Gas Turbine Components Research Articles

Temperature uniformity characteristics of array jet impingement cooling with the maximum cross-flow scheme

Temperature uniformity of the impingement cooling is commonly needed in many fields in order to enhance performance, reliability, and to ensure material quality. In particular, operating life of the hot components in gas turbine depends heavily on how uniformly they are being cooled to mitigate the development of thermal stresses. However, there are rather limited literatures addressing these, and the cooling uniformities of jet impingement in extreme conditions, such as the cooling of turbine vane and combustor liner, are seldom discussed. This study focused on the temperature uniformity of array jet impingement cooling with the maximum crossflow scheme, where the detailed distribution of the nonuniformly cooled areas on the target wall, as well as their correlations with the impinging flow field, and the effects of typical geometrical and fluid parameters on the uniformity were investigated. Results indicated that the arising of the high temperature zones and inverse temperature gradient pairs around them, essentially induced by the entrainment vortex and counter rotating vortex pair in the streamwise and spanwise directions respectively, are the sources of temperature nonuniformities over the impingement target surface. Moreover, increasing the impingement Reynolds number or shortening the jet-to-target spacing for higher jet Reynolds numbers could improve the temperature uniformity.

Computational study on subsonic impact resistance of lattice structures in 3D printed thin Ti6Al4V parts

Additive manufacturing (AM) is a set of digital manufacturing processes which is gaining momentum in the industries for its flexibility, versatility and ability to manufacture complex geometries with limited human interaction. It has enabled relatively fast materialization of a conceptualized design for testing, inspecting and examining the components. AM is highly suitable for fabricating functional gas turbine components owing to its low volume production requirements, lightweight components and geometrical complexity requirements. Laser powder bed fusion (LPBF), is the most common form of metal AM method used. The shape complexity attribute of LPBF can be taken advantage of to fabricate lattice-induced gas turbine inlet components prone to hail or bird impact. In this study, a computational approach was implemented to assess the behaviour of thin Ti6Al4V parts induced with a single-layer lattice subjected to projectile impact. Homogenization of lattice structures was carried out in nTopology to shortlist them for impact studies based on Young’s modulus distribution. The impact analysis was performed on eight lattice structures, two of which were derived from topology optimization, along with a solid plate and hollow plate acting as benchmarks for comparison. The high-velocity impact (250 m/s) was simulated using the “Explicit Dynamics” module in Ansys. It was observed that the lattice geometry directly below the impact site influenced the deformation, stress and energy values. It was concluded that lattices such as isotruss, kelvin cell and FCC, which have more struts interfacing with the impact region, tend to show deformation comparable to solid plates (4.89E-04 m). The equivalent stress values were within the material's elastic limit, indicating elastic deformation. The reduction in kinetic energy of the projectile for lattice-induced plates was also comparable with the values for solid plates (68 %). A correlation coefficient of −0.807 was obtained between packing factor and minimum kinetic energy, indicating denser lattices resulted in higher deceleration.

Investigation of the Machinability of GTD-111 Type Nickel-Base Superalloy During Face Milling

In this paper, the authors investigate the effect of technological parameters on the face milling of GTD-111 type nickel-base superalloys. These alloys are among the most difficult to machine and are widely used as a base material for gas turbine components in the aerospace and energy industries. The aim of this paper is to determine, using the Taguchi method, those parameters that have the greatest influence on cutting force and tool wear. A rotary force meter was used to measure the cutting force and cutting torque, and then the inserts used were examined used under a microscope. Results show that feed per tooth has the greatest effect on cutting forces and tool wear. In order to avoid the formation of edge deposits, it is advisable to use higher cutting speeds and compressed air cooling.

An effect of process parameters during wire cut electrical discharge machining of Inconel 738

In the recent days, super alloys especially nickel based materials are used more than 50% of aerospace gas turbine components such as turbine disc, blades etc., It becomes very hard to shape these materials with the use of traditional machining processes due to its improved strength at higher temperature. To overcome the issues faced during conventional machining, the various advanced machining techniques are tried for machining these super alloys. In the present study, Inconel 738 was cut by wire electrical discharge machining using 0.25 mm diameter copper wire. Demineralized water was used as dielectric fluid between tool and workpiece electrode. During the process, voltage, wire feed rate, time of pulse on and pulse off were adjusted at four different values and totally sixteen slots were cut to analyze the machining characteristics. The machined surfaces were tested for its surface finish, rate of material removal and kerf width. The ANOVA was performed using Minitab software to find out the optimized variables and percentage contribution of each parameter in providing the influencing results. Wire feed rate was the most influencing parameter to have the lowest kerf width. As far as Material removal rate, the four parameters were had the significant impact in increasing the MRR. Voltage is the important process parameter to reduce the surface roughness.

