Influence of the threshold stress on the creep properties of a CuCrZr alloy containing dispersoid particles

1994 ◽  
Vol 30 (7) ◽  
pp. 827-832 ◽  
Author(s):  
C. Dubois ◽  
M.A. Morris
Keyword(s):  
Threshold Stress ◽  
Creep Properties ◽  
Zr Alloy

The Effect of Carbon Diffusion on Creep Behaviours for a Dissimilar Joint Between P91 and 12Cr1MoV Steels

2016 ◽  
Author(s):  
Yanping Zhao ◽  
Jianming Gong ◽  
Yong Jiang
Keyword(s):  
Power Law ◽  
Threshold Stress ◽  
Carbon Diffusion ◽  
Dissimilar Joint ◽  
Multiphase Model ◽  
High Alloy ◽  
Dissimilar Joints ◽  
Premature Failure ◽  
Creep Properties ◽  
Alloy Part

Dissimilar joints have been widely used in many applications, especially for steam piping in the superheater and reheater of power plants. However, these dissimilar metal welds tend to fail less than half of their design life, and carbon diffusion is the main cause of the premature failure. Dissimilar joints operated at high temperature or after post-weld heat treatment (PWHT) exhibit carbon-enriched zone (CEZ) in the high alloy part and carbon-depleted zone (CDZ) in the low alloy part, causing by the chemical potential gradients across the weld interface. The carbides dissolute in the low alloy part while precipitate in the high alloy part. At the same time, a consequent of strength gradients are generated between the CEZ and CDE. The CDZ results in a loss of creep strength due to the carbides dissolution while an increase of strength due to the carbides precipitation. In this work, welding consumable of GTR-2CM was used to join P91 and 12Cr1MoV metals together. The stable phases and carbon activities of these metals are calculated by THERMO-CALC software. Carbon diffusion between P91/GTR-2CM/12Cr1MoV dissimilar joint after aging at 550 °C for varying time are predicted by employing dispersed multiphase model in DICTRA software. Volume fractions of carbides varying with distance from both sides of the weld interfaces were also investigated, showing that the formation of CDZs and CEZs is related to the dissolution and precipitation of M23C6 and M7C3 carbides. The dissolution and coarsening of M7C3 and M23C6 particles in the CDZ and CEZ were also modelled by DICTRA software. The creep properties of base metals, weld metal and the dissimilar joint were investigated at 550 °C. The stress dependence of minimum creep rate and rupture life obeyed the Norton’s power law, and the stress exponents can be used to identify the creep mechanism. Monkman-Grant (MG) relations were also used to study the creep rupture data. The simulation results of carbon diffusion can be used to study the creep properties of CDZ and CEZ for the P91/GTR-2CM/12Cr1MoV dissimilar joint. The threshold stress concept can be incorporated into the analysis of creep power law. The magnitudes of threshold stress within CEZ and CDZ can be calculated according to the volume fraction and average diameter of carbides from carbon diffusion.

scholarly journals Low temperature super ductility and threshold stress of an ultrafine-grained Al–Zn–Mg–Zr alloy processed by equal-channel angular pressing

2021 ◽  
Author(s):  
Bálint Boldizsár ◽  
Péter Jenei ◽  
Anwar Q. Ahmed ◽  
Maxim Yu. Murashkin ◽  
Ruslan Z. Valiev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Deformation Process ◽  
Threshold Stress ◽  
Rate Sensitivity ◽  
Impression Creep ◽  
Creep Tests ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Zr Alloy

AbstractLow temperature tensile and impression creep tests were carried out on an ultrafine-grained 7xxx series Al–4.8Zn–1.2 Mg–0.14Zr (wt%) alloy, which can be deformed for maximum elongation of about 200% at 150 °C. The characteristics of the deformation process, such as the strain rate sensitivity (SRS) and activation energy (Q) were determined by considering also the effect of threshold stress. Relatively high SRS of $$\sim$$ ∼ 0.35 and low activation energy of $$\sim$$ ∼ 92 kJ/mole were obtained, confirming the super ductility of the investigated ultrafine-grained alloy in the low temperature region between 140 and 160 °C. Graphical abstract

Microstructure Stability and Creep Behaviour of a Cu-0.2wt.%Zr Alloy Processed by Equal-Channel Angular Pressing

2010 ◽  
Vol 667-669 ◽  
pp. 821-826 ◽  
Author(s):  
Jiří Dvořák ◽  
Petr Král ◽  
Marie Kvapilová ◽  
Milan Svoboda ◽  
Vàclav Sklenička
Keyword(s):  
Electron Microscopy ◽  
Equal Channel Angular Pressing ◽  
Creep Behaviour ◽  
Tensile Creep ◽  
Creep Tests ◽  
Creep Properties ◽  
Angular Pressing ◽  
Microstructure Stability ◽  
Transmission Electron ◽  
Zr Alloy

A dispersion-strengthened Cu-0.2 wt.% Zr alloy was subjected to equal-channel angular pressing (ECAP) at room temperature for up to 12 passes through route BC using a die having a channel angle of 90°. The microstructural investigations were performed using both transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Tensile creep tests were conducted at temperature 673 K and at the applied stress in the range from 80 to 180 MPa. The migration of boundaries and subsequent grain growth were restricted by Cu9Zr2 precipitates. The study was performed in order to evaluate the effects of severe plastic deformation and precipitation on creep behaviour and microstructure of the pressed alloy. It was found that creep behaviour is strongly dependent on number of ECAP passes. The pressed alloy after up to 4 ECAP passes exhibited a considerable improvement in creep properties in comparison with the unpressed alloy.

