Effect of melt spinning on the microstructure and mechanical properties of three Ni-base superalloys (original) (raw)
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Microstructure of an experimental Ni base superalloy under various casting conditions
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
The effect of casting parameters such as melt superheat and solidification rate on the microstructure of an experimental Ni-based superalloy made by vacuum melting and investment casting methods was investigated. The results show that the as cast microstructure of this alloy consists of dendritic ␥ matrix, interdendritic ␥/␥ , ␥ phase, MC carbides and minor phases in interdendritic regions. DSC analyses in addition to SEM and EDS proved that the nodular phase found in minor phases is phase, while the phase was found to solidify in two forms; as plate-like and blocky shape. The volume fraction (V f ) of and phases increases as the melt superheat increases and the solidification cooling rate decreases. Additionally, the V f of interdendritic ␥/␥ increases with higher solidification rate and lower melt superheat. It was found that higher melt superheating temperature enlarges the size of the primary ␥ dendrites; however the higher solidification rate diminishes it.
Effects of solidification substructure on the mechanical properties of a nickel base superalloy
1977
Rod specimens of HASTELLOY alloy X were unidirectionally solidified by the floating zone method in an electron-beam zone melter. Temperature gradient (VT) and growth rate (R) were controlled to produce three types of solidification substructures: cellular, cellulardendritic, and dendritic. Qualitative agreement with the solidification treatment of Tiller and Rutter was obtained, in that a decrease in the parameter VT/R changed the solidification mode away from cellular toward dendritic. Room-and elevated-temperature tensile tests indicate that the dendritic form of the alloy is stronger and more ductile than the cellular form, probably because there is less tendency for brittle, low-melting grain-boundary phases to form during dendritic solidification.
Materials Science and Technology, 2013
To provide insight into the factors causing recrystallisation of nickel-based single crystal superalloys, analysis of the thermal-mechanical deformation caused by investment casting of these components is presented. Three dimensional thermal-mechanical finite element analysis is first used to demonstrate that the reaction of the casting and mould -- at least in the aerofoil section -- can be approximated as one dimensional. One-dimensional models are then built based upon static equilibrium for plasticity on the microscale caused by differential thermal contraction of metal, mould and core, using temperature-dependent materials properties. The models take various forms to study the mechanical response under different situations relevant to practical applications. The results indicate that the plastic strain causing recrystallisation is likely to induced during cooling at temperatures above 1000 deg C. The relative importance of thicker and stiffer ceramic shells is studied. Our analysis indicates that it is important to account for creep deformation, for such applications.
Microstructure of a rapidly-solidified Ni-base eutectic superalloy
Metallurgical Transactions A, 1986
A 7-3' '-MC eutectic nickel-base superalloy was rapidly solidified by melt-spinning. The resulting ribbon microstructure was studied using light microscopy and transmission electron microscopy. In the as-spun ribbon, a chill zone was found at the surface in contact with the wheel, consisting of grains 0.2 to 2.0/zm in diameter with Ta-rich MC carbides, 25 nm in diameter, decorating the grain boundaries. An intragranular cell structure was seen with 10 to 20 nm MC carbides at cell walls. A uniform dispersion of y' particles, 20 to 40 nm in diameter, was also present. In the ribbon center, a columnar dendritic structure was observed, with a slight increase in grain size. Carbides were found in this region at grain boundaries, along secondary dendrite arm boundaries, and in extended intercellular regions. A randomly-oriented dendritic structure was present at the ribbon top surface. The chill zone structure and the cellular-to-dendritic transition are described in terms of classical solidification models. Heat treatment of the as-spun ribbon for 2 hours at 1000 ~ caused significant coarsening of the 3,' particles, but the grain size and carbide size and distribution were only slightly altered. An additional Lie-rich sigma phase precipitated at grain boundaries during the heat treatment. After heat treatment for 2 hours at 1200 ~ some grain growth occurred, the MC and 3,' particles coarsened, and the Re-rich sigma phase was found.