Gas path diagnosis method for gas turbine fusing performance analysis models and extreme learning machine

The gas path analysis, which can quantify the performance degradation of gas turbine components, has been extensively applied to the gas path diagnosis. However, the precondition of this method is that the number of measurable parameters for the gas turbine to be diagnosed should not be less than the number of its health factors. In the existing research, this precondition can be guaranteed through common approaches such as screening the degraded components by a model-based prediagnosis process or recognizing the degraded components by using tools such as an ANN or a support vector machine. However, the diagnosis speed, recognition accuracy, and robustness of these approaches need to be improved. Therefore, a diagnosis method fusing the gas path performance analysis model and the extreme learning machine was proposed in this paper and applied to a GE LM2500+SAC gas turbine. The working mechanism of similarity ranking-gas path diagnosis-rationality check was introduced in the fusion method, endowing it with a higher recognition accuracy rate, stronger robustness, and higher diagnostic accuracy.

Effects of critical plasma spraying parameters on microstructure and mechanical properties of LaPO4-8YSZ thick composite coatings

LaPO4-8YSZ composite coatings with a thickness of ∼1 mm have been developed for increasing thermal protection of combustion chamber components in gas turbines and diesel engines. A serious problem concerning the thick coatings is the high residual stress, which results in poor adhesion and low thermal shock resistance. In this study, thick LaPO4-8YSZ composite coatings in different compositions were produced by atmospheric plasma spraying at four different critical plasma spraying parameters (CPSP; 0.83, 0.94, 1.06 and 1.17 kW/Lpm). The effects of CPSP on microstructure, residual stress and mechanical properties of LaPO4-8YSZ thick composite coatings were investigated. The results shows that the porosity of the coatings is decreased with the increase of CPSP from 0.83 to 1.17. The decreasing porosity leads to the increase of Young’s modulus and microhardness of the coatings, while the fracture toughness of the coatings shows a decreasing tendency. The residual stress in the composite coatings increases with increasing CPSP. Correspondingly, the thermal shock resistance of the coatings decreases with the increase of CPSP. The 5 wt% LaPO4-8YSZ composite coating has the lowest residual stress at CPSP 0.83 and it exhibits the longest thermal cycle life at 1000 °C (1355 ± 134 cycles).

Effects of Hole Blockage on Endwall Film Cooling and Vane Phantom Cooling Performances of a Transonic Turbine Vane

Abstract Although the thermal-barrier coating (TBC) can protect the gas turbine components from the hot mainstream gas, it is not uncommon that the TBC partially blocks the film cooling holes during the spraying process. The film cooling hole blockage will alter the coolant flow behaviors and lead to a significant variation in film cooling performance. In this paper, a physical model of blockage holes including two key parameters of blockage ratios (B) and blockage angles (α), was proposed to analyze the effects of hole blockage on endwall film cooling performance, phantom cooling performance of vane pressure side surface (PS), and overall cooling performance. Based on a proposed double-coolant-temperature prediction method, the endwall film cooling effectiveness, phantom cooling effectiveness of the vane PS and area-averaged cooling effectiveness of an actual vane passage were numerically calculated and analyzed, for the common holes and blockage holes (three different blockage ratios of B and three different blockage angles of α) at the similarly realistic operating conditions of a gas turbine. Results indicated the hole blockage is pernicious to endwall film cooling performance, leading to a significant decrement of endwall film cooling effectiveness (up to 30% at B = 0.4), where the decrement magnitudes increase with increasing the blockage ratios (B). Compared to the blockage ratios (B), the effects of blockage angle (α) on endwall film cooling effectiveness are secondary and slight (less than 10% in η). Nonetheless, the hole blockage is beneficial to phantom cooling performance of the vane PS, leading to an obvious enhancement (more than 40%) in area-averaged phantom cooling effectiveness with increasing blockage ratios (B), due to the increase of the local blowing ratio (BReff). The area-averaged cooling effectiveness including endwall film cooling and phantom cooling on PS, decreases with the increase of blockage angle (α), and the benefits of hole blockage in overall cooling performance are negative at α = 20 deg. This suggests that the overlarge blockage ratios and short blockage lengths (correspond to the blockage position near film cooling holes exit or large blockage angle of α), should be utmost avoided during the spraying process of the TBC, otherwise, the film cooling scheme designs, based on the geometry of the pristine holes, may be inefficient.

