scholarly journals Creep Damage Assessment of Notched Material Made of a Solidification Control Ni-Base Superalloy Using the EBSD Method

2018 ◽  
Vol 67 (2) ◽  
pp. 276-283
Author(s):  
Daisuke KOBAYASHI ◽  
Tsutomu TAKEUCHI ◽  
Katsushi NAKABEPPU ◽  
A. Toshimitsu YOKOBORI Jr.
Keyword(s):  
Damage Assessment ◽  
Creep Damage ◽  
Ebsd Method ◽  
Solidification Control ◽  
Base Superalloy

Atomic Diffusion Induced Damage of Ni-Base Super Alloy at Elevated Temperature

2016 ◽  
Author(s):  
Motoki Takahashi ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Power Plants ◽  
Creep Damage ◽  
Rotor Blades ◽  
Atomic Scale ◽  
Atomic Diffusion ◽  
Kernel Average Misorientation ◽  
Damage Process ◽  
Creep Loading ◽  
Ebsd Method ◽  
Base Superalloy

Ni-base superalloys consisting of binary phases such as cuboidal γ’ (Ni3Al) precipitates orderly dispersed in the γ matrix (Ni-rich matrix) have been generally used for rotor blades in energy power plants. However, fine dispersed γ’ precipitates are coarsened perpendicularly to the applied load direction during high temperature creep loading. As this phenomenon called “Rafting” proceeds, the strengthened micro texture disappears and then, cracks starts to grow rapidly along the boundaries of the layered texture. Thus, it is very important to evaluate the change of the crystallinity of the alloy in detail for explicating the atomic scale damage process. In this study, the change of the micro-texture of the Ni-base superalloy (CM247LC) was observed by using EBSD method. The change in the crystallinity was evaluated using both Kernel Average Misorientation (KAM) and image quality (IQ) values. The KAM value indicates the dislocation density and the IQ value shows the order of atom arrangement in the observed area. As a result, KAM value showed no significant change with increasing the creep damage. On the other hand, the IQ value monotonically shifted to lower values and the average IQ value gradually decreased as the creep loading time increased. Decreasing IQ value without change in KAM value implies that the density of point defects such as vacancies mainly increased under creep loading and ordered Ll2 structure became disordered. Therefore, the creep damage of this alloy is mainly dominated by not the accumulation of dislocations, but the increase in the disorder of atom arrangement in the micro texture caused by the diffusion of component elements.

scholarly journals Creep Damage Assessment of High Chromium Steel Forging through EBSD Method and Hardness Measurement

2008 ◽  
Vol 74 (739) ◽  
pp. 323-328 ◽  
Author(s):  
Kazunari FUJIYAMA ◽  
Keita MORI ◽  
Daisuke KANEKO ◽  
Takahide MATSUNAGA ◽  
Hirohisa KIMACHI
Keyword(s):  
Damage Assessment ◽  
Creep Damage ◽  
Hardness Measurement ◽  
Chromium Steel ◽  
High Chromium ◽  
Steel Forging ◽  
Ebsd Method

scholarly journals Damage Evaluation Based on EBSD Method for Nickel-Base Superalloy Notched Specimen Under Creep and/or Fatigue Conditions

2015 ◽  
Vol 64 (2) ◽  
pp. 113-119
Author(s):  
Daisuke KOBAYASHI ◽  
Masamichi MIYABE ◽  
Masahiro ACHIWA ◽  
Ruji SUGIURA ◽  
A. Toshimitsu. YOKOBORI Jr.
Keyword(s):  
Nickel Base Superalloy ◽  
Damage Evaluation ◽  
Notched Specimen ◽  
Nickel Base ◽  
Ebsd Method ◽  
Base Superalloy

High Temperature Damage of Ni-Base Superalloy Caused by the Change of Microtexture due to the Strain-Induced Anisotropic Diffusion of Component Elements

