Simulations of Creep in Ductile-Phase Toughened Nb5Si3/Nb In-Situ Composites

1994 ◽  
Vol 364 ◽  
Author(s):  
G. A. Henshall ◽  
M. J. Strum ◽  
P. R. Subramanian ◽  
M. G. Mendiratta
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Bulk Material ◽  
Continuous Phase ◽  
Primary Creep ◽  
Equation Model ◽  
Solid Solution Phase ◽  
Ductile Phase

AbstractThe primary and steady-state creep behavior of ductile-phase toughened Nb5Si3/Nb in-situ composites has been simulated using analytical and finite element (FE) continuum techniques. The microstructure of these composites is complex, consisting of large, elongated primary dendrites of the ductile (Nb) solid-solution phase in a eutectoid matrix with the silicide as the continuous phase. This microstructure has been idealized to facilitate the modeling; the effects of these idealizations on the predicted composite creep rates are discussed. Further, it has been assumed that the intrinsic creep behavior of each phase within the composite is the same as that of the corresponding bulk material. Thus, the experimentally measured creep properties of the bulk Nb5Si3 and (Nb) phases have been analyzed to provide the required material constants in the creep constitutive equation. Model predictions of the steady-state composite creep rate have been compared with the experimental results for a Nb-10 at.% Si alloy. While accurate at low stress, the models underpredict the composite creep rate at large stresses because the composite stress exponent is underpredicted. In the case of primary creep, the models somewhat over-predict the composite creep strain but are reasonably accurate given uncertainties in the primary creep data. Finally, FE predictions of the tensile stress distributions within the composites have been shown to be qualitatively consistent with the cracking observed experimentally during tertiary creep.

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.

The Investigation of Creep Behavior for NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P Alloy at High Temperature

2011 ◽  
Vol 279 ◽  
pp. 28-32
Author(s):  
Guang Ye Zhang ◽  
Dong Wen Ye ◽  
Jin Lin Wang ◽  
You Ming Chen ◽  
Long Fei Liu ◽  
...  
Keyword(s):  
Steady State ◽  
High Temperature ◽  
Creep Behavior ◽  
Fracture Behavior ◽  
Primary Creep ◽  
Dislocation Climb ◽  
Steady State Creep ◽  
Creep Fracture ◽  
Creep Mechanisms ◽  
Higher Temperature

The Microstructure and creep behavior for NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P alloy at high temperature have been investigated in this paper. The results reveal that the high temperature creep behavior of the NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P alloy is characterized by transient primary creep and dominant steady-state creep as well as ternary creep behavior. The primary creep can be described by Garofalo equation and the steady-state creep can be depicted by Dorn equation. The creep mechanisms are viscous glide of dislocations at lower and middle testing temperatures and dislocation climb at higher temperature. No change of the microstructure for the testing alloy indicates that the creep fracture is controlled by the formation and propagation of cavities and cracks, and the creep fracture behavior obeys Monk man-Grant relationship.

Creep Mechanisms in Niobium-Silicide Based In-Situ Composites

1998 ◽  
Vol 552 ◽  
Author(s):  
B. P. Bewlay ◽  
P. W. Whiting ◽  
A. W. Davis ◽  
C. L. Briant
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Detrimental Effect ◽  
Higher Order ◽  
In Situ Composites ◽  
Niobium Silicide ◽  
Creep Mechanisms ◽  
Stress Levels ◽  
The Relationship

ABSTRACTThis paper will discuss the relationship between microstructure and creep behavior in hightemperature niobium-silicide based in-situ composites. The creep behavior of composites generated from binary Nb-Si alloys, and higher order alloys containing Mo, Hf and Ti additions, will be described. In-situ composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280MPa. It was found that the Hf concentration can be increased to 7.5 with little increase in creep rate, over that for the binary Nb3Si-Nb composite, but at higher concentrations the creep rate is increased at stress levels higher than 21OMPa. At stresses less than 21OMPa the Ti concentration can be increased to 21 without a detrimental effect on creep performance, but at higher concentrations there is a substantial increase in the creep rate.

