Gas Turbine Hot Section Components Research Articles

Prediction of thermo-mechanical performance for effusion cooling by machine learning method

Fast and accurate evaluation of performance of cooling structures is very critical to the design of hot-section components in gas turbines. In the present study, machine learning method was developed to predict thermo-mechanical performance for effusion cooling on flat plate. The geometric and thermodynamic parameters including blowing ratio, density ratio, hole inclination angle, hole pitch and spacing were studied. Latin hypercube sampling was used for the design of numerical experiments, and the data sets for training model were generated by computational fluid dynamics (CFD) solutions. A kind of deep neural networks (DNNs) was used to predict the distributions of solid temperature and stress. Based on the outputs of neural network, the effects of the geometric and thermodynamic parameters on thermo-mechanical performance were investigated in detail. The results show that thermal stress decreases with the increases of density ratio and blowing ratio, while the increases of hole spacing and pitch cause the increase of thermal stress. Compared with the CFD results, the proposed DNN method has mean absolute percent error of 0.5% and 0.08% and root mean square error of 6.95 K and 5.1 MPa as applying for predicting solid temperature and stress. On the whole, machine learning is a promising method for modelling effusion cooling with high accuracy.

Interaction of crack-tip constraint and welding residual stresses on the fracture behavior of Ni-based alloy

The present paper aims to study the effect of crack-tip geometrical constraints and welding residual stresses (WRS), as well as their interaction on fracture behavior of IN939 superalloy, which is widely used in gas turbine hot section components, such as turbine vanes. For the thermal–mechanical simulation of welding processes, a finite element (FE) model was developed, and the predicted WRS was verified through experiments. Two welding paths and two mechanical boundary conditions were considered to develop four different WRS distributions within the same geometry. These results were mapped to the validated fracture finite element models. By varying the loading conditions, two sets of specimens with high and low geometrical constraints were achieved in the same geometry. Two-parameter fracture mechanics analyses were then used to examine the effects of four WRS profiles and geometrical constraints on the fracture behavior of each set. Generally, the impact of WRS is more evident in specimens with lower geometrical constraints. The fracture behavior might be unexpectedly affected if the WRS changes from tensile to compressive near the crack tip. Using the maximum stress triaxiality factor, it was shown that the fracture behavior as a function of WRS is better demonstrated than that of the Q-constraint parameter.

Interfacial peeling loads in the TBC with an air hole: Analytical solutions and viscoplasticity modelling

This work evaluates the temperature field, stresses, and peeling loads in thermal barrier coatings (TBCs) with air holes subjected to cyclic thermo-mechanical loads during a complete flight. Analytical formulae for the steady-state temperature field and interfacial peeling loads are developed considering thermal gradients in the thickness and longitudinal directions. In addition, viscoplasticity finite element modelling is conducted for the mechanical behaviors of the TBC system. A unified Chaboche-Lemaitre constitutive model that combines a power flow rule with non-linear anisothermal evolution of isotropic and kinematic hardening is integrated into the numerical framework. The results show tensile peeling stress and shear stress are generated in the vicinity of the hole, which motivates the initiation and propagation of hole-edge cracks. The maximum peeling and shear stresses locate close to the thermally grown oxide/bond coat interface and they increase with increasing hole radius. The interfacial peeling moment and shear force could characterize edge cracking in TBCs. As the hole radius increases, the interfacial peeling moment and shear force increase quickly when the hole radius is less than 1 mm but remain stable when the hole radius is beyond 2 mm. This work not only helps to explain the failure mechanisms of hole-edge delamination and spallation in TBCs but also guides the design of thermal barrier coated hot-section components in gas turbines.

