scholarly journals Enhancing the phase stability of ceramics under radiation via multilayer engineering

2021 ◽  
Vol 7 (26) ◽  
pp. eabg7678
Author(s):  
Hongliang Zhang ◽  
Jianqi Xi ◽  
Ranran Su ◽  
Xuanxin Hu ◽  
Jun Young Kim ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Phase Stability ◽  
First Principles Calculations ◽  
Tem Analysis ◽  
Promising Strategy ◽  
Transmission Electron ◽  
Radiation Induced ◽  
Composition Changes ◽  
Annealing Defects

In metallic systems, increasing the density of interfaces has been shown to be a promising strategy for annealing defects introduced during irradiation. The role of interfaces during irradiation of ceramics is more unclear because of the complex defect energy landscape that exists in these materials. Here, we report the effects of interfaces on radiation-induced phase transformation and chemical composition changes in SiC-Ti3SiC2-TiCx multilayer materials based on combined transmission electron microscopy (TEM) analysis and first-principles calculations. We found that the undesirable phase transformation of Ti3SiC2 is substantially enhanced near the SiC/Ti3SiC2 interface, and it is suppressed near the Ti3SiC2/TiC interface. The results have been explained by ab initio calculations of trends in defect segregation to the above interfaces. Our finding suggests that the phase stability of Ti3SiC2 under irradiation can be improved by adding TiCx, and it demonstrates that, in ceramics, interfaces are not necessarily beneficial to radiation resistance.

Phase Stability and Mechanical Properties of Ti(Ni, Ru) Alloys

2002 ◽  
Vol 753 ◽  
Author(s):  
Masahiro Tsuji ◽  
Hideki Hosoda ◽  
Kenji Wakashima ◽  
Yoko Yamabe-Mitarai
Keyword(s):  
Mechanical Properties ◽  
Phase Transformation ◽  
Phase Stability ◽  
Hot Forging ◽  
Tensile Tests ◽  
Lattice Parameter ◽  
Solid Solution Hardening ◽  
Scanning Calorimetry ◽  
Arc Melting ◽  
Transmission Electron

ABSTRACTEffects of ruthenium (Ru) substitution on constituent phases, phase transformation temperatures and mechanical properties were investigated for Ti-Ni shape memory alloys. Ti50Ni50-XRuX alloys with Ru contents (X) from 0mol% (binary TiNi) to 50mol% (binary TiRu) were systematically prepared by Ar arc-melting followed by hot-forging at temperatures from 1173K to 1673K depending on chemical composition. Phase stability was assessed by DSC (differential scanning calorimetry), XRD (X-ray diffractometry) and TEM (transmission electron microscopy). Mechanical properties were investigated using hardness and tensile tests at room temperature. With increasing Ru content, it was found that the lattice parameter of B2 phase increases, the martensitic transformation temperature slightly decreases, and the melting temperature increases monotonously. Besides, R-phase appears for Ti-Ni alloys containing 3mol% and 20mol%Ru but no diffusionless phase transformation is seen in Ti-Ni alloy containing 5mol%Ru. Vickers hardness shows the maximum at an intermediate composition (HV1030 at 30mol%Ru); this suggests that large solid solution hardening is caused by Ru substitution for the Ni-sites in TiNi.

The Role of Phase Stability in Ductile, Ordered B2 Intermetallics

2006 ◽  
Vol 980 ◽  
Author(s):  
James R. Morris ◽  
Yiying Ye ◽  
Maja Krcmar ◽  
Chong Long Fu
Keyword(s):  
Phase Stability ◽  
First Principles ◽  
Tensile Ductility ◽  
Stacking Faults ◽  
Low Energy ◽  
First Principles Calculations ◽  
Phase Competition ◽  
Transformation Pathway ◽  
Shape Memory Materials

AbstractWe discuss the underlying atomistic mechanism for experimentally observed large tensile ductility in various strongly ordered B2 intermetallic compounds. First-principles calculations demonstrate that all of the compounds exhibit little energy differences between the B2, B27 and B33 phases. These calculations relate observations of ductility in YAg, YCu and ZrCo to shape-memory materials including NiTi. One transformation pathway between the B2 and B33 phases establishes a connection between this phase competition, and stacking faults on the {011}B2 plane. The low energy of such a stacking fault will lead to splitting of the b=<100> dislocations into b/2 partials, observed in ZrCo, TiCo, and in the B19' phase of NiTi. Calculations demonstrate that this pathway is competitive with the traditional pathway for NiTi.

