Papers by Keyword: Microstructure Characterization

Abstract: X-ray micro-computed tomography enables three-dimensional inspection of fiber-reinforced polymer composites. Quantitative mesostructural characterization remains challenging when voxel size does not permit reliable phase segmentation. This study presents a CT-based methodology for mesostructural characterization of unidirectional continuous-fiber polymer composites using line-profile descriptors. The approach extracts fixed one-dimensional intensity profiles within a defined internal volume of interest and computes a compact set of statistical and spatial descriptors. These include distributional moments, entropy, gradient-based measures, autocorrelation-derived correlation length, spectral band-energy ratios, and percentile-based run-length metrics. A technical quality control procedure verifies numerical consistency of the extracted feature tables. A one-at-a-time sensitivity analysis quantifies the influence of descriptor hyperparameters and identifies parameter groups that alter signal partitioning, particularly spectral cut-offs and run-length thresholds. Applied to pultruded composites, the descriptors resolve transverse heterogeneity across the section and systematic through-thickness trends in attenuation level, dispersion, spatial scale, and persistence of low-attenuation domains. The methodology provides a traceable low-dimensional representation of attenuation structure that can inform finite-element modeling through spatially parameterized material fields. Mechanical validation and descriptor–property calibration remain subjects for future work.

Abstract: A connecting rod manufacturer faced excessive reject rate in production. One of the manufacturing operations involves fracture-splitting the big end of the connecting rod. However, some rods showed excessive deformation after the operation. These connecting rods had to be scrapped. Conforming and nonconforming connecting rods were compared in order to identify the cause of the issue. In one of the nonconforming connecting rods, ductile fracture was found after fracture splitting. Generally, ductile fracture is the preferred mode of fracture. In this case, however, there is a need for the big end bore to split without substantial plastic deformation and therefore, ductile fracture is undesirable. Nonconforming rods were found to have low yield strength. To eliminate ductile fracture and facilitate cleavage fracture, it was recommended to increase yield strength of the connecting rods.

Abstract: This paper aims to review the methodologies used to conduct microstructure evaluation of the photovoltaic (PV) interconnection. This analysis is important to identify the microstructural properties of the interconnection for failure analysis purposes. The interconnection becomes a major concern towards the efficiency and reliability of PV technology. In this paper, the common techniques used for the interconnection technology such as soldering, conductive adhesive and ultrasonic were presented with the assessment method to identify the failure mode and failure mechanism at the bonding interface. The identification of the failure mode and failure mechanism through visual analysis and conformation of failure phenomenon was important to highlight the risks and develop the countermeasures. The evaluation of microstructure characterization techniques in the electronics and PV industry has been presented by identifying the outcomes of each technique with different reliability tests. The discoveries of failure analysis in the electronics industry were more matured and becomes the reference to the PV development. The outcomes from this review could be beneficial to improve the interconnection bond in the PV industry by eliminating or minimizing the failure through design modification at the earliest point in the development process.

Abstract: The success of Dissimilar Metal Welding (DMW) occurred in optimal Heat-input (HI) parameters. The quality of welding joints was affected by dilution, hardness value, and intermetallic microstructure. DMW quality research was carried out on stainless steel SA SS312-TP304 and SA 53GrB carbon steel using the GTAW (Gas Tungsten Arc Welding) process with Heat-input of 1866.6 to 2362.2 J/mm. Visual observation on weld joints was not found weld defects. The optimal dilution area in the Schaeffler Diagram was obtained 35.35% austenitic area and without ferrite content. The lowest hardness value on carbon steel was 145 HV. The highest hardness value of 197 HV occurred in filler-metal dilution on carbon steel, so the difference in the value of hardness was high. The hardness value on stainless steel was 184 HV and in filler-metal stainless steel dilution was 172– 90 HV, so the difference in hardness value was low. Microstructure filler-metal dilution on stainless steel was austenite-dendritic, filler-metal dilution on carbon steel was fine-grained dendritic, and on allweld metal coarse-grained dendritic metal. HAZ stainless steel austenite microstructure and ferrite-pearlite carbon steel with an indication of a ferrite net. Observation of dilution, hardness value, and microstructure in DMW did not have a significant effect. This welded joint could be used as a reference in the DMW fabrication process for stainless steel and carbon steel pipe connections.

Abstract: Microstructure characterization and defects formation of a joint fabricated by friction stir welding on two plates of Al 6061 were studied. In this study, plates were in the height of 2mm and input parameters were pin profile (square and cylindrical shape), rotating speed (800 and 1600 rpm) and traverse speed (40, 80 and 120 mm/min). Also, some experiments were conducted and the effects of input variables on the microstructure of the samples are studied by using an optical microscope. Based on the results, a sound defect-free weld could be achieved by optimizing the ratio of traverse speed to rotational one, due to the influence of this ratio on the amount of heat generated during the FSW process. It has been also concluded that higher ratios of traverse speed to rotating speed can result in poor welds.

