Change in Creep Deformation of PST Crystals with Different Stress Axes

2006 ◽  
Vol 980 ◽  
Author(s):  
Xiaohua Min ◽  
Eisaku Sakurada ◽  
Masao Takeyama ◽  
Takashi Matsuo
Keyword(s):  
Creep Rate ◽  
Slip System ◽  
Initial Stress ◽  
Creep Deformation ◽  
Strain Curve ◽  
Stage I ◽  
Stress Axis ◽  
Creep Tests ◽  
Transient Stage ◽  
Stereographic Triangle

AbstractBased on our analysis of a lot of creep rate-strain curves of PST crystals with the different angles between the lamellar plate and the stress axis, designated as ø, it was confirmed that the creep rate and the creep deformation manner strongly depend on the ø. It was supposed that the predominant creep deformation using γ plate during the transient stage is derived by the fully suppression of the operation of another slip systems not parallel to γ plate through α2 plate. It was also confirmed that the initial stress axes of the PST crystals within the standard stereographic triangle move for the [001]-[111] line, and then turn their directions for [111] pole during the transient stage. This moving manner of the stress axis indicated that the first slip system of [101](111) continues to the area near the [001]-[111] line in the standard stereographic triangle, and then, the second slip system of [110](111) operates. By comparing this moving manner to the creep rate-strain curve, it is suggested that the first slip system of [101](111) operates during the Stage I where the light decrease in the creep rate remains, after that, the second slip system of [110](111) appears and leads to steep decrease in the creep rate. This stage was designated as the Stage II. According to this conception, it is supposed that the strain at the end of the Stage I is directly correlated with the angle from the initial stress axis to the [001]-[111] line in the standard stereographic triangle. In this study, this supposition was confirmed by conducting the creep tests at 1148 K/68.6 MPa using two PST crystals with ø of 31° and 34°. The initial stress axis of the PST crystal with ø of 31° locates nearer to the [001]-[-111] line than that of the PST crystal with ø of 34°. The strain at the end of the Stage I of the PST crystal with ø of 31° is half that of the PST crystal with ø of 34°. By analyzing the inverse pole figures of the creep interrupted PST crystals, it was confirmed that the angle from the initial stress axis to the [001]-[111] line is correlated with the strain of the transient stage.

Change in Stress Axis with Creep Deformation in γ-Single Phase Ni-20mass%Cr Single Crystal within Standard Stereographic Triangle

2006 ◽  
Vol 15-17 ◽  
pp. 864-869 ◽  
Author(s):  
Kentaro Yuge ◽  
Yoshihiro Terada ◽  
Takashi Matsuo
Keyword(s):  
Creep Rate ◽  
Slip System ◽  
Single Crystals ◽  
Slip Plane ◽  
Creep Deformation ◽  
Single Phase ◽  
Stage I ◽  
Stress Axis ◽  
Stereographic Triangle ◽  
Primary Slip Plane

The creep deformations of γ-single phase Ni-20mass%Cr single crystals with stress axes within standard stereographic triangle and at the three pole positions have been investigated. The most of the creep life is occupied by the transient stage, which consists of Stage I and Stage II. In Stage I, the creep rate just after loading remains constant. In Stage II, the creep rate decreases continuously. Except for the single crystals with stress axes of [001] and [1,–11] poles, the single crystals make the creep deformation using the primary slip plane of (111). As a result, the cross section of the specimens turns from circular to elliptical in shape. However, there are marked difference in deformation manner among single crystals with the stress axes within standard stereographic triangle. The single crystals whose angle between stress axis and primary slip plane of (111), θ. is more than 45° shows the heterogeneous deformation during creep. While, the homogeneous deformation will be expected in the single crystals with θ less than 45°. In this study, by using the four single crystals with θ less than 45°, the change in the stress axis with the creep deformation at 1173K-29.4MPa, is investigated and the deformation manner due to the primary slip plane of (111) is estimated by conducting the creep interrupting tests. In the two single crystals with stress axes in the standard stereographic triangle where the moving range of θ is narrow, comparing to the others, the spot of the stress axis in the inverse pole figure moves for <1,– 01> direction by using (111)<1,–01> slip system, and after arriving at the [001]-[1,–11] line, the spot turns to its direction for [1,–11] pole using (111)<1,–10> slip system. While, in the other two single crystals whose stress axes located in the area with wider moving range of θ, the spot of stress axis only move for <1,–01> direction. And, the widely spread spot of the stress axis is confirmed after subjecting the small strain.