The Effects of in-Situ Processing Methods on the Microstructure and Fracture Toughness of V-V3Si Composites

1993 ◽  
Vol 322 ◽  
Author(s):  
M. J. Strum ◽  
G. A. Henshall ◽  
B. P. Bewlay ◽  
J. A. Sutliff ◽  
M. R. Jackson
Keyword(s):  
Fracture Toughness ◽  
Synthesis Method ◽  
Solid Solution Phase ◽  
Synthesis Methods ◽  
Induction Melting ◽  
Ductile Phase ◽  
Three Point Bending ◽  
Surface Profiling ◽  
Temperature Fracture

AbstractThe present paper describes ductile-phase toughening in V-V3Si in-situ composites that were produced by conventional arc melting (AM), cold-crucible induction melting (IM), and coldcrucible directional solidification (DS). Notched three-point bending tests were performed to determine the effects of synthesis method on the room temperature fracture toughness of eutectic compositions, which contain nearly equal volume fractions of V3Si and the V(Si) solid solution phase. Fracture toughness values ranged from 10 MPa√m for the AM eutectic to over 20 MPa√m for the IM and DS eutectic alloys. SEM fractography, fracture surface profiling, and chemical analyses were performed to correlate the toughness values with the microstructures and interstitial concentrations produced by the three synthesis methods.

Creep behavior of eutectic Sn–Ag lead-free solder alloy

2002 ◽  
Vol 17 (11) ◽  
pp. 2897-2903 ◽  
Author(s):  
M. L. Huang ◽  
L. Wang ◽  
C. M. L. Wu
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Absolute Temperature ◽  
Steady State Creep ◽  
Steady State Creep Rate ◽  
Straight Line ◽  
The Matrix ◽  
Dislocation Pipe ◽  
Free Solder

Precipitation-strengthened tin-based eutectic Sn–3.5 Ag alloy was investigated for its creep behavior at three temperatures ranging from 303 to 393 K, under the tensile stress range of σ/E = 10−4 to 10−3. The steady-state creep rates cover seven orders of magnitude (10−3 to 10−9 s−1). The initial microstructure was found to have Ag3Sn intermetallic compound finely dispersed in the matrix of β–Sn. By incorporation of a threshold stress, σth, into the analysis, the creep data of eutectic Sn–Ag at all temperatures can be fitted by a single straight line with a slope of seven after normalizing the steady-state creep rate and the effective stress, indicating that the creep rates are controlled by the dislocation-pipe diffusion in the Sn matrix. The steady-state creep rate, , can then be expressed as , where QC is the creep activation energy, G is the temperature-dependent shear modulus, b is Burger's vector, R is the universal gas constant, T is the absolute temperature, σ is the applied stress, A is a material-dependent constant, and , in which σOB is the Orowan bowing stress and kR is the relaxation factor.

High-temperature deformation of mullite and analysis of creep curves

2003 ◽  
Vol 18 (8) ◽  
pp. 1771-1776 ◽  
Author(s):  
H. Rhanim ◽  
C. Olagnon ◽  
G. Fantozzi ◽  
A. Azim
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Slow Crack Growth ◽  
Steady State Creep ◽  
The Other ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Steady State Creep Rate ◽  
Creep Curves

The creep behavior of mullite was studied under different stresses and in the temperature range 1200–1450 °C, and an analysis of creep curves was proposed. The study of creep behavior of mullite at high temperatures clearly indicates that this material exhibits concurrent creep and slow crack growth. An effective transition stress exists at each temperature. The analysis takes account of the total creep curve; in particular, the primary and stationary stages. It is now possible to determine by extrapolation the steady-state creep rate for specimens that break in the transient domain during tests. Thus, one can verify the influence of the stress on the steady-state creep rate over a wide stress range. On the other hand, this analysis clearly indicates the existence of two values of the activation energy around 1300 °C; this suggests a change of creep mechanism at this temperature.

The Effect of Silicide Volume Fraction on the Creep Behavior of Nb-Silicide Based In-Situ Composites

2000 ◽  
Vol 646 ◽  
Author(s):  
B.P. Bewlay ◽  
C.L. Briant ◽  
A.W. Davis ◽  
M.R. Jackson
Keyword(s):  
High Temperature ◽  
Creep Rate ◽  
Creep Behavior ◽  
Volume Fraction ◽  
Phase Volume ◽  
In Situ Composites ◽  
Volume Fractions ◽  
Stress Levels

ABSTRACTThis paper will describe the creep behavior of high-temperature Nb-silicide in-situ composites based on quaternary Nb-Hf-Ti-Si alloys. The effect of volume fraction of silicide on creep behavior, and the effects of Hf and Ti additions, will be described. The composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280 MPa. At high (Nb) phase volume fractions the creep behavior is controlled by deformation of the (Nb) and, as the volume fraction of silicide is increased, the creep rate is reduced. However, at large silicide volume fractions (>0.7) damage in the silicide begins to degrade the creep performance. The creep rate has a minimum at a volume fraction of ∼0.6 silicide. The creep performance of the monolithic and silicide phases will also be discussed.

