Creep of a niobium beryllide, Nb2Be17

1993 ◽  
Vol 8 (4) ◽  
pp. 757-763 ◽  
Author(s):  
T.G. Nieh ◽  
J. Wadsworth ◽  
T.C. Chou ◽  
D. Owen ◽  
A.H. Chokshi
Keyword(s):  
Low Temperatures ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Hardness Test ◽  
Transient Creep ◽  
Test Results ◽  
Creep Properties ◽  
Dislocation Glide ◽  
Applied Stresses ◽  
Hot Hardness

A niobium beryllide, Nb2Be17, has been prepared by powder-metallurgy techniques and the mechanical properties characterized both at room and elevated temperatures. Microhardness and fracture toughness were measured at room temperature. Hardness and hot-hardness test results indicated that, although the material was brittle at low temperatures, it became plastic at elevated temperatures (>1000 °C). Creep properties of Nb2Be17 were studied at temperatures from 1250 to 1350 °C and applied stresses from 10 to 90 MPa. The stress exponent, determined from stress-change tests, was about 3, and the activation energy, determined from temperature-change tests, was about 575 kJ/mol. The creep of Nb2Be17 at high temperature is apparently controlled by dislocation glide; this proposal was supported by transient creep experiments. Comparisons have been made between the creep properties of Nb2Be17 and other intermetallics.

The use of a bree simulation to investigate strain accumulation in 316 stainless steel at temperatures between room temperature and 500°c

1989 ◽  
Vol 24 (2) ◽  
pp. 95-102 ◽  
Author(s):  
D J Brookfield ◽  
D N Moreton
Keyword(s):  
Stainless Steel ◽  
Transition Temperature ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Cyclic Change ◽  
Strain Accumulation ◽  
Temperature Behaviour ◽  
Design Rules ◽  
Axial Tension ◽  
Applied Stresses

This paper details tests undertaken to determine the 1 per cent strain accumulation boundary in stainless steel type 316 strip subjected to constant axial tension and a cyclic change of curvature. Boundaries are obtained for temperatures between 300 and 500°C. These are compared with two design rules, both of which are shown to be conservative. Additionally, the temperature at which the transition from the characteristic room temperature behaviour of continued ratchetting to the ‘shakedown’ observed at elevated temperatures is investigated. Results obtained indicate that this transition temperature is influenced by the magnitude of the applied stresses.

Microstructure and Indentation Fracture of Dysprosium Niobate

2005 ◽  
Vol 20 (6) ◽  
pp. 1422-1427 ◽  
Author(s):  
Byong-Taek Lee ◽  
Waltraud M. Kriven
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Deformation ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Indentation Fracture ◽  
Optical Scanning ◽  
Periodic Arrays ◽  
Transmission Electron ◽  
Hot Hardness

The high-temperature indentation fracture and microstructures of dysprosium niobate (DyNbO4) were investigated by optical, scanning, and transmission electron microscopy (OM, SEM, and TEM). Polycrystalline samples were sintered at 1350 °C for 3 h and cut into 3 mm disks for TEM. The disks were indented in a Nikon QM (Tokyo, Japan) hot hardness indenter at room temperature up to 1000 °C. Many lamellar twins having different widths were observed by TEM as well as intergranular microcracks. The room temperature hardness was relatively low at 5.64 GPa and decreased with elevated temperatures. Crack lengths were short, showing a typical micro-cracking effect. In the sample indented at 1000 °C, dislocations in periodic arrays were evident, and their density increased markedly due to heavy plastic deformation.

Preparation of Al2O3/Al-Si Composites by In Situ Reaction of Fe2O3+MnO2/Al System

2015 ◽  
Vol 816 ◽  
pp. 48-53
Author(s):  
Jing Zhang ◽  
Hua Shun Yu ◽  
Xin Ting Shuai ◽  
Hong Mei Chen ◽  
Guang Hui Min
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Electron Probe ◽  
Room Temperature ◽  
Manganese Content ◽  
Hardness Test ◽  
Test Results ◽  
Electron Probe Micro Analyzer ◽  
Transmission Electron ◽  
Polygonal Shape

Al2O3 particles reinforced ZL109 composites were prepared by in-situ reaction between Fe2O3+MnO2 and Al in this paper. The influence of ratio of Mn to Fe on the morphologies of Al-Si-Mn-Fe phase and mechanical properties of the composites was investigated. The microstructure was studied by electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM). The results show that the Al2O3 particles displaced by the Fe2O3+MnO2/Al system are in nanosize. The acicular Al-Si-Fe phases change from acicular to polygonal shape and become smaller with the increase manganese content. The hardness test results have no big difference on the composites. However, the ultimate tensile strength at room temperature and 350°C enhance evidently with the increasing of Mn/Fe.

