The Creep Deformation and Elevated Temperature Microstructural Stability of a Two-Phase TiAl/Ti3Al Lamellar Alloy.

1994 ◽  
Vol 364 ◽  
Author(s):  
M. F. Bartholomeusz ◽  
J. A. Wert
Keyword(s):  
Elevated Temperature ◽  
Creep Rate ◽  
Microstructural Evolution ◽  
Creep Deformation ◽  
Minimum Creep Rate ◽  
Single Phase ◽  
Lamellar Microstructure ◽  
Microstructural Stability ◽  
Two Phase ◽  
The Individual

AbstractEnhanced work hardening of the phases in the lamellar microstructure has been cited as an explanation for the lower minimum creep rates of a two-phase TiAl/Ti3Al lamellar alloy compared with the minimum creep rates of the individual TiAl and Ti3Al single-phase alloys tested between 980 K and 1130 K. This proposition is confirmed by TEM observations. Thermal and thermomechanical exposure result in the microstructural evolution, which increases the minimum creep rate (εmin) of the lamellar alloy. The effect of microstructural evolution on εmin will be discussed in the present paper.

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.

Evaluation of Creep Deformation Property of Grade 91 Steels

2015 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Hideaki Kushima
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Minimum Creep Rate ◽  
Deformation Property ◽  
Time Dependent ◽  
Tertiary Creep ◽  
Total Strain ◽  
Dominant Factor ◽  
Creep Equation ◽  
Time To Rupture

Creep deformation property of Grade T91 steels over a range of temperatures from 550 to 625°C was analyzed by means of the empirical creep equation reported in the previous study [1]. The creep equation consists of four time dependent terms and one constant and time to rupture is estimated as a time to total strain of 10%. Accuracy of the creep equation to represent creep curve and to predict time to rupture and minimum creep rate was indicated. Times to minimum creep rate, total strain of 1%, initiation of tertiary creep and rupture were evaluated by the creep equation. Stress dependence of strains at minimum creep rate and the initiation of tertiary creep were analyzed. Contribution of four time dependent terms to the strains at minimum creep rate, total strain of 1% and initiation of tertiary creep was investigated. Three parameters to determine a temperature and time-dependent stress intensity limit, St, were compared and a dominant factor of St was examined. Heat-to-heat variation of the creep deformation property was investigated on two heats of T91 steels contain low and high nickel concentrations.

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.

Creep Deformation Behavior and Microstructural Degradation During Creep of Pre-Strained 25Cr-20Ni-Nb-N Steel

2007 ◽  
Author(s):  
Nobuhiko Saito ◽  
Nobuyoshi Komai
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Deformation Behavior ◽  
Minimum Creep Rate ◽  
Strengthening Mechanism ◽  
Creep Rupture ◽  
Microstructural Degradation ◽  
Solution Treated ◽  
Long Time ◽  
Strained Materials

The purpose of this study is to clarify the creep deformation behavior and microstructural degradation during creep of pre-strained 25Cr-20Ni-Nb-N steel (TP310HCbN), which has the highest creep strength among austenite stainless steels used for boiler tubes. The creep rupture strengths of the 20% pre-strained materials tested at 650°C under 210 MPa and 180 MPa were higher than those of solution-treated materials. However, the long time creep rupture strengths of the 20% pre-strained materials tested at 700°C and 750°C were lower than those of solution-treated materials. Thus, the creep strengths of the prestrained materials depend on test temperature and stress. Furthermore, the minimum creep rate of the 20% pre-strained materials and re-solution-treated materials tested at 650°C under 300MPa were 1.2 × 10−9 and 1.6 × 10−8 s−1, respectively. Thus, the minimum creep rate of the 20% pre-strained materials was lower than for re-solution-treated materials. The creep strengthening mechanism of the pre-strained materials at 650°C was considered to be that high-density dislocations were maintained until the late stage of creep. On the other hand, the creep rupture strengths of the 20% pre-strained materials were lower than those of solution-treated materials tested at over 700°C because of agglomeration and coarsening of precipitates and the recovery of dislocations.

Processing, Structure, Texture and Microtexture in Titanium Alloys

2012 ◽  
Vol 710 ◽  
pp. 66-84 ◽  
Author(s):  
Dipankar Banerjee ◽  
Adam L. Pilchak ◽  
James C. Williams
Keyword(s):  
Titanium Alloys ◽  
Single Phase ◽  
Thermomechanical Processing ◽  
Strong Dependence ◽  
Two Phase ◽  
Β Phase ◽  
Phase Fields ◽  
Deformation And Heat Treatment ◽  
Two Phases ◽  
The Individual

We review the effect of processing on structure and texture in titanium alloys, focusing on the understanding of this relationship that has evolved over the last decade. Thermomechanical processing cycles for these alloys involve deformation and heat treatment in single phase β and two phase, α+β, phase fields, and involves a complex interplay between deformation and recrystallization textures of the individual phases, textures arising from the crystallographic relationship between the two phases, and the scale of microstructure evolution. We explore these interactions and trace the strong dependence of thermomechanical pathways on the final structure and texture.