Facet crystallography of fractured V(2.7 wt% Si) solid solution

1994 ◽  
Vol 52 ◽  
pp. 622-623
Author(s):  
J. A. Sutliff ◽  
B. P. Bewlay ◽  
G. A. Henshall ◽  
M. J. Strum
Keyword(s):  
Solid Solution ◽  
Morphological Structure ◽  
Crystallographic Analysis ◽  
Solid Solution Alloy ◽  
Solid Solution Phase ◽  
Ductile Phase ◽  
High Temperature Alloys ◽  
Sem Micrograph ◽  
Facet Surface

V-Si binary alloys have been investigated as model high temperature alloys. Alloys with compositions between ~4 and 11 wt% Si can be fabricated as in-situ composites composed of the intermetallic V3Si phase and the V(Si) solid solution phase with a eutectic temperature of ~1870°C. The V(Si) phase is thought to be a ductile phase which provides toughness to the composite. We have previously reported on the fracture toughness of V-Si alloys.In this paper we present results on the fracture surface fractography and fracture facet crystallography of an arc-melted V(2.7 wt% Si) solid solution alloy fractured in bending. Figure 1 is a low magnification SEM micrograph of the surface of one half of a fractured bend bar. Many macroscopically flat facets can be seen and those for which crystallographic analysis was done have been labeled. Actually, the macro-facet surface as seen at higher magnification exhibits significant morphological structure, as can be observed in Figure 2 which shows detail of the facet labeled k.

scholarly journals Numerical Simulations of Creep in Ductile-Phase Toughened Intermetallic Matrix Composites

1994 ◽  
Vol 350 ◽  
Author(s):  
Gregory A. Henshall ◽  
Michael J. Strum
Keyword(s):  
Creep Rate ◽  
Volume Fraction ◽  
Fem Analysis ◽  
Primary Creep ◽  
Matrix Composites ◽  
Ductile Phase ◽  
Similar Time ◽  
Intermetallic Matrix ◽  
Intermetallic Matrix Composites ◽  
The Individual

AbstractAnalytical and finite element method (FEM) simulations of creep in idealized ductilephase toughened intermetallic composites are described. For these strong-matrix materials, the two types of analyses predict similar time-independent composite creep rates if each phase individually exhibits only steady-state creep. The composite creep rate increases above that of the monolithic intermetallic with increases in the stress exponent of the intermetallic, the volume fraction of the ductile phase, and the creep rate of the ductile phase. FEM analysis shows that the shape of the ductile phase does not affect the creep rate but may affect the internal stress and strain distributions, and thus damage accumulation rates. If primary creep occurs in one or both of the individual phases, the composite also exhibits primary creep. In this case, there can be significant deviations in the creep curves computed by the analytical and FEM models. The model predictions are compared with data for the Nb5Si3/Nb system.

Extrapolation of Creep Curve and Creep Rate by Strain Acceleration Parameter in Al-Mg Solid Solution Alloys

2014 ◽  
Vol 794-796 ◽  
pp. 307-312
Author(s):  
Hiroyuki Sato ◽  
Kosuke Omote ◽  
Akira Sato
Keyword(s):  
Solid Solution ◽  
Steady State ◽  
Creep Rate ◽  
Creep Curve ◽  
Creep Behavior ◽  
Minimum Creep Rate ◽  
Strain Rate Change ◽  
Acceleration Parameter ◽  
Creep Characteristics ◽  
Creep Curves

It has been widely accepted that the creep characteristics at high temperatures are mainly evaluated by a minimum creep rate. Although, a shape of creep curve may vary depending on deformation conditions, the apparent steady state or minimum creep rates be the same. Thus,for detailed analysis and prediction of creep behavior, other values which reflect the shape of each creep curve should be considered. For the purpose, authors have proposed Sato’s strain- acceleration-parameter (Strain Acceleration and Transition Objective index, SATO-index) which reflects strain rate change during creep deformation. Based on the concept of SATO-index, the whole creep curve can be represented by a set of small number of numerical parameters, and can be extrapolated from a part of creep curve. In this paper, application of the concept of SATO-index to the creep curves of aluminum-magnesium solid solutions that the creep behavior of the alloys are well investigated and analyzed. The creep curve can be extrapolated by the concept from transient part of creep curve, and the extrapolated creep rates at the minimum creep rate agree well with experiment. Efficiency of the concept of SATO-index to creep experiments is pronounced.

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