Analysis of Creep Tests of the in 792-5 a Alloy (original) (raw)
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ANALYSIS OF CREEP TESTS OF THE IN 792-5A ALLOY Jiří Zýka a
IN 792-5A, a variant within the IN 792 alloy series, is a high-temperature cast nickel alloy strengthened by the presence of precipitates of the γ' phase and carbides. This alloy is currently used, for instance, as the material of cast blades for jet engines. The companies UJP PRAHA a.s and PBS Velká Bíteš a.s. have joined their research capacities in a project aimed to identify the properties of the alloy with focus on its heat treatment. Within the project, creep tests of the IN792-5A alloy as cast and following three-step heat treatment were performed in cooperation with the Institute of Physics of Materials, Academy of Sciences of the Czech Republic. Such heat treatment was found to extend appreciably the alloy's creep life. In the as-cast state the alloy fails to meet the requirements for its lifetime. The present contribution discusses the causes of the differences in the creep behaviour of the IN792-5A alloy between the two structure states. The structure of the alloy and the crack formation and propagation were investigated on sections perpendicular to the fracture plane. The fracture planes were also analysed.
Microstructural analysis of creep exposed IN617 alloy
2010
Nickel base alloys such as IN617 are one of the preferred choices for steam turbine components used by fossil fuelled power generation plants. IN617 is a solid-solutionstrengthened nickel-based superalloy containing ~23% Cr, 12% Co, and 9% Mo with low content of precipitation-strengthening elements Al, Ti and Nb. In the 'as-received' (solution-annealed condition), the microstructure consists of primary carbides (M 23 C 6 ) and occasional TiN particles dispersed in a single-phase austenitic matrix. Owing to high temperature exposure and the creep deformation processes that occur in-service, evolution of the microstructure occurs. This results in secondary precipitation and precipitate coarsening, both on grain boundaries and intragranularly in areas of high dislocation density. The influence of creep deformation on the solution-treated IN617 alloy at an operating condition of 650˚C/574 Hrs, with emphasis on the morphology and distribution of carbide/nitride precipitation is discussed. The applied stress was at an intermediate level.
The Microstructure Changes in IN713LC during the Creep Exposure
Advanced Materials Research, 2011
Nickel-based creep resisting alloys (strengthened by γ´) are the basic materials for high-temperature constructional parts in aircraft engines and energy units. These parts are exposed to combined effects of mechanical stresses, high temperature and dioxide-corrosion conditions. The microstructure changes of cast polycrystalline Ni-based superalloy IN713LC after creep exposure were studied. Three specimens with three different diameters were used for creep tests. The degradation stage (damage parameter π) was determined for all parts of specimens. Individual parts of specimens were metallographic observed and analyzed by image analysis after rupture. The results were compared with model of stress distribution in the specimen with potential damage in the centre of the specimen.
Metals
In this research, we studied the creep properties of a selective laser melting (SLM)-processed γ′-strengthened IN939 superalloy along the building direction compared to a conventional cast alloy as a reference specimen. In the as-built condition, high-density dislocations were formed as a result of the SLM process due to the generation of the larger thermal gradient. Post-heat treatment was necessary to obtain specific mechanical properties to match industrial requirements. Two heat treatment conditions were used: the first was lower temperature heat treatment (LTH: solution treatment at 1160 °C/4 h + aging at 850 °C/16 h). The second was higher temperature heat treatment (HTH: solution treatment at 1240 °C/6 h + aging at 850 °C/16 h). Creep tests were conducted at 816 °C/250 MPa. The first and second heat treatment conditions were used for the SLM specimens, but only the first condition was used for the cast alloy (cast-LTH). The SLM specimens in the as-built and LTH conditions sho...
Creep behavior of INCOLOY alloy 617
Journal of Materials Science, 2007
The microstructural features of INCOLOY alloy 617 in the solution annealed condition and after longterm creep tests at 700 and 800°C were characterized and correlated with hardness and creep strength. Major precipitates included (Cr,Mo,Fe) 23 C 6 carbides and the d-Ni 3 Mo phase. M 6 C and MC carbides were also detected within the austenitic grains. However, minor precipitates particularly c¢-Ni 3 (Al,Ti) was found to play an important role. At different exposure temperatures, the microstructural features of the Ni-22Cr-12Co-9Mo alloy changed compared with the as-received condition. The presence of discontinuously precipitated (Cr,Mo,Fe) 23 C 6 carbides and their coarsening until the formation of an intergranular film morphology could be responsible both for a reduction in rupture strength and for enhanced intergranular embrittlement. The fraction and morphology of the c¢-phase, precipitated during exposure to high temperature, also changed after 700 or 800°C exposure. At the latter test temperature, a lower volume fraction of coarsened and more cubic c¢ precipitates were observed. These microstructural modifications, together with the presence of the d-phase, detected only in specimens exposed to 700°C, were clearly responsible for the substantially good creep response observed at 700°C, compared with that found at 800°C.