Change in Stress Axis with Creep Deformation in PST Crystal

2006 ◽  
Vol 15-17 ◽  
pp. 858-863
Author(s):  
Eisaku Sakurada ◽  
Takashi Matsuo
Keyword(s):  
Slip System ◽  
Creep Deformation ◽  
Inverse Pole Figure ◽  
Small Strain ◽  
Pole Position ◽  
Stress Axis ◽  
Al Alloy ◽  
Creep Tests ◽  
Transient Stage ◽  
Schmid Factor

The superiority of creep in Ti-48at%Al alloy with fully transformed lamellar structure to that in Ti-50at%Al alloy with γ single phase is characterized by the extension of transient stage. This extension of the transient stage derives by the retarding effect of α2 plate on the onset of the accelerating stage, through suppressing the dynamically recrystallization which is the main reason of the accelerating stage. This superiority in Ti-48at%Al alloy will become more clear by investigating the creep of the single crystal designated as the PST crystal, because of removing the grain boundaries which is the formation site of dynamic recrystallization. By using the PST crystal, the predominant deformation using primary slip plane of γ plate will continue, because the α2 plate restricts the operation of other slip planes. In PST crystals with the angle between the stress axis and the lamellar plates, designated as φ, less than 45°, the uniform deformation will proceed, because of the decrease in creep rate due to the decreasing in Schmid factor through the monotonous decrease in φ. But these suppositions have not confirmed. In this study, the deformation manner of the PST crystals with φ of less than 45° is investigated by the analyzing of creep curve, macrostructure and inverse pole figure of the PST crystals interrupted the creep tests at 1148K/68.6MPa at the strains of 0.20 and 0.65. Inverse pole figures of PST crystal are obtained using SEM-EBSD method. By accepting the creep deformation, the stress axes of the PST crystals move for [001]-[1, – 11] line with slip system of (111)<1, – 01>, and after reaching at this line, the stress axis turn to [1, – 11] pole position with (111)<1, – 10> slip system. The change in stress axis is not homogeneous in gauge portion accepting small strain, by subjecting the further creep deformation up to the onset of the accelerating stage, this heterogeneous deformation in gauge portion disappeared.

Role of Transient Creep in γ-Single Phase Ni-20Mass%Cr Alloy

2007 ◽  
Vol 539-543 ◽  
pp. 3030-3035
Author(s):  
Takashi Matsuo
Keyword(s):  
Creep Rate ◽  
Slip System ◽  
Single Crystal ◽  
Single Crystals ◽  
Slip Plane ◽  
Single Phase ◽  
Stage I ◽  
Stage Ii ◽  
Stress Axis ◽  
Transient Stage

Through the analysis of many creep rate-strain curves of γ-single phase Ni-20mass%Cr alloy single crystals with various stress axes, it has been elucidated that the ratio of transient stage to rupture life becomes larger with decreasing the stress. And the transient stage consists of Stage I and Stage II. In Stage I, the creep rate just after loading remains constant, and in Stage II, a steep decrease in creep rate continues. It is noticeable that there is a marked difference in transient stage among single crystals with different stress axes. The aim of this study is to elucidate the mechanisms leading to the different transient stages as the function of stress axes. The deformation during transient stage in the single crystals except for the single crystals with the stress axes of the [001] and [1,–11] poles in the standard stereographic triangle, proceeds using the primary slip plane. And they are divided into two groups of the single crystals with the angle between stress axis and primary slip plane, θ, less than 45° and the single crystals with θ more than 45°. The deformations of Stage I and Stage II in these single crystals proceed using the slip system of (111)<1,–01> and the slip system of (111)<1,–10>, and in Stage I, the former slip system acts mainly except for that of single crystals with stress axis of [011]. While, in the single crystal with stress axis of [011], two slip systems above described operate at the beginning of Stage I, and the stress axis moves along [011]-[1,–11] line. And this moving gives slight increase in the Schmid factor, therefore, in Stage I slight increase in creep rate was confirmed. The {111} pole figure of the single crystal with stress axis of [1,–11] whose deformation proceeds using the plural slip planes are obtained by SEM-EBSD method. It becomes clear that the smallest strains of Stage I and Stage II derived from the increase in the torsion with creep deformation.

Change in Stress Axis with Creep Deformation in Ni-20mass%Cr Single Crystal with Orientation of [011]

2006 ◽  
Vol 15-17 ◽  
pp. 870-875 ◽  
Author(s):  
Masaomi Mitsutake ◽  
Yoshihiro Terada ◽  
Takashi Matsuo
Keyword(s):  
Creep Rate ◽  
Single Crystal ◽  
Single Crystals ◽  
Slip Plane ◽  
Creep Deformation ◽  
Stage I ◽  
Stage Ii ◽  
Stress Axis ◽  
Transient Stage ◽  
Primary Slip Plane