Silicate ash-resistant novel thermal barrier coatings in gas turbines

Gas turbines, used to propel aircraft or generate electricity, are vulnerable to attack by environmental silicate debris. When silicate ash is ingested into gas turbines, it melts and may adhere to the hot-section components of gas turbines (typically operating at > 1250 °C), infiltrating into their thermal barrier coatings (TBCs). These ash-related TBC issues pose a critical hazard for aircraft aviation. Here, we have developed here a novel NdYbZr2O7 coating substrate which addresses these challenges. We have quantitatively analyzed the in-situ wetting process of three representative silicate ash compositions—CMAS, volcanic ash and fly ash, and compare their infiltration behavior in the newly-developed NdYbZr2O7 coating substrate. The widely differing chemical compositions of the three ash samples yield differences in their high temperature viscosities which in turn impact their respective propensities for wetting and infiltration. CMAS exhibits the greatest dynamic wettability due to its lower viscosity over the entire range of temperature. Volcanic ash exhibits the largest infiltration depth, probably related to the relatively high solubility of rare-earth oxides (RE2O3) in volcanic ash melt. Nevertheless, compared with a traditional YSZ coating, the NdYbZr2O7 coating exhibits a better corrosion resistance in the presence of all three silicate ash samples due to the rapid precipitation of (Nd, Yb)-apatite and c-ZrO2 phases, which build a dense reaction layer, inhibiting further melt infiltration.

Microstructure of IN738LC Fabricated Using Laser Powder Bed Fusion Additive Manufacturing

Abstract Nickel-base superalloys are extensively used in the production of gas turbine hot-section components as they offer exceptional creep strength and superior fatigue resistance at high temperatures. Such improved properties are due to the presence of precipitate-strengthening phases such as Ni3Ti or Ni3Al (γ′ phases) in the normally face-centered cubic (FCC) structure of the solidified nickel. Although this second phase is the main reason for the improvements in properties, the presence of such phases also results in increased processing difficulties as these alloys are prone to crack formation. In this work, specimens of IN738LC are fabricated on a Coherent Creator laser powder bed fusion (L-PBF) additive manufacturing (AM) equipment. Optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) are carried out to characterize the deposit region. Metallurgical continuity is achieved in the entire deposit region and the specimens do not show any warpage. However, the specimens show voids (e.g., pores and cracks) in the deposit region. The results show that the percentage void area decreases along the build height direction. The deposited IN738LC shows polycrystalline grains in the entire deposit region as confirmed by XRD and EBSD. The grain size also shows variations along the build direction. In summary, the results open opportunities for academic researchers and small-scale businesses in fabricating high-γ′ nickel-base superalloys on a desktop laser powder bed fusion AM equipment.

Evolution behavior of liquid film in the heat-affected zone of laser cladding non-weldable nickel-based superalloy

Laser cladding with a paraxial powder-feeding device was used to repair as-cast K447A nickel-based superalloy, a kind of non-weldable alloy with a high Hf content and working as gas-turbine hot-section components. In the present study, the metallurgical evolution behavior of liquid film and liquation cracking mechanisms are studied. The results showed that a kind of uncommon Ni21Hf8 phase was found in the incipient melting regions (IMR) of the intergranular region. In the thermal cycle, γ/Ni21Hf8 eutectic liquefaction, M5B3 dissolved, and γ/γ’ eutectic liquefaction successively occurred in the heating process in IMR, and liquid → γ + γ/γ’ + M5B3 + γ/Ni21Hf8 → γ + γ’(3) + γ/γ’ + γ/Ni21Hf8 + M5B3 occurred in the cooling process. The inhomogeneity of the intergranular structure leads to the liquid film with the characteristics of discontinuous distribution and uneven width. The cracking criterion of the liquid film was established based on pressure drop. When the closed liquid film meets the condition of 2γsl<1/K*(ρs/ρl−1*R*dt+∆hε), the liquid film with a thickness that is greater than critical thickness will be induced into a liquation cracking.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ТЕХНОЛОГИИ ПРОИЗВОДСТВА МАГНЕТРОННЫХ МИШЕНЕЙ НА МИКРОСТРУКТУРУ И ФАЗОВЫЙ СОСТАВ СПЛАВА СИСТЕМЫ Zr–Y

The Zr–Y-based alloy targets are used for spraying of heat-resisting ceramic coatings on the gas-turbine hot section components surface by the plasma-chemical deposition techniques. The comparative study of the microstructure and phase composition for target specimens, which manufactured by vacuum-induction melting or vacuum-arc melting, are performed. The patterns of change in a microstructure and a phase composition in the experimental Zr–Y-based alloy, depending of manufacturing technology are shown. The aspects which have led to transformation of microstructure and phase composition of VTsM-1 Zr–Y-based alloy at the change of the manufacturing technology of targets are detected.