First-principles investigation of possible martensitic transformation and magnetic properties of Heusler-type Pt2-xMn1+xIn alloys

2015 ◽  
Vol 08 (06) ◽  
pp. 1550064 ◽  
Author(s):  
Lin Feng ◽  
Wenxing Zhang ◽  
Enke Liu ◽  
Wenhong Wang ◽  
Guangheng Wu
Keyword(s):  
Magnetic Properties ◽  
Phase Transformation ◽  
Electronic Structure ◽  
Martensitic Transformation ◽  
Phase Stability ◽  
First Principles ◽  
Electronic Structures ◽  
First Principles Calculations ◽  
Magnetic Structures

The phase stability, electronic structure and magnetism of Pt 2-x Mn 1+x In (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied by first-principles calculations. The possible magnetic martensitic transformation in this series has been investigated. For all the five compounds, the energy minimums occur around c/a = 1.30, and the energy differences between the austenitic and martensitic phases are large enough to overcome the resistance of phase transformation. By comparing the electronic structures of austenitic and martensitic phases, we can find that the phase stability is enhanced by the martensitic transformation. The magnetic structures of the austenitic and martensitic phases are also discussed.

scholarly journals THE EFFECT OF CARBOXYMETHYL CHITOSAN/AMORPHOUS CALCIUM PHOSPHATE TO GUIDE TISSUE REMINERALIZATION OF DENTIN COLLAGEN

2019 ◽  
pp. 181-183
Author(s):  
ROSDIANA NURUL ANNISA ◽  
NILAKESUMA DJAUHARIE ◽  
ENDANG SUPRASTIWI ◽  
NORMA AVANTI
Keyword(s):  
Calcium Phosphate ◽  
Amorphous Calcium Phosphate ◽  
Matrix Protein ◽  
Carboxymethyl Chitosan ◽  
Control Group ◽  
Group 14 ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Dentin Collagen

Objective: Carboxymethyl chitosan/amorphous calcium phosphate (CMC/ACP) can replace the role of dentine matrix protein 1. Guided tissueremineralization (GTR) is a method of extrafibrillar and intrafibrillar collagen remineralization. This study analyzed the ability of CMC/ACP to achieveintrafibrillar and extrafibrillar remineralization on demineralized dentin.Methods: We divided 12 demineralized occlusal cavities into four groups: 7 days control group, 14 days control group, 7 days CMC/ACP group, and14 days CMC/ACP group. In the control group, the cavities were directly filled with temporary restoration material, while the cavities of the CMC/ACPgroups first underwent application of CMC/ACP and were then filled with temporary restoration material. All samples were stored in a 37°C shakingincubator. 12 samples were analyzed by energy-dispersive X-ray (EDX) spectroscopy and four were analyzed by transmission electron microscope(TEM).Results: From day 7 to day 14, there was a significant increase in calcium and phosphate levels within the CMC/APC groups. The phosphate levelswere much lower than the calcium or minerals formed on the 7th day, in the form of hydroxyapatite. TEM analysis shows that the CMC/ACP groupexhibited more intrafibrillar and extrafibrillar remineralization.Conclusion: CMC/ACP can improve the GTR process.

Phase stability of B2O3-added Ba2Ti9O20 ceramic: Processing effects

2003 ◽  
Vol 18 (1) ◽  
pp. 201-207 ◽  
Author(s):  
Sea-Fue Wang ◽  
Chuang-Chung Chiang ◽  
Chai-Hui Wang ◽  
Jinn P. Chu
Keyword(s):  
Phase Transformation ◽  
Phase Stability ◽  
Sintering Temperature ◽  
Host Material ◽  
Minor Amount ◽  
Reaction Products ◽  
Effective Role ◽  
Processing Effects ◽  
A Minor