Reduction of Folate and Dihydrofolate by Dithionite

1972 ◽  
Vol 50 (11) ◽  
pp. 1191-1198 ◽  
Author(s):  
M. Kawai ◽  
K. G. Scrimgeour
Keyword(s):  
Free Radical ◽  
Low Temperatures ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Kinetic Method ◽  
Sodium Dithionite ◽  
Nucleophilic Attack ◽  
Stopped Flow ◽  
Reduction Processes ◽  
Radical Reduction

Sodium dithionite reduces folate to 7,8-dihydrofolate at room temperature, but further reduction to the tetrahydro level can be obtained at elevated temperatures (11). Both folate and dihydrofolate form adducts with dithionite (presumably sulfinates), and these adducts appear to be intermediates in the reduction processes. The adduct of dihydrofolate is not converted to tetrahydrofolate at low temperatures, and is thus more amenable to examination. The mechanism of reduction of the folate compounds and of the nicotinamide ring by dithionite involves nucleophilic attack by the dithionite, not a free radical reduction as with p-nitrophenol. The rate of addition of bisulfite to folate and dihydrofolate has been measured by the stopped-flow kinetic method, and the nonenzymic and enzyme-catalyzed addition of nucleophiles to folate compounds is discussed.

Substantiation of a Technique of Determining Stress in Thin Films at Very Low Temperatures

2015 ◽  
Vol 14 ◽  
pp. 28-36
Author(s):  
C.C. Chama
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Low Temperatures ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
High Temperature Stress ◽  
Hysteresis Curves ◽  
Stress Hysteresis

Substantiation of a technique earlier employed in determining stress in Copper-Silver thin films at very low temperatures is presented. It is shown that the stress measured at elevated temperatures using Stoney’s equation can be utilized in the determination of stress at very low temperatures. To demonstrate the application of this technique, a case study has been conducted by utilizing stress hysteresis curves obtained from the Cu-6at%Ag thin film heated from room temperature to 400°C and cooled back to room temperature in two cycles. The stresses in the Cu-6at%Ag thin film at various low temperatures up to-197°C have been determined by utilizing data from high temperature stress hysteresis curves.

Effect of Sodium Exposure On the Mechanical Properties of Zirconium

CORROSION ◽  
1961 ◽  
Vol 17 (1) ◽  
pp. 31t-34t ◽  
Author(s):  
J. C. BOKROS
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Tensile Properties ◽  
High Temperatures ◽  
Low Temperatures ◽  
Hydrogen Absorption ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Surface Oxide ◽  
The Other

Abstract It was found that surface oxide which developed on zirconium in impure sodium significantly lowered the fatigue life at elevated temperatures. Hydrogen absorption, on the other hand, had little effect on the fatigue life at elevated temperatures but lowered the fatigue life at room temperature. Also, critical recrystallization which occurred above 950 F in zirconium (a phenomenon unrelated to the presence of sodium) reduced the fatigue life at elevated as well as low temperatures. The effects attributable to sodium (i.e., the formation of surface oxide and absorption of reasonable amounts of hydrogen), did not significantly alter the tensile properties of zirconium at high temperatures. 6.3.20, 4.7, 3.5.8, 3.2.3

Springback Behavior of an Invar Sheet and Its Perforated Form

2006 ◽  
Vol 505-507 ◽  
pp. 781-786
Author(s):  
Yi Che Lee ◽  
Fuh Kuo Chen
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Tensile Tests ◽  
Test Results ◽  
Bending Tests ◽  
Predicted Values ◽  
Springback Behavior ◽  
Good Agreement

The springback behavior of an invar sheet and its perforated form were examined in the present study. The mechanical properties for invar sheet and perforated invar-sheet at elevated temperatures were first obtained from tensile tests. The test results suggest that both invar sheet and perforated invar-sheet have favorable formability at temperature higher than 200oC. An analytical model was also established to predict the springback of the invar sheet and its perforated form under bending conditions at various elevated temperatures. In order to verify the predicted results, the V-bending tests were conducted for the invar sheet at various temperatures ranging from room temperature to 300. The experimental data indicate that the springback decreases with the rise in temperature for both invar sheet and perforated invar-sheet. The good agreement between the experimental data and the predicted values confirms the validity of the proposed theoretical model as well.

