Creep Deformation of Ta Modified Gamma Prime Single Crystals

1986 ◽  
Vol 81 ◽  
Author(s):  
D.L. Anton ◽  
D.D. Pearson ◽  
D.B. Snow
Keyword(s):  
Single Crystals ◽  
Single Phase ◽  
High Ratio ◽  
Tertiary Creep ◽  
Creep Tests ◽  
Two Phase ◽  
Surface Stability ◽  
Substitutional Element ◽  
Gamma Prime

AbstractThe role of substitutional element alloying of single phase γ' has become of primary interest to alloy designers who would like to exploit its low density and excellent oxidation resistance. Current γ' alloys have not shown sufficient strength to be useful in a creep limited environment. In order to maximize the potential of single phase γ' alloys and to more fully understand the creep strengthening mechanisms in two phase Ni-base superalloys, it has become necessary to clarify the role of Al-substitution elements. Ta is a potent strengthening element in γ' as well as imparting beneficial surface stability to superalloys; its effect on the creep properties of Ni3Al is the subject of this paper. The 1300°C isotherm of the Ni-Al-Ta system was determined in order to establish the γ' single phase field. Comrpositions were fabricated having chemistries which systematically varied both the Al:Ta ratio at Ni=75% and Ni:(AI+Ta) ratio at Ta=6%. Creep tests were conducted on <001> oriented single crystals at 760, 871 and 982°C. Electron microscopy was used to characterize the nature of slip deformation, confirm phase purity and to determine the existence of tetragonal distortions in these crystals. In this manner the strengthening due to Ta was examined in the absence of grain boundary effects. These γ' mono—crystals did not display classical creep response. Incubation creep was observed in all of the specimens tested. Surprisingly, the maximum incubation time was found to occur in the high ratio Ni:(Al+Ta) compounds, where less than 0.5% creep strain was obtained after 200 hours at stress. After incubation, either tertiary creep leading to failure, or apparently classic primary, secondary and tertiary creep ensued. In addition extremely long elongations, to 85%, were measured.

Fundamental Modelling of Mechanisms Contributing to Tertiary Creep in Copper at 215 and 250°C

2018 ◽  
Author(s):  
Fangfei Sui ◽  
Rolf Sandström
Keyword(s):  
Spent Nuclear Fuel ◽  
Creep Damage ◽  
Back Stress ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Creep Tests ◽  
Long Time ◽  
Higher Temperature ◽  
Good Agreement

Extensive creep tests have been performed on oxygen free copper with 50 ppm phosphorus at both low and high temperatures. It is the candidate material for storage of spent nuclear fuel in Sweden. Basic models without fitting parameters have been formulated to reproduce primary and secondary creep. For a long time, only empirical models existed for fitting of tertiary creep. To understand the role of creep damage, including recovery, cavitation and necking, basic models that do not involve adjustable parameters are in urgent demand. Only recently, basic models taking the relevant mechanisms into account have been developed. These models were used to predict the tertiary creep for copper at 75°C. The modelled results were compared with experimental creep curves and good agreement has been found. In the present paper, the models are applied to creep tests at higher temperatures (215 and 250°C). A similar representation with good accuracy is obtained. This demonstrates that the fundamental model for back stress is applicable for the higher temperature tests as well.

Ultra-Hard Nanostructured Al-Si Thin Films

2005 ◽  
Vol 494 ◽  
pp. 13-18
Author(s):  
Velimir Radmilović ◽  
D. Mitlin ◽  
U. Dahmen
Keyword(s):  
Room Temperature ◽  
Single Phase ◽  
Mechanical Performance ◽  
High Rate ◽  
Hard Phase ◽  
Two Phase ◽  
Transmission Electron ◽  
Order Of Magnitude ◽  
Dense Distribution

We show that it is possible to use high rate co-evaporation of Al and Si onto room temperature substrates to achieve a novel two-phase nanoscale microstructure. These nanocomposites have a hardness as high as 4GPa (Al-23at.%Si), and display noticeable plasticity. Films with compositions of Al-12at.%Si and pure Al (used as baseline) were analyzed using transmission electron microscopy (TEM). The scale of the Al-12at.%Si microstructure is an order of magnitude finer compared to that of pure Al films. It consists of a dense distribution of spherical nanoscale Si particles separating irregularly-shaped small Al grains. These new structures may have a mechanical performance advantage over conventional single phase nanomaterials due to the role of the dispersed hard phase in promoting strain hardening.

Modelling of Tertiary Creep In Copper at 215 and 250°C

2020 ◽  
pp. 1-31
Author(s):  
Rolf Sandström ◽  
Fangfei Sui
Keyword(s):  
Dislocation Structure ◽  
Creep Damage ◽  
Empirical Models ◽  
Tertiary Creep ◽  
Creep Tests ◽  
Tertiary Stage ◽  
Creep Curves ◽  
Long Time ◽  
Lower Temperature

Abstract For a long time, only empirical models existed for creep curves in the tertiary stage. To understand the role of creep damage, including changes in the dislocation structure, cavitation and necking, basic models that do not involve adjustable parameters have however, recently been developed. These models were used to predict tertiary creep for copper at 75°C. In the present paper, these models are applied to creep tests at higher temperatures (215 and 250°C). These results demonstrate again that tertiary creep in copper is primarily controlled accelerated recovery of the dislocation structure and not by cavitation. The modelling results suggest that the role of cavitation is modest also in other creep exposed ductile alloys, which should be of importance to consider in the formulation of models for creep damage. Necking was only found to be of significance very close to rupture again in agreement with results at lower temperature.

