An Analysis of High Temperature Metal Creep—Part I: Experimental Definition of an Alloy

1978 ◽  
Vol 100 (4) ◽  
pp. 363-370 ◽  
Author(s):  
J. H. Laflen ◽  
D. C. Stouffer
Keyword(s):  
Creep Rate ◽  
Constitutive Modeling ◽  
Minimum Creep Rate ◽  
Major Part ◽  
Primary Creep ◽  
Rate Function ◽  
Creep Tests ◽  
Load Rate ◽  
Metal Creep ◽  
Definition Of

The general objective of the research reported is to develop a constitutive theory for the elevated temperature behavior of Wrought Udiment 700. A major part of this work was to establish a data base for this material and evaluate the observed response using many of the modern approaches to constitutive modeling. The phenomenological description of the material was evaluated by a series of load rate, strain rate, and creep tests. These data clearly showed the existence of a finite primary creep rate response function similar to the minimum creep rate function. Also the concept of material stress rate coordinate is introduced to describe the change from the primary to the minimum creep rate.

High Temperature Creep of Alpha-2 Ti-34mo1%Al Polycrystals

1994 ◽  
Vol 364 ◽  
Author(s):  
Hiroshi Oikawa ◽  
Toshihiko Fukuda ◽  
Makoto Ohtsuka
Keyword(s):  
Creep Rate ◽  
Minimum Creep Rate ◽  
Single Phase ◽  
Creep Condition ◽  
Primary Creep ◽  
High Temperature Creep ◽  
Creep Tests ◽  
Creep Stage ◽  
Fine Grained ◽  
Equiaxed Grains

AbstractConstant-stress compressive creep tests were carried out on an Al-rich a2 single-phase material, which had equiaxed-grains of 60μim in grain size, at 1050∼1250 K under 100∼500MPa. The type of the primary creep stage and the microstructures developed during creep depend greatly on the creep condition. The minimum creep-rate, however, can be represented by one set of parameters over the whole range of experimental condition. The stress exponent is 5.0±0.2 and the (modulus-compensated) activation energy is 360 ± 10kJ/mol. The Dorn-type plot of the minimum creep rate reveals that the normalized creep strength of fine-grained Ti-34mol%Al is not greatly different from that of disordered solid-solution hardened alloys.

Creep Behavior and Microstructural Stability of Lamellar γ-T1AI (Cr, Mo, Si, B) with Extremely Fine Lamellar Spacing

2000 ◽  
Vol 646 ◽  
Author(s):  
Wolfram Schillinger ◽  
Dezhi Zhang ◽  
Gerhard Dehm ◽  
Arno Bartels ◽  
Helmut Clemens
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Primary Creep ◽  
Vacuum Arc ◽  
Internal Stresses ◽  
Microstructural Stability ◽  
Thermodynamical Equilibrium ◽  
Creep Tests

ABSTRACTγ-T1AI (Cr, Mo, Si, B) specimens with two different fine lamellar microstructures were produced by vacuum arc melting followed by a two-stage heat treatment. The average lamellar spacing was determined to be 200 nm and 25–50 nm, respectively. Creep tests at 700°C showed a very strong primary creep for both samples. After annealing for 24 hours at 1000 °C the primary creep for both materials is significantly decreased. The steady-state creep for the specimens with the wider lamellar spacing appears to be similar to the creep behavior prior to annealing while the creep rate of the material with the previously smaller lamellar spacing is significantly higher. Optical microscopy and TEM-studies show that the microstructure of the specimens with the wider lamellar specing is nearly unchanged, whereas the previously finer material was completely recrystallized to a globular microstructure with a low creep resistance. The dissolution of the fine lamellar microstructure was also observed during creep tests at 800 °C as manifested in an acceleration of the creep rate. It is concluded that extremely fine lamellar microstructures come along with a very high dislocation density and internal stresses which causes the observed high primary creep. The microstructure has a composition far away from the thermodynamical equilibrium which leads to a dissolution of the structure even at relatively low temperatures close to the intended operating temperature of γ-T1AI structural parts. As a consequence this limits the benefit of fine lamellar microstructures on the creep behavior.

