scholarly journals Nanoscale investigation of deformation characteristics in a polycrystalline silicon carbide

2019 ◽  
Vol 56 (3) ◽  
pp. 951-967 ◽  
Author(s):  
D. Zhang ◽  
L. G. Zhao ◽  
A. Roy ◽  
Y.-L. Chiu
Keyword(s):  
Electron Microscopy ◽  
Fracture Toughness ◽  
Silicon Carbide ◽  
Grain Orientation ◽  
Indentation Depth ◽  
Mechanical Response ◽  
Electron Backscatter Diffraction ◽  
High Dose ◽  
Grain Orientations ◽  
Dislocation Movement

AbstractIn this paper, we study the mechanical behaviour of silicon carbide at the nanoscale, with a focus on the effects of grain orientation and high-dose irradiation. Grain orientation effect was studied through nanoindentation with the aid of scanning electron microscopy (SEM) and EBSD (electron backscatter diffraction) analyses. Mechanical properties such as hardness, elastic modulus and fracture toughness were assessed for different grain orientations. Increased plasticity and fracture toughness were observed during indentations on crystallographic planes which favour dislocation movement. In addition, for SiC subjected to irradiation, increases in hardness and embrittlement were observed in nanoindentations at lower imposed loads, whereas a decrease in hardness and an increase in toughness were obtained in nanoindentations at higher loads. Transmission electron microscopy (TEM) analyses revealed that the mechanical response observed at a shallow indentation depth was due to Ga ion implantation, which hardened and embrittled the surface layer of the material. With an increased indentation depth, irradiation-induced amorphization led to a decrease in hardness and an increase in fracture toughness of the material.

On the Role of Grain-Boundary Films in Optimizing the Mechanical Properties of Silicon Carbide Ceramics

2004 ◽  
Vol 818 ◽  
Author(s):  
R. O. Ritchie ◽  
X.-F. Zhang ◽  
L. C. De Jonghe
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Fracture Toughness ◽  
Silicon Carbide ◽  
Grain Boundary ◽  
Elevated Temperatures ◽  
Boundary Structure ◽  
Intergranular Films ◽  
Grain Boundary Structure ◽  
Silicon Carbide Ceramics

AbstractThrough control of the grain-boundary structure, principally in the nature of the nanoscale intergranular films, a silicon carbide with a fracture toughness as high as 9.1 MPa.m1/2 has been developed by hot pressing β-SiC powder with aluminum, boron, and carbon additions (ABC-SiC). Central in this material development has been systematic transmission electron microscopy (TEM) and mechanical characterizations. In particular, atomic-resolution electron microscopy and nanoprobe composition quantification were combined in analyzing grain boundary structure and nanoscale structural features. Elongated SiC grains with 1 nm-wide amorphous intergranular films were believed to be responsible for the in situ toughening of this material, specifically by mechanisms of crack deflection and grain bridging. Two methods were found to be effective in modifying microstructure and optimizing mechanical performance. First, prescribed post-annealing treatments at temperatures between 1100 and 1500°C were seen to cause full crystallization of the amorphous intergranular films and to introduce uniformly dispersed nanoprecipitates within SiC matrix grains; in addition, lattice diffusion of aluminum at elevated temperatures was seen to alter grain-boundary composition. Second, adjusting the nominal content of sintering additives was also observed to change the grain morphology, the grain-boundary structure, and the phase composition of the ABC-SiC. In this regard, the roles of individual additives in developing boundary microstructures were identified; this was demonstrated to be critical in optimizing the mechanical properties, including fracture toughness and fatigue resistance at ambient and elevated temperatures, flexural strength, wear resistance, and creep resistance.

