scholarly journals Nanoindentation pop‐in in oxides at room temperature: dislocation activation or crack formation?

2021 ◽  
Author(s):  
Xufei Fang ◽  
Hanna Bishara ◽  
Kuan Ding ◽  
Hanna Tsybenko ◽  
Lukas Porz ◽  
...  
Keyword(s):  
Room Temperature ◽  
Crack Formation

Thermal Cycling Fatigue In Aluminum-Alloy Thin Films On Silicon Substrate

1997 ◽  
Vol 505 ◽  
Author(s):  
J. Koike ◽  
S. Utsunomiya ◽  
K. Maruyama
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Aluminum Alloy ◽  
Thermal Cycling ◽  
Silicon Substrate ◽  
Room Temperature ◽  
Crack Formation ◽  
Continuous Decrease ◽  
Thermal Cycling Fatigue

ABSTRACTThermal cycling was performed in Al-lmo%Si thin films deposited on Si wafers. After a given number of cycling between room temperature and 723 K, residual stress was measured at room temperure. Residual stress was found to increase with increasing the cycling number up to the 4th cycle, followed by further a continuous decrease by further cycling. The intial increase was found to be related to the increase of lattice dislcocations and their tangling. The following decrease was caused by crack formation along grain boundaties or by film delamination in some cases.

Deformation Characteristics and Ductile Fracture of 1040 Steel in Simple Upsetting of Solid Cylinders and Rings

1970 ◽  
Vol 92 (2) ◽  
pp. 391-398 ◽  
Author(s):  
Shiro Kobayashi
Keyword(s):  
Free Surface ◽  
Ductile Fracture ◽  
Surface Crack ◽  
Room Temperature ◽  
Crack Formation ◽  
Experimental Measurements ◽  
Deformation Characteristics ◽  
Interface Deformation ◽  
End Conditions ◽  
The Relationship

Experiments were conducted involving the upsetting of solid cylinders and rings of annealed SAE 1040 steel at room temperature for various end conditions. Measurements were made on the displacement distributions at the tool-workpiece interface, and on the development of barreling and strain variations at the free surface. Crack formation at the free surface was observed. The relationship between friction at the interface, deformation characteristics, and fracturing is discussed, and a tentative analysis is given for formulating the strains at the free surface, based on the experimental measurements for upsetting solid cylinders.

scholarly journals Nanoscale stacking fault–assisted room temperature plasticity in flash-sintered TiO2

2019 ◽  
Vol 5 (9) ◽  
pp. eaaw5519 ◽  
Author(s):  
Jin Li ◽  
Jaehun Cho ◽  
Jie Ding ◽  
Harry Charalambous ◽  
Sichuang Xue ◽  
...  
Keyword(s):  
Room Temperature ◽  
Oxygen Vacancies ◽  
Crack Formation ◽  
High Stress ◽  
Ceramic Materials ◽  
Sintering Process ◽  
Flash Sintering ◽  
Structural Applications ◽  
Deformation Behaviors

Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures and fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here, we have investigated the deformability of TiO2 prepared by a flash-sintering technique. Our in situ studies show that the flash-sintered TiO2 can be compressed to ~10% strain under room temperature without noticeable crack formation. The room temperature plasticity in flash-sintered TiO2 is attributed to the formation of nanoscale stacking faults and nanotwins, which may be assisted by the high-density preexisting defects and oxygen vacancies introduced by the flash-sintering process. Distinct deformation behaviors have been observed in flash-sintered TiO2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed.

The effects of combined cyclic close die forging and aging process on microstructure and mechanical properties of AA7075

2020 ◽  
Vol 234 (9) ◽  
pp. 1242-1251
Author(s):  
MA Moazam ◽  
M Honarpisheh
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Room Temperature ◽  
Crack Formation ◽  
Experimental Tests ◽  
Ultimate Tensile Stress ◽  
X Ray ◽  
Die Forging ◽  
Transmission Electron ◽  
Processed Sample

