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The current study aimed at the optimization of process parameters for microchannel fabrication on thermal sprayed carbide coatings using rotary ultrasonic machining (RUSM). Rare earth oxides (REOs) such as La₂O₃, CeO₂, and Er₂O₃ have been incorporated into WC-Co-Cr coatings to enhance machinability and improve coating characteristics. The research has demonstrated that La₂O₃ doped coatings have significantly increased the material removal rate (MRR), with a 15 % improvement when compared to undoped coatings. Additionally, surface roughness has been reduced by 20 %, resulting in a smoother and more uniform finish. The inclusion of REOs has refined the microstructure of the coatings, yielding denser and more compact layers, which has reduced defects and improved the overall surface quality. Furthermore, the hardness of the coatings has been enhanced by 45 %, with La₂O₃ doped coatings achieving a maximum hardness value of 1313 ± 11 HV. The findings have highlighted the potential of REO doping to enhance the performance and efficiency of microchannel fabrication on WC-Co-Cr coatings using RUSM, contributing valuable insights to industrial applications. [ABSTRACT FROM AUTHOR]

This study examined the impact of abrasive slurry assisted Rotating Ultrasonic Machining (RUM) using Boron Carbide (B 4 C) powder of three mesh sizes: 400 Mesh, 600 Mesh, and 800 Mesh. The effects of abrasive size, feed rate, and tool rotation on Material Removal Rate (MRR) and Surface Roughness (SR) were investigated. The highest MRR of 3.454 mm³/min was achieved with 400 mesh, 30 mm/min feed rate, and 1250 rpm due to larger abrasive size, medium feed rate, and medium tool rotation velocity, while the lowest MRR of 0.284 mm³/min was noted with 600 mesh, 30 mm/min feed rate, and 1500 rpm, attributed to intermediate abrasive size and high tool rotation. The lowest SR of 1.16 μm was observed at 800 mesh, 15 mm/min feed rate, and 1500 rpm, resulting from smaller abrasive size and higher tool rotation facilitating polishing action and vibrational dampening. The highest SR of 3.71 μm occurred at 400 mesh, 45 mm/min feed rate, and 1500 rpm, due to larger abrasive size, higher feed rate, and tool rotation, increasing surface corrosion. ANOVA and regression analyses highlighted mesh size as the most significant parameter for both MRR and SR, with strong model-experimental value correlations. The findings demonstrate the suitability of abrasive slurry assisted RUM for fabricating micro-channels in X-Ray, optoelectronic, and semiconductor applications. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the noise-induced dynamics of a lean premixed combustion system operating on natural gas–air mixtures that exhibit thermoacoustic instability via a subcritical Hopf bifurcation. The investigation is done before the bistable region with equivalence ratio (ϕ) as the control parameter. We analyze the acoustic pressure oscillations (p ′) in the combustor and fluctuations in the heat release rate (q ′) from the laminar quasi-flat flame at increasing levels of white noise. We show the effects of noise intensity on the reliability of various types of early warning indicators (EWIs) to predict the onset of the impending thermoacoustic oscillations. We investigate the indicators based on statistical measures (variance, skewness, and kurtosis), autocorrelation and spectral properties (coherence factor), system identification (growth/decay rates of p ′), multi-fractality (Hurst exponent), and time series complexity (permutation entropy and Jensen–Shannon complexity). The coherence factor, variance, and decay rates of p ′ always increases as the system approaches thermoacoustic instability, indicating their robustness as an EWI under most noise levels. An increase in kurtosis cannot be employed as an EWI. Implementing autocorrelation, skewness, Hurst exponent, permutation entropy and Jensen–Shannon complexity as effective EWIs has limitations: they can be estimated accurately only from pressure oscillations (p ′) data and work only above a particular threshold value of noise intensity. Our results have direct implication on early prediction and control of thermoacoustic instability in practical gas turbine combustors. Novelty and significance statement Developing effective early warning indicators (EWIs) to anticipate the onset of thermoacoustic instability is crucial for preventing potential damage and ensuring the reliable operation of lean premixed gas turbine combustion systems. In such systems, inherent noise dynamics undergo variations with changing operating conditions and combustor designs. Specifically, noise intensity increases as the system becomes more turbulent. In this study, we demonstrate that the inherent noise dynamics in a lean premixed combustion system play a crucial role in influencing the trends observed in early warning indicators of thermoacoustic instability. We address several key questions, including (a) whether comparative reliability assessments of different classes of EWIs exist, (b) the effect of variations in noise properties on the efficacy of EWIs, and (c) which EWIs are most reliable considering that noise characteristics depend on the system and may even change with operating conditions within a specific system. This information is critical for engine designers/users, facilitating the development of robust and effective monitoring systems for gas turbine combustion systems. [ABSTRACT FROM AUTHOR]