Transmission Electron Microscopy Studies of Silicon Nitride / Silicon Carbide Interfaces

1989 ◽  
Vol 170 ◽  
Author(s):  
H. J. Kleebe ◽  
N. Corbin ◽  
C. Willkens ◽  
M. Rühle
Keyword(s):  
Electron Microscopy ◽  
Fracture Toughness ◽  
Silicon Carbide ◽  
Silicon Nitride ◽  
Interface Fracture ◽  
Silicon Carbide Whiskers ◽  
Microchemical Analysis ◽  
Transmission Electron ◽  
Interface Fracture Toughness ◽  
Carbon Coated

AbstractMicrostructural investigations of HIP'ed silicon nitride reinforced with silicon carbide whiskers were performed using a 400 kV high resolution analytical transmission electron microscope. Two different whisker sources as well as uncoated and carbon coated whiskers were evaluated for their effectiveness in improving mechanical properties.This paper focuses on microstructural and microchemical analysis of interface and grain boundary regions within the composites. Combined HREM and AEM investigations reveal that variations in fracture toughness are mainly influenced by the microstructural and chemical development of the interface. Fracture toughness can be related to the surface chemistry of the reinforcements.

Electron Beam Damage of Biomolecules Assessed by Energy Loss Spectroscopy

1978 ◽  
Vol 36 (3) ◽  
pp. 61-69
Author(s):  
M. Isaacson ◽  
M.L. Collins ◽  
M. Listvan
Keyword(s):  
Electron Microscopy ◽  
Radiation Damage ◽  
Structural Integrity ◽  
Analytical Electron Microscopy ◽  
High Dose ◽  
Dose Rates ◽  
Special Cases ◽  
Analytical Electron ◽  
Atom Migration ◽  
Beam Damage

Over the past five years it has become evident that radiation damage provides the fundamental limit to the study of blomolecular structure by electron microscopy. In some special cases structural determinations at very low doses can be achieved through superposition techniques to study periodic (Unwin & Henderson, 1975) and nonperiodic (Saxton & Frank, 1977) specimens. In addition, protection methods such as glucose embedding (Unwin & Henderson, 1975) and maintenance of specimen hydration at low temperatures (Taylor & Glaeser, 1976) have also shown promise. Despite these successes, the basic nature of radiation damage in the electron microscope is far from clear. In general we cannot predict exactly how different structures will behave during electron Irradiation at high dose rates. Moreover, with the rapid rise of analytical electron microscopy over the last few years, nvicroscopists are becoming concerned with questions of compositional as well as structural integrity. It is important to measure changes in elemental composition arising from atom migration in or loss from the specimen as a result of electron bombardment.

Dechannealing Study of Nanocrystalline Si:H Layers Produced by High Dose Hydrogen Irradiation of Silicon Crystals

1998 ◽  
Vol 536 ◽  
Author(s):  
V. P. Popov ◽  
A. K. Gutakovsky ◽  
I. V. Antonova ◽  
K. S. Zhuravlev ◽  
E. V. Spesivtsev ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Rutherford Backscattering Spectrometry ◽  
Nanocrystalline Structure ◽  
Structural Defects ◽  
High Dose ◽  
Silicon Crystals ◽  
Strong Energy ◽  
Transmission Electron ◽  
Hydrogen Implantation

AbstractA study of Si:H layers formed by high dose hydrogen implantation (up to 3x107cm-2) using pulsed beams with mean currents up 40 mA/cm2 was carried out in the present work. The Rutherford backscattering spectrometry (RBS), channeling of He ions, and transmission electron microscopy (TEM) were used to study the implanted silicon, and to identify the structural defects (a-Si islands and nanocrystallites). Implantation regimes used in this work lead to creation of the layers, which contain hydrogen concentrations higher than 15 at.% as well as the high defect concentrations. As a result, the nano- and microcavities that are created in the silicon fill with hydrogen. Annealing of this silicon removes the radiation defects and leads to a nanocrystalline structure of implanted layer. A strong energy dependence of dechanneling, connected with formation of quasi nanocrystallites, which have mutual small angle disorientation (<1.50), was found after moderate annealing in the range 200-500°C. The nanocrystalline regions are in the range of 2-4 nm were estimated on the basis of the suggested dechanneling model and transmission electron microscopy (TEM) measurements. Correlation between spectroscopic ellipsometry, visible photoluminescence, and sizes of nanocrystallites in hydrogenated nc-Si:H is observed.

