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Hiroshi Harada - One of the best experts on this subject based on the ideXlab platform.

  • deformation twinning and twinning related fracture in nickel base Single Crystal Superalloys during thermomechanical fatigue cycling
    Acta Materialia, 2014
    Co-Authors: Fei Sun, Jian-xin Zhang, Hiroshi Harada
    Abstract:

    Abstract Thermomechanical fatigue (TMF) tests in four 〈0 0 1〉-oriented nickel-base Single-Crystal Superalloys were studied with the aid of microstructural investigation. Three experimental observation methods – optical microscopy, scanning electron microscope and transmission electron microscopy – were combined to obtain new insights into the microstructural and fractographic characteristics after TMF cycling with and without a compressive hold time. After the TMF cycling, the fracture surface shows different fractographic characteristics due to the introduction of the hold time. Fundamental differences in the crack propagation mechanisms have also been discovered under the influence of the compressive hold time. Without a compressive hold time, the crack propagates inwards perpendicular to the axial stress with the aid of oxidation. During the propagation, the crack reaches the twinning plate and propagates rapidly along it with the aid of the stress field at the crack tip. There appear to be obvious steps at this propagation stage. With a compressive hold time, the crack could only propagate in approximately one twinning plate. It appears in only one Crystallographic fracture plane. Due to a few deformation twins being formed in this section, the crack propagation path may change to run along other twinning plates.

  • High-temperature ultrasonic fatigue testing of Single-Crystal Superalloys
    Materials Letters, 2012
    Co-Authors: Yoshiyuki Furuya, Kazuo Kobayashi, Masao Hayakawa, Masao Sakamoto, Yutaka Koizumi, Hiroshi Harada
    Abstract:

    Abstract A high-temperature ultrasonic fatigue testing system was developed to evaluate the gigacycle fatigue properties of Single-Crystal Superalloys used in aircraft engine turbine blades. In this development, a commercial ultrasonic fatigue testing machine was considerably modified to achieve high-temperature fatigue testing. The testing system was first applied to a heat-resistant steel at 650 °C to check its accuracy, and next to SC superalloy samples at 1000 °C. As a result, the ultrasonic fatigue testing showed good agreement with the conventional fatigue testing, demonstrating the high accuracy of the developed system. In these results, the SC Superalloys showed no fatigue limit, indicating gigacycle fatigue tests to be necessary.

  • atom probe investigation of ruthenium distributions around rhenium molybdenum and tungsten in a gamma phase of 5th generation nickel base Single Crystal Superalloys
    Materials Transactions, 2007
    Co-Authors: Tomonori Kitashima, Hiroshi Harada, D H Ping, Toshiharu Kobayashi
    Abstract:

    The three-dimensional atom-probe microanalysis was performed to investigate Ru distributions around Re, Mo and W in the γ phase of a fifth-generation nickel-base Single Crystal Superalloys. Ru-concentration-frequency distributions within Re-, Mo- and W-centered spheres of 100 atoms in the γ phase were analyzed. Any concentration deviation of Ru around Re, Mo and W were not detected under the condition employed in the present study.

  • effect of aluminide coating on creep properties of ni base Single Crystal Superalloys
    Journal of The Japan Institute of Metals, 2007
    Co-Authors: Akihiro Sato, Yasuhiro Aoki, Mikiya Arai, Hiroshi Harada
    Abstract:

    This article compares the creep rupture responses of aluminide coated samples with uncoated ones to elucidate the effect of diffusion layers on resistance against creep. Three Ni-base Single Crystal Superalloys, CMSX-4, TMS-75 and TMS-138, were chosen for present study. Creep specimens had thicknesses ranged from 1 mm to 4 mm to simulate the varying dimensions across the actual turbine blade. Creep conditions were set at 1060°C-137 MPa and 1100°C-137 MPa. Experimental results indicated that the creep-rupture lives of coated specimens were shorter than those of the bare samples. In particular, the coated TMS-138 specimen with 1 mm thickness had an 86% reduction in creep rupture life. Microstructural observations on coated samples indicated the formation of diffusion zones beneath the coating; a creep life model was then developed to taken account the reduction in load bearing cross sectional area. In conclusions, the creep-rupture lives predicted by the model have shown good agreement with the experimental values.