Investigation on Creep Behavior of Grade 91 Heat-Resistant Steel at 923K

2016 ◽  
Vol 853 ◽  
pp. 163-167
Author(s):  
Fa Cai Ren ◽  
Xiao Ying Tang
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Behavior ◽  
Minimum Creep Rate ◽  
Resistant Steel ◽  
Creep Tests ◽  
Heat Resistant Steel ◽  
Heat Resistant ◽  
Grade 91

Creep deformation behavior of SA387Gr91Cl2 heat-resistant steel used for steam cooler has been investigated. Creep tests were carried out using flat creep specimens machined from the normalized and tempered plate at 973K with stresses of 100, 125 and 150MPa. The minimum creep rate and rupture time dependence on applied stress was analyzed. The analysis showed that the heat-resistant steel obey Monkman-Grant and modified Monkman-Grant relationships.

A Modified Theta Projection Creep Model for a Nickel-Based Super-Alloy

2013 ◽  
Author(s):  
W. David Day ◽  
Ali P. Gordon
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Primary Creep ◽  
Tertiary Creep ◽  
Creep Model ◽  
Creep Tests ◽  
Creep Equation ◽  
Physical Constraints ◽  
Primary Creep Strain ◽  
Super Alloy

Accurate prediction of creep deformation is critical to assuring the mechanical integrity of heavy-duty, industrial gas turbine (IGT) hardware. The classical description of the creep deformation curve consists of a brief primary, followed by a longer secondary, and then a brief tertiary creep phase. An examination of creep tests at four temperatures for a proprietary, nickel-based, equiaxed, super-alloy revealed many occasions where there is no clear transition from secondary to tertiary creep. This paper presents a new creep model for a Nickel-based super-alloy, with some similarities to the Theta Projection (TP) creep model by Evans and all [1]. The alternative creep equation presented here was developed using meaningful parameters, or θ’s, such as: the primary creep strain, time at primary creep strain, minimum (or secondary) creep rate, and time that tertiary creep begins. By plotting the first and second derivative of creep, the authors were able to develop a creep equation that accurately matches tests. This creep equation is identical to the primary creep portion of the theta projection model, but has a modified second term. An additional term is included to simulate tertiary creep. An overall scaling factor is used to satisfy physical constraints and ensure solution stability. The new model allows a constant creep rate phase to be maintained, captures tertiary creep, and satisfies physical constraints. The coefficients of the creep equations were developed using results from 27 creep tests performed at 4 temperatures. An automated routine was developed to directly fit the θ coefficients for each phase, resulting in a close overall fit for the material. The resultant constitutive creep model can be applied to components which are subjected to a wide range of temperatures and stresses. Useful information is provided to designers in the form of time to secondary and tertiary creep for a given stress and temperature. More accurate creep predictions allow PSM to improve the structural integrity of its turbine blades and vanes.

scholarly journals Lattice continuum and diffusional creep

2016 ◽  
Vol 472 (2188) ◽  
pp. 20160039 ◽  
Author(s):  
Sinisa Dj. Mesarovic
Keyword(s):  
Creep Rate ◽  
Continuum Theory ◽  
Primary Creep ◽  
Diffusional Creep ◽  
Secondary Creep ◽  
Diffusional Flux ◽  
Coupled Diffusion ◽  
Boundary Dissipation ◽  
Definition Of ◽  
Secondary Creep Rate

Diffusional creep is characterized by growth/disappearance of lattice planes at the crystal boundaries that serve as sources/sinks of vacancies, and by diffusion of vacancies. The lattice continuum theory developed here represents a natural and intuitive framework for the analysis of diffusion in crystals and lattice growth/loss at the boundaries. The formulation includes the definition of the Lagrangian reference configuration for the newly created lattice, the transport theorem and the definition of the creep rate tensor for a polycrystal as a piecewise uniform, discontinuous field. The values associated with each crystalline grain are related to the normal diffusional flux at grain boundaries. The governing equations for Nabarro–Herring creep are derived with coupled diffusion and elasticity with compositional eigenstrain. Both, bulk diffusional dissipation and boundary dissipation accompanying vacancy nucleation and absorption, are considered, but the latter is found to be negligible. For periodic arrangements of grains, diffusion formally decouples from elasticity but at the cost of a complicated boundary condition. The equilibrium of deviatorically stressed polycrystals is impossible without inclusion of interface energies. The secondary creep rate estimates correspond to the standard Nabarro–Herring model, and the volumetric creep is small. The initial (primary) creep rate is estimated to be much larger than the secondary creep rate.