Physical and Mechanical Properties of Single Crystals of Co-Al-W Based Alloys with L12 Single-Phase and L12/fcc Two-Phase Microstructures

2008 ◽  
Vol 1128 ◽  
Author(s):  
Haruyuki Inui ◽  
Katsushi Tanaka ◽  
Kyosuke Kishida ◽  
Norihiko L. Okamoto ◽  
Takashi Oohashi
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Single Crystals ◽  
Yield Stress ◽  
Liquid Helium ◽  
Elastic Constants ◽  
Single Phase ◽  
Physical And Mechanical Properties ◽  
Helium Temperature ◽  
Two Phase

AbstractSingle-crystal elastic constants of Co3(Al,W) with the cubic L12 structure have been experimentally measured by resonance ultrasound spectroscopy at liquid helium temperature. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously reported. Two-phase microstructures with cuboidal L12 precipitates being well aligned parallel to <100> and well faceted parallel to {100} are expected to form very easily in Co-base superalloys because of the large value of E111/E100 and cij of Co3(Al,W). This is indeed confirmed by experiment. Values of yield stress obtained for both [001] and [¯123] orientations of L12/fcc two-phase single crystals moderately decrease with the increase in temperature up to 800°C and then decrease rapidly with temperature above 800°C without any anomaly in yield stress. Slip on {111} is observed to occur for both orientations in the whole temperature range investigated.

Cobalt Effect on Creep Behavior of Nickel Solid Solution Alloys

1981 ◽  
Vol 39 ◽  
pp. 54-55
Author(s):  
L. S. Lin ◽  
C. C. Law ◽  
M. J. Blackburn
Keyword(s):  
Solid Solution ◽  
Solid Solutions ◽  
Thin Foil ◽  
Weight Percent ◽  
Cobalt Alloy ◽  
Creep Tests ◽  
Gamma Prime ◽  
Nickel Base ◽  
Cobalt Effect

To understand the role of cobalt in nickel-base superalloys, multicomponent nickel solid solutions with various amounts of cobalt were studied. Alloys A, B, C and D which contain cobalt at 30, 17, 8 and 0, respectively, and constant concentrations of Cr(25), Mo(5), Al(0.5), Ti(0.5), Nb(0.4), Hf(0.1), all in weight percent, were produced by casting. Compressive creep tests of these alloys were conducted at temperatures between 650°C and 810°C. Table 1 shows the minimum creep rates at 704°C at a stress of 120% of their respective yield strengths. It can be seen that the alloy without cobalt (Alloy D) creeps at a rate 20 times faster than Alloy A with 30 wt.% cobalt and the values for Alloys B and C with intermediate cobalt contents fall between Alloys A and D. Thin foil studies have revealed that the differences can be attributed, in part, to (i) change of stacking fault energy with cobalt, (ii) precipitation of fine gamma prime particles during creep.

Physical and Mechanical Properties of Single Crystals of Co-Al-W Based Alloys with L12 Single-Phase and L12/fcc Two-Phase Microstructures

2010 ◽  
Vol 638-642 ◽  
pp. 1342-1347 ◽  
Author(s):  
Haruyuki Inui ◽  
Takashi Oohashi ◽  
Norihiko L. Okamoto ◽  
Kyosuke Kishida ◽  
Katsushi Tanaka
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Single Crystals ◽  
Yield Stress ◽  
Liquid Helium ◽  
Elastic Constants ◽  
Single Phase ◽  
Physical And Mechanical Properties ◽  
Helium Temperature ◽  
Two Phase

The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously calculated. Because of the large value of E111/E100 and cij of Co3(Al,W), two-phase microstructures with cuboidal L12 precipitates well aligned parallel to <100> and well faceted parallel to {100} are expected to form very easily in Co-base alloys, as confirmed indeed by experiment. Values of yield stress obtained for [001]-oriented L12/fcc two-phase single crystals moderately decrease with the increase in temperature up to 800°C and then decrease rapidly with temperature above 800°C without any anomaly in yield stress.

A TEM study of the influence of microstructure on the superplastic behavior of a U-5.8 wt.% Nb alloy

1986 ◽  
Vol 44 ◽  
pp. 568-569
Author(s):  
G. Mackiewicz Ludtka
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Phase Field ◽  
Single Phase ◽  
Superplastic Behavior ◽  
Two Phase ◽  
Single Phase Field

Historically, metals exhibit superplasticity only while forming in a two-phase field because a two-phase microstructure helps ensure a fine, stable grain size. In the U-5.8 Nb alloy, superplastici ty exists for up to 2 h in the single phase field (γ1) at 670°C. This is above the equilibrium monotectoid temperature of 647°C. Utilizing dilatometry, the superplastic (SP) U-5.8 Nb alloy requires superheating to 658°C to initiate the α+γ2 → γ1 transformation at a heating rate of 1.5°C/s. Hence, the U-5.8 Nb alloy exhibits an anomolous superplastic behavior.

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