It is well known that applying severe plastic deformation methods on the precipitation hardenable aluminum alloys at room temperature is very difficult because of crack formation and segmentation of the specimen during the processes. In this study, several procedures were experimentally examined for performing the cyclic close die forging (CCDF) and improving the mechanical properties of AA7075. The experimental tests revealed that supersaturated solid solution of AA7075 after water quenching is formable for only about 5 min and performing the CCDF process in this limited time is possible. Optical and scanning electron microscopy and transmission electron microscopy were used to study the microstructure of the processed samples. It was observed that by applying two passes of CCDF, the grain size of the material reduced from 30 µm to about 200–300 nm. In addition, the X-ray diffractometer results demonstrated that Guinier–Preston zone picks of the processed samples are very weak and the equilibrium η-phase does not exist in none of the suggested procedures. Furthermore, it was found that by combining CCDF and aging processes according to the proposed procedures, the mechanical properties of the processed AA7075 were improved when compared with the AA7075-T6. To put it more clearly, micro-hardness, yield strength and ultimate tensile stress of the processed sample were improved as much as 38.6%, 25% and 23%, respectively.

Fly Ash/Rare Earth Oxide Coatings by EPD: Processing and Characterization

2012 ◽  
Vol 507 ◽  
pp. 197-202
Author(s):  
Ana Arizmendi-Morquecho ◽  
Alejandra Chávez-Valdez ◽  
Josué Aguilar ◽  
Jaime Álvarez
Keyword(s):  
Thermal Conductivity ◽  
Fly Ash ◽  
Room Temperature ◽  
Deposition Time ◽  
Crack Formation ◽  
Rare Earth Oxide ◽  
Thermal Barrier ◽  
New Materials ◽  
Oxide Coatings ◽  
Free Silica

Novel materials that can be used as thermal barrier coatings in high temperature applications were obtained by homogenization, mechanical milling and thermal treatment. Samarium oxide was investigated as an alternative to react with the free silica from fly ash and to form new silicate compounds. The main phases found in fly ash-Sm2O3 mixtures were mullite and samarium silicate Sm4.66O(SiO4)3. Electrophoretically deposited coatings from these materials were obtained at 50 V and 3 minutes deposition time. The surface microstructure of the coatings was characterized by scanning electron microscopy (SEM-EDXS). The coatings were homogeneous and showed no crack formation. Additionally, thermal conductivity of the bulk samples at room temperature was determined. The thermal conductivity values of the new materials were below 1 W/mK which makes them suitable for thermal and environmental barrier applications.

Growth of Uncracked Al0.80Ga0.20N/GaN DBR on Si(111)

2004 ◽  
Vol 831 ◽  
Author(s):  
M. B. Charles ◽  
M. J. Kappers ◽  
C. J. Humphreys
Keyword(s):  
Room Temperature ◽  
Crack Formation ◽  
Compressive Strain ◽  
Vapour Phase ◽  
Bragg Reflectors ◽  
Distributed Bragg Reflectors ◽  
X Ray Diffraction ◽  
Vapour Phase Epitaxy ◽  
X Ray ◽  
Metalorganic Vapour Phase Epitaxy

ABSTRACTThe strain in Al0.80Ga0.20N/GaN distributed Bragg reflectors (DBRs) grown by metalorganic vapour phase epitaxy (MOVPE) on Si(111) was studied using high resolution X-ray diffraction (XRD). Previous studies have shown that a 50nm Al0.80Ga0.20N layer induced a compressive strain in Al0.12Ga0.88N capping layers and prevented crack formation. A seven period Al0.80Ga0.20N/GaN DBR was grown, but this was found to be cracked at room temperature, despite compression in the GaN layers. This problem was solved by growing an identical structure with the addition of a 650nm GaN cap, and due to the compression in this layer, the structure was crack-free.

Dependence of Intergranular Fracture on Boundary Topography and Cohesion

1973 ◽  
Vol 31 ◽  
pp. 150-151
Author(s):  
J. E. Doherty ◽  
A. F. Giamei ◽  
B. H. Kear ◽  
C. W. Steinke
Keyword(s):  
Grain Boundary ◽  
Room Temperature ◽  
Nickel Base Superalloy ◽  
Boundary Shear ◽  
Room Temperature Ductility ◽  
Solid Solution Matrix ◽  
Nickel Base ◽  
Solution Matrix ◽  
Different Levels ◽  
Base Superalloy

Recently we have been investigating a class of nickel-base superalloys which possess substantial room temperature ductility. This improvement in ductility is directly related to improvements in grain boundary strength due to increased boundary cohesion through control of detrimental impurities and improved boundary shear strength by controlled grain boundary micros true tures.For these investigations an experimental nickel-base superalloy was doped with different levels of sulphur impurity. The micros tructure after a heat treatment of 1360°C for 2 hr, 1200°C for 16 hr consists of coherent precipitates of γ’ Ni3(Al,X) in a nickel solid solution matrix.