Wear Characteristics of Superalloy and Hardface Coatings in Gas Turbine Applications–A Review

In the gas-turbine research field, superalloys are some of the most widely used materials as they offer excellent strength, particularly at extreme temperatures. Vital components such as combustion liners, transition pieces, blades, and vanes, which are often severely affected by wear, have been identified. These critical components are exposed to very high temperatures (ranging from 570 to 1300 °C) in hot-gas-path systems and are generally subjected to heavy repair processes for maintenance works. Major degradation such as abrasive wear and fretting fatigue wear are predominant mechanisms in combustion liners and transition pieces during start–stop or peaking operation, resulting in high cost if inadequately protected. Another type of wear-like erosion is also prominent in turbine blades and vanes. Nimonic 263, Hastelloy X, and GTD 111 are examples of superalloys used in the gas-turbine industry. This review covers the development of hardface coatings used to protect the surfaces of components from wear and erosion. The application of hardface coatings helps reduce friction and wear, which can increase the lifespan of materials. Moreover, chromium carbide and Stellite 6 hardface coatings are widely used for hot-section components in gas turbines because they offer excellent resistance against wear and erosion. The effectiveness of these coatings to mitigate wear and increase the performance is further investigated. We also discuss in detail the current developments in combining these coating with other hard particles to improve wear resistance. The principles of this coating development can be extended to other high-temperature applications in the power-generation industry.

Investigation on the formation of grain boundary serrations in additively manufactured superalloy Haynes 230

Solid-solution and carbide-strengthened superalloys such as Haynes 230 are the materials of choice for the hot-section components of gas turbines, e.g., combustion cans and transition ducts. Under severe thermal conditions, to which those parts are exposed, creep strength is a crucial property of the related materials during their lifetime. Recently, the introduction of serrated grain boundaries in Haynes 230 has been intensively studied [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, “Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,” Mater. Charact. 101, 49–57 (2015); L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, “The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,” Mater. Sci. Eng. A 536, 37–44 (2012)], and nearly a triplication of the time to creep failure at high temperature and low stress conditions has been observed [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, “Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,” Mater. Charact. 101, 49–57 (2015)]. The aim of this paper is to achieve serrated grain boundaries in Haynes 230 through an appropriate thermal process chain including the intrinsic heat treatments of the laser metal deposition (LMD) process, subsequent hot isostatic pressing and suitable heat treatments. The formation of serrations is a relatively new technique for Haynes 230 (i.e., first paper in 2012), and similar alloys and thus serrations have only been introduced in conventionally cast or wrought alloys so far. Optical and scanning electron microscopies are employed in this work to investigate the created microstructures, whose grain and carbide structure is finer compared to the recently studied conventionally processed alloys. Within the LMD samples, serrations were already found on almost all of the observed grain boundaries even in the as-build condition. This result was rather unexpected, as literature reports slow-cooling to be responsible for the formation of serrations, while fast-cooling is prevalent in LMD. Some authors associated the formation of serrations to the precipitation of M23C6-carbides at the grain boundaries during slow cooling conditions [L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, “The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,” Mater. Sci. Eng. A 536, 37–44 (2012)]. The lower density of carbides along grain boundaries in the as-build state, however, makes this mechanism seem unlikely. Other authors attributed the emergence of serrations to a phenomenon similar to the faceting mechanism [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, “Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,” Mater. Charact. 101, 49–57 (2015)]. It can be said that no uniform theory for the emergence of grain boundary serrations exists as of now. The electron backscatter diffraction (EBSD) investigations performed in this work indicated a correlation between serrated grain boundary segments, the {111}-directions of the crystal lattice, and possibly segregations along dendritic subgrain boundaries for a two-dimensional case. Serial sectioning in combination with EBSD analysis confirmed an agreement between the three-dimensional orientation of serrated grain boundary segments and the {111}-direction of adjacent grains. Hence, a mechanism different from the ones described in previous works is proposed for the formation of grain boundary serrations in the additively manufactured Haynes 230 alloy.

