain rates, and alloy performance, offering insights for optimizing magnesium alloys for advanced engineering applications.

Abstract: Biodegradable magnesium alloy WE43 (Mg-4Y-3RE) has received great attention in orthopaedic applications as it can dissolve completely after bone tissue repair, eliminating the need for a second surgery to remove the WE43 implant. However, the rapid degradation of WE43 implants during bone healing remains a concern. Rapid degradation can deteriorate the mechanical strength and generate a significant amount of hydrogen gas via corrosion in physiological environments, negatively affecting bone healing and the surrounding tissues. To overcome the rapid degradation of medical implants, one commonly used method is surface modification via laser surface melting (LSM) to alter the surface microstructures and improve the corrosion resistance. This paper investigates the possibility of applying LSM technique to refine the surface microstructures of WE43 alloy and compares the microstructures induced by LSM with the extruded alloy without laser treatment. Results show significant grain refinement after LSM with average grain size decreased to 3μm as compared to 5μm before LSM, approximately 40% reduction in grain size. Different types of grain morphology are also identified at different locations in the melt pool due to different temperature gradients and cooling rates. It is observed that the depth of the melt pool increases with increasing laser power and decreasing laser scanning speed due to the higher heat input. It is also observed that grain size decreases with decreasing laser power and increasing laser scanning speed due to increased cooling rate. Results from this study show that LSM, a form of rapid solidification processing, can form a predominantly basal crystallographic texture, homogenise and refine the surface microstructures of WE43, which are beneficial for corrosion resistance.

Abstract: Solid-state diffusion bonding (DB) of Copper-Copper (Cu/Cu) was carried out under varying bonding parameters (time and temperature) in argon shielding gas environment. Initially, the bonding was performed at bonding temperatures of 800, 850, and 900 °C for 60 minutes. Secondly, the bonding was carried out at holding times of 90, 120, and 150 minutes at 900 °C. The microstructural and mechanical properties of the bonding interface were evaluated via lap shear and micro hardness tests, X-ray diffraction, and Optical microscopy. It was found that the optimal bonding parameters for the joint interface was 950 °C for 150 minutes, resulting in maximum shear strength of 133 MPa. The X-ray diffraction also shows the formation of solid solution of Cu without the formation of any intermetallic compounds (IMC). The micro hardness test revealed a maximum hardness of 89 HV at the joint interface. Optical microscopy shows the formation of voids at the joint interface take place due to the Kirkendall effect, which increased with higher temperatures for longer time, and cause a wide diffusion-affected zone (DAZ).

Abstract: Considering its very good mechanical properties, especially the high strength and toughness, and also its well-known case-hardening ability, the AMS 6265 (9310 VAR) low alloy steel is widely used in the aeronautical industry for manufacturing heavy-duty products and parts, like pinions, shafts, gears, piston pins, and other critical aircraft components. In this study, a surface modification treatment via shot peening method was applied to an initially case-hardened (quenched and carburized) AMS 6265 aircraft steel. In shot peening, the mechanical properties of the surface layer are improved, by generating plastically deformed micro-areas when exposing the metal surface to a stream of steel, glass, or ceramic shots. The initial case-hardened AMS 6265 alloy steel and all surface treated samples were structurally investigated by means of OM (optical microscopy), SEM-BSE (scanning electron microscopy – backscattered electrons imaging), and XRD (X-Ray diffraction) analysis, being also mechanically tested in tensile and microhardness tests. The influence of different shot peening parameters (shot size, peening pressure, and exposure time) on mechanical properties evolution and microstructural features, for the analyzed AMS 6265 alloy steel, was established in this present research.

Abstract: Friction Stir Back Extrusion (FSBE) is a new grade of severe plastic deformation process capable of producing metallic tubular geometries that exhibit ultrafine grain structure and superior mechanical properties. FSBE of tubular sections provide opportunities for producing lightweight rigid structures for the automotive, aerospace and construction industries. This research investigates the effect of submerging conditions (in water at 25 °C and 2 °C) for Magnesium AZ31-B tubes on the grain size, mechanical properties, temperature history and power consumption. Submerged FSBE is compared to FSBE in air at fixed process parameters of 90 mm/min and 2000 rpm. It is shown that the impact of submerging is statistically insignificant in terms of the mechanical properties, ultimate tensile strength and percent elongation, of the produced tubes according to the conducted t-tests. On the other hand, the optical microscopy results indicated finer grains at the inner wall of the seamless tubes for FSBE in air and underwater FSBE at 25 °C when compared to underwater FSBE at 2 °C.