The features of the creep deformation of γ-single phase single crystals with the composition of Ni-20mass%Cr are characterized by the extended transient stage, which consists of Stage I and Stage II. In the Stage I, the creep rate just after loading remains unchanged, while the creep rate decreases continuously in Stage II. In the single crystals except for the single crystals with the stress axis of [001] and [1, – 11], the predominant creep deformation using the primary slip plane continues. By this deformation, the cross section of specimen turns to elliptical in shape. However, in the single crystals with the angle between stress axis and primary slip plane (111) is more than 45°, the deformation using the primary slip plane does not continue, as a result, the duration of Stage II turn to shorter one. The single crystal with the stress axis of [011] has the largest angle of 55°. In this study, the deformation manner during transient stage of single crystal with the stress axis of [011] orientation is investigated from the two viewpoints. The first one is to clarify the change in deformation manner with decreasing the stress. As a result, with decreasing the stress, the Stage I become clear and strain during Stage I and Stage II become small, furthermore, the decreasing ratio of creep rate with definite strain becomes larger. While, the second viewpoint is to investigate the change in crystallographic orientation of the [011] single crystals with creep deformation using the inverse pole figure obtained by the EBSD method. As a result, at the stress of 29.4 MPa, the spot of stress axis turns from the [011]-[1, – 11] line to the <1, – 01> direction. While, at the stress of 19.6 MPa, the stress axis moves for the [1, – 11] pole along the [011]-[1, – 11] line from the [011] pole. And, it is noteworthy that the spot widely spread from the [011] pole during transient stage. This indicates the large distortion in the primary slip plane and the evidence of heterogeneous deformation.

scholarly journals New Creep Deformation Concept Based on Creep under Lower Stresses

2010 ◽  
Vol 638-642 ◽  
pp. 2297-2302
Author(s):  
Takashi Matsuo
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Slip System ◽  
Single Crystals ◽  
Creep Deformation ◽  
Single Phase ◽  
Rupture Life ◽  
Stage Iii ◽  
Transient Stage ◽  
Primary Slip System

Through the analysis of many creep rate-time or creep rate-strain curves of -single phase Ni-20mass% Cr alloy single crystals with various stress axes, it was clarified that the creep deformation manners at lower stresses are drastically different to those at higher stresses. These creep features at lower stresses are summarized into three ones as follows. (i) The fully extended transient stage occupies the considerable ratio of rupture life. (ii) The steady state stage disappears, because the transient stage directly connected with the accelerating stage. (iii) The origin of the onset of accelerating stage is regarded as the formation of the dynamic recrystallized grain. These difference in creep deformation manner were caused by the predominant operation of the primary slip system and then the homogeneous evolution of dislocation substructures.

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.

Evaluation of Creep Deformation Mechanism of Heat Resistant Steel by Stress Change Test

2007 ◽  
Author(s):  
Hiroyuki Hayakawa ◽  
Satoshi Nakashima ◽  
Junichi Kusumoto ◽  
Akihiro Kanaya ◽  
Daisuke Terada ◽  
...  
Keyword(s):  
Creep Rate ◽  
Dislocation Density ◽  
Creep Deformation ◽  
Deformation Mechanism ◽  
Mobile Dislocation ◽  
Stress Increment ◽  
Mobile Dislocation Density ◽  
Creep Tests ◽  
Heat Resistant ◽  
Heat Resistant Steels

In order to evaluate creep deformation mechanism of heat resistant steels, stress change tests were conducted during creep tests. In this study, it was confirmed that the dislocation behavior during the creep tests was in viscous manner, because no instantaneous plastic strain was observed at stress increments. Transient behavior was observed after stress changes for all kinds of steel in this work. Mobility of dislocation was evaluated by the observed backward creep behavior after stress reduction. Internal stress was evaluated by the change of creep rate in stress increment, and mobile dislocation density was evaluated with the estimated mobility of dislocation and the change of creep rate in stress increment. It was found that the variation of mobile dislocation density during creep deformation showed the same tendency as the variation of creep rate. Therefore mobile dislocation density is the dominant factor that influences the creep rate variation in creep deformation of heat resistant steels investigated in this work. The mobility of dislocation showed a good correlation with 1/T and it is related with the amount of solute Mo that is a solution strengthening element. Microstructure of crept specimens was observed by TEM to discuss the validation of these results.

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 Deformation of Floating Ice Shelves

1957 ◽  
Vol 3 (21) ◽  
pp. 38-42 ◽  
Author(s):  
J. Weertman
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Deformation ◽  
Plasticity Theory ◽  
Steady State Creep ◽  
Creep Tests ◽  
Ice Shelves ◽  
The Antarctic ◽  
Good Agreement

AbstractThe problem of the creep deformation of floating ice shelves is considered. The problem is solved using Glen’s creep law for ice and Nye’s relation of steady-state creep (the analogue of the Lévy-Miles relation in plasticity theory). Good agreement is obtained between an observed creep rate at Maudheim in the Antarctic and that predicted from the results of creep tests made by Glen.

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