Materials Science and Technology, 2013
To provide insight into the factors causing recrystallisation of nickel-based single crystal superalloys, analysis of the thermal-mechanical deformation caused by investment casting of these components is presented. Three-dimensional thermal-mechanical finite element analysis is first used to demonstrate that the reaction of the casting and mould-at least in the aerofoil section-can be approximated as one-dimensional. One-dimensional models are then built based upon static equilibrium for plasticity on the microscale caused by differential thermal contraction of metal, mould and core, using temperature dependent material properties. The models take various forms to study the mechanical response under different situations relevant to practical applications. The results indicate that the plastic strain causing recrystallisation is likely to be induced during cooling at temperatures above 1000uC. The relative importance of thicker and stiffer ceramic shells is studied. Our analysis indicates that it is important to account for creep deformation for such applications.
Quantitative Microstructural Analysis of a Ni-based Superalloy After Different Heat Treatments
Revista de Chimie, 2020
The efficiency of time-temperature treatment (T-TT) on metal melts can be microstructurally analysed through their degree of purity in non-metallic inclusions. In the case of the Ni-based super alloy under discussion (MSRR 7045) the heat treatment was the undercooling consequences both on the durability of the casting environment (ingots-refractories) and on the internal structure of the metal (porosity, microstructural isotropy). Keywords: time-temperature treatment, undercooled melt, non-metallic inclusions, purity, microstructural isotropy
Journal of Materials Engineering and Performance, 2018
High-temperature tensile deformation behavior of directionally solidified nickel base superalloy CM 247 DS is studied by conducting tensile tests in temperature range RT-955°C employing a constant strain rate of 10 23 s 21 and carrying out extensive electron microscopic examinations to understand the concomitant substructural evolution. The alloy exhibits yield strength anomaly (YSA) behavior like many other superalloys, and the yield strength maxima occur at 750°C. However, unlike in most of the superalloys, ductility continuously increases with temperature. The deformation behavior of the alloy changes significantly with temperature. Transmission electron microscopic examination confirmed that at lower temperature (£ 750°C), c¢ shearing is the dominant deformation mechanism; whereas at temperatures above 750°C, thermally activated dislocation looping around c¢ precipitate is dominant. Substructures evolved during deformation at 750°C consists mainly of superlattice stacking faults (SSFs) inside c¢ precipitates, whereas at 850°C uniform dislocation tangles are observed in c matrix. Superlattice stacking faults result from shearing of c¢ precipitate by a/3AE112ae dislocations, which arise from the decomposition of a/2AE110ae matrix dislocations. YSA in this alloy is attributed to dislocation interactions inside c¢; however, the enhanced ductility even at 750°C is due to formation of SSFs.
The Effect of Cooling Rate on Selected Structural Parameters of Advanced Cast Ni – Base Superalloys
Quality Production Improvement
The Nibase superalloys are used in aircraft industry for production of aero engine most stressed parts, as are turbine blades or turbine discs. The most stressing factor at Nibase superalloys loading or working conditions are high temperature range of 700°C up to 850°C and, of course, centrifugal forces, and small vibrations, which produce bending of turbine blades inserted into turbine discs. All these factors cause various forms of microstructure degradation closely connected with decreasing of mechanical properties and shortening of working life as well. From this reason a dendrite arm spacing, carbides size and distribution, morphology, number and value of -phase are very important structural characteristics for blade lifetime prediction as well as aero engine its self. In this article are used methods of quantitative metallography for evaluation of structural characteristics mentioned above on experimental materials-Ni base superalloys ŽS6K and Inconel IN 738. The high temperature effect represented here by heat treatment at 800°C for 10 hours, and cooling rate, here represented by three various cooling mediums as water, air, and oil, on structural characteristics and application of quantitative methods evaluation with using of SEM are presented in this paper.