Effects of volume fraction of fine grains on the tensile creep properties of a hot-deformed Mg-Gd-Y-Zr alloy

2020 ◽  
Vol 777 ◽  
pp. 139052 ◽  
Author(s):  
Yi Yang ◽  
Qinghuan Huo ◽  
Yuxiu Zhang ◽  
Lu Luo ◽  
Zhenyu Xiao ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Tensile Creep ◽  
Creep Properties ◽  
Zr Alloy

EFFECT OF ZIRCONIUM ON HIGH TEMPERATURE TENSILE PROPERTIES OF PRECIPITATION-HARDENEDMG-ND-ZNCASTING ALLOY

2009 ◽  
Vol 23 (06n07) ◽  
pp. 966-971
Author(s):  
JOONG-HWAN JUN ◽  
KI-DUG SEONG ◽  
MIN-HA LEE
Keyword(s):  
Tensile Properties ◽  
Creep Resistance ◽  
Elevated Temperatures ◽  
Creep Properties ◽  
Casting Alloys ◽  
Average Grain Size ◽  
High Temperature Tensile ◽  
Treated State ◽  
High Temperature Tensile Properties ◽  
Zr Alloy

Influences of Zr addition on microstructure and tensile properties at ambient and elevated temperatures have been investigated for precipitation-hardened Mg -3% Nd -0.6% Zn and Mg -3% Nd -0.6% Zn -0.2% Zr casting alloys. By the addition of Zr , the average grain size of α-( Mg ) phase decreases remarkably. In T6-treated state, the Mg -3% Nd -0.6% Zn -0.2% Zr alloy shows higher YS, UTS and elongation at RT, 150°C and 200°C, compared to those of the Zr -free alloy. Better creep resistance is observed in the Zr -containing alloy at 175°C/120MPa condition, while its creep resistance becomes inferior to that of the Zr -free alloy at 215°C/80MPa and 250°C/40MPa conditions. The discrepancy between tensile and creep properties is discussed in relation to microstructural evolution.

scholarly journals Creep Behavior and Threshold Stress of an Al–Al2O3–Zr Alloy

1990 ◽  
Vol 31 (5) ◽  
pp. 386-395 ◽  
Author(s):  
Norio Matsuda ◽  
Keisuke Matsuura
Keyword(s):  
Creep Behavior ◽  
Threshold Stress ◽  
Zr Alloy

The effects of strain and strain rate on residual microstructures in copper

1986 ◽  
Vol 44 ◽  
pp. 420-421
Author(s):  
M. F. Stevens ◽  
P. S. Follansbee
Keyword(s):  
Strain Rate ◽  
Applied Stress ◽  
Threshold Stress ◽  
Rate Sensitivity ◽  
Viscous Drag ◽  
Strain Rates ◽  
Strain And Strain Rate ◽  
Threshold Strength ◽  
Mechanism Transition ◽  
Intrinsic Strength

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.

Microtwinning Evidence For The Apparent Five-Fold Symmetry in T2(Al6Li3Cu)

1987 ◽  
Vol 45 ◽  
pp. 24-25
Author(s):  
Kenneth S. Vecchio ◽  
David B. Williams
Keyword(s):  
Stable Equilibrium ◽  
Equilibrium Phase ◽  
Convergent Beam Electron Diffraction ◽  
Icosahedral Structure ◽  
Cubic Crystals ◽  
Icosahedral Phases ◽  
Heat Treated ◽  
Zero Layer ◽  
Convergent Beam ◽  
Zr Alloy

Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symmetry, extensive effort has been given to establishing a theoretical basis for the existence of icosahedral phases (eg.2.). Several other investigations have been centered on explaining these observations based on twinning of cubic crystals (eg.3.). Recently, the existence of a stable, equilibrium phase T2Al6 Li3Cu) possessing an icosahedral structure has been reported in the Al-Li-Cu system(4-6).In the present study an Al-2.6wt.%Li-l.5wt.%Cu-0.lwt.%Zr alloy was heat treated at 300°C for 100hrs. to produce large T2 precipitates. Convergent Beam Electron Diffraction (CBED) patterns were obtained from two-fold, three-fold, and apparent five-fold axes of T2 particles. Figure 1 shows the five-fold symmetric zero layer CBED pattern obtained from T2 particles.

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