The addition of zirconium to aluminide coatings: The effect of the aluminide growth mode

Alumina-former coatings such as nickel aluminides have been the essential approach to combating the aggressive service environment of gas turbine hot section components. The positive effects of zirconium on the cyclic oxidation lifetime of aluminide coatings have been reported. The current paper has reported the effect of the growth mode of the aluminide coating on the microstructure of the Zr-modified aluminide coating. The aluminization process was carried out using the halide activated pack cementation process in the powder mixtures of aluminum, ammonium chloride, zirconium oxide, and alumina at 760 and 1040 °C for the inward and outward growth, respectively. The microstructures of the coatings were studied using FESEM, EDS and XRD. The results showed that the outward coatings contain a high level of Zr mainly incorporating it in the second phases such as AlNi2Zr in a matrix of NiAl. In contrast, the Zr concentration in the inwardly grown aluminide coatings did not exceed the 1 atomic percentage and the typical microstructure of the high activity aluminide coatings was observed. The chemical reactions involved in the pack cementation process and the mechanism of the coating formation were discussed.

Qualitative phenomenological investigation of the transient temperature gradient during gas turbine's hot section component cooling

In this study, the temporal variation of temperature gradient in the gas turbine hot section components in the transient process is raised, and according to its impact on life expectancy computations, the accuracy of the usual methods is investigated qualitatively. It is worth noting that in such two-phase problems, existing different time-scales prevent some common simplifications that are usually used for unsteady investigations like a quasi-steady assumption, and so there is no choice but to conduct coupled transient studies despite their high time-consuming manner. Hence, the phenomenological and qualitative model is introduced to analyze the cooling problem and show the transient behavior. The results show that during unsteady operations, if the time rate of changes is high, some considerable overshoots (more than 30%) of temperature gradients in hot sections may be ignored in common quasi-steady predictions, which must be predicted only by using the unsteady and coupled simulations.

Influence of heat treatment on microstructures and mechanical properties of K447A cladding layers obtained by laser solid forming

Laser solid forming employing a paraxial powder-feeding system was developed to repair gas-turbine hot-section components composed of the non-weldable nickel-based superalloy K447A. In the present study, hot isostatic pressing, solid solution, and double-aging heat treatments were applied to research the influence of heat treatments on the forming characteristics, microstructural characteristics, and tensile properties of cladding zones obtained by laser solid forming. The results showed that cladding layers (CLs) without hot cracking or blowholes were obtained after heat treatment. Shrinkage elimination and γʹ precipitate growth were observed, MC-type carbides precipitated from the solidification grain boundary (SGB) and partly transformed into M23C6-type carbides in the CL. The hardness in CLs became uniform and nearly equal to that of the base metal (BM). The strength of the heat-treated half-BM, half-CL (HBC) specimen was nearly equal to that of the heat-treated BM specimen, but the elongation of the HBC specimen was reduced by ∼40%. In the BM side of the HBC specimen, cracks initiated at script-like carbides and extended along the grain boundaries, while in the CL side, cracks extended along the SGB with massive granular carbides, which reduced the elongation of the HBC specimen.

Experimental and Numerical Analysis of Additively Manufactured Coupons With Parallel Channels and Inline Wall Jets

Present paper developed a series of additively manufactured parallel cooling channels with streamwise wall jets inside, which could be suitable for double-wall and near-wall cooling configurations in gas turbine hot section components. The tested coupons consisted of parallel channels, each channel further divided into small chambers using several spanwise separation walls. Height of these walls was kept less than channel height, thus forming a slot with one of the end walls. Coolant entered from one side of channel and formed streamwise wall jet while crossing through the slot over to the downstream chamber. The test coupons were additively manufactured by selective laser sintering (SLS) technique using Inconel 718 alloy. Steady-state heat transfer experiments with constant wall temperature boundary condition were performed to analyze effect of pitch between subsequent slots and blockage ratio (ratio of separation wall height to channel height) on heat transfer. The channel Reynolds number ranged from 1800 to 5000. Numerical simulations were performed using ANSYS cfx solver with SST k–ω turbulence model to obtain detailed understanding of existing flow field. Experimental results showed heat transfer enhancement of up to 6.5 times that of a smooth channel for the highest blockage ratio of 0.75. Numerical results revealed complex flow field which consisted of wall jets along with impingement, separation, and recirculation zones in each chamber. For all configurations, gain in heat transfer was accompanied with high pressure drops. However, coupled with the high heat transfer, this design could lead to potential coolant savings.

