scholarly journals Microstructure Evolution of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y Alloy during Long-Term Thermal Exposure

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1638
Author(s):  
Zhiyuan Chen ◽  
Zhengkun Cai ◽  
Xiaosong Jiang ◽  
Song Chen ◽  
Zewen Huang ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Volume Fraction ◽  
Thermal Exposure ◽  
Electron Microscopies ◽  
The Third ◽  
Transmission Electron ◽  
Hot Rolled ◽  
Thermodynamic Instability ◽  
Exposure Process

The hot-rolled alloy Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y was exposed to 700 °C air for up to 10,000 h. The changes in microstructure were observed using scanning and transmission electron microscopies. It was found that the α2 laths, α2 + γ lamellae, and B2(ω) structure of the alloy showed thermodynamic instability. There were three types of phase transformation in the alloy during long-term thermal exposure. The first was α2 → γ, which occurs in the interior and boundary of the α2 + γ lamellae. The second was α2 + γ → B2(ω), which occurs on the α2 + γ boundary. In addition, B2(ω) also precipitates on the γ/γ interfaces. The third was B2(ω) → γ, which describes the precipitation of micron-scale γ phases in the B2(ω) area after thermal exposure of 5000 h. The volume fraction and size of the B2(ω) area and equiaxed γ grains continued to increase throughout the exposure process. Large-sized γ grains and a B2 area of tens of microns appeared in the microstructure after long-term thermal exposure. The volume fractions of the B2 area and the equiaxed γ grains after thermal exposure of 10,000 h reached 16.8% and 63.2%, respectively.

scholarly journals PHASE-TRANSFORMATION DYNAMICS AND CHARACTERIZATION OF PRECIPITATES IN THE Cu-3Ti-3Ni-0.5Si ALLOY

2021 ◽  
Vol 55 (4) ◽  
Author(s):  
Jia Liu ◽  
Jituo Liu ◽  
Xianhui Wang ◽  
Chong Fu ◽  
Yanlong Wang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electrical Conductivity ◽  
Phase Transformation ◽  
Volume Fraction ◽  
Formation Enthalpy ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
The Matrix ◽  
Diffraction Patterns ◽  
Precipitated Phases

In this paper we investigated the phase-transformation dynamics of the Cu-3Ti-3Ni-0.5Si alloy by applying the Avrami method to phase-transformation dynamics and electrical conductivity based on the relationship between the electrical conductivity and the volume fraction of precipitates in the Cu-3Ti-3Ni-0.5Si alloy. The results corroborated well with the experimental data. The microstructure and precipitated phases were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analysis of the selected-area electron-diffraction patterns indicated that the precipitates formed in the matrix of the Cu-3Ti-3Ni-0.5Si alloy during aging, correspond to the Ni3Ti, Ni3Si, and Ni2Si phases. According to the values of formation enthalpy and cohesive energy determined by first-principle calculations, the formation of the Ni2Si phase is more favorable compared to the Ni3Si and Ni3Ti phases, and the Ni3Ti exhibits improved structural stability compared to the Ni2Si and Ni3Si phases.

Cluster Dynamics Study of Neutron Irradiation Induced Defects in Fe-12.5at%Cr Alloy

2011 ◽  
Vol 172-174 ◽  
pp. 449-457 ◽  
Author(s):  
Aleksandr R. Gokhman ◽  
Andreas Ulbricht ◽  
Uwe Birkenheuer ◽  
Frank Bergner
Keyword(s):  
Interstitial Atom ◽  
Volume Fraction ◽  
Size Distributions ◽  
Number Density ◽  
Vacancy Clusters ◽  
Transmission Electron ◽  
Induced Defects ◽  
Irradiation Induced Defects ◽  
Best Fit

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters(SIAC) and Cr precipitates in neutron irradiated Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 12 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. A saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC and the volume fraction of the Cr precipitates for neutron exposures above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. A specific surface tension of about 0.028 J/m2 between the a matrix and the Cr-rich a' precipitate was found as best fit value for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS.