  • the effects of ruthenium on the phase stability of fourth generation ni base Single Crystal Superalloys
    Scripta Materialia, 2006
    Co-Authors: Atsushi Sato, Yutaka Koizumi, Hiroshi Harada, Tadaharu Yokokawa, Takao Murakumo, Toshiharu Kobayashi, Hachiro Imai
    Abstract:

    Abstract The formation of topologically close-packed (TCP) phases in nickel-base Single Crystal Superalloys causes considerable degradation of the mechanical properties. It has recently been found that platinum-group metals can be effective in controlling the precipitation of such phases, and this extent of precipitation control requires further investigation. This study compares Ru-containing and non-Ru-containing Single Crystal Superalloys. Scanning electron microscopy microstructural observations showed that the rate of TCP phase precipitations decreased through Ru addition. Transmission electron microscopy microstructural observations showed that the P phase, one of the TCP phases, was eliminated through the addition of Ru. The occurrence of this phenomenon will be discussed.

R C Reed - One of the best experts on this subject based on the ideXlab platform.

  • isolation and testing of new Single Crystal Superalloys using alloys by design method
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: R C Reed, Atsushi Sato, Zailing Zhu, D J Crudden
    Abstract:

    Abstract Three new Single Crystal Superalloys are isolated using theory-based computational modelling approaches, termed alloys-by-design methods. They are (i) an oxidation-resistant low Re-containing alloy with balanced properties, intended for general-purpose gas turbine applications; (ii) an alloy containing 5.6 wt% Re and 2.6 wt% Ru suitable for high performance jet engine applications, when creep resistance needs to be maximised without oxidation performance being excessively compromised and (iii) a cheap, corrosion-resistant alloy for power generation applications designed with ease-of-processing in mind. The new alloys have been manufactured using investment casting techniques, and their creep and oxidation behaviour evaluated. The robustness of the so-called alloys-by-design methods is demonstrated, although the predictions for microstructural stability need to be improved.

  • what is the role of rhenium in Single Crystal Superalloys
    MATEC Web of Conferences, 2014
    Co-Authors: Alessandro Mottura, R C Reed
    Abstract:

    Rhenium plays a critical role in Single-Crystal Superalloys –its addition to first generation alloys improves creep life by a factor of at least two, with further benefits for fatigue performance. Its use in alloys such as PWA1484, CMSX-4 and Rene N5 is now widespread, and many in this community regard Re as the “magic dust”. In this paper, the latest thinking concerning the origins of the “rhenium-effect” is presented. We start by reviewing the hypothesis that rhenium clusters represent barriers to dislocation motion. Recent atom probe tomography experiments have shown that Re may instead form a solid solution with Ni at low concentrations ( ′ interfaces, which require non-conservative climb and thus an associated vacancy flux.

  • a model for the creep deformation behaviour of nickel based Single Crystal Superalloys
    Acta Materialia, 2012
    Co-Authors: Zailing Zhu, Nils Warnken, Hector Basoalto, R C Reed
    Abstract:

    Abstract A physical model for the creep deformation of Single Crystal Superalloys is presented that is sensitive to chemical composition and microstructure. The rate-controlling step is assumed to be climb of dislocations at the matrix/particle interfaces and their rate of escape from trapped configurations; a strong dependence on alloy composition then arises. By testing the predictions of the model against the considerable body of published experimental data, the dependence of the kinetics of creep deformation on alloy chemistry is rationalized. The effects of microstructural scale – precipitate size, geometry and spacing – are also studied. The climb processes assumed at the matrix/precipitate interfaces give rise to the vacancy flux required for the mass transport needed for rafting. For creep deformation at higher temperatures, a modification to the basic theory is proposed to account for a rafting-induced strengthening effect. A first-order estimate for the rate of creep deformation emerges from the model, which is useful for the purposes of alloy design.

  • oxidation of nickel based Single Crystal Superalloys for industrial gas turbine applications
    Acta Materialia, 2011
    Co-Authors: A Sato, Y L Chiu, R C Reed
    Abstract:

    Abstract The oxidation resistance of three prototype Single-Crystal nickel-based Superalloys for industrial (electricity-generating) gas turbine applications is studied. All contain greater quantities of Cr than in most existing Single-Crystal Superalloys; two are alloyed with Si. All alloys are found to be marginal Al 2 O 3 -formers, with the performance being better at 1000 °C rather than 900 °C, and when Si is added. Microstructural analysis indicates that the ability to form an Al 2 O 3 layer is better in the interdendritic regions; the dendritic regions are prone to internal oxidation. In all cases, an outer scale of Cr 2 O 3 is formed which is in contact with either Ta 2 O 5 (at 1000 °C) or NiTa 2 O 6 (at 900 °C). To explain the results, the factors known to influence the rate of Al 2 O 3 scale formation are considered. A model is developed to predict whether any given alloy composition will form a continuous Al 2 O 3 scale. This is used to rationalize the dependence of Al 2 O 3 scale formation on alloy composition in these systems. It is useful for the purposes of alloy design.

