Study on Relationship Between Dislocation Density and Creep Strain Rate of Single Crystal Ni Based Superalloy for Gas Turbines Using the Discrete Cosine Transform

2021 ◽  
Author(s):  
Hideo Hiraguchi
Keyword(s):  
Dislocation Density ◽  
Strain Rate ◽  
Single Crystal ◽  
Creep Strain ◽  
Discrete Cosine Transform ◽  
Gas Turbines ◽  
Elevated Temperatures ◽  
Creep Strain Rate ◽  
Cosine Transform ◽  
Term Creep

Abstract The discrete cosine transform (DCT) is known to be able to express the relation curve between creep strain and time, or the relation curve between creep strain rate and time very well. Moreover, recently it has been found out that the DCT can draw electron density distribution maps of crystals. In addition, the DCT always passes through all the points measured at an equal interval in any continuous curves and its interpolated values between adjacent points are very reasonable. Furthermore, a new prediction method for long term creep curves from short term creep data by using the DCT was reported at TurboExpo2020. Up to the present, the strength of single crystal Nickel based superalloys for gas turbines at elevated temperatures has been advanced by controlling the interface dislocation density and the lattice misfit at the γ/γ’ interfaces. For this reason, it has to be understood how to evaluate a relationship between interface dislocation density and creep strain rate to develop more advanced single crystal Nickel based superalloys. Therefore, in this research it was studied how to evaluate the relationship between interface dislocation density and creep strain rate of a single crystal Nickel based superalloy for gas turbines by using the DCT. As a result, useful properties on the effective stress have been obtained from the coefficients of the DCT.

Application of the Wilshire Stress-Rupture and Minimum-Creep-Strain-Rate Prediction Models for Alloy P91 in Tube, Plate and Pipe Form

2019 ◽  
Author(s):  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Stress Rupture ◽  
Creep Strain Rate ◽  
Tube Plate ◽  
Short Term ◽  
Design Life ◽  
Term Creep ◽  
Term Data

Abstract There exists a challenge in predicting the long-term creep of materials (3 105 hours) where 11+ years of continuous testing is required to physically collect creep data. As an alternative to physical testing, constitutive models are calibrated to short-term data (< 104 hours) and employed to extrapolate the long-term creep behavior. The Wilshire model was introduced to predict the stress-rupture and minimum-creep-strain-rate behavior of materials and the model is well-accepted due to the explicit description of stress- and temperature-dependence allowing predictions across isotherms and stress levels. There is an ongoing effort to determine how alloy form affects the long-term creep predictions of the Wilshire model. In this study, stress-rupture and minimum-creep-strain-rate predictions are generated for alloy P91 in tube, plate, and pipe form. Data is gathered from the National Institute of Materials Science (NIMS) material database for alloy P91 at multiple isotherms. Following the establish calibration method for the Wilshire model, post-audit validation is performed using short-term data from NIMS to vet the extrapolations accuracy of each form at different isotherms. The Wilshire model demonstrates successful extrapolative techniques for the stress-rupture and minimum-creep-strain-rate of tube, plate, and pipe forms across multiple isotherms. Overall the form with the highest extrapolative accuracy for both stress-rupture and minimum-creep-strain-rate is the plate and the lowest one is the pipe. Stress-rupture design maps are provided where stress and temperature are axes and rupture-time is in contour. The design maps can be applied to: (a) given the boundary conditions, determine the design life (b) given the design life, determine the acceptable range of a boundary conditions. The latter is more useful in turbomachinery design.

Effects of ternary additions on the deformation behavior of single crystals of MoSi2

2000 ◽  
Vol 646 ◽  
Author(s):  
Haruyuki Inui ◽  
Koji Ishikawa ◽  
Masaharu Yamaguchi
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
Single Crystals ◽  
Creep Strain ◽  
High Temperatures ◽  
Low Temperatures ◽  
Deformation Behavior ◽  
Creep Strain Rate ◽  
Compression Creep ◽  
Ternary Additions

ABSTRACTEffects of ternary additions on the deformation behavior of single crystals of MoSi2 with the hard [001] and soft [0 15 1] orientations have been investigated in compression and compression creep. The alloying elements studied include V, Cr, Nb and Al that form a C40 disilicide with Si and W and Re that form a C11b disilicide with Si. The addition of Al is found to decrease the yield strength of MoSi2 at all temperatures while the additions of V, Cr and Nb are found to decrease the yield strength at low temperatures and to increase the yield strength at high temperatures. In contrast, the additions of W and Re are found to increase the yield strength at all temperatures. The creep strain rate for the [001] orientation is significantly lower than that for the [0 15 1] orientation. The creep strain rate for both orientations is significantly improved by alloying with ternary elements such as Re and Nb.

scholarly journals Creep Strain and Permeability Evolution in Cracked Granite Subjected to Triaxial Stress and Reactive Flow

