Prakash Patnaik

The present study focuses on advancing one of the most popular AM techniques, namely, laser powder bed fusion (LPBF) technology, which has the ability to produce complex geometry parts with minimum material waste but continues to face challenges in minimizing the surface roughness. For this purpose, a novel hybrid manufacturing technology, which applies in a single setup (in-envelope) both LPBF technology and high-speed machining, was examined in this research for the fabrication of tensile specimens with three different surface finish conditions: as-built, hybrid (in-envelope machining) and post-machining (out-of-envelope) on Inconel^® alloy 718, hereafter referred to as IN718. As the application of the IN718 alloy in service is typically specified in the precipitation-hardened condition, three different heat treatments were applied to the tensile specimens based on the most promising thermal cycles identified previously for room-temperature tensile properties by the authors. The as-built (AB) specimens had the highest average surface roughness (R_a) of 5.1 μm ± 1.6 μm, which was a significant improvement (five-fold) on the hybrid (1.0 μm ± 0.2 μm) and post-machined (0.8 μm ± 0.5 μm) surfaces. The influence of this surface roughness on the mechanical properties was studied both at ambient temperature and at 650 °C, which is close to the maximum service temperature of this alloy. Regardless of the surface conditions, the room-temperature mechanical properties of the as-fabricated IN718 specimens were within the range of properties reported for standard wrought IN718 in the annealed condition. Nonetheless, detailed examination of the strain localization behavior during tensile testing using digital image correlation showed that the IN718 specimens with AB surfaces exhibited lower ductility (global and local) relative to the hybrid and post-machined ones, most likely due to the higher surface roughness and near-surface porosity in the former. At 650 °C, even though the mechanical properties of all the heat-treated IN718 specimens surpassed the minimum specifications for the wrought precipitation-hardened IN718, the AB surface condition showed up to 4% lower strength and 33–50% lower ductility compared with the hybrid and PM surface conditions. Microfocus X-ray computed tomography (µXCT) of the fractured specimens revealed the presence of numerous open cracks on the AB surface and a predisposition for the near-surface pores to accelerate rupture, leading to premature failure at lower strains.

Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to improve their durability has long been a challenging task in the gas turbine industry. In this paper, a literature review on ML principles and its various associated algorithms was presented first and then followed by its application to investigate thermal conductivity of TBCs. This combined approach can help better understand the physics behind thermal conductivity, and on the other hand, can also boost the design of low thermal conductivity of the TBCs system in terms of microstructure–property relationships. Several ML models and algorithms such as support vector regression (SVR), Gaussian process regression (GPR) and convolution neural network and regression algorithms were used via Python. A large volume of thermal conductivity data was compiled and extracted from the literature for TBCs using PlotDigitizer software and then used to test and validate ML models. It was found that the test data were strongly associated with five key factors as identifiers. The prediction of thermal conductivity was performed using three approaches: polynomial regression, neural network (NN) and gradient boosting regression (GBR). The results suggest that NN using the BR model and GBR have better prediction capability.

This research study investigated the hybrid processing of 316L stainless steel using laser powder bed (LPB) processing with high-speed machining in the same build envelope. Benchmarking at four laser powers (160 W, 240 W, 320 W, and 380 W) was undertaken by building additively with machining passes integrated sequentially after every ten deposited layers, followed by the final finishing of select surfaces. The final geometry was inspected against the computer-aided design (CAD) model and showed deviations smaller than 280 µm for the as-built and machined surfaces, which demonstrate the good efficacy of hybrid processing for the net-shape manufacturing of stainless steel products. The arithmetic average roughness values for the printed surfaces, Ra (linear) and Sa (surface), were 11.4 um and 14.9 um, respectively. On the other hand, the vertical and horizontal machined surfaces had considerably lower roughness, with Ra and Sa values ranging between 0.33 µm and 0.70 µm. The 160 W coupon contained layered, interconnected lack of fusion defects which affected the density (7.84 g·cm⁻³), yield strength (494 MPa), ultimate tensile strength (604 MPa), Young’s modulus (175 GPa), and elongation at break (17.3%). By contrast, at higher laser powers, near-full density was obtained for the 240 W (7.96 g·cm⁻³), 320 W (7.94 g·cm⁻³), and 380 W (7.92 g·cm⁻³) conditions. This, combined with the isolated nature of the small pores, led to the tensile properties surpassing the requirements stipulated in ASTM F3184—16 for 316L stainless steel.

