The Influence of delta-Phase on the Environmentally Assisted Cracking Resistance of an Additively Manufactured Nickel-based Superalloy (original) (raw)
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Materials
Inconel 738LC (IN738LC) is a nickel-based superalloy specially used in the hot section components of turbine engines. One of its main drawbacks relies on the cracking susceptibility when it is manufactured by laser powder bed fusion (LPBF). This paper analyzes the influence of minor alloying element concentration on cracking tendency of IN738LC superalloy manufactured by LPBF. For that objective, samples were manufactured using two powders, which presented different minor alloying elements concentration (Si, Zr and B). It was shown that the samples crack tendency was very different depending on the powder used for their manufacturing. In fact, the measured crack density value was 2.73 mm/mm2 for the samples manufactured with the powder with higher minor alloying elements concentration, while 0.25 mm/mm2 for the others. Additionally, a special emphasis has been put on elemental composition characterization in cracked grain boundaries in order to quantify possible Si or Zr enrichment....
Contribution of Microstructural Constituents on Hot Cracking of MAR-M247 Nickel Based Superalloy
Archives of Metallurgy and Materials, 2018
The aim of this study is to investigate influence of selected parameters of gas tungsten arc welding on microstructure of MAR-M247 nickel based superalloy originating from turbine vane. MAR-M247 is a precipitation-strengthened superalloy which is widely used in aerospace engines. The main strengthening phase in this material is ordered L12 intermetallic γ' phase Ni3(Al, Ti). The surface of alloy was modified by electric arc in order to present microstructural changes in weld and heat affected zone. Investigation of the heat affected zone revealed that constitutional liquation of γ' particles and primary carbides is responsible for the formation of a liquid grain boundary layer which finally contributed to cracking. Scanning electron microscopy indicated high susceptibility to cracking of MAR-M247 alloy which is connected with high content of γ'-formers aluminum and titanium.
Cracking susceptibility after post-weld heat treatment in Haynes 282 nickel based superalloy
Acta Metallurgica Sinica (English Letters), 2013
This paper presents a study of the standard post-weld heat treatment (PWHT) behaviour of autogenous laser welded γ' age-hardenable precipitation strengthened nickel based superalloy Haynes 282 (HY 282). The study involves a careful and detailed microstructural characterisation as well as an analysis of the weld cracking susceptibility during welding and Gleeble thermo-mechanical physical simulation. Various factors that could influence post-weld cracking in superalloys weld were experimentally examined. Our microstructural examination of the as-solution heat treated (SHTed) material and the thermo-mechanically refined grain material shows that intergranular heat affected zone (HAZ) cracking is observable in only the as-welded SHTed material. There was no indication of post-weld heat treatment cracking in all welded materials. Our conclusion, in this study, is that the chemistry of superalloy HY 282 which aids the preclusion/ formation of deleterious solidification microconstituents during welding as well as its relatively slow aging kinetics enhances its resistance to PWHT cracking.
Materials Science and Engineering: A, 2003
Ni Á/Fe base superalloy, Inconel 718, was processed through powder metallurgy (P/M) hot isostatic pressing (HIP) route. In order to balance the strength and ductility, the HIPed material was given the standard heat treatment, viz. solution treatment at 980 8C for 1 h/water quenched (WQ) to room temperature and a two-step ageing treatment consisting of 720 8C for 8 h/furnace cooling (FC) at 55 8C h (1 to 620 8C and holding at 620 8C for 8 h before air cooling (AC) to room temperature. Optical microscopy and scanning electron microscopy (SEM) studies on the heat treated alloy have shown a homogeneous microstructure with fine grain size (25 mm) along with the presence of prior particle boundary (PPB) networks. Transmission electron microscopy (TEM) on the heat treated material has revealed the presence of oxides, MC carbides and d-precipitates at the grain boundaries and a uniform precipitation of fine gƒ and g? strengthening phases in the matrix. Tensile and stress rupture tests were performed on the heat treated material. While the yield strength (YS) and ultimate tensile strength (UTS) of the HIPed and heat treated alloy at room temperature and 650 8C were comparable to those of conventionally processed wrought IN 718, its ductility was lower. The stress rupture life of the HIPed alloy improved marginally due to heat treatment and met the minimum specification requirement of life hours but the rupture ductility was found to be inferior to that of the wrought material. The fractography of the failed samples has revealed the transgranular ductile mode of fracture in the as-solution treated alloy, while intergranular mode of failure with the decohesion of PPBs occurred more predominantly in the aged condition. This change of fracture mode with ageing treatment shows the ductility dependence on the relative strength of the matrix and PPBs. The TEM studies on the deformed alloy have revealed that the brittle oxides and carbides at the prior particle boundaries coupled with the fine gƒ and g?-precipitates in the matrix are responsible for low ductility at 650 8C. The investigations of the present study have led to better understanding of the structure Á/property relationships in HIP'/heat treated alloy 718 and suggest that the standard heat treatment recommended for wrought IN 718 is not suitable for HIPed alloy and has to be modified to realise optimum properties.