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Fan Zhang ◽  
Jianjian Zhao ◽  
Dawei Hu ◽  
Qian Sheng ◽  
Jianfu Shao
Keyword(s):  
Acid Solution ◽  
Strain Rate ◽  
Creep Strain ◽  
Alkaline Solution ◽  
Confining Pressure ◽  
Creep Strain Rate ◽  
Reactive Flow ◽  
Secondary Creep ◽  
Creep Tests ◽  
Creep Stage

Fluid flow and fluid-rock interaction mainly take place in fracture network, consequently resulting in deformation and permeability variation of rock and deterioration of the wellbore performance. Mechanical-reactive flow coupling creep tests are performed on cracked granite under various confining pressures and acid and alkaline solution flows. The testing results show that the confining pressure and solution pH significantly influence the creep deformation, creep strain rate, and permeability. A primary creep stage and secondary creep stage are observed in all creep tests in this study; notably, the sample under a confining pressure of 10 MPa and acid solution injection undergoes creep failure for over 2700 hours. The acid solution has a more obvious influence on the creep behavior than that of the alkaline solution. With an increase in confining pressure, the total creep strain and creep strain rate in the samples gradually decrease during the injection of either solution. The permeability of the samples injected with either solution gradually deceases during the testing process, and this deceasing rate increases with the confining pressure. The scanning electron microscopy observations on the crack surfaces after the creep tests show that the surfaces of the fractures injected with the acid solution are smooth due to the dissolution of the matrix, while those injected with the alkaline solution include voids due to the dissolution of quartz. These experimental results could improve the understanding of the long-term transport and mechanical behaviors of wellbore.

scholarly journals New Numerical Analysis Method for Creep Lifetime of Gas Turbine Materials by Using the Discrete Cosine Transform

2020 ◽  
Author(s):  
Hideo Hiraguchi
Keyword(s):  
Discrete Cosine Transform ◽  
Creep Curve ◽  
Creep Data ◽  
Short Term ◽  
Cosine Transform ◽  
Discrete Signals ◽  
Creep Region ◽  
Term Creep ◽  
Short Term Creep

Abstract Recently the Discrete Cosine Transform[1], [2], [3] which is a modified Fourier Transform has begun to be used to express coefficients of creep equations using the power law or the exponential law such as Bailey-Norton law[4], [5] and θ Projection[6], [7], [8], [9], [10]. In addition, the Discrete Cosine Transform has begun to be used to express a creep equation itself. We have already found that the Discrete Cosine Transform can express the temperature and stress dependence property of the coefficients of the creep equations at the same time by the two-dimensional Discrete Cosine Transform using 8 × 8 discrete signals[11]. Furthermore, we have already found that the Discrete Cosine Transform can fit measured creep strain values very well from the primary creep region to the tertiary creep region using 8 discrete signals and it can estimate creep strain values between the measured points by interpolation very well[12]. However it has not been known if the Discrete Cosine Transform can predict the long term creep curve by using the short term creep data yet. Therefore, as a next stage, we tried to estimate the long term creep curve from the short term creep data of gas turbine materials by extrapolation using the Discrete Cosine Transform. As a result, we were able to obtain a useful numerical analysis method by utilizing the Discrete Cosine Transform Coefficients and others as a new extrapolation method. It is found that this new numerical method would be able to predict the configuration of 150,000-hour creep curve by using 500-hour to 13,000-hour short term creep data.

Creep Strength Evaluation of a New and a Used Grade 91 Welded Joints by Using a Miniature Specimen

2018 ◽  
Author(s):  
Takashi Ogata
Keyword(s):  
Weld Metal ◽  
Strain Rate ◽  
Creep Strain ◽  
Base Metal ◽  
Welded Joints ◽  
Welded Joint ◽  
Creep Damage ◽  
Creep Strain Rate ◽  
Standard Size ◽  
Grade 91

Grade 91 is widely used for steam pipes and tubes in high temperature boilers of ultra-super critical power plants in Japan. It was reported that creep damage may initiate at the fine grain region within the heat affected zone (HAZ) in welded joints prior to the base metal, so called “Type IV” damage, which causes steam leakage in existing power plants. Therefore, development of creep damage assessment methods is not only an important but also an urgent subject to maintain operation reliability. In order to evaluate creep damage of welded joints based on finite element analyses, creep deformation properties of a base metal, a weld metal and a HAZ have to be obtained from creep tests. However, it is difficult to cut a standard size creep specimen from the HAZ region. Only a miniature size specimen is available from the narrow HAZ region. Therefore, development of creep testing and evaluation technique for miniature size specimens is highly expected. In this study, a miniature tensile type solid bar specimen with 1mm diameter was machined from a base metal, a weld metal and a HAZ of a new and a used Grade 91 welded joints, and creep tests of these miniature specimens were conducted by using a special developed creep testing machine. It was found that creep deformation property is almost identical between the base metal and weld metal, and creep strain rate of the HAZ is much faster than that of these metals in the new welded joint. Relationships between stress and creep strain rates of the base metal and the HAZ in the used welded joint are within scatter bands of those in the new material. On the other hand, creep strain rate of the weld metal in the used welded joint became much faster than that in the new one. Then both the standard size and the miniature size cross weld specimens were machined from the new and the used welded joints and were tested under the same temperature and stress conditions. Rupture time of the miniature cross weld specimen is much shorter than that of the standard size cross weld specimen. The finite element creep analysis of the specimens indicates that higher triaxiality stress yields within the HAZ of the standard size specimen than that of the miniature specimen causing faster creep strain rate in the HAZ of the miniature cross weld specimen.