Abstract: Ultrasonic inspection is one of the most widely used non-destructive testing methods for inspection of fabricated structures and components. During ultrasonic inspection, mechanical waves in form of ultrasound are transmitted and propagate through volume of parts or components and reflect when the waves meet with the existing interface such as flaws in the welds. In addition to detection of flaws or defects within the structures, ultrasonic inspection is also used for determination of component thickness as well as characterization of microstructure of different materials. As the ultrasound is transmitted through media, the loss of ultrasound amplitude is referred to as acoustic attenuation. This attenuation effects greatly result from heterogeneity, anisotropy, and different grain sizes of crystalline media the ultrasound goes through. In order to develop the ultrasonic backscattering models for polycrystalline materials, experimental results of the correlation between the changes in attenuation coefficient and the actual microstructure of polycrystalline materials are necessary. This research article presents the preliminary results of this correlation study in stainless steel 304L specimens in as-received conditions compared with different annealed and heat-treated conditions. Such correlations of attenuation coefficient, hardness, and grain size will be used as baseline for future additional characterization technique such as electron backscattered diffraction to better understand the attenuation effects for textured polycrystalline materials.

Abstract: Corrosion behavior of martensitic heat resisting steel T91 in high-temperature carbon dioxide environment at 500-700 °C was investigated. X-ray diffraction, scanning electron microscopy and glow-discharge optical emission spectrometry were employed to characterize the corrosion products. The results showed that the corrosion kinetics of T91 followed a parabolic law with experimental time. The oxide scale thickness of T91 followed an exponential growth law from 500 °C to 700 °C. Internal carburization was detected underneath the corrosion scale. What’s more, the carburization depth was larger than the corrosion scale. The variations of Cr and C elements distribution were discussed.

Abstract: Three novel low carbon microalloyed steels with various additions of Mo, Nb and V were investigated after thermomechanical processing simulations designed to obtain ferrite-bainite microstructure. With the increase in microalloying element additions from the High V- to NbV- to MoNbV-microalloyed steel, the high temperature flow stresses increased. The MoNbV and NbV steels have shown a slightly higher non-recrystallization temperature (1000 °C) than the High V steel (975 °C) due to the solute drag from Nb and Mo atoms and austenite precipitation of Nb-rich particles. The ambient temperature microstructures of all steels consisted predominantly of polygonal ferrite with a small amount of granular bainite. Precipitation of Nb-and Mo-containing carbonitrides (>20 nm size) was observed in the MoNbV and NbV steels, whereas only coarser (~40 nm) iron carbides were present in the High V steel. Finer grain size and larger granular bainite fraction resulted in a higher hardness of MoNbV steel (293 HV) compared to the NbV (265 HV) and High V (285 HV) steels.

Abstract: Strength and ductility are the two most important mechanical properties of a structural material. However, they are often mutually exclusive. In this study, a 6 wt. % TiB₂ nanoparticle reinforced 7075Al (i.e. TiB₂/7075Al) composite was designed and produced by the processing route combining casting, friction stir processing, hot extrusion and T6 heat treatment. The result of tensile testing demonstrates that the as-processed composite sample presents an ultimate tensile strength of 677 MPa and a total elongation to failure of around 15 %, being higher than any Al or Al based materials ever reported. The typical microstructure contains the TiB₂ reinforcement nanoparticles uniformly distributed in the equiaxed Al grain matrix (2 μm in average grain size). In addition to the dispersed nanoprecipitates of the 7075Al (Al-Zn-Mg-Cu) matrix, the integrated TiB₂ nanoparticles are systematically decorated by a shell corresponding to (Zn_1.5Cu_0.5)Mg. This finding challenges our understanding and opens a door for further enhancing strength and ductility being easily scalable for industrial applications.

Abstract: Autogenous gas tungsten arc welding (GTAW) using different non-consumable pure tungsten electrodes (EWP) from eight different manufacturers was performed on aluminum alloy 5083 samples. Due to the limited literatures of how tungsten microstructure may affect the weld quality, this paper attempts to investigate the change in microstructure of tungsten electrode after welding compared to the original microstructure in as-received condition. The scanning electron micrograph results reveal different grain shapes and sizes and also different grain growth rate during welding. It was found that the ability to control the grain growth or limit grain size within the balled end of pure tungsten electrode during aluminum welding plays a very important role in determining the quality of the electrode and how long the electrode would last.