Precipitation of the δ-Ni 3 Nb phase in two nickel base superalloys
01 Mar 1988-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer-Verlag)-Vol. 19, Iss: 3, pp 453-465
TL;DR: In this article, the precipitation of the metastable δ-Ni3Nb phase has been studied in two niobium bearing nickel base superalloys and the morphology and distribution of precipitates have been examined and the crystallographic orientation relationship between the austenite and the δ phases has been determined.
Abstract: The precipitation of the equilibrium δ-Ni3Nb phase has been studied in two niobium bearing nickel base superalloys—INCONEL 718 and INCONEL* 625—both of which are hardenable by the precipitation of the metastableγ″-Ni3Nb phase. The morphology and the distribution of precipitates have been examined and the crystallographic orientation relationship between the austenite and theδ phases has been determined. The nucleation of theδ phase at stacking faults within pre-existing δ" precipitates has been discussed.
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TL;DR: It is demonstrated that abnormal γ″ precipitation along TBs accounts for the premature dislocation activities and pronounced strain localisation associated with TBs during mechanical loading, which serves as a precursor for crack initiation.
Abstract: Twin boundaries (TBs) in Ni-based superalloys are vulnerable sites for failure in demanding environments, and a current lack of mechanistic understanding hampers the reliable lifetime prediction and performance optimisation of these alloys. Here we report the discovery of an unexpected γ″ precipitation mechanism at TBs that takes the responsibility for alloy failure in demanding environments. Using multiscale microstructural and mechanical characterisations (from millimetre down to atomic level) and DFT calculations, we demonstrate that abnormal γ″ precipitation along TBs accounts for the premature dislocation activities and pronounced strain localisation associated with TBs during mechanical loading, which serves as a precursor for crack initiation. We clarify the physical origin of the TBs-related cracking at the atomic level of γ″-strengthened Ni-based superalloys in a hydrogen containing environment, and provide practical methods to mitigate the adverse effect of TBs on the performance of these alloys.
48 citations
23 Sep 2019-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors used scanning and transmission microscopy and electron backscatter diffraction to clarify the microstructure of Inconel 718 alloy cylindrical rods before and after creep.
Abstract: Horizontal-direction Inconel 718 alloy cylindrical rods were fabricated by selective laser melting (SLM) and subsequently subjected to solution or homogenization plus double aging (SA or HA) treatments. Lever arm creep tests were performed with the creep tensile axis perpendicular to the building direction of the samples with a constant stress of 650 MPa at 650 °C. Scanning and transmission microscopy and electron backscatter diffraction were used to clarify the microstructure of the SA and HA samples before and after creep. The experimental results revealed that the average grain sizes of the SA and HA samples were basically the same before creep, and larger γ′ and γ″ strengthening phases existed in the HA sample. The grains tended to grow, and the higher dislocation density within grains and lower local misorientation values close to the grain boundaries occurred in the HA sample during creep, which contributed to the longer creep rupture life in comparison with the SA sample. The fracture surfaces of the SA and HA samples displayed intergranular features, and the creep voids and micro-cracks were formed around the δ or Laves phases at the grain boundaries. The creep fracture mechanism was also discussed.
47 citations
25 May 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of the δ phase on the deformation behavior, including flow stress-strain curve, strain rate sensitivity exponent, strain hardening exponent and kinetic analysis, was investigated by isothermal compression of superalloy GH4169 with two kinds of solution treatment.
Abstract: The effect of the δ phase on the deformation behavior, including flow stress–strain curve, strain rate sensitivity exponent, strain hardening exponent and kinetic analysis, was investigated by isothermal compression of superalloy GH4169 with two kinds of solution treatment. The experimental results show that the existence of δ phase results in the decreasing of flow stress, and makes the flow stress reach a peak value at small strain. The strain rate sensitivity exponent (m) increases with the increasing of deformation temperature. The existence of δ phase leads to the increasing of strain rate sensitivity exponent (m) at a certain deformation temperature and strain. Moreover, the strain hardening exponent (n) has a close relationship with the deformation temperature, strain rate and strain, especially the strain affects n more significantly. The existence of δ phase results in the decreasing of n values, and makes the n values reach a negative value at small strain. It was observed that the changes in strain rate sensitivity exponent and strain hardening exponent were closely related to the microstructural evolution in the deformation process. Based on the kinetic analysis of superalloy GH4169 with two kinds of solution treatment, the apparent activation energy of superalloy GH4169 containing δ phase was calculated to be 476.136 kJ mol−1, which was slightly higher than that of superalloy GH4169 (455.434 kJ mol−1) without δ phase. And the peak flow stress in the isothermal compression of superalloy GH4169 was observed to increase with the increasing of parameter Z.
47 citations
20 Dec 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the nickel-based superalloy 625 has been examined in an as-processed condition and following creep-rupture testing in air at 750 ÂC and 100 ÂMPa.