2011 ◽  
Author(s):  
Hideo Miura ◽  
Ken Suzuki ◽  
Yamato Sasaki ◽  
Tomohiro Sano ◽  
Naokazu Murata
Keyword(s):  
High Temperature ◽  
Anisotropic Diffusion ◽  
Axial Strain ◽  
Creep Damage ◽  
Face Centered Cubic ◽  
Directional Coarsening ◽  
Damage Process ◽  
Temperature Damage ◽  
Face Centered ◽  
Base Superalloy

In order to assure the reliability of advanced gas turbine systems, it is very important to evaluate the damage of high temperature materials such as Ni-base superalloys under creep and fatigue conditions quantitatively. Since the micro texture of the gamma-prime (γ′) phase was found to vary during the creep damage process, it is possible, therefore, to evaluate the creep damage of this material quantitatively by measuring the change of the micro texture. The mechanism of the directional coarsening of γ′ phasesof Ni-base superalloy under uni-axial strain at high temperatures, which is called rafting, was analyzed by using molecular dynamics (MD) analysis. The stress-induced anisotropic diffusion of Al atoms perpendicular to the finely dispersed γ/γ′ interface in the superalloy was observed clearly in a Ni(001)/Ni3Al(001) interface structure. The stress-induced anisotropic diffusion was validated by experiment using the stacked thin films structures which consisted of the (001) face-centered cubic (FCC) interface. The reduction of the diffusion of Al atoms perpendicular to the interface is thus, effective for improving the creep and fatigue resistance of the alloy. It was also found by MD analysis that the dopant elements in the superalloy also affected the strain-induced diffusion of Al atoms. Both palladium and tantalum were effective elements which restrain Al atoms from moving around the interface under the applied stress, while titanium and tungsten accelerated the strain-induced anisotropic diffusion, and thus, the rafting phenomenon.

A Metallographic Technique for High Temperature Creep Damage Assessment in Single Crystal Alloys

1998 ◽  
Author(s):  
Pamela Henderson ◽  
Jacek Komenda
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Creep Strain ◽  
Creep Deformation ◽  
Damage Assessment ◽  
Creep Damage ◽  
High Temperature Creep ◽  
Gamma Prime ◽  
Aspect Ratios ◽  
Metallographic Technique

The use of single crystal (SX) nickel-base superalloys will increase in the future with the introduction of SX blades into large gas turbines for base-load electricity production. Prolonged periods of use at high temperatures may cause creep deformation and the assessment of damage can give large financial savings. A number of techniques can be applied for life assessment, e.g. calculations based on operational data, non-destructive testing or material interrogation, but because of the uncertainties involved the techniques are often used in combination. This paper describes a material interrogation (metallographic) technique for creep strain assessment in SX alloys. Creep tests have been performed at 950°C on the SX alloy CMSX-4 and quantitative microstructural studies performed on specimens interrupted at various levels of strain. It was found that the strengthening γ′-particles, initially cuboidal in shape, coalesced to form large plates or rafts normal to the applied stress. The γ-matrix phase also formed plates. CMSX-4 contains ∼ 70 vol % γ′-particles and after creep deformation the microstructure turned itself inside out, i.e. the gamma “matrix” became the isolated phase surrounded by the γ′-“particles”. This can cause problems for computerised image analysis, which in this case, were overcome with the choice of a suitable measurement parameter. The rafts reached their maximum length before 2% strain, but continued to thicken with increasing strain. Although of different dimensions, the aspect ratios (length/thickness ratio) of the gamma-prime rafts and the gamma plates were similar at similar levels of strain, increasing from ∼1 at zero strain to a maximum of ∼3 at about 1–2 % strain. Analysis of microstructural measurements from rafting studies on SX alloys presented in the literature showed that the aspect ratios of the γ- and γ′-phases were similar and that at a temperature of 950–1000°C a maximum length/thickness ratio of about 2.5–3.5 is reached at 1 to 2% creep strain. Measurement of gamma-prime raft or (or gamma plate) dimensions on longitudinal sections of blades is thus a suitable method for high temperature creep damage assessment of SX alloys. This gives a considerable advantage over conventional Ni-base superalloys whose microstructures are usually very stable with respect to increasing creep strain.

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