To better support the transition to more industrial uses of additive manufacturing, this study examined the use of an Arcam Q20+ industrial 3D printer for producing heavily nested Ti-6Al-4V parts with both in-specification (IS) and out of specification (OS) oxygen content in reused grade 5 powder chemistries. Both the OS and IS powder chemistries were evaluated to understand their impact on build integrity and on static and fatigue performance. The results from our evaluations showed that controlling the bed preheat temperature in the Q20+ to relatively low values (326–556 °C) was effective in limiting microstructural coarsening during the long build time and enabled adequate/balanced performance vis à vis the tensile strength and ductility. Overall, the tensile properties of the IS Ti-6Al-4V material in the as-built and machined states fully met the requirements of ASTM F2924-14. By contrast, the ductility was compromised at oxygen levels above 0.2 wt.% (OS) in Ti-6Al-4V produced by EBM. Removal of the surface layer by machining increased the consistency and performance of the IS and OS Ti-6Al-4V materials. The fatigue behaviour of the EBM Ti-6Al-4V material was in the range of properties produced by casting. Due to the strong influence of both the surface finish and oxygen content on the fatigue strength, the IS Ti-6Al-4V material exhibited the highest performance, with results that were in the range of parts that had been cast plus hot isostatically pressed.

Beneficial properties achieved by nanostructuring effects in materials have generated tremendous interests in applications in surface engineering, especially in thermal barrier coatings (TBC). Limitations in conventional TBC processing for gas turbines and aero-propulsion systems have been exposed during past decades when rapid progress was made in nano-structuring coating research and developments. The present work is a comprehensive review of the current state of progress in nanostructured TBC (Ntbc) in reference to its microstructure, damage progression, failure mechanisms and a wide range of properties. The review aims to address the comparative performance analysis between the nanostructured and conventional (microstructured) 6–8 wt.% yttrium stabilized zirconia (YSZ) TBC systems. Oxidation resistance and sintering behavior in two TBCs are considered as the central focus of discussion. A few schematics are used to represent major microstructural features and failure progression. A performance analysis is performed for standard 2-layer, as well as functionally graded multilayer, TBC systems. A comparison of TBC characteristics processed by plasma spray and vapor deposition techniques is also made as reference. Compared to the sea of R&D efforts made for conventional TBC (Ctbc), limited experimental studies on Ntbc offers conflicting data, and prediction modeling and computational research are scarce.

Detecting and identifying drones is of great interest due to the proliferation of highly manoeuverable drones with on-board sensors of increasing sensing capabilities. In this paper, we investigate the use of radars for tackling this problem. In particular, we focus on the problem of detecting rotary drones and distinguishing between single-propeller and multi-propeller drones using a micro-Doppler analysis. Two different radars were used, an ultra wideband (UWB) continuous wave (CW) C-band radar and an automotive frequency modulated continuous wave (FMCW) W-band radar, to collect micro-Doppler signatures of the drones. By taking a closer look at HElicopter Rotor Modulation (HERM) lines, the spool and chopping lines are identified for the first time in the context of drones to determine the number of propeller blades. Furthermore, a new multi-frequency analysis method using HERM lines is developed, which allows the detection of propeller rotation rates (spool and chopping frequencies) of single and multi-propeller drones. Therefore, the presented method is a promising technique to aid in the classification of drones.