Additive Manufacturing of Nickel-Base Superalloy IN100 Through Scanning Laser Epitaxy

Scanning laser epitaxy (SLE) is a laser powder bed fusion (LPBF)-based additive manufacturing process that uses a high-power laser to consolidate metal powders facilitating the fabrication of three-dimensional objects. In the present study, SLE is used to produce samples of IN100, a high-γ′ non-weldable nickel-base superalloy on similar chemistry substrates. A thorough analysis is performed using various advanced material characterization techniques such as high-resolution optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and Vickers microhardness measurements to characterize and compare the quality of the SLE-fabricated IN100 deposits with the investment cast IN100 substrates. The results show that the IN100 deposits have a finer γ/γ′ microstructure, weaker elemental segregation, and higher microhardness compared with the substrate. Through this study, it is demonstrated that the SLE process has tremendous potential in the repair and manufacture of gas turbine hot-section components.

Microstructures and Microhardness Properties of CMSX-4® Additively Fabricated Through Scanning Laser Epitaxy (SLE)

Epitaxial CMSX-4® deposition is achieved on CMSX-4® substrates through the scanning laser epitaxy (SLE) process. A thorough analysis is performed using various advanced material characterization techniques, namely high-resolution optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction, and Vickers microhardness measurements, to characterize and compare the quality of the SLE-fabricated CMSX-4® deposits to the CMSX-4® substrates. The results show that the CMSX-4® deposits have smaller primary dendritic arm spacing, finer γ/γ′ size, weaker elemental segregation, and higher microhardness compared to the investment cast CMSX-4® substrates. The results presented here demonstrate that CMSX-4® is an attractive material for laser-based AM processing and, therefore, can be used in the fabrication of gas turbine hot-section components through AM processing.

Two-phase flow simulation of mist film cooling with deposition for various boundary conditions

ABSTRACTAir film cooling is a conventional cooling technique that has been successfully used for gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes and blades. However, the increased benefit seems to approach a limit. This paper investigates the film cooling effectiveness considering mist injection. All the studies for various boundary conditions are conducted numerically, including the effects of droplet size, the flow rates of droplet injection, and the coolant air. Film cooling is also affected by the interaction between deposition and mist injection. A deposition configuration is located near the film hole with an inclination angle of 35°. Results show that the combined effect of injection and deposition is to weaken the film cooling effectiveness, especially upstream of x/d = 19. For the coolant air at a low speed, the mist injection cannot provide better cooling protection than without the mist injection.

Microstructure of nickel-base superalloy MAR-M247 additively manufactured through scanning laser epitaxy (SLE)

Abstract Scanning laser epitaxy (SLE) is a laser powder bed fusion (LPBF) based additive manufacturing (AM) process developed for the repair and manufacture of gas turbine hot-section components made of nickel-base superalloys. In the present study, the single-pass fabrication of more than 1500 μm thick deposits of MAR-M247, a non-weldable superalloy atop similar chemistry substrates using a high-power laser beam is demonstrated. Metallurgical continuity is achieved across the entire deposit-substrate interface and the samples show little or no warpage across a broad range of processing parameters. In order to relieve the residual stresses and enable precipitation of the strengthening phases, the SLE-deposited MAR-M247 samples are subjected to a commercially available heat treatment process. Microstructures of the as-deposited and the heat-treated MAR-M247 samples are investigated using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Vickers microhardness measurements. The crack-free deposits obtained here for MAR-M247 represent one of the first few successes reported for a non-weldable alloy of its kind. The results demonstrate that the SLE process has significant potential for the AM-based repair of existing and fabrication of entirely new gas turbine hot-section components utilizing feedstocks of high γ′ content nickel-base superalloy powders. The results also establish that MAR-M247 is an attractive material for the LPBF-based AM processes.

