Analysis of the influence of chemical composition and temperature on mechanical properties of superalloys NIMONIC 80A
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Nickel-based superalloys are employed in a variety of gas turbine components due to their excellent high-temperature properties. Unfortunately, several of these superalloys have proved to shrin ...
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The hot workability of lnconel Alloy 706 (IN 706) extends over a temperature range of 1700°F to 21OO'F (925°C to 1150°C).The good hot workability of IN 706 in relatively large ingot sizes makes this alloy fabricable into large forgings utilized by important end markets including power generation, chemical processing, and others.Successful utilization of large IN 706 forgings in critical components requires control of important microstructural and mechanical property features.Grain size, grain boundary precipitates, and matrix precipitates vary widely in IN 706 as a result of fabrication history and post-fabrication thermal treatments (TMP).TMP conditions which favor heavy grain boundary precipitates, such as y, y and 6 or n phases, affect ductility (elongation or reduction in area [RA]) and impact toughness (Charpy V-notch [CVN]) properties.Coarse matrix precipitates may also be observed.While tensile yield and ultimate strengths may increase slightly due to within grain and/or grain boundary precipitates, thicker, more continuous grain boundary precipitates result in lower ductility and toughness.Presented are fractographic and microscopic evaluations of IN 706 forgings illustrating key relationships between microstructure and ductility and fracture-related properties.Fracture behavior changes as grain interior and/or grain boundary precipitate and morphological features are changed.Critical impact properties of IN 706 are rationalized by microstructural observations.
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Effect of Heat Treatment and Structure Upon Creep Properties of Nimonic Alloys Between 750 and 950 C
Tests on nickel-chromium-cobalt alloys hardened with titanium and aluminum have shown that differences in the stress-rupture properties at 750 C, whether due to differences in content of hardening elements or to differences in heat treatment, are maintained at all temperatures up to 950 C. Results are also presented for a cobalt-free alloy of comparable type. These show that the 100- and 300-hr rupture stresses decrease smoothly with increase of temperature up to 950 C. The absence of a discontinuity in the region of the temperature at which the hardening phase is completely soluble can be interpreted as showing that rupture strength is a consequence of both precipitation and solid-solution hardening.
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Experimental results on hot deformation and dynamic structural processes of nickel based alloy Inconel 718 are reviewed.The focus is the analysis of dynamic precipitation processes which operate during hot deformation of these materials at elevated temperatures.Hot compression tests were performed on the solution treated precipitation hardenable nickel based superalloy Inconel 718 at 720-1150°C with a constant true strain rates of 10 -4 and 4x10 -4 s -1 .True stress -true strain curves and microstructure analysis of the deformed nickel based superalloy is presented.The properties and dynamic behaviour are explained through observation of the microstructure using standard optical, scanning and transmission electron microscopy.Structural observations of solution treated Inconel 718 deformed at high temperatures, reveal non uniform deformation effects.The distribution of molybdenum-rich and niobium-rich carbides were affected by localized flow within the strain range investigated at relatively low deformation temperatures 720 -850°C.Microstructural examination of the alloy also shows that shear banding, cavity growth and intergranular cracks penetrating through the whole grains were responsible for decreased flow stresses at temperature of 720, 800 and 850°C and might result in sample fracture at larger strains.On the basis of the measured flow stress activation energies of high-temperature deformation processes were estimated.The mathematical dependence of the effect of flow stress on temperature and strain rate (σ pl -T and σ pl -• ε ) as well as compression data were used to determine material's constants.These constants allowed the derivation of a formula that describes the relationship between strain rate ( • ε ), deformation temperature (T) and flow stress σ pl .Interaction of precipitates developed during deformation below the solvus temperature and heterogeneous deformation (flow localization) can become a significant aspect of high temperature performance of precipitation hardenable alloys.This interaction could also potentially allow production of specific microstructures in deformed materials.The contribution of flow localization to the strain hardening or flow softening and the flow stress-strain behavior during hot deformation of precipitation hardenable alloys is still a subject of extensive research.
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Nimonic 80A is a material used in extreme conditions in the automotive industry and everywhere where elements work in extreme environment (high temperature and aggressive environment). This is an alloy which is very difficult to process. The aim of this paper is research in field of machinability of superalloy Nimonic 80A. Experimental investigations with defined cutting conditions will determine the influence of the chemical composition of superalloy Nimonic 80A on the machinability.
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Machinability
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The degradation of creep resistance in Nickel-based single crystal superalloys is essentially ascribed to their microstructure evolution. Yet there is a lack of work that manages to simulate the effect of alloying element concentrations on microstructure degradation. In this research, a computational model is developed to connect the rafting kinetics of Ni superalloys with their chemical composition, by combining thermodynamics calculation and an energy-based microstructure model. The isotropic coarsening rate and γ/γ misfit stresses have been selected as composition related parameter, and the effect of service temperature, time and applied stress are also taken into consideration to simulate the evolutions of microstructure parameters during creep process. The different generations of commercial Ni superalloys are selected and their chemical compositions are calculated based on this model. The simulated microstructure parameters are validated by the results from experimental results and the existing analytical model. The capability of the model in predicting the microstructure characteristics may provide instructional thought in developing a novel computational guided design approach in Ni superalloys.
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Microstructures and tensile properties of a novel monocrystalline Co‐based superalloy are investigated by experiments and finite element simulation. Microstructures of heat‐treated alloys are composed of γ and cubical γ ' precipitates without the presence of the secondary phase, and the fraction of γ ' phase is about 86%. The experimental results show that tensile properties of the novel monocrystalline Co‐based superalloy have abnormal yield behavior. In low and medium temperature ranges (R.T. 850 °C), the yield stress increases gradually with temperature increase and the tensile fracture surface is characterized by cleavage rupture. At 850 °C, fracture mechanism is composite of cleavage and microporous. While above 850 °C, the yield stress decreases rapidly, and fracture surface is constituted of mixed fracture surface of dimples and micropores. The simulation results show that the tensile stress‐–strain curves are well fitted to the experimental data at different temperatures.
Cleavage (geology)
Dimple
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