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Journal ArticleDOI

Precipitation of the δ-Ni 3 Nb phase in two nickel base superalloys

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.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution of V207M, a new δ containing, nickel-base superalloy, has been investigated following heat treatment and forging, and the solvus temperatures of the γ′ and δ phases, determined by differential scanning calorimetry and microscopy, were found to be ~985 and ~1060°C respectively.
Abstract: The next generation of aerospace gas turbine engines need to operate at higher temperatures and stresses to improve their efficiency and reduce emissions. These operating conditions are beyond the capability of existing nickel-base superalloys, requiring the development of new high temperature materials. Controlling the microstructures of these new materials is key to obtaining the required properties and, therefore, it is critical to understand how these alloys respond to processing and heat treatment. Here, the microstructural evolution of V207M, a new δ containing, nickel-base superalloy, has been investigated following heat treatment and forging. The solvus temperatures of the γ′ and δ phases, determined by differential scanning calorimetry and microscopy, were found to be ~985 and ~1060 °C respectively. Isothermal forging of the alloy was conducted at 1000, 1050 and 1100 °C, corresponding to different volume fractions of retained δ. Considerable softening was observed prior to steady state flow when forging at 1000 °C, whilst only steady state flow occurred at 1050 and 1100 °C. The steady state flow process was believed to be dominated by dynamic recovery in the γ phase, with an activation energy of 407 kJmol −1 . Samples that exhibited flow softening also showed a significant change in the orientation of the δ precipitates, preferentially aligning normal to the forging axis, and this reorientation was thought to be the cause of the observed flow softening.

32 citations

Journal ArticleDOI
TL;DR: In this article, low cycle fatigue performance of IN718 superalloy under different heat treatment conditions were investigated with controlled strain amplitudes from 0.6% to 1.0% at 350°C and 650°C.
Abstract: Low cycle fatigue (LCF) performance of IN718 superalloy under different heat treatment conditions are investigated with controlled strain amplitudes from 0.6% to 1.0% at 350 °C and 650 °C. Standard heat treatment (ST) and delta-phase aging treatment (DA) are applied to produce two types of precipitation microstructures. Under the same strain amplitude and temperature, the fatigue lives of ST specimens exceed that of DA specimens. And strikingly, ST specimens exhibit cyclic softening behavior in contrast to cyclic hardening behavior for DA specimens. The different stress responses can be rationalized by the dislocation interaction mechanisms with the precipitates. For the ST specimens, the dislocation shearing of γ′′ precipitates governs the microscopic deformation process, while the micrometer-sized δ phases are not shearable but act as the obstacles against dislocation slipping and lead to the cyclic hardening. Our TEM observations clearly show that recrystallization nucleation is prevalent in the DA specimens under 650 °C, which is interpreted by the high dislocation density induced by the δ phases. The results shed new lights on the fatigue microscopic deformation mechanisms of IN718 superalloy.

32 citations

Journal ArticleDOI
TL;DR: In this paper, a multi-phase, multi-component mean-field model has been developed for simulating the intermetallic precipitation kinetics in Inconel 718.

31 citations

Journal ArticleDOI
TL;DR: Wang et al. as mentioned in this paper investigated the creep behaviors of two alloys, including Inconel718 and Allvac718Plus, under the temperature of 700°C and three applied stresses (560,MPa, 650, MPa and 720 MPa).
Abstract: To investigate creep mechanisms of Inconel718 and Allvac718Plus, creep behaviors of two alloys are studied under the temperature of 700 °C and three applied stresses (560 MPa, 650 MPa and 720 MPa) by using multiple microstructural analysis methods, including scanning electron microscope (SEM), emission scanning electron microscope (FSEM) and transmission electron microscopy (TEM). Result shows that steady-state region is not observed in these two alloys. Creep curves of two alloys are composed of primary region and tertiary region. Tertiary region occupies a dominant position. Ductile dimples are observed on creep fracture surface, indicating creep mechanisms of two alloys are the formation of creep voids. In this study, the formation of creep voids is found to be correlated with three factors which are dislocation multiplication, dislocation motion and dislocation obstacles. Inconel718 has higher dislocation multiplication rate, larger dislocation motion rate, more δ phases and less bands than Allvac718Plus. Therefore, Inconel718 has higher creep voids rate than Allvac718Plus, leading to the result that Inconel718 has shorter creep life than Allvac718Plus.

30 citations

Journal ArticleDOI
TL;DR: In this paper, a method for quantitatively evaluating the content of δ phase was proposed based on SEM micrograph, which was verified by X-ray diffraction (XRD) analysis.
Abstract: The precipitation and dissolution behaviors of δ phase inside a deformed nickel-based superalloy during annealing treatment are investigated. A new method for quantitatively evaluating the content of δ phase was proposed based on SEM micrograph, which was verified by X-ray diffraction (XRD) analysis. The effects of recrystallization during pre-annealing at 980 °C on the precipitation and dissolution behaviors of δ phase in the subsequent annealing treatment at 900 °C and 980 °C are discussed. Moreover, the improved precipitation and dissolution kinetics models are proposed to consider the effects of recrystallization fraction. The results show that: (1) for the precipitation of δ phase at 900 °C, δ phases precipitate first in grain boundaries and then within grains after a long incubation period. Moreover, the interval between adjacent δ phases increases first and then drops with the increasing recrystallization fraction during pre-annealing treatment. A balance between the precipitation and solution of δ phase at the aging temperature of 900 °C can be reached when the holding time is about 12 h; (2) for the dissolution of δ phase at 980 °C, the dissolution equilibrium can be obtained at approximate 200 min. Moreover, more rod-like δ phases can be remained with the increasing recrystallization fraction in pre-annealing treatment.

30 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

Book ChapterDOI
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

Journal ArticleDOI
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