Influence of Step Aging on Creep Behavior and Microstructural Evolution of Fine-Grained Fully Lamellar XD TiAl Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 1525-1530
Author(s):  
Han Liang Zhu ◽  
Dong Yi Seo ◽  
Kouichi Maruyama ◽  
Peter Au
Keyword(s):  
Creep Rate ◽  
Microstructural Evolution ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Lamellar Structure ◽  
Aging Condition ◽  
Tial Alloys ◽  
Fine Grained ◽  
Fully Lamellar ◽  
Multiple Step

Fine-grained fully lamellar (FGFL) structures of XD TiAl alloys (Ti-45 and 47Al-2Nb-2Mn+0.8vol.%TiB2) (at.%) were stabilized to varying degrees by different aging treatments. Specimens with and without aging were creep tested at 760°C and 207 MPa. It was found that during creep deformation, degradation of the lamellar structure involving coarsening within the colonies and spheroidization at colony boundaries occurred, forming fine globular structures at the colony boundaries and increasing the creep rate. Aging treatments stabilized the lamellar structure and retarded the coarsening and spheroidization processes during creep deformation. As a result, the aged specimens exhibited lower minimum creep rates and longer creep lives than the unaged specimens. A multiple step aging stabilized the lamellar structure to the greatest extent and suppressed other degradation processes during aging, resulting in the best creep resistance. These results demonstrate that the multiple step aging is the optimal aging condition for stabilizing FGFL XD TiAl alloys.

Creep of Rheocast 7075 Aluminum Alloy at 300 °C

2013 ◽  
Vol 372 ◽  
pp. 288-291 ◽  
Author(s):  
Saravut Thongkam ◽  
Sirikul Wisutmethangoon ◽  
Jessada Wannasin ◽  
Suchart Chantaramanee ◽  
Thawatchai Plookphol
Keyword(s):  
Aluminum Alloy ◽  
Creep Rate ◽  
Creep Deformation ◽  
Minimum Creep Rate ◽  
7075 Aluminum Alloy ◽  
Stress Range ◽  
Dislocation Glide ◽  
Semi Solid ◽  
Power Law Creep ◽  
Rupture Strain

Creep of rheocast 7075-T6 aluminum alloy produced by the Gas Induced Semi-Solid (GISS) process was investigated at temperature of 300 °C and stress range of 20-70 MPa and compared to that of wrought 7075-T651 aluminum alloy. The rheocast 7075-T6 alloy exhibited lower minimum creep rate and longer rupture time than the wrought 7075-T651 alloy. The total rupture strain of the rheocast alloy was shorter than that of the wrought one. According to the power law creep, the stress exponents, n of the rheocast 7075-T6 and the wrought 7075-T651 alloys were 5.9 and 7.9 respectively. Based on the determined n values, the creep deformation of both alloys was possibly controlled by the dislocation glide and climb-controlled mechanism.

Creep Deformation Parameters and Creep Life of Gr.91

2013 ◽  
Author(s):  
Fujio Abe
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Minimum Creep Rate ◽  
Creep Data ◽  
Creep Life ◽  
Deformation Parameters ◽  
Austenite Grain ◽  
Strain Data ◽  
Downward Deviation ◽  
Prior Austenite Grain

The correlation between the creep deformation parameters and creep life has been investigated for Gr.91 by analyzing creep strain data at 450 to 725 °C, 40 to 450 MPa and tr = 11.4 to 68,755 h in the NIMS Creep Data Sheet. The creep life tr is correlated with the time to minimum creep rate tm as t r = 3.7 t m . Taking the stress dependence of tm / tr into account, the creep life could be predicted more reliably. The minimum creep rate ε̇min depends on both the tm and the strain to minimum creep rate εm as ε . min = 0.54 ε m / t m . The εm is evaluated to be 0.02 to 0.03 at high stresses at each temperature but it decreases with decreasing stress at temperatures above 550 °C, suggesting that the creep deformation in the transient region becomes more inhomogeneous with decreasing stress probably due to localized creep deformation within 1 μm in the vicinity of prior austenite grain boundaries. The downward deviation takes place in the the tr versus ε̇min curves (Monkman-Grant plot). At the same ε̇min, both the εm and tm change upon the condition of tm ∝ εm as can be seen from the above equation. The decrease in εm with decreasing stress, corresponding to decreasing ε̇min, causes a decrease in tm, indicating the downward deviation of the tr versus ε̇min curves.

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