DURALCAN F3S.xxS

Alloy Digest ◽  
1994 ◽  
Vol 43 (10) ◽  
Keyword(s):  
Fracture Toughness ◽  
Silicon Carbide ◽  
Compressive Strength ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Base Alloy ◽  
Alloy Matrix ◽  
Reinforced Composite ◽  
Temperature Performance ◽  
Aluminum Alloy Matrix

Abstract Duralcan F3S.xxS is a heat treatable aluminum alloy-matrix gravity composite. The base alloy is similar to Aluminum 359 (Alloy Digest Al-188, July 1969); the discontinuously reinforced composite is silicon carbide. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and compressive strength as well as fracture toughness and fatigue. It also includes information on high temperature performance. Filing Code: AL-329. Producer or source: Alcan Aluminum Corporation.

Electron backscatter diffraction determination of grain orientation and constituent phases

1999 ◽  
Vol 4 (2) ◽  
pp. 174-174
Author(s):  
Chen Xiaomei ◽  
Liu Jing ◽  
Wang Jianbo ◽  
Zhang Ruikang ◽  
Wang Dahai ◽  
...  
Keyword(s):  
Grain Orientation ◽  
Electron Backscatter Diffraction ◽  
Diffraction Determination ◽  
Electron Backscatter ◽  
Backscatter Diffraction

scholarly journals Mechanical and thermal stability of retained austenite in plastically deformed bainite-based TRIP-aided medium-Mn steels

2021 ◽  
Vol 21 (3) ◽  
Author(s):  
Aleksandra Kozłowska ◽  
Adam Grajcar ◽  
Aleksandra Janik ◽  
Krzysztof Radwański ◽  
Ulrich Krupp ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Thermal Stability ◽  
Retained Austenite ◽  
Elevated Temperatures ◽  
Mechanical Performance ◽  
Mechanical Stability ◽  
Electron Backscatter Diffraction ◽  
Cost Effective ◽  
Tensile Tests ◽  
Thermal Stability Of

AbstractAdvanced medium-Mn sheet steels show an opportunity for the development of cost-effective and light-weight automotive parts with improved safety and optimized environmental performance. These steels utilize the strain-induced martensitic transformation of metastable retained austenite to improve the strength–ductility balance. The improvement of mechanical performance is related to the tailored thermal and mechanical stabilities of retained austenite. The mechanical stability of retained austenite was estimated in static tensile tests over a wide temperature range from 20 °C to 200 °C. The thermal stability of retained austenite during heating at elevated temperatures was assessed by means of dilatometry. The phase composition and microstructure evolution were investigated by means of scanning electron microscopy, electron backscatter diffraction, X-ray diffraction and transmission electron microscopy techniques. It was shown that the retained austenite stability shows a pronounced temperature dependence and is also stimulated by the manganese addition in a 3–5% range.

scholarly journals Oxygen Induced Phase Transformation in TC21 Alloy with a Lamellar Microstructure

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 163
Author(s):  
Shu Wang ◽  
Yilong Liang ◽  
Hao Sun ◽  
Xin Feng ◽  
Chaowen Huang
Keyword(s):  
Electron Microscopy ◽  
Phase Transformation ◽  
Oxygen Uptake ◽  
Titanium Alloys ◽  
Electron Backscatter Diffraction ◽  
Lamellar Microstructure ◽  
Α Phase ◽  
Transmission Electron ◽  
The Matrix ◽  
Oxygen Ingress

The main objective of the present study was to understand the oxygen ingress in titanium alloys at high temperatures. Investigations reveal that the oxygen diffusion layer (ODL) caused by oxygen ingress significantly affects the mechanical properties of titanium alloys. In the present study, the high-temperature oxygen ingress behavior of TC21 alloy with a lamellar microstructure was investigated. Microstructural characterizations were analyzed through optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Obtained results demonstrate that oxygen-induced phase transformation not only enhances the precipitation of secondary α-phase (αs) and forms more primary α phase (αp), but also promotes the recrystallization of the ODL. It was found that as the temperature of oxygen uptake increases, the thickness of the ODL initially increases and then decreases. The maximum depth of the ODL was obtained for the oxygen uptake temperature of 960 °C. In addition, a gradient microstructure (αp + β + βtrans)/(αp + βtrans)/(αp + β) was observed in the experiment. Meanwhile, it was also found that the hardness and dislocation density in the ODL is higher than that that of the matrix.

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