Creep Constitutive Equations for 1CrMoV Bolt Material

2002 ◽  
Author(s):  
Fred V. Ellis ◽  
Robert L. Zielke
Keyword(s):  
Creep Rate ◽  
Power Law ◽  
Constitutive Equations ◽  
Minimum Creep Rate ◽  
Good Description ◽  
Primary Creep ◽  
Primary Component ◽  
Creep Equation ◽  
Statistical Measures ◽  
Rational Polynomial

Creep constitutive equations were developed for 1CrMoV bolt material using the NRIM creep data at temperatures of 450°C, 500°C and 550°C. The creep constitutive equations were those used by the ANSYS FEM stress analysis program. Three types of creep equations were developed: (1) primary, (2) secondary, and (3) primary plus secondary. The primary creep equation had a power law in stress and time with an exponential inverse temperature dependence. The secondary models for log minimum creep rate had either log stress alone or stress and log stress terms. Two primary plus secondary models were used: (1) a power law primary and (2) the rational polynomial. For the rational polynomial, the constant p was estimated as nineteen over the time to the end of primary creep. The time to end of primary creep was defined by the attainment of a low value for the ratio of the primary creep rate to minimum creep rate. The primary creep rate was calculated using the power law primary component of the power law primary plus steady state creep equation. To evaluate the fits, comparisons of calculated and observed creep curves were made as well as plots of residual in log creep strain. Based on these comparisons and the statistical measures (R2 and standard deviation), the derived creep equations were judged to be a good description of the creep behavior.

A Flow Potential Function for Hyperbolic Sine Creep

1978 ◽  
Vol 45 (3) ◽  
pp. 679-681
Author(s):  
E. A. Davis
Keyword(s):  
Creep Rate ◽  
Uniaxial Tension ◽  
Potential Function ◽  
Yield Surface ◽  
Minimum Creep Rate ◽  
Creep Tests ◽  
Hyperbolic Sine ◽  
Flow Potential ◽  
Sine Law

A new flow potential function or yield surface is presented. This function produces the hyperbolic sine law relating stress to minimum creep rate for creep tests in uniaxial tension.

Creep and Creep-rupture Behavior of 2124-T851 Aluminum Alloy

2013 ◽  
Vol 32 (6) ◽  
pp. 533-540 ◽  
Author(s):  
Yu-Qiang Jiang ◽  
Y.C. Lin ◽  
C. Phaniraj ◽  
Yu-Chi Xia ◽  
Hua-Min Zhou
Keyword(s):  
Aluminum Alloy ◽  
Creep Rate ◽  
Power Law ◽  
Minimum Creep Rate ◽  
Tensile Creep ◽  
Uniaxial Tensile ◽  
Secondary Creep ◽  
Creep Life ◽  
Creep Tests ◽  
Creep Equation

AbstractHigh temperature creep and useful creep life behavior of Al-Cu-Mg (2124-T851 aluminum) alloy was investigated by conducting constant stress uniaxial tensile creep tests at different temperatures (473–563 K) and at stresses ranging from 80 to 200 MPa. It was found that the stress and temperature dependence of minimum creep rate could be successfully described by the power-law creep equation. The power-law stress exponent, n = 5.2 and the activation energy for secondary creep, Q = 164 kJ mol−1, which is close to that observed for self diffusion of aluminum (~140 kJ mol−1). The observed values of n and Q suggest that the secondary creep of 2124-T851 aluminum alloy is governed by the lattice diffusion controlled dislocation climb process. A Monkman-Grant type relationship between minimum creep rate and time for reaching 1.5% creep strain is proposed and could be employed for predicting the useful creep life of 2124-T851 aluminum alloy.

Sign in / Sign up

Export Citation Format

Share Document