Preparation of dense and phase-pure Ba2Ti9O20 is generally difficult to achieve using solid-state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition. This study investigated the effects of B2O3 on the densification, microstructural evolution, and phase stability of Ba2Ti9O20. Samples from the host material (2BaO · 9TiO2) with and without the addition of 5 wt% B2O3 were prepared through different processing routes. For the pure host material sintered at temperatures ranging from 800 to 1100 °C, the reaction products followed the sequence of BaTi2O5 → BaTi4O9 → BaTi5O11 → Ba2Ti9O20. The phase transformation proceeded faster in the bulk compared to the free surface of the sample. BaTi5O11 and BaTi4O9 with a minor amount of Ba2Ti9O20 were found in the ground powder of ceramics sintered at 1100 °C. For the samples prepared from host material with the addition of 5 wt% B2O3, Ba2Ti9O20 started to form at temperatures as low as 800 °C. The sequence of reaction products followed Ba4Ti13O30 → BaTi4O9 → BaTi5O11 → Ba2Ti9O20. Sintering at above 1000 °C yielded pure Ba2Ti9O20 phase, suggesting the effective role of B2O3 on the phase stability of Ba2Ti9O20. It was found that precalcination of host material before the addition of B2O3 gives an additional benefit to the Ba2Ti9O20 formation. Crystallization of pure Ba2Ti9O20 phase was completed at a sintering temperature as low as 900 °C without any solid solution additive such as SnO2 or ZrO2, due to the fact that the phase transformation of the samples began with BaTi4O9 and BaTi5O11 during sintering. Also, B2O3 was found to be unstable during the high-temperature sintering at 1200 °C, and the results are discussed.

scholarly journals Understanding the Effect of Aluminum Addition on the Forming of Second Phase Particles on Grain Growth of Micro-Alloyed Steel

2020 ◽  
Vol 10 (1) ◽  
pp. 5153-5156
Author(s):  
S. H. Abro ◽  
H. A. Moria ◽  
A. Chandio ◽  
A. Z. Al-Khazaal
Keyword(s):  
Weight Percent ◽  
Rolling Process ◽  
Second Phase ◽  
Steel Matrix ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Second Phase Particles ◽  
The Matrix ◽  
Micro Alloyed Steel

The formation of second phase particles in the steel matrix during melting and casting plays an important role in controlling the grain size of steel. An attempt is made in the present work to find the role of nitrogen on forming nitride particles either with aluminum or titanium. Two steel samples with the same titanium and aluminum weight percent in their chemical composition were collected after the hot rolling process. Solution heat treatment at 1350°C for 60min holding time was used to dissolve the particles and then the steel samples were reheated at 800°C for 60min, water quenched and their microstructure was revealed by usual grinding and polishing process using 2% Nital. A transmission electron microscope connected with EDS was used to reveal the morphology of the second phase particles. The samples for TEM analysis were prepared by the replica extraction method in 5% Nital solution. The samples were then caught in 3mm copper grid for TEM analysis. TEM micrographs revealed the second phase particles in the matrix of steel. EDS peaks were studied and titanium peaks were found in both samples and surprisingly there was not any peak found for aluminum.

The role of specimen morphology in the preparation of High-TC superconductors for Transmission Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 66-67
Author(s):  
M. Powers
Keyword(s):  
Low Cost ◽  
Oxide Superconductors ◽  
Specimen Preparation ◽  
Layered Crystal ◽  
Preparation Technique ◽  
Ion Milling ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Preparation Techniques

It is vital in TEM investigations, especially for high resolution studies, that specimen quality be optimized and the information desired in a particular TEM analysis often prescribes the method of specimen preparation required. We have found that the morphology of a bulk superconductor sample can significantly influence the ultimate success of the preparation technique utilized.Methods employed for the production of electron transparent foils of ceramic oxide superconductors include mechanical grinding, cleavage, jet polishing, ultramicrotomy and ion milling. Grinding and cleavage are both low cost, quick and easy specimen preparation techniques. However, because of the layered crystal structures of these materials, they display a marked tendency to cleave along (001) planes, and hence the range of crystallographic orientations available with these methods is restricted. With grinding in particular, mechanical deformation can be a problem while with cleavage, transparent areas are confined to the vicinity of particle edges.