One advantage of computational fluid dynamics (CFD) is its ability to reveal the physics or nature of practical engineering problems in detail, allowing engineers and scientists to develop rigorous, effective, and efficient solutions. In this chapter, an effective approach to investigate gas turbine hot component failure is demonstrated, and the mid-span cracking of nozzle guide vanes (NGVs) is used as an example. It is a two-step approach. In the first step, a 60° combustor sector with simplified NGVs and thermocouples attached is simulated; and in the second step, NGV sectors are simulated, where each NGV sector is comprised of one high-fidelity probe NGV and several dummy NGVs. The former identifies the NGV having the highest thermodynamic load and provides the inlet boundary conditions for the latter. The CFD analysis successfully identified the root causes of the NGV damage pattern and mid-span cracking, i.e., the hot streaks from the combustor and inadequate internal cooling.

The effect of hot streaks from a gas turbine combustor on the thermodynamic load of internally air-cooled nozzle guide vanes (NGVs) and shrouds has been numerically investigated under flight conditions. The study follows two steps: one for the high-fidelity 60° combustor sector with simplified ten NGVs and three thermocouples attached; and the other for the NGV sectors where each sector consists of one high-fidelity NGV (probe NGV) and nine dummy NGVs. The first step identifies which NGV has the highest thermal load and provides the inlet flow boundary conditions for the second step. In the second step, the flow fields and thermal loads of the probe NGVs are resolved in detail.With the systematically validated physical models, the two-phase flowfield of the combustor-NGVs sector has been successfully simulated. The predicted mean and maximum temperature at the combustor sector exit are in excellent agreement with the experimental data, which provides a solid basis for the hot-streak effect investigation. The results indicate that the second NGV, looking upstream from left, has the highest thermal load. Its maximum surface temperature is 8.4% higher than that for the same NGV but with the mean inlet boundary conditions, and 14.1% higher than the ninth NGV. The finding is consistent with the field-observed NGV damage pattern. To extend the service life of these vulnerable NGVs, some protection methods should be considered.

MCrAl (M = Fe, Ni, or Co) alloys have exceptional corrosion and oxidation resistance and can be used as both oxidation resistant structural materials and coatings. As coatings, they protect high temperature steels or Ni based alloys by forming a dense alumina layer on the surface and thus impeding further oxidation. In order to assess its potential usage as an overlay coating on components used in supercritical water-cooled nuclear reactors (SCWRs), an Fe-2 3Cr-5Al alloy in the form of wire was tested under two different super-heated steam (SHS) conditions (625 °C and 800 °C) and also in supercritical water (SCW) (625 °C and 26 MPa), for 500 h. The corrosion behavior of samples was assessed by measuring the weight change per unit surface area and by examining the surface, cross-sectional microstructure and the phase compositions using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The tested samples showed different oxidation behavior after exposure to these three conditions. SEM and XRD results showed that FeCrAl has the ability to form protective Al- and Cr-containing oxide(s) under all three conditions. Based on the findings, it is concluded that the oxidation behavior of Fe–23Cr–5Al is highly influenced by pressure and temperature within the range of testing conditions. SHS exposure at low temperature led to greater weight gain while that in SCW resulted in weight loss. Overall, its performance is better under SHS conditions compared to CoCrWC S16 but worse under the SCW condition.

The accurate evaluation of the aero-thermodynamic working environments of gas turbine critical components is essential in the development of advanced gas turbine engines, such as cooling flow arrangement and service life assessment. In this chapter, as a technology demonstration, the conjugate heat transfers of the internally air-cooled nozzle guide vane (NGV) and shrouds of a gas turbine engine at flight conditions are numerically examined. The simulations are performed with a high-fidelity CFD model and adequately defined boundary conditions. The effect of the non-dimensional distance from wall surfaces, y+, on the wall temperature is studied. The characteristics of the complex three-dimensional flow and temperature fields are revealed, and the heat fluxes between the hot gas, NGV body, and cooling airflow at selected cross sections are presented and discussed. It is clear that the traditional one-dimensional semiempirical approach is no longer suitable. Generally, the Mach number is higher, and the temperature is lower on the NGV suction side than on the pressure side. It is found that two high-temperature zones occur on the NGV pressure side and the temperature over the middle section is relatively low. These findings are related to where the cooling holes and outlets are located and consistent with the field observation of NGV damages.