Effects of Ruthenium on Microstructure and Stress Rupture Properties of a Nickel-Base Single Crystal Superalloy

2013 ◽  
Vol 747-748 ◽  
pp. 777-782
Author(s):  
Shuai Yang ◽  
Jian Zhang ◽  
Yu Shi Luo ◽  
Yun Song Zhao ◽  
Ding Zhong Tang ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Stress Rupture ◽  
Thermal Exposure ◽  
Microstructural Stability ◽  
Stress Rupture Properties ◽  
Tcp Phases ◽  
Mean Size ◽  
Nickel Base ◽  
Rupture Properties

The effect of Ru addition (0 wt.%, 3 wt.%, 5 wt.%), on γ morphology, elemental segregation, microstructural stability under long-term thermal exposure at 980 and stress rupture properties at 1100°C/130MPa have been studied. The results showed that with the increase of Ru content, the γ/γ eutectic volume fraction and the dendrite arm spacing decreased gradually. The γ' phase mean size in three alloys decreased with the increase of the Ru content. On the other hand, the dendrite segregation of Al, Ta towards interdendrite area and ReW towards dendrite core area was alleviated gradually with the increase of the Ru content. The increase of Ru content from 0 wt.% to 5 wt.% pronouncedly enhanced the stress rupture properties by suppressing the precipitation of TCP phases effectively at high temperature.

scholarly journals Temperature Dependent Phase Transformation Kinetics of Reverted Austenite during Tempering in 13Cr Supermartensitic Stainless Steel

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1203 ◽  
Author(s):  
Yiwei Zhang ◽  
Yuande Yin ◽  
Diankai Li ◽  
Ping Ma ◽  
Qingyun Liu ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Phase Transformation ◽  
Growth Kinetics ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Orientation Relationships ◽  
Supermartensitic Stainless Steel ◽  
Transmission Electron ◽  
Reverted Austenite ◽  
Kinetics Of

The formation and growth kinetics of the reverted austenite during tempering in 13Cr supermartensitic stainless steel were investigated by a combination X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM). The reverted austenite precipitated at the martensite blocks, sub-blocks, laths and grain boundaries. The growth kinetics was established by Johnson-Mehl-Avrami (JAM) kinetics equation according to the volume fraction of the equilibrium reverted austenite at room temperature. The Avrami exponent value is 0.5, and the activation energy was estimated to be 369 kJ/mol, the kinetic model indicates that the mechanism of reverted austenite is diffusion-controlled and the growth of reverted austenite closely relies on the diffusion of the nickel (Ni) element. The experimental measured orientations of the reverted austenite are in good agreement with the theoretical ones, implying that the reverted austenite has the same orientation with the surrounding martensite, which meets the Kurdjumov–Sachs (K-S) orientation relationship. The orientation relationships minimize the strain energy of the phase transformation by reducing the crystallographic mismatch between phases.

Long-Term Results from Unsaturated Durability Testing of Actinide-Doped DWPF and WVDP Waste Glasses

1995 ◽  
Vol 412 ◽  
Author(s):  
Jeffrey A. Fortner ◽  
John K. Bates
Keyword(s):  
Stainless Steel ◽  
Long Term Results ◽  
Electron Microscopies ◽  
Complex Interactions ◽  
Glass Corrosion ◽  
Transmission Electron ◽  
Doped Glasses ◽  
Durability Testing ◽  
Colloid Formation

AbstractResults from durability drip tests designed to simulate the unsaturated conditions in the proposed Yucca Mountain Repository are reported for two actinide-doped glasses used as model waste forms. These tests are being conducted with reference glass compositions doped with neptunium, plutonium, and americium from the Defense Waste Processing Facility (DWPF) and the West Valley Demonstration Project (WVDP), and have been ongoing for over 8 years. Solution compositions, including transuranics, have been periodically determined, and selected analyses of colloid formation and composition, glass corrosion layers, and solid alteration phases have been obtained by scanning and analytical transmission electron microscopies. The importance of integrated testing has been demonstrated, as complex interactions among the glass, the groundwater, and the sensitized stainless steel have been observed. The cumulative releases of both glassforming and dopant elements are presented along with identification of reaction phases and their partitioning between solution and solid phases. Alteration phases, including smectite clay, iron silicates, uranium silicates, and calcium thorium phosphate, have been observed forming on the glass and stainless steel and have occasionally been found suspended in solution as colloids. Actinides, except neptunium, concentrate into alteration phases or sorb onto the stainless steel. The subsequent transport of the actinides is then controlled by these phases.

Microstructural Evolution and Micro-Texture in Zr-2.5Nb Tubes

2005 ◽  
Vol 475-479 ◽  
pp. 1421-1424 ◽  
Author(s):  
P. Zhao ◽  
R.A. Holt
Keyword(s):  
Phase Transformation ◽  
Electron Microscope ◽  
Extrusion Ratio ◽  
Electron Backscattered Diffraction ◽  
Full Size ◽  
The Third ◽  
Transmission Electron ◽  
Pole Figures ◽  
Pressure Tubes ◽  
Scanning Electron

Both small experimental extruded tubes and full-size pressure tubes were examined using scanning electron microscope/electron backscattered diffraction (SEM/EBSD) and transmission electron microscope/selected area diffraction (TEM/SAD). The final microstructures and textures vary with billet microstructure, extrusion temperature and extrusion ratio. Three components in {0002} pole figures were determined. The first component (radial) is produced by a and c+a slip in a-grains during extrusion. The second component (transverse) is associated with the elongated a- grains with their c-axes parallel to their long dimension. The third component (axial) is produced by b-a phase transformation after extrusion with a preferred variant of the Burgers relationship.