Abstract: Foil and sheet forms of the nickel-based superalloy 625 have been examined in an ‘as-processed’ condition and following creep-rupture testing in air at 750 °C and 100 MPa. Both scanning and transmission electron microscopies were employed to correlate microstructures with creep behavior, and indicate the additional processing required to achieve foil form reduces creep life compared to thicker-section wrought product forms. Prior to creep testing, the microstructure consists of γ phase with M6C precipitates. This microstructure changes during creep into one consisting of orthorhombic δ phase extending across the γ grains, and grain boundaries dominated by the presence of rhombohedral μ phase, δ phase, and a Si-rich variant of diamond-cubic M6C (η phase). Thermodynamic modeling was also used to calculate the stable temperature ranges and compositions of equilibrium phases. The phases predicted by modeling and their compositions generally agree with those observed within alloy 625 after creep testing.
45 citations
TL;DR: A method for in-situ monitoring of residual strain/stress evolution during annealing treatments has been developed using a new induction heating setup designed for neutron strain-scanning instruments as discussed by the authors.
44 citations
References
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Book•
01 Jan 1958
TL;DR: The Handbook of Lattice spacings and structures of metals and alloys as discussed by the authors is a handbook of argumentative essay structure spacing and lattice plane model modified by the incorporation of thermodynamic functions appropriate to the f.c.
Abstract: For the best product experience, a Handbook of of argumentative essay structure spacing Lattice Spacings and Structures of Metals and Alloys ScienceDirect. Get this from a library! A handbook of lattice spacings and structures of metals and alloys. (W B Pearson) Acm metal). Vol. lattice plane model modified by the incorporation of thermodynamic functions appropriate to the f.c.c. Al—Ag solid zones in the alloys. W. B. Pearson, Handbook of Lattice Spacings. Structures of Metals and Alloys.
3,090 citations
Book•
01 Jan 1962
TL;DR: Modern Physical Metallurgy as mentioned in this paper describes the fundamental principles of physical metallurgy and the basic techniques for assessing microstructure and provides a balanced coverage of properties, characterization, phase transformations, crystal structure, and corrosion not available in other texts.
Abstract: Modern Physical Metallurgy describes, in a very readable form, the fundamental principles of physical metallurgy and the basic techniques for assessing microstructure This book enables you to understand the properties and applications of metals and alloys at a deeper level than that provided in an introductory materials course The eighth edition of this classic text has been updated to provide a balanced coverage of properties, characterization, phase transformations, crystal structure, and corrosion not available in other texts, and includes updated illustrations along with extensive new real-world examples and homework problems It offers renowned coverage of metals and alloys from one of the world's leading metallurgy educators It covers new materials characterization techniques, including scanning tunneling microscopy (STM), atomic force microscopy (AFM), and nanoindentation It provides the most thorough coverage of characterization, mechanical properties, surface engineering and corrosion of any textbook in its field It includes new worked examples with real-world applications, case studies, extensive homework exercises, and a full online solutions manual and image bank
421 citations
TL;DR: In this article, a review of theoretical models applicable to concentrated solid solutions is presented, focusing on concentrated solutions because dilute ones can be considered as special cases and because the interesting effects of clustering and ordering are most apparent at high solute concentrations.
Abstract: Publisher Summary This chapter reviews current theoretical models applicable to concentrated solid solutions. It focuses on concentrated solutions because dilute ones can be considered as special cases and because the interesting effects of clustering and ordering are most apparent at high solute concentrations. The extended ranges of solubility are often found in metallic systems, and for this reason most examples selected will refer to metals and alloys, although the models presented are equally applied to off-stoichiometric compounds, metallic or inorganic, and to amorphous solids. The chapter provides description of the state of the order of the system through suitable averaging procedures. It discusses the internal energy of solutions, from both electronic and elastic standpoints. The chapter presents free energy models, such as generalized Bragg- Williams's model, Landau theory, and cluster variation method. These models are applied to the study of phase equilibrium.
308 citations
01 Jan 1971-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, a heat treatment for 706 alloy was developed which effectively optimizes the 1200°F stress-rupture properties of the alloy by precipitation of globular to plate-like Ni3Cb/Ni3Ti at the grain boundaries in conjunction with maintaining a fine as-forged grain structure.
Abstract: Evaluation of a commercial heat treatment for 706 alloy indicated that it resulted in relatively low 1200° F stress rupture ductility. It was determined that this was caused by a solution treatment which dissolved all of the age-hardening phases in the alloy and caused a coarse grain size and supersaturated matrix condition. Based upon extensive fine structure study of the 706 alloy as well as previous experience with 718 alloy and other Fe−Ni-base superalloys, a heat treatment is developed which effectively optimizes the 1200°F stress-rupture properties of the alloy. The key to best properties was found to be the precipitation of globular to plate-like Ni3Cb/Ni3Ti at the grain boundaries in conjunction with maintaining a fine as-forged grain structure.
44 citations