INDENTATION SIZE EFFECT ON THE CREEP BEHAVIOR OF A SnAgCu SOLDER

2010 ◽  
Vol 24 (01n02) ◽  
pp. 267-275 ◽  
Author(s):  
Y. D. HAN ◽  
H. Y. JING ◽  
S. M. L. NAI ◽  
L. Y. XU ◽  
C. M. TAN ◽  
...  
Keyword(s):  
Creep Rate ◽  
Strain Rate ◽  
Creep Strain ◽  
Creep Behavior ◽  
Maximum Load ◽  
Creep Strain Rate ◽  
Lead Free ◽  
Lead Free Solder ◽  
Snagcu Solder ◽  
Free Solder

In the present study, nanoindentation studies of the 95.8 Sn -3.5 Ag -0.7 Cu lead-free solder were conducted over a range of maximum loads from 20 mN to 100 mN, under a constant ramp rate of 0.05 s-1. The indentation scale dependence of creep behavior was investigated. The results revealed that the creep rate, creep strain rate and indentation stress are all dependent on the indentation depth. As the maximum load increased, an increasing trend in the creep rate was observed, while a decreasing trend in creep strain rate and indentation stress were observed. On the contrary, for the case of stress exponent value, no trend was observed and the values were found to range from 6.16 to 7.38. Furthermore, the experimental results also showed that the creep mechanism of the lead-free solder is dominated by dislocation climb.

scholarly journals Small Two-Bar Specimen Creep Testing of Grade P91 Steel at 650°C

2016 ◽  
Vol 35 (3) ◽  
pp. 243-252
Author(s):  
Balhassn S. M. Ali ◽  
Tom H. Hyde ◽  
Wei Sun
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Test Data ◽  
Creep Test ◽  
Uniaxial Stress ◽  
Creep Rupture ◽  
Creep Strain Rate ◽  
P91 Steel ◽  
Uniaxial Creep ◽  
Rupture Data

AbstractCommonly used small creep specimen types, such as ring and impression creep specimens, are capable of providing minimum creep strain rate data from small volumes of material. However, these test types are unable to provide the creep rupture data. In this paper the recently developed two-bar specimen type, which can be used to obtain minimum creep strain rate and creep rupture creep data from small volumes of material, is described. Conversion relationships are used to convert (i) the applied load to the equivalent uniaxial stress, and (ii) the load line deformation rate to the equivalent uniaxial creep strain rate. The effects of the specimen dimension ratios on the conversion factors are also discussed in this paper. This paper also shows comparisons between two-bar specimen creep test data and the corresponding uniaxial creep test data, for grade P91 steel at 650°C.

scholarly journals Influence of Mo Segregation at Grain Boundaries on the High Temperature Creep Behavior of Ni-Mo Alloys: An Atomistic Study

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 6966
Author(s):  
Qian Li ◽  
Jiayong Zhang ◽  
Huayuan Tang ◽  
Hongwu Zhang ◽  
Hongfei Ye ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Creep Strain ◽  
High Stress ◽  
External Stress ◽  
Creep Strain Rate ◽  
Creep Process ◽  
Boundary Slip

Based on molecular dynamics simulations, the creep behaviors of nanocrystalline Ni before and after the segregation of Mo atoms at grain boundaries are comparatively investigated with the influences of external stress, grain size, temperature, and the concentration of Mo atoms taken into consideration. The results show that the creep strain rate of nanocrystalline Ni decreases significantly after the segregation of Mo atoms at grain boundaries due to the increase of the activation energy. The creep mechanisms corresponding to low, medium, and high stress states are respectively diffusion, grain boundary slip and dislocation activities based on the analysis of stress exponent and grain size exponent for both pure Ni and segregated Ni-Mo samples. Importantly, the influence of external stress and grain size on the creep strain rate of segregated Ni-Mo samples agrees well with the classical Bird-Dorn-Mukherjee model. The results also show that segregation has little effect on the creep process dominated by lattice diffusion. However, it can effectively reduce the strain rate of the creep deformation dominated by grain boundary behaviors and dislocation activities, where the creep rate decreases when increasing the concentration of Mo atoms at grain boundaries within a certain range.

Sign in / Sign up

Export Citation Format

Share Document