Effect of Ageing on Microstructure, Mechanical Properties and Creep Behavior of Alloy 740H
Metallurgical and Materials Transactions A, 2020
A study on the mechanical property changes and the creep behavior of a Ni-based alloy 740H on ageing at 800°C for 10250 hours is conducted. Microstructural characterization reveals that the alloy initially contains fine c¢ phase and carbide precipitates within grains and at grain boundaries. Ageing does not affect the grain size but coarsens the c¢ phase and facilitates further precipitation of carbides at grain boundaries, which gradually form a continuous network. This significantly deteriorates the mechanical properties in ambient conditions with marked reductions in the impact energy and yield strength. The strength of the aged alloy further reduces at 710°C. In contrast, ageing appears to have insignificant influence on the ductility, which is > 30 pct at both testing temperatures. Ageing also reduces the creep strength of the alloy and accelerates the creep rate. The creep stress exponent was found to increase from 6.7 to 11.2 after ageing, suggesting a transition in the deformation mechanism. The observed reductions in yield strength, impact toughness and creep strength are attributed to the coarsening of the c¢ precipitate, formation of network carbides at grain boundaries and formation of c¢ precipitate-free zone adjacent to grain boundary carbide network. This c¢ precipitate-free zone also weakens the grain boundary and facilitates grain boundary sliding at higher temperatures. However, under quasi-static conditions, c¢ precipitate-free zone undergoes plastic deformation and helps in preserving the ductility of the aged alloy. Implications of these changes are discussed in the context of high-temperature structural applications, such as in power plants.
Microstructural Changes in IN617 Superalloy during Creep at High Temperatures
Procedia Engineering, 2014
In an Ultra super critical power plant, it is considered to be necessary to use Ni-base super alloys with higher strength in addition to conventional heat-resistant steel. Out of various materials in the pipe line, one important alloy i.e. IN 617 super alloy is selected for the Ultra Supercritical power plant applications for operation. Creep is one of the major properties to be assessed for the material to be used in USC power plants. In this paper, creep behaviour of IN 617 super alloy is studied at various stress and temperatures and microstructures are correlated with high temperature properties. Microstructures of crept samples tested at two temperatures of 650 o C and 700 o C at different stress level were analysed and compared using optical and scanning electron microscopy techniques.
Effect of Double Aging Heat Treatment on the Short-Term Creep Behavior of the Inconel 718
Journal of Materials Engineering and Performance, 2016
This research studies the effect of double aging heat treatment on the short-term creep behavior of the superalloy Inconel 718. The superalloy, received in the solution treated state, was subjected to an aging treatment which comprises a solid solution at 1095°C for 1 h, a first aging step of 955°C for 1 h, then aged at 720 and 620°C, 8 h each step. Creep tests at constant load mode, under temperatures of 650, 675, 700°C and stress of 510, 625 and 700 MPa, were performed before and after heat treatment. The results indicate that after the double aging heat treatment creep resistance is increased, influenced by the presence of precipitates c¢ and c¢¢ and its interaction with the dislocations, by grain size growth (from 8.20 to 7.23 ASTM) and the increase of hardness by approximately 98%. Creep parameters of primary and secondary stages have been determined. There is a breakdown relationship between _ e s and stress at 650°C of Inconel 718 as received, around 600 MPa. By considering the internal stress values, effective stress exponent, effective activation energy, and TEM images of Inconel 718 double aged, it is suggested that the creep mechanism is controlled by the interaction of dislocations with precipitates. The fracture mechanism of Inconel 718 as received is transgranular (coalescence of dimples) and mixed (transgranular-intergranular), whereas the Inconel 718 double aged condition crept surfaces evidenced the intergranular fracture mechanism.
Creep behavior of a new cast austenitic alloy
International Journal of Pressure Vessels and Piping, 2007
A new cast austenitic alloy, CF8C-Plus, has been developed by Oak Ridge National Laboratory (ORNL) and Caterpillar for a wide range of high temperature applications including diesel exhaust components and turbine casings. The creep strength of CF8C-Plus is over ten times greater than that of the standard cast CF8C stainless steel and comparable to the highest strength wrought commercial austenitic stainless steels and alloys, such as NF709. The creep properties of CF8C-Plus will be discussed in terms of alloy design methodology and the evaluation of long-term creep tested specimens (over 20,000 hours). Microcharacterization shows that the excellent creep strength is due to the precipitation of very fine nanoscale and stable MC carbides without the formation of deleterious intermetallic phases.