Abstract: Steel grade SS34 has found wide application in the oil and gas industry. This steel is low-carbon. The choice of this steel is explained by its good properties for industrial facilities, such as weldability, non-hardening. A number of studies were carried out in the work, which included testing samples in a heat-treated state and free. To obtain an equilibrium structure, annealing was carried out. As a result of the experiment, it was shown that after annealing, the structure of SS34 steel acquired high plasticity, but low hardness and strength indicators were noted. Tensile tests of steel samples under static uniaxial loading were also carried out. As a result of such experiments, the main indicators of plasticity and strength of the metal under study were determined. Using the Rockwell method, the changes in the hardness of metal samples were studied. An optical microscope was used to determine the changes in the microstructure, and it was shown that the structure of the steel is ferrite-pearlite. The difference between the structure of the metal in the free and heat-treated state is also noted. In the initial state, it is fine – grained; in the processed state, it is homogeneous, the texture of deformation disappears. In the initial state of the steel grade SS34, scribbling was detected, and the liquation band was also clearly traced. It is shown that there is a chemical heterogeneity on the metal at this point, which is explained by the presence of impurities (oxides, nitrides, sulfides, silicides).

Abstract: Mortar is another construction medium made of cement, which is mixed with sands and water, and lime is applied to increase the product's longevity. The gypsum renders workability to make mortar or concrete by keeping the cement in plastic state at early age of hydration. The gypsum is called the retarding agent of cement because the gypsum which is mainly used for regulating the setting time of cement. To get the optimal setting time for optimum compressive strength, gypsum in the cement needs to be control. Cement setting time when it hydrates and renders cement paste when combined with water. The objective of this research is to analyze the effect of different amount in Ordinary Portland Cement (OPC). Vicat apparatus was used to analyze the initial setting time of cement paste. Gypsum and clinker were used in production of mortar with the size 50 mm x 50 mm x 50 mm. This research deals with observation of the cement setting time to point out some differences that would effect to strength of mortar. The results reveal that control gypsum with 4% of gypsum has the highest strength as compared to 0% of gypsum and 8% of gypsum. The setting time of cement paste are discussed with respect to their influence on the strength of mortar.

Abstract: Property of metallurgical slag generated in smelting or refining process of ferrous production can be determined by its microstructure which depends on chemical composition and production process. This study proposes a deep learning method which is a subfield of artificial intelligence for autonomous slag classification by microstructure recognition. This present work focus on the implementation of a convolutional neural network (CNN) to classify four types of slags that the variance microstructure resulted from the difference of their formation condition. Both secondary electron (SE) and backscattered electron (BSE) image type captured by scanning electron microscope (SEM) are used as dataset. ResNet50, InceptionV3 and DenseNet201 network architectures are selected in this study to evaluate their classification performance. In addition, data augmentation manipulated by the software is randomly flipped both horizontally and vertically to avoid overfitting from a limited number of training images. The results showed that the best approach to classification accuracy is reached 98.89% by CNN. Therefore, it can be concluded that CNN is excellent potential method for autonomous slag microstructure classification systems.

Abstract: The investigation of the corrosion resistance of Ti6Al4V alloy components produced by additive technology is still lacking in the literature. This paper aims to study the electrochemical behaviour of Ti6Al4V components fabricated by laser powder-bed fusion additive manufacturing process. The metallographic analysis was carried out by an optical microscope. The electrochemical behaviour has been evaluated in 3.5 wt. % of natural aerated NaCl aqueous solution by potentiodynamic polarization test. The results have been compared to a conventionally manufactured Ti6Al4V component. The typical martensitic structure has been shown by the additive manufactured sample. As expected, the metallographic analysis revealed a martensitic microstructure. The electrochemical tests carried out on the surface of the as-received additive manufactured specimen showed an influence of its morphology on the values of passive current density, higher than that recorded for the conventionally manufactured sample, used as the control. After mechanical polishing, the electrochemical tests were repeated on the "bulk" of the samples. The open circuit potential values were higher than the value recorded for the conventionally manufactured sample. The conditions of the additive process affect the corrosion resistance of the components due to the roughness of the surface and to the microstructure created.