Hepatocyte Alterations in Guinea Pigs FED Polychlorinated Biphenyls (PCBs), Dibenzodioxins (PCDD), AND DIBENZOFURANS (PCDF)

1982 ◽  
Vol 40 ◽  
pp. 56-57
Author(s):  
J. N. Turner ◽  
D. N. Collins
Keyword(s):  
Guinea Pigs ◽  
Room Temperature ◽  
Dose Group ◽  
Methyl Cellulose ◽  
Uranyl Acetate ◽  
Target Organ ◽  
Office Building ◽  
Lead Citrate ◽  
Control Groups ◽  
Cooling Fluid

A fire involving an electric service transformer and its cooling fluid, a mixture of PCBs and chlorinated benzenes, contaminated an office building with a fine soot. Chemical analysis showed PCDDs and PCDFs including the highly toxic tetra isomers. Guinea pigs were chosen as an experimental animal to test the soot's toxicity because of their sensitivity to these compounds, and the liver was examined because it is a target organ. The soot was suspended in 0.75% methyl cellulose and administered in a single dose by gavage at levels of 1,10,100, and 500mgm soot/kgm body weight. Each dose group was composed of 6 males and 6 females. Control groups included 12 (6 male, 6 female) animals fed activated carbon in methyl cellulose, 6 males fed methyl cellulose, and 16 males and 10 females untreated. The guinea pigs were sacrificed at 42 days by suffocation in CO2. Liver samples were immediately immersed and minced in 2% gluteraldehyde in cacadylate buffer at pH 7.4 and 4°C. After overnight fixation, samples were postfixed in 1% OsO4 in cacodylate for 1 hr at room temperature, embedded in epon, sectioned and stained with uranyl acetate and lead citrate.

Domain Formation in Synthetic Quartz

1971 ◽  
Vol 29 ◽  
pp. 156-157
Author(s):  
Joseph J. Comer
Keyword(s):  
Electron Beam ◽  
Room Temperature ◽  
Domain Formation ◽  
Synthetic Quartz ◽  
Transmission Electron ◽  
Black Spots ◽  
Diffraction Mode ◽  
Domain Boundaries ◽  
Kikuchi Lines ◽  
Straight Lines

Domains visible by transmission electron microscopy, believed to be Dauphiné inversion twins, were found in some specimens of synthetic quartz heated to 680°C and cooled to room temperature. With the electron beam close to parallel to the [0001] direction the domain boundaries appeared as straight lines normal to <100> and <410> or <510> directions. In the selected area diffraction mode, a shift of the Kikuchi lines was observed when the electron beam was made to traverse the specimen across a boundary. This shift indicates a change in orientation which accounts for the visibility of the domain by diffraction contrast when the specimen is tilted. Upon exposure to a 100 KV electron beam with a flux of 5x 1018 electrons/cm2sec the boundaries are rapidly decorated by radiation damage centers appearing as black spots. Similar crystallographio boundaries were sometimes found in unannealed (0001) quartz damaged by electrons.

A Liquid Nitrogen Cooled Stage for STEM

1974 ◽  
Vol 32 ◽  
pp. 444-445
Author(s):  
Louis T. Germinario
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Liquid Nitrogen ◽  
Room Temperature ◽  
Objective Lens ◽  
Thermal Drift ◽  
Specimen Holder ◽  
Resolution Capability ◽  
Focal Position

A liquid nitrogen stage has been developed for the JEOL JEM-100B electron microscope equipped with a scanning attachment. The design is a modification of the standard JEM-100B SEM specimen holder with specimen cooling to any temperatures In the range ~ 55°K to room temperature. Since the specimen plane is maintained at the ‘high resolution’ focal position of the objective lens and ‘bumping’ and thermal drift la minimized by supercooling the liquid nitrogen, the high resolution capability of the microscope is maintained (Fig.4).

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