  • alloys by design application to nickel based Single Crystal Superalloys
    Acta Materialia, 2009
    Co-Authors: R C Reed, T Tao, Nils Warnken
    Abstract:

    Design rules are proposed by which the compositions of nickel-based Single Crystal Superalloys can be chosen systematically, using models for the most important characteristics: creep resistance, microstructural stability, castability, density and cost. Application of the rules allows the very large compositional space to be reduced to just a few ideal compositions, which are likely to be close to the optimal ones. The procedures have the potential to remove much of the traditional reliance placed upon empiricism and trial-and-error-based testing. It appears that trade-offs must be accepted, however; for example, the most creep-resistant alloys are more dense, more costly and more inherently susceptible to casting-related defects such as freckles during processing. Compositions suitable for both jet propulsion and land-based applications are proposed, for future experimental testing.

Tresa M Pollock - One of the best experts on this subject based on the ideXlab platform.

Tao Jin - One of the best experts on this subject based on the ideXlab platform.

  • in situ tem investigation on the precipitation behavior of μ phase in ni base Single Crystal Superalloys
    Acta Materialia, 2016
    Co-Authors: Shuang Gao, Yizhou Zhou, Zhiquan Liu, Tao Jin
    Abstract:

    Abstract The precipitation behavior of μ phase in Ni-base Single Crystal Superalloys was investigated by in situ transmission electron microscopy (TEM). A layer-by-layer growth process with a ledge propagation mechanism was first observed during in situ precipitation. Three types of μ phase with different morphologies were found, which grow along [001]μ with (001)μ planar defects, [-111]μ with (1–12)μ planar defects, as well as both directions with mixed planar defects. High-resolution TEM image and established atomic models reveal a basic growth mechanism of μ phase by stacking on (001)μ plane and randomly forming coherent planar defects, while the nucleation of incoherent (1–12)μ planar defects at the early stage of precipitation plays an important role in affecting the basic growth mechanism. The frequent faults during the stacking process of the sub-unit layers within μ lattice should be responsible for the defect formation.

  • comparison of low cycle fatigue behaviors between two nickel based Single Crystal Superalloys
    International Journal of Fatigue, 2014
    Co-Authors: Tao Jin, Y.z. Zhou, X.f. Sun, Z.f. Zhang
    Abstract:

    Abstract The deformation mechanisms of nickel-base Single-Crystal Superalloys containing 3 wt.% Re (3Re) and without Re (0Re) were systematically investigated in the temperature range from room temperature to 900 °C. At all testing temperatures, the alloy 3Re showed higher stress amplitudes and longer fatigue lives. With increasing temperature, slip mode gradually changes from planar to wavy slip. Dislocation climb and cross-slip, even by-passing became dominant deformation mechanisms of the two alloys and the addition of Re further reinforced this trend. In this process, the deformation homogenization became dominant, which resulted in the transition of cracking mode from shear fracture to normal fracture. At low temperature the specimen eventually cracks along the slip bands by shear, but at high temperature the specimen cracks by normal and shows mode I cracking.

  • Effect of orientations on in situ tensile deformation and fracture behaviours of nickel-base Single-Crystal Superalloys
    Philosophical Magazine, 2014
    Co-Authors: Bin Zhou, Y.z. Zhou, Tao Jin, X.f. Sun, Z.f. Zhang
    Abstract:

    After systematically investigating in situ tensile deformation and fracture behaviours of nickel-base Single-Crystal Superalloys with four different orientations, their slip and fracture modes in relation to the orientations are obtained and shown as follows. In [0 0 1] oriented specimen, four slip systems were activated and the crack initiated along the interactive location between the third slip bands (SBs) and deformation bands in priority. The crack propagation involves all three crack opening types of I, II and III. [0 1 1] oriented specimens exhibited obvious low strain hardening rate and high ductility, which can be attributed to the balance between the softening caused by the propagation of SBs and the latent hardening caused by the propagation of deformation bands. Except for case, the critical resolved shear stress (CRSS) of the other oriented Superalloys at room temperature is approximate, which is due to non-Schmid behaviour in Superalloys. Lall–Chin–Pope model is used to explain the orientati...