Microstructures, Mechanical and Creep Properties of Rapidly Solidification/Powder Metallurgy Mg-6wt.%Zn Alloys with 5wt.%Ce and 1.5wt.%Ca Additions

2016 ◽  
Vol 861 ◽  
pp. 253-263
Author(s):  
Tao Zhou ◽  
Deng Hui Song ◽  
Zhen Hua Chen
Keyword(s):  
Compressive Strength ◽  
Powder Metallurgy ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Hot Extrusion ◽  
Creep Properties ◽  
High Compressive Strength ◽  
Rapidly Solidification ◽  
Twin Roll ◽  
Thermal Stability Of

Rapidly solidification/powder metallurgy (RS/PM) Mg-6Zn, Mg-6Zn-5Ce and Mg-6Zn-5Ce-1.5Ca (wt.%) alloys were produced via hot extrusion with RS powders, produced by atomization-twin roll quenching. Microstructures, mechanical and creep properties of the alloys were investigated. The results showed that for the Mg-6Zn alloys with 5wt.%Ce and 1.5wt.%Ca additions, the microstructures of the alloys were gradually refined, which caused the strength of the alloy at room temperature to increase remarkably, especially for the RS/PM Mg-6Zn-5Ce-1.5Ca alloy, exhibited a high compressive strength of 394MPa at room temperature. At elevated temperatures, due to the fine and stable intermetallic compounds i.e. MgxZnyCez and MgxZnyCez-(Ca) phases were formed for the Mg-6Zn-5Ce alloy and Mg-6Zn-5Ce-1.5Ca alloys, respectively, and the thermal stability of the ternary phase was a little lower than that of the quaternary phase because of the dissolving of Ca into the MgxZnyCez phase, the mechanical and creep properties at elevated temperatures increased remarkably with Ce and Ca additions, especially for the RS/PM Mg-6Zn-5Ce-1.5Ca alloy, which exhibited a high compressive strength of 258MPa at 200°C, and the minimum creep rate was decreased about 2 times, compared with that of the Mg-6Zn-5Ce alloy.

A Study on Microstructures and Creep Behaviors in the Mg-3Sr-xY Alloys

2011 ◽  
Vol 418-420 ◽  
pp. 602-605
Author(s):  
Ming Hu ◽  
Han Fei ◽  
Jing Gao ◽  
Fang Fang Zhao
Keyword(s):  
Dynamic Recrystallization ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Reduction Method ◽  
Creep Mechanism ◽  
Creep Limit ◽  
Creep Properties ◽  
Second Phases ◽  
Thermal Extrusion

In this paper, the author successfully fabricated Mg-3Sr-xY alloys by melting-leaching reduction method using SF6 and N2 as protected gas. The microstructures of the Mg-3Sr-xY alloys were investigated in details，and the results showed that Mg-3Sr-xY alloys are composed of dendrite α-Mg and eutectic α-Mg and Mg17Sr2 and Mg24Y5 particulates, the second phases distribute in the α-Mg dendrites and interdendrites. The fiber microstructures form after thermal extrusion and the dynamic recrystallization occurs. In Mg-3Sr-xY alloy, the tensile strengths, the yield strengths and elongation rates increase firstly, reach the peak values, decrease with the increasing in Y content. Mg-3Sr-xY alloy have the best mechanics properties, including yield strengths and ultimate strengths and elongation rates and creep properties by the addition of 0.6%Y content. The tensile behaviors at elevated temperatures are accord to general laws for the metals at room temperature. The Mg-3Sr-xY alloys with 0.4-1.0% Y are of best creep limit. The dislocation sliding and climbing is the main creep mechanism for Mg-3Sr-0.6Y alloys.

Temporary-Creep and Post-Creep Properties of Aquaculture Netting Materials With UHMWPE Fibres

2013 ◽  
Author(s):  
Heidi Moe Føre ◽  
Per Christian Endresen ◽  
Østen Jensen
Keyword(s):  
Tensile Strength ◽  
Room Temperature ◽  
Breaking Strength ◽  
Tensile Tests ◽  
Test Results ◽  
Load History ◽  
Elongation At Break ◽  
Creep Properties ◽  
Mean Values ◽  
Creep Strains

This paper presents test results on temporary-creep properties, recovery of strain post creep and post-creep tensile properties of a Raschel knitted netting material with a combination of UHMWPE and Polyester fibres. Specimens of the material were subjected to uniaxial loading over a period of 30 minutes, at a constant creep target load of 10–90 % of average tensile strength. The specimens were wet and tested in room temperature. The netting structure experienced significant creep strain, with mean values in the range of 1.3–4.5 %, increasing with increased creep target load. Large proportions of the elongation accumulated during on-loading and creep were long lasting and possibly permanent. Tensile tests showed that for the highest creep target load, strength and elongation at break increased by 17 %. The UHMWPE-netting experienced larger creep strains than PA6-netting for relatively large creep target loads (60–90 % of the average breaking strength), while creep strains were smaller for low loads. PA6-netting had a larger and faster recovery of strain post creep than the UHMWPE-netting, and the length and force at break were not significantly affected by the creep load history.

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