Digital twin for directional solidification of a single-crystal turbine blade

Single-crystal superalloy turbine blades (TBs) fabricated using directional solidification are key components of aeroengines and gas turbines. Owing to thermal–solutal convection during solidification, such components are susceptible to flow-induced defects such as freckles and/or eutectic accumulation. The formation mechanisms of the above defects are well understood, but reliable theories or empirical laws are unavailable to guide the engineering production process as the thermal–solutal convection is sensitive to the alloy, Bridgeman furnace design, shape and internal structure of the TB, withdrawal parameters, etc. This study proposes a novel method to ‘digitally twin’ the directional solidification of the TB, i.e. to utilise a physically based numerical model to quantitatively simulate the solidification process, including freckle formation and eutectic accumulation. It includes two simulations: one for the global thermal field in the Bridgeman furnace, including the casting system, and the other for the flow and solidification within the casting component. The former is modelled using ProCAST, the latter is modelled using a volume-average-based multiphase solidification model, and both are coupled. To verify the digital twin concept, an actual industrial TB with slight geometrical modification (removal of the fins while maintaining the inner surface profile) was cast in a Bridgman furnace, and the as-solidified TB was inspected for freckles. An excellent agreement between the simulation and experimental results was obtained. Typically, an actual TB features a complex inner structure (fins) that connects the front and back blades with an average wall thickness of 1.5 mm. A fresh simulation was performed for the TB with inner fins. It was observed that the inner fins of the TB along with other process conditions, such as the shadowing effect of the furnace, play an important role in freckle formation. This study demonstrates the necessity of the digital twin in future TB production.

Modelling and validation of surface roughness in micro-turned nickel-based alloys (Nimonic 90)

Nickel-based alloys (Nimonic 90) are one of the most used materials for aircraft parts, gas turbine components and fasteners due to their inherent properties such as high strength at elevated temperature, good corrosion resistance, high stability, high wear resistance and low thermal conductivity. Because of the above-mentioned properties, Nimonic 90 alloy is difficult to machine, and the roughness obtained by machining of nimonic alloy is comparatively rough. The existing theoretically developed mathematical equations for roughness measurement do not consist of all the machining parameters. It lacks some of the effective roughness parameters such as depth of cut, spindle speed and cutting-edge angle. This article proposes a novel mathematical/geometrical model for the prediction of surface roughness using fundamental geometrical properties of tool and workpiece. For developing the mathematical model, the nose radius of the cutting tool insert is assumed as a straight line (arc length). The principal cutting-edge angle is introduced in the geometrically developed novel model. The developed mathematical/geometrical model comprises mainly depth of cut, principal cutting-edge angle, nose radius, spindle speed and feed. In micro turning, surface roughness increases with an increase in feed and depth of cut. A rough surface, compared to conventional turning, is produced while micro turning due to edge ploughing and rubbing when the chip thickness is lesser than the edge radius. This model is validated by conducting micro-turning experiments on nickel-based superalloy (Nimonic 90) using aluminium titanium nitride physical vapour deposition coated tungsten carbide micro inserts. The surface roughness is significantly affected when the cutting-edge comes in contact with the workpiece; it is because of the imperfect geometry of the nose of the cutting tool. A slight variation of surface roughness with the depth of cut has also been observed. A good correlation is observed between the predicted and experimentally measured roughness values.

Effect of two-step heating transient liquid phase bonding on microstructure and mechanical behaviour of IN-738LC gas turbine components

The long isothermal solidification and homogenization time is the major concern in repairing turbine parts by the conventional transient liquid phase method. In this study, microstructure and morphology of the proposed two-step heating transient liquid phase joints were compared to results of the conventional ones conducted at the same temperature. After the isothermal solidification, deleterious precipitates such as Ni3Si, Ni3B and CrB were removed. The application of the two-step technique increased the shear strength of the joints up to 28% (516–674 MPa) due to collision of two non-planar interfaces and formation of the longer bonding line. The shear fracture surfaces of all bonds with the complete isothermal solidification stage represent a dimple pattern that is characterized by ductile fracture. The stress-rupture life of the joint at 982 °C was about 85% of the superalloy service life at this temperature.