Superalloys 718, 625, 706 and Various Derivatives (2001), 2001
Inert gas atomized superalloy Inconel 718 powder was hot isostatically processed (HIPed) at 1200 "C / 120 MPa / 3h. This material was then subjected to a standard heat treatment schedule adopted for wrought IN 718 (955 "C / 1 h. / water quenching and twostep ageing at 720 "C / 8 h. / furnace cooling to 620 "C / 8 h. 1 followed by air cooling to room temperature), which showed substantial improvement in strength but a drastic decrease in ductility. Since, the solution treatment temperature has a significant influence on microstructure development, the HIPed compacts were subjected to various solution treatment temperatures between 850 and 1270 "C, while the same ageing treatment was retained. The microstructure of the compacts in the as-HIPed, solution treated and aged conditions was studied in detail. The tensile properties of these samples were evaluated at room temperature and at 650 "C. The microstructure corresponding to the solution treatment temperature of 1270 "C, showed incipient melting at the particle boundaries leading to enhanced bonding across the particles and resulting in a considerable improvement of ductility.
Applied Physics A, 2020
Due to their high thermal stability under severe working conditions and harsh environment, nickel (Ni)-based superalloys, such as Inconel 718, Inconel 738, GTD11, and René 40, are largely used in gas turbine industry. The gamma prime (γʹ) precipitates, that are coherent with the gamma (γ) matrix in these superalloys, provide excellent mechanical properties at high operating temperatures. However, after a long time of functioning, (γʹ) precipitates coarsen and lose their coherency with the matrix, which causes damages in gas turbine blades. The main purpose of this paper is to study the effect of both solid solution and aging heat treatments temperatures on the microstructural evolution in an Inconel 738 superalloy blade, which was received after few tens of thousands of service hours. The resulting microstructures were analyzed by using scanning electron microscopy and optical microscopy along with Vickers microhardness measurements. The obtained results show that the Vickers microhardness of the studied superalloy is related to size, shape, volume fraction, and distribution of the hardening phase (γʹ) [Ni 3 (Al, Ti)], and to its carbides as well. It was found that the microstructural stability is related to the working temperature.
Superalloy Metallurgy a Gleeble Study of Environmental Fracture in Inconel 601
2017
At temperatures above 0.5 Tm and in aggressive atmospheres predicting alloy performance is particularly challenging. Nickel alloys used in regimes where microstructure and properties are altered dynamically present unique requirements. Exposure may alter properties with unexpected early failure. The Gleeble is a valuable tool for investigation and simulation of thermo-mechanical properties of an alloy in various regimes up to the threshold of melting. In this study, four regimes of temperature and strain rate were simulated in an argon atmosphere to both investigate and document normal and abnormal failure modes. Commercial Inconel 601 was tested in selected regimes and in two treatments (as received and strain aged). Next two exposed conditions (TEOS and Hydride) were tested. Slow strain-rate and high temperature produced brittle intergranular fracture. Exposure at elevated temperature to process gases reduced both strength and ductility in both TEOS and Hydride. TEOS exposure reduced reduction in area in the alloy significantly more than the Hydride exposure.
Journal of Materials Engineering and Performance, 2021
IN718 is a Ni-based superalloy usually manufactured by conventional processes such as wrought or casting. However, recently additive manufacturing (AM) technologies, such as Powder bed fusion (PBF), are used to produce IN718 parts. Heat treatments, also designed for conventional processes, are usually used in AM parts to improve mechanical properties. Unlike traditional techniques, AM processes involve rapid cooling rates, large thermal gradients, and multiple reheat cycles, which might cause high residual stresses and elemental segregations in the printed parts affecting their final mechanical properties. In this work, a detailed comparative study of microstructural features was carried out in both wrought-and PBF-produced IN718. It was found differences in size, shape, and location of MC carbides. According to experimental results and the phase fraction diagram obtained from Thermo-Calc, these MC carbides cannot be dissolved in a conventional solution heat treatment. In consequence, these carbides continue their evolution during complete aging heat treatment, affecting the material hardness. Nevertheless, similar hardness in the wrought and AM sample was obtained after applying a modified aging treatment proposed in this work.
Journal of Engineering for Gas Turbines and Power
Nickel-base superalloys containing 30 to 50% gamma prime (γ') volume fraction are typically used in hot section components (e.g., guide vanes or blades) for power generating gas turbines, and suitable time-dependent properties are required for long-term elevated temperature operation. Additive manufacturing (AM) has recently been used to develop complex hot-section parts utilizing innovative designs with enhanced cooling features which improve efficiencies by reducing cooling air consumption. To further explore the opportunity to improve time-dependent AM superalloys, this paper focuses on a fundamental creep study and characterization of a novel nickel-base superalloy (ABD-900AM) that was manufactured using a laser-based powder bed fusion (LBPBF) AM process. The material was subjected to a subsolvus solution anneal and multistep aging heat treatment (HT) to produce a bi-modal distribution with ∼35% volume fraction of gamma prime without postprocessing hot isostatic pressing (HI...
Metals
In this paper, Inconel 718 (IN718) superalloy was processed by laser powder-bed fusion additive manufacturing (L-PBFAM), followed by heat treatment. High-resolution nanoindentation was used to investigate the complex deformation mechanisms that occurred at various length scales in both conditions. The nanoindentation elastoplastic maps show a strong crystal orientation dependency of modulus and hardness, which is attributed to the high mechanical anisotropy of IN718. The hardness map effectively resolves complex microscale strength variation imparted due to the hierarchical heat distribution associated with the thermal cycles of L-PBFAM. The disproportionately high hardening effect of Nb, Mo-rich chemical segregations and Laves phases in dendritic structures is also observed. The heat treatment resulted in a 67% increase in yield strength (from 731 MPa in the L-PBFAM condition to 1217 MPa in the heat-treated condition) due to the activation of multiple precipitation-strengthening me...