HRTEM Study of the Role of Nanoparticles in ODS Ferritic Steel under Dual-Ion Irradiation

2011 ◽  
Vol 1296 ◽  
Author(s):  
Luke Hsiung ◽  
Scott Tumey ◽  
Michael Fluss ◽  
Yves Serruys ◽  
Francois Willaime
Keyword(s):  
Mechanical Alloying ◽  
Ferritic Steel ◽  
Ion Irradiation ◽  
Complex Oxide ◽  
Helium Bubbles ◽  
Ods Steel ◽  
Transmission Electron ◽  
Radiation Induced ◽  
State Amorphization

ABSTRACTStructures of nanoparticles and their role in dual-ion irradiated Fe-16Cr-4.5Al-0.3Ti-2W-0.37Y2O3 (K3) ODS ferritic steel produced by mechanical alloying (MA) were studied using high-resolution transmission electron microscopy (HRTEM) techniques. The observation of Y4Al2O9 complex-oxide nanoparticles in the ODS steel imply that decomposition of Y2O3 in association with internal oxidation of Al occurred during mechanical alloying. HRTEM observations of crystalline and partially crystalline nanoparticles larger than ~2 nm and amorphous cluster-domains smaller than ~2 nm provide an insight into the formation mechanism of nanoparticles/clusters in MA/ODS steels, which we believe involves solid-state amorphization and re-crystallization. The role of nanoparticles/clusters in suppressing radiation-induced swelling is revealed through TEM examinations of cavity distributions in (Fe + He) dual-ion irradiated K3-ODS steel. HRTEM observations of helium-filled cavities (helium bubbles) preferably trapped at nanoparticle/clusters in dual-ion irradiated K3-ODS are presented.

scholarly journals Ion irradiation induced phase transformation in gold nanocrystalline films

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Pranav K. Suri ◽  
James E. Nathaniel ◽  
Nan Li ◽  
Jon K. Baldwin ◽  
Yongqiang Wang ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Ion Irradiation ◽  
Face Centered Cubic ◽  
Ambient Conditions ◽  
Free Standing ◽  
Hexagonal Close Packed ◽  
Transmission Electron ◽  
Precession Electron Diffraction ◽  
Radiation Induced ◽  
Face Centered

Abstract Gold is a noble metal typically stable as a solid in a face-centered cubic (FCC) structure under ambient conditions; however, under particular circumstances aberrant allotropes have been synthesized. In this work, we document the phase transformation of 25 nm thick nanocrystalline (NC) free-standing gold thin-film via in situ ion irradiation studied using atomic-resolution transmission electron microscopy (TEM). Utilizing precession electron diffraction (PED) techniques, crystallographic orientation and the radiation-induced relative strains were measured and furthermore used to determine that a combination of surface and radiation-induced strains lead to an FCC to hexagonal close packed (HCP) crystallographic phase transformation upon a 10 dpa radiation dose of Au4+ ions. Contrary to previous studies, HCP phase in nanostructures of gold was stabilized and did not transform back to FCC due to a combination of size effects and defects imparted by damage cascades.

scholarly journals Controllable Combustion Synthesis of SiC Nanowhiskers in a Si-C-N System: The Role of the Catalyst

2019 ◽  
Vol 10 (1) ◽  
pp. 252
Author(s):  
Min Xia ◽  
Hong-Yan Guo ◽  
Muhammad Irfan Hussain
Keyword(s):  
Electron Microscopy ◽  
First Principles ◽  
Morphological Characterization ◽  
First Principles Calculations ◽  
X Ray Diffraction ◽  
X Ray ◽  
Absorption Energy ◽  
Transmission Electron ◽  
Nanometer Catalysts

Silicon carbide (SiC) nanowhiskers (NWs) constitute an important type of optical and structural materials. Herein, SiC NWs were successfully combustion synthesized (CSed) in a Si-C-N system using tungsten (W) as a catalyst. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were used to characterize the SiC NWs. Results of morphological characterization indicated that the W-catalyzed CSed SiC NWs products were fluffy from surface to the core, and they were about several hundred micrometers in length with diameters less than 1 μm. For the comprehensive understanding of the initial growing progress of W-catalyzed CSed SiC NWs, the absorption behavior of C, N, and Si atoms on the crystal planes of W (100), W (110), and W (111) surfaces was investigated by using first-principles calculations. The calculated surface energy (Esurf) of the studied W surfaces and the absorption energy of C, N, and Si atoms on different sites, indicate that the C atom has a priority to sink to the nanometer catalysts grain of W, and the pre-sunk C atom then reacts with Si atom to form NWs.

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