Aviation, energy, exergy, sustainability, exergoenvironmental and thermoeconomic analyses of a turbojet engine fueled with jet fuel and biofuel used on a pilot trainer aircraft

In this study, J69 military turbojet aero engine of Cessna T-37B/C pilot trainer aircraft fueled by jet fuel and %100-biofuel is assessed with aviation, energy, exergy, sustainability, exergoenvironment and thermoeconomic perspectives to show the reliability of the biofuel in terms of various aspects. The methyl-oleate (C19H36O2) is selected as a model substance for biodiesel for this study, because it is similar to the C:H:O ratio of the commercial biodiesel. J69 turbojet engine's exergy efficiency increases from 17.058% to 17.103% by using biofuel instead of jet fuel. J69 engine's environmental effect factor rises from 5.261 to 5.299 by the utilization of biofuel. Sustainability index reduces 1.463% for the combustion chamber component, 1.201% for the gas turbine component and 0.735% for the overall J69 engine by using biofuel instead of jet fuel. Fuel cost rates of the jet fuel mode is found as 533.355 $/h, while this cost of the biofuel mode is determined to be 846.058 $/h for take-off operation mode. Thereby, fuel cost of biofuel is higher than jet fuel. Specific exergy cost of jet fuel is determined as 20.14 $/GJ, while it is found as 31.667 $/GJ for biofuel. Results of the biofuel and jet fuel modes are close to each other. Thus, biofuel can be considered as a sustainable aviation fuel for J69 military turbojet engine used on the Cessna T-37B/C pilot trainer aircraft.

Abrasive Water Jet Milling as An Efficient Manufacturing Method for Superalloy Gas Turbine Components

In order to improve efficiency when manufacturing gas turbine components, alternative machining techniques need to be explored. In this work, abrasive water jet (AWJ) machining by milling has been investigated as an alternative to traditional milling. Various test campaigns have been conducted to show different aspects of using AWJ milling for the machining of superalloys, such as alloy 718. The test campaigns span from studies of individual AWJ-milled tracks, multi-pass tracks, and the machining of larger components and features with complex geometry. In regard to material removal rates, these studies show that AWJ milling is able to compete with traditional semi/finish milling but may not reach as high an MRR as rough milling when machining in alloy 718. However, AWJ milling requires post-processing which decreases the total MRR. It has been shown that a strong advantage with AWJ milling is to manufacture difficult geometries such as narrow radii, holes, or sharp transitions with kept material removal rates and low impact on the surface integrity of the cut surface. Additionally, abrasive water jet machining (AWJM) offers a range of machining possibilities as it can alter between cutting through and milling. The surface integrity of the AWJM surface is also advantageous as it introduces compressive residual stress but may require post-processing to meet similar surface roughness levels as traditional milling and to remove unwanted AWJM particles from the machined surface.

Amplitude and Wavelength Effects for Wavy Channels

Abstract To improve the efficiency and durability of gas turbine components, advancements are needed in cooling technologies. To accomplish this task, some manufacturers are turning to additive manufacturing (AM), as it offers the ability to both rapidly iterate on component design as well as incorporate unique internal cooling structures directly into parts. As one example, wavy microchannels can be readily integrated into turbine components. This study investigates wavy channels of varying channel amplitude and wavelength through experimental measurements of heat transfer and pressure loss. In addition to experimental testing, computational fluid dynamics (CFD) predictions were made to identify internal flow features that impacted performance. Five channel geometries were integrated into test coupons that were additively manufactured out of Hastelloy-X using direct metal laser sintering. True coupon geometric characteristics and wall roughness values were captured non-destructively using computed tomography (CT) scans. Geometric analyses indicated that coupons were reproduced accurately with minimal deviation from design intent. Experimental results indicated that decreasing the channel wavelength and increasing the channel amplitude resulted in substantial increases in both bulk friction factor and Nusselt number with respect to the nominal case and were scaled using a relative waviness parameter. CFD simulations predicted significant mixing of flow in the cases with the smallest wavelength and greatest amplitude.