  • isothermal solidification stage during transient liquid phase bonding Single Crystal Superalloys
    Philosophical Magazine, 2014
    Co-Authors: Naicheng Sheng, Tao Jin, Jide Liu, Xiaofeng Sun
    Abstract:

    In this work, the isothermal solidification stage during transient liquid-phase bonding (TLP) Single-Crystal Superalloys has been investigated. Experiments were performed to ascertain the bonding microstructures and the kinetics during the isothermal solidification. The results have shown that the isothermal solidification stage deviates from the standard parabolic TLP models. Lots of the borides with fine, short bar and acicular morphologies formed in the diffusion affected zone (DAZ) in the thick wall and thin wall substrate specimens at the isothermal solidification stage. Electron probe microanalysis results have shown that there exists B composition peak in the DAZ. Examination of the bonding kinetics presented that there are three stages in the isothermal solidification stage: initial stage, transient stage and final stage with different growth velocity of the isothermal solidification zone (ISZ). And the relationship of the width of the ISZ with the square root of the bonding time didn’t satisfy th...

  • effect of re on low cycle fatigue behaviors of ni based Single Crystal Superalloys at 900 c
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Tao Jin, Y.z. Zhou, X.f. Sun, Z.f. Zhang
    Abstract:

    Abstract The effects of Re on low-cycle fatigue (LCF) behaviors of Single-Crystal Superalloys can be summarized mainly in the following aspects. On one hand, the addition of Re strongly retards the coarsening process of γ'-Ni3Al phase and maintains the uniformity of the phase structure. On the other hand, the Re addition can promote the segregation, which usually increases the lattice mismatch of the superalloy and further impedes any individual dislocation to move in the γ-Ni matrix freely and induces the activation of more dislocation movement by a combined glide-climb process. All these factors have improved the LCF properties of Single-Crystal Superalloys at 900 °C, for instance, the deformation becomes more homogeneous, the strengthening of γ' phase is more effective and therefore the fatigue life becomes longer due to the addition of Re.

Jonathan Cormier - One of the best experts on this subject based on the ideXlab platform.

  • a tensorial thermodynamic framework to account for the γ rafting in nickel based Single Crystal Superalloys
    International Journal of Plasticity, 2017
    Co-Authors: Rodrigue Desmorat, Adriana Mattiello, Jonathan Cormier
    Abstract:

    Abstract A new model is developed in order to account for the effect of microstructural degradation (i.e. precipitate-directional-coarsening) on the viscoplastic behavior of Single Crystal Superalloys under high temperature exposure. Microstructural changes are modeled by a tensorial description of γ channel width evolution and coupled to the Kelvin modes based viscoplasticity thanks to the Orowan stress. Such a coupling is performed within a thermodynamics framework. Isotropic and directional coarsening of the γ ' hardening phase are modeled as well as its dissolution with temperature changes. Results are presented for isothermal creep of CMSX-4 alloy at 1050 ∘ C along 001 > and 111 > Crystal directions but the formulation allows to account for anisothermal loadings, isotropization of the creep response at high temperature and misaligned loadings. This newly developed tensorial framework for rafting can also apply to Single Crystal Superalloys having a positive misfit.

  • A tensorial thermodynamic framework to account for the γ ′ rafting in Nickel-based Single Crystal Superalloys
    2016
    Co-Authors: Rodrigue Desmorat, Adriana Mattiello, Jonathan Cormier
    Abstract:

    A new model is developed in order to account for the effect of microstructural degradation (i.e. precipitate-directional-coarsening) on the viscoplastic behavior of Single Crystal Superalloys under high temperature exposure. Microstructural changes are modeled by a tensorial description of γ channel width evolution formulated in the natural anisotropy basis of the material. The tensorial description of microstructural evolution is combined with the Kelvin modes based viscoplasticity laws thanks to the coupling with the Orowan stress performed within a thermodynamics framework. Isotropic and directional coarsening of the γ ′ hardening phase are modeled as well as its dissolution with temperature changes. Results are presented for isothermal creep of CMSX-4 alloy at 1050 • C along < 001 > and < 111 > Crystal directions but the formulation allows to account for anisothermal loadings, isotropization of the creep response at high temperature and misaligned loadings. This newly developed tensorial framework for rafting can also apply to Single Crystal Superalloys having a positive misfit.