Effect of Long-Term Aging on the Evolution of γ' and TCP Phases of a Ni3Al Based Single Crystal Superalloy

2016 ◽  
Vol 849 ◽  
pp. 482-487 ◽  
Author(s):  
Xin Zhou ◽  
Jie Xiao ◽  
Yan Ling Pei ◽  
Shu Suo Li ◽  
Sheng Kai Gong
Keyword(s):  
Single Crystal ◽  
Volume Fraction ◽  
Thermal Exposure ◽  
Single Crystal Superalloy ◽  
High Temperature Strength ◽  
Coarsening Behavior ◽  
Heat Treated ◽  
Tcp Phases ◽  
Tcp Phase

The coarsening behavior of γ' phase and precipitation behavior of TCP phase in a Ni3Al based single crystal superalloy were investigated by experimental and calculation. The Re-containing and Mo-rich single crystal superalloy used in this study exhibit good high-temperature strength and oxidation resistance. After fully heat-treated, the experimental superalloys were aged at 1050°C and 1150°C for different time periods from 50h to 1000h. The microstructure after thermal exposure was examined by field emission-scanning electron microscopy (FE-SEM). The results indicated that the coarsening behavior of γ' phase agrees well with the typical Lifshitz-Slyozov-Wagner (LSW) theory. After thermal exposure, both the size and the volume fraction of the TCP phase changed perceptibly.

Microstructural characterization of a rapidly solidified Al-Fe-V-Si alloy for elevated temperature applications

1988 ◽  
Vol 46 ◽  
pp. 550-551
Author(s):  
R. E. Franck ◽  
J. A. Hawk ◽  
G. J. Shiflet
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Grain Growth ◽  
Volume Fraction ◽  
Microstructural Characterization ◽  
Second Phase ◽  
Microstructural Stability ◽  
Elevated Temperature Strength ◽  
Temperature Applications

Rapid solidification processing (RSP) is one method of producing high strength aluminum alloys for elevated temperature applications. Allied-Signal, Inc. has produced an Al-12.4 Fe-1.2 V-2.3 Si (composition in wt pct) alloy which possesses good microstructural stability up to 425°C. This alloy contains a high volume fraction (37 v/o) of fine nearly spherical, α-Al12(Fe, V)3Si dispersoids. The improved elevated temperature strength and stability of this alloy is due to the slower dispersoid coarsening rate of the silicide particles. Additionally, the high v/o of second phase particles should inhibit recrystallization and grain growth, and thus reduce any loss in strength due to long term, high temperature annealing.The focus of this research is to investigate microstructural changes induced by long term, high temperature static annealing heat-treatments. Annealing treatments for up to 1000 hours were carried out on this alloy at 500°C, 550°C and 600°C. Particle coarsening and/or recrystallization and grain growth would be accelerated in these temperature regimes.

EELS characterization of “Smut” layer films on steel surface prepared for chrome plating by anodic etching

1995 ◽  
Vol 53 ◽  
pp. 538-539
Author(s):  
E Y. Wang ◽  
J. T. Cherian ◽  
A. Madsen ◽  
R. M. Fisher
Keyword(s):  
Steel Surface ◽  
Surface Preparation ◽  
Treatment Method ◽  
Chrome Plating ◽  
Transmission Electron ◽  
Alloy Steels ◽  
Pre Treatment ◽  
Hard Chrome ◽  
Electron Energy Loss

Many steel parts are electro-plated with chromium to protect them against corrosion and to improve their wear-resistance. Good adhesion of the chrome plate to the steel surface, which is essential for long term durability of the part, is extremely dependent on surface preparation prior to plating. Recently, McDonnell Douglas developed a new pre-treatment method for chrome plating in which the steel is anodically etched in a sulfuric acid and hydrofluoric acid solution. On carbon steel surfaces, this anodic pre-treatment produces a dark, loosely adhering material that is commonly called the “smut” layer. On stainless steels and nickel alloys, the surface is only darkened by the anodic pre-treatment and little residue is produced. Anodic pre-treatment prior to hard chrome plating results in much better adherence to both carbon and alloy steels.We have characterized the anodic pre-treated steel surface and the resulting “smut” layer using various techniques including electron spectroscopy for chemical analysis (ESCA) on bulk samples and transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) on stripped films.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

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