Interaction of Gd2Si2O7 with CMAS melts for environmental barrier coatings

Environmental barrier coatings (EBCs) prevent the oxidation of ceramic matrix composites (CMC), which are used as components in gas turbines. However, EBCs deteriorate more rapidly in real environments, molten silicate deposits accelerate the deterioration of EBCs. In this study, high-temperature behavior sintered Gd2Si2O7 with calcia-magnesia-alumina-silica (CMAS) melt at 1400 °C for 0.5, 2, 12, 48, and 100 h was investigated. HT-XRD results showed that at 1300 °C, CMAS and Gd2Si2O7 chemically reacted to form Ca2Gd8(SiO4)6O2 (apatite). The reaction layer became thicker as the heat-treatment time increased, and the thickness of the reaction layer has increased following a parabolic curve. With the extension of the reaction time from 0.5 to 100 h, the thickness of the reaction layer increased from approximately 98 to 315 µm. It was confirmed that Ca2Gd8(SiO4)6O2 grew vertically on the Gd2Si2O7 surface. Vertical and horizontal cracks were found after reacting at 1400 °C for 100 h, but no interfacial delamination occurred in this study. In addition, the effects of CaO:SiO2 molar ratios, monosilicates (RE2SiO5) and disilicates (RE2Si2O7), heat-treatment time, and cation size were determined and compared with the results of previous studies (Gd2SiO5, Yb2SiO5, and Er2Si2O7).

Numerical Investigation on the Cooling Effectiveness and Pressure Loss of a Novel Laminated Cooling Configuration With Cellular Partition

Abstract The laminated cooling is believed to be a promising cooling scheme for the next generation of advanced gas turbines. In order to build a cooling system with high performance, it is necessary to develop a more revolutionary cooling configuration for hot components in gas turbines. In this study, a novel laminated cooling configuration with cellular partition has been proposed. The local/average heat transfer parameters and pressure loss coefficient have been evaluated by comparing with traditional laminated cooling configurations with and without circular pin. Different adiabatic and conjugate cooling configurations are explored numerically to investigate the external film coverage and internal heat transfer. Seven different flow conditions with blowing ratios ranging from 0.2 to 1.4 are investigated for all numerical models. Results indicate that the novel laminated cooling configuration exhibits a higher cooling advantage. With the blowing ratios investigated, the cooling effectiveness of laminated cooling configuration with cellular partition increased by 4.5–13.4% and 10.8–23.4% compared with the cases with and without circular pin, respectively. With higher cooling performance, the pressure loss coefficient only increased by 4.4%. Two mechanisms have been identified for heat transfer enhancement of the novel laminated cooling configuration: (1) the cellular partition increases the transverse diffusion of film cooling outflow resulting in an increased external film cooling effectiveness and (2) the film hole area and partition area have been increased in the new structure, which enhances the internal heat transfer. The proposed structure has the potential for cooling the high-pressure turbines in the future.

Review of Film Cooling in Gas Turbines with an Emphasis on Additive Manufacturing-Based Design Evolutions

Film-cooling technology is used in high-temperature components of gas turbines to extend their service lives. Hot-gas path components are susceptible to damage or failure in the absence of film cooling. Much of the optimization research efforts have been focused on film hole shapes, heat/mass transfer measurement techniques, and film cooling performance under various mainstream and coolant side operating conditions. Due to recent rapid advancements in the areas of measurement techniques (e.g., pressure-sensitive paints and fast high-resolution imaging) and metal additive manufacturing (AM), film cooling technology has undergone significant changes and shows potential new development. In this review, a historical perspective is discussed covering over five decades of innovation: the geometrical effects from injection angle and hole shapes; flow effects from density ratio, momentum-flux ratio, blowing ratio, advective capacity ratio, and freestream conditions; and more items related to AM. The impact of AM on film hole design strategies, the challenges posed by state-of-the-art AM technology, and pathways for future research are discussed. A comparative analysis of AM assisted film hole fabrication and conventionally manufactured film holes is elaborated.

A Comprehensive Study of Ceramic Matrix Composites for Space Applications

Ceramic matrix composites (CMCs) have grown in popularity as a material for a range of high as well as protection components, increasing the need to better understand the impacts of multiple machining methods. It is primarily composed of ceramic fibers embedded in the matrix. Ceramic materials, especially carbon fibers and carbon were used to create the matrix and fibers. These ceramics include a huge variety of non-metallic inorganic materials that are regularly utilized under high temperatures. The aircraft industry became revolutionized by this unique combination of materials, which made parts better resistant under extreme conditions as well as lighter than the earlier technology. The development, properties, and production of ceramic matrix composites, as well as space applications, are discussed in this article. Ceramic materials have an interesting set of properties, including great strength and stiffness under extremely high temperatures, chemical inertness, low density, etc. In CMC, ceramics are used in the matrix as well as reinforcement. The matrix material keeps things running smoothly while the reinforcement delivers unique special properties. Ceramic matrix composites are developed for applications that required high thermal and mechanical characteristics, which include nuclear power plants, aircraft, chemical plants, space structures, and transportation services. Even though advanced aircraft relies on high-performance propulsion systems, improving the total impulses over the total mass ratio for rocket engines becomes essential for improving their performance that demands reduced engine structural weight as well as higher component heat resistance. The evolution of new ultra-high-temperature composites having high-temperature resistance as well as low density that a substitute super alloy and refractory metal material has become so essential and laid the foundation for high-performance engine design. The benefits of continuous fiber- reinforced CMC with high-temperature engine designs have long been recognized as a better measure of a country’s ability to design and produce spacecraft, modern aircraft, and weapons. Ceramic matrix composites materials are used in various aircraft type engines, aircraft brake disks, high-temperature gas turbines components, slide bearing components, hot gas duct, flame holders and components for burners are made by using oxide CMCs.