Green Engines: Possible Damages by Firing Alternative Fuels and Protection

With the rising cost of fossil fuels along with greenhouse gas emission such as NOx and COx, use of alternative fuels such as syngas and biofuels is intense interesting, and in the meantime using ceramic matrix composites that eliminate the need of film cooling in combustors, vanes and other hot section components to improve the efficiency of gas turbine engine and reduce the NOx and COx emission becomes increasingly attractive for green engines. However, the alternative fuels have an increased hydrogen/carbon ratio; in turn during combustion it produces more water vapor than the conventional jet fuels. The increased water vapor level will have an impact on the protective oxide scale developed on the gas turbine hot section components, particularly on those made of SiC/SiC ceramic matrix composites (CMC), leading to an accelerated degradation of the turbine components. In addition, some alternative fuels derived from biomass may contain alkali elements such as potassium, sodium and calcium, as well as chlorine, sulfur and/or phosphorus, which may result in possible corrosion of the hot section components in gas turbines, leading to premature failure during service. This paper will review some of the alternative fuels and their combustion products, the possible damages to gas turbine hot section components, as well as some potential protective coatings that may mitigate such damage

Aerodynamics Performance of Endwall Film Cooling under the Influence of Purge Flow in High Pressure Turbine Cascade

Modern gas turbine requires sophisticated cooling technologies to avoid thermal failure due to the extreme operating environment. Film cooling is one of the most important cooling technologies used for gas turbine hot-section components, particularly for blade aerofoil surfaces and endwall. Previous research has shown that the endwall region is considerably more difficult to cool than the blade aerofoil surfaces because of the existence of complex secondary flow structures such as horse-shoe vortex, cross flow and passage vortex in the blade passage. Therefore, this study focuses on aerodynamics interaction of the cooling air through the upstream slot with the secondary flow field. Experiments carried out using 5-holes Pitot tube have revealed the secondary flow field at blade downstream of linear cascade of high pressure turbine. A baseline condition without any leakage flows was compared with the leakage ejection case. Finally, both cases were validated by simulations from commercial software, ANSYS CFX.

Fatigue Properties of Narrow and Wide Gap Braze Repaired Joints

With the increasing utilization of braze repair in the gas turbine industry, the properties of braze joints under simulated service conditions become vital in selecting braze repair over other processes. While braze repair has often been claimed to deliver mechanical properties equivalent to that of the parent material, this is largely based on the results of tensile or accelerated creep tests for most gas turbine hot section components failure occurs as a result of thermal fatigue or thermomechanical fatigue. The damage that occurs under such conditions cannot be assessed from tensile or creep testing. This study was undertaken to characterize the fatigue properties of narrow and wide gap brazed X-40 cobalt-based superalloy and compare these properties to that of the X-40 parent material. Butt joint narrow gap and wide gap specimens were vacuum brazed using BNi-9 braze alloy. X-40 and IN-738 were used as additive materials in wide gap braze joints. To characterize the fatigue properties of the braze joints and parent material, isothermal fatigue tests were conducted at 950°C and under load control using a fully reversed sinusoidal wave form having stress amplitude of 75% of the yield strength of the parent material. The braze specimens were fatigue tested in the as-brazed condition. The fatigue test results showed that the fatigue lives of the brazed specimens were lower than that of the parent material, particularly for the narrow gap samples and wide gap samples containing IN-738 additive alloy. All fatigue failures in the brazed samples occurred in the braze joints. An analysis of the fracture surfaces using a scanning electron microscope revealed that porosity was the major contributing factor to fatigue failures in the wide gap braze joints. The testing life debit observed in the narrow gap braze samples can be attributed to the presence of brittle boride phases in the braze joint. This study also included examination of techniques for reducing the aforementioned porosity and presence of brittle intermetallic phases.