ABSTRACT The directionally solidified (DS) CM247LC superalloy is widely used in gas turbine applications because of its excellent mechanical properties at elevated temperatures, which are strongly influenced by its microstructure and γ′ precipitate distribution. This study investigates the effects of solution annealing (SA) and low-temperature aging (LTA) on the alloy’s microstructure and performance. A high SA temperature of 1,270°C, exceeding the eutectic temperature, was deliberately selected to induce incipient melting and replicate localized overheating conditions that may occur in industrial components such as turbine blades, nozzle guide vanes, and combustor liners. The microstructural analysis revealed that annealing at this elevated temperature led to localized melting, particularly in regions enriched with refractory elements such as Aluminum (Al), Hafnium (Hf), and Tungsten (W). This incipient melting hindered complete homogenization and disrupted the uniform dissolution of carbides, resulting in reduced γ′ phase formation within the γ matrix during subsequent cooling and LTA. These findings highlight that exceeding the eutectic temperature during heat treatment can adversely affect microstructure refinement and stability, ultimately influencing the microstructural characteristics and hardness response of DS-CM247LC in high-temperature applications.
ABSTRACT A comprehensive study was conducted on high-temperature thermal stability of a multifunctional injection-molded polyphenylene sulfide (PPS)-matrix composite containing random short carbon fibers (CFs), graphite flakes (Gr), and polytetrafluoroethylene (PTFE) particles. Specimen were heated to 98–200°C for up to 48 h and examined for oxidative-reaction-induced changes. Thermal stability on morphology and chemical composition of the thermoplastic composite is first investigated, using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Negligible changes are found in the composite glass transition temperature, crystallinity, and melting temperature after up to 48 h of high-temperature exposure. The study further finds no change in the composite microstructure and chemical composition, under sustained high-temperature exposure. Therefore, results obtained in the study with DSC, optical microscopy, scanning electron microscopy, and XRD indicate that the CF/Gr/PTFE/PPS composite remains thermally stable in high-temperature environment.
ABSTRACT Improvements in dielectric properties, energy density, and charge–discharge efficiency pave the way for scalable, efficient solutions for modern energy storage systems and applications. The present review offers an outline of the very recent developments of ferroelectric (FE) polymer composite materials specifically for energy storage applications. It is focused on material innovations, structural design, and processing techniques. It also covers the composition of materials, integration techniques, and characteristics of emerging materials. The dielectric breakdown strength, energy storage density, power density, discharge speed, and thermal stability of the developed composite materials are conversed. This review discusses the impact of recent production techniques such as interface engineering and optimization, multilayer and core–shell structures on the characteristics of the FE polymer composite materials. The second part focuses on effective strategies for integrating polymers with FE ceramics to enhance energy storage performance. In the concluding section, the study critically reviews the limitations and challenges associated with these recent developments, while also highlighting future research directions and the scientific advancements required for the effective utilization of FE polymer composites as a high-performance energy storage material.
The information provided by today's standardized test methods used to assess the environment-induced cracking (EIC) sensitivity of high-strength 7xxx series Al-Zn-Mg-Cu alloys fails to provide the quantitative data needed for engineering design and service-lifetime prediction. Current EIC test output is qualitative in nature and is based on historical comparisons. The environmental test conditions and initial alloy surface conditions used are not related/relevant to those anticipated during commercial use. The reported in-service EIC issues for the current latest generation of Al-Zn-Mg-Cu alloys repeat the 1960's experience of "unexpected" major service failure issues for AA7079-T651 components. There is a critical need for EIC test methods that consistently differentiate EIC susceptibilities for relatively resistant alloy tempers in a reasonable time frame that are directly relatable to service performance. A novel test method is proposed to quantitatively assess an alloy's inherent EIC sensitivity.
Abstract Corrosion fatigue is a major damage mechanism responsible for the premature failure of the aircrafts and turbine parts, especially in the marine environment. The process starts with the surface degradation caused by the corrosion pits, which become fatigue initiation sites for the initial damage when the part is loaded. Microstructure and morphology of the surface pits is critical for the crack initiation. Cracks are initiated at sharp corners and at the bottoms of the narrow “micropits.” The paper provides a statistical characterization of the crack initiation process based on the pit density and microstructure distribution. Based on the analysis of surface damage initiation, new morphological characteristics combining pit size and highest curvature are introduced. The distribution of these introduced morphological characteristics is estimated from the measured data and have exhibited to be an efficient metric for pitting fatigue. The effects of pitting morphology are evaluated for various heat-treated 2024 aluminum alloy specimens with varying distribution of pit shapes and curvatures. The statistical distribution of specimen life is estimated using the “weakest link” approach; that is, by computing the probability that at least one crack is initiated somewhere on the surface. The paper contains a detailed description of crack initiation’s statistical model, the methodology for corrosion parameter estimation and representative numerical examples of statistical modeling. Surface pit characterization has been nondestructively measured on a Zygo ZeGage 3D surface profiler. The ZeGage uses a coherence scanning interferometry (CSI) technique based on the wavelength of light. This profiler can measure a wide range of surface qualities with repeatable results in sub-nanometer precision. Large-area scanning was done using a segmentation approach. A large field of view of the selected lens and automated rapid scanning allowed for reasonably smaller data files after stitching these individual segments.