Creep detection of Hastelloy X material for gas turbine components with nonlinear ultrasonic frequency modulation

Creep damage is one of the main failure modes in hot-gas‑leading components in gas turbines, which results from high temperatures along with mechanical loads. The aim of this study is to clarify the metallurgical creep behaviour of the Hastelloy X material and detect and evaluate creep damage at an early stage with a nonlinear ultrasonic modulation technique. For this purpose, multiple samples were examined to demonstrate that pores and microcracks in grain boundaries spread from the outside to the inside. Inside the specimen, molybdenum was identified as the main precipitation element. In addition, the chromium diffusion in the outer areas led to the depletion of this element and favoured the formation of pores and microcracks. Failures were proven with nonlinear dual-frequency ultrasound technology. Moreover, two different longitudinal waves were sent into the samples to use harmonic and modulated response frequencies for evaluation. As a result, harmonic frequencies offered a favourable prediction of pore sizes, whereas defined sideband frequencies reacted very sensitively to the damage density and area distribution of the failures. This study offers a method for detecting creep damage with nonlinear ultrasound techniques at an early stage as well as for differentiating between pores, microcracks, dislocations and precipitation. Therefore, the design of future gas turbine components made of Hastelloy X can be adapted with regard to the shown metallurgical behaviour and damage signatures.

Self-coupling: an effective method to mitigate thermoacoustic instability

The presence of undesirable large-amplitude self-sustained oscillations in combustors resulting from thermoacoustic instability can lead to performance loss and structural damage to components of gas turbine and rocket engines. Traditional feedback controls to mitigate thermoacoustic instability possess electromechanical components, which are expensive to maintain regularly and unreliable in the harsh environments of combustors. In this study, we demonstrate the quenching of thermoacoustic instability through self-coupling—a method wherein a hollow tube is used to provide acoustic self-feedback to a thermoacoustic system. Through experiments and modeling, we identify the optimal coupling conditions for attaining amplitude death, i.e., complete suppression of thermoacoustic instabilities, in a horizontal Rijke tube. We examine the effect of both system and coupling parameters on the occurrence of amplitude death. We thereby show that the parametric regions of amplitude death occur when the coupling tube length is close to an odd multiple of the length of the Rijke tube. The optimal location to place the coupling tube for achieving amplitude death is near the antinode of the acoustic pressure standing wave in the Rijke tube. Furthermore, we find that self-coupling mitigates thermoacoustic instability in a Rijke tube more effectively than mutual coupling of two identical Rijke tubes. Thus, we believe that self-coupling can prove to be a simple, cost-effective solution for mitigating thermoacoustic instability in gas turbine and rocket combustors.

Thermo-mechanical approach to study the residual stress evolution in part-scale component during laser additive manufacturing of alloy 718

Laser Additive Manufacturing (LAM) is a promising technology for manufacturing gas turbine components with enhanced design capability and a significant reduction in part weight. Additive manufacturing of alloy 718 using Laser Powder Bed fusion (L-PBF) process poses certain challenges pertaining to complex residual stress, micro-segregation of Nb, and undesired Laves phase formation in the as-printed state. The built-up residual stress and undesired brittle phase may lead to cracks and build failures. This article studied residual stress evolution during L-PBF of alloy 718 using Finite Element (FE) thermo-mechanical simulation implemented in Simufact Additive® software. The model adopted the bundling of physical powder in voxel mesh to minimize the computational time and mimic the actual process scenario during part-scale simulation. Experimental flow curves generated from Gleeble 3800® tests at elevated temperatures were utilized to calibrate material property for better accuracy in the FE simulation. The calibrated model was used to study the residual stress evolution during support structure removal. Verification and validation of simulated results were performed using X-ray diffraction (XRD) measurements. The simulated value agrees well with the experimental value with a maximum deviation of 7%. Finally, the experimentally validated model was used to correlate the effect of layer thickness variation on residual stress evolution.