scholarly journals Formation Mechanism of Aluminide Diffusion Coatings on Ti and Ti-6Al-4V Alloy at the Early Stages of Deposition by Pack Cementation

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3097
Author(s):  
Hailiang Du ◽  
Ning Tan ◽  
Li Fan ◽  
Jiajie Zhuang ◽  
Zhichao Qiu ◽  
...  
Keyword(s):  
Outer Layer ◽  
Aluminide Coating ◽  
Energy Dispersive Spectrometer ◽  
Pack Cementation ◽  
X Ray Diffraction ◽  
Diffusion Coatings ◽  
Early Stages ◽  
Outward Migration ◽  
Kinetics Of ◽  
Precision Balance

The diffusion coatings were deposited on commercially pure Ti and Ti-6Al-4V alloy at up to 1000 °C for up to 10 h using the pack cementation method. The pack powders consisted of 4 wt% Al (Al reservoir) and 4 wt% NH4Cl (activator) which were balanced with Al2O3 (inert filler). The growth kinetics of coatings were gravimetrically measured by a high precision balance. The aluminised specimens were characterised by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). At the early stages of deposition, a TiO2 (rutile) scale, other than aluminide coating, was developed on both materials at <900 °C. As the experimental temperature arose above 900 °C, the rutile layer became unstable and reduced to the low oxidation state of Ti oxides. When the temperature increased to 1000 °C, the TiO2 scale dissociated almost completely and the aluminide coating began to develop. After a triple-layered coating was generated, the coating growth was governed by the outward migration of Ti species from the substrates and obeyed the parabolic law. The coating formed consisted of an outer layer of Al3Ti, a mid-layer of Al2Ti and an inner layer of AlTi. The outer layer of Al3Ti dominated the thickness of the aluminide coating.

The early stages of phase formation during mechanical alloying of Ti–Al

1994 ◽  
Vol 9 (1) ◽  
pp. 47-52 ◽  
Author(s):  
T. Klassen ◽  
M. Oehring ◽  
R. Bormann
Keyword(s):  
Mechanical Alloying ◽  
Phase Formation ◽  
X Ray Diffraction ◽  
Annealing Behavior ◽  
Early Stages ◽  
Transmission Electron ◽  
Fcc Phase ◽  
Multilayered Thin Films ◽  
Kinetics Of ◽  
Structural Disordering

The early stages of phase formation during mechanical alloying of Ti/Al powder blends were investigated using x-ray diffraction and transmission electron microscopy. After the initial formation of an hep solid solution by the diffusion of Al into Ti, the first phase nucleated at the Ti/Al interface is a (partially) Ll2-ordered fcc phase with a crystallite size of about 10–30 nm. This observation is ascribed to the kinetics of phase formation and the energetic destabilization of the equilibrium intermetallic compounds during milling due to chemical and structural disordering. A mechanism of phase formation during mechanical alloying is proposed, and comparisons are made with the thermal annealing behavior of Ti/Al multilayered thin films.

Diffusion Layers with Ti and Ti+Al Formed on 316L Austenitic Steel by a Pack Cementation Procedure

2011 ◽  
Vol 312-315 ◽  
pp. 13-19 ◽  
Author(s):  
Iulia Mirela Britchi ◽  
Mircea Olteanu ◽  
Niculae Ene ◽  
Petru Nita
Keyword(s):  
Activation Energy ◽  
Powder Mixture ◽  
Pack Cementation ◽  
X Ray Diffraction ◽  
Powder Mixtures ◽  
X Ray ◽  
Diffusion Coatings ◽  
Diffusion Layers ◽  
316L Steel ◽  
Temperature Activation

Pack cementation procedure implies the use of a powder mixture containing the diffusive elements, which in our case are either Ti or Ti+Al, Al2O3 and NHCl as activator. In the case of titanizing the powder mixture contained 77% in weight Ti, while for alumino-titanizing Al/Ti = 1/5 ratio was employed. NH4Cl content was 3% in weight in all cases. Aluminium additions to the powder mixtures led to a decrease of the process temperature. Activation energy for the aluminizing of austenitic 316L steel is 73.87 KJ/mol, much smaller than for the titanizing, 257.86 KJ/mol. Activation energy for alumino-titanizing, in the same conditions, is 146.01 KJ/mol. All diffusion coatings, in the Ti – 316L and Ti+Al – 316L couples are formed of two layers having different structures and compositions. All couples were investigated by optical microscopy, electron microscopy (SEM and EDX), X-ray diffraction and microhardness trials.

Microstructural characterization and crystallization kinetics of (1-x)TeO2-0.10CdF2-xPbF2 (x = 0.05, 0.10, and 0.15 mol) glasses

2009 ◽  
Vol 24 (10) ◽  
pp. 3087-3094 ◽  
Author(s):  
Demet Tatar ◽  
M. Lutfi Öveçoğlu ◽  
Gonul Özen ◽  
Scott A. Speakman
Keyword(s):  
Crystallization Kinetics ◽  
Energy Dispersive Spectrometer ◽  
Glass Structure ◽  
Glass Network ◽  
Microstructural Characterization ◽  
Exothermic Peak ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
Heating Rates ◽  
Kinetics Of

Microstructural characterization and crystallization kinetics of (1-x)TeO2-0.10CdF2-xPbF2 (x = 0.05, 0.10, and 0.15 in molar ratio) glasses were investigated using differential thermal analysis (DTA), x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy/energy dispersive spectrometer (SEM/EDS), and absorbance spectroscopy techniques. For all of the glass compositions only one exothermic peak was observed on the DTA plots, and on the basis of the XRD and Raman spectrophotometry investigations it was understood that they refer to the formation of the α-TeO2 phase. SEM/EDS investigations revealed the presence of oriented needle-like α-TeO2 crystals in the 0.85TeO2-0.10CdF2-0.05PbF2 glass, rectangle-shaped α-TeO2 crystals in the 0.80TeO2-0.10CdF2-0.10PbF2 glass, and disoriented needle-like crystals in the 0.75TeO2-0.10CdF2-0.15PbF2 glass. DTA analyses were carried out at different heating rates, and the Avrami constants for all of the glasses were approximately 1. The activation energy calculations and SEM investigations demonstrated that the formation of the crystalline phases occurred via surface crystallization mechanism for all of the glasses. Activation energies for crystallization in these glasses were determined from the modified Kissinger plots and were found to vary between 67 and 183 kJ/mol. The addition of PbF2 as a network modifier into the glass structure contributes to the intensity of the Raman peaks change and forced the transition of the glass network from TeO4 trigonal bipyramid units to the TeO3 trigonal pyramid structural units.

Corrosion Behavior of Incoloy 800 in Molten Nitrate Salt

2014 ◽  
Vol 887-888 ◽  
pp. 357-361
Author(s):  
Yu Jun Zhang ◽  
Lei Lei Xiao ◽  
Jun Hua Liu ◽  
Mei Ling Liu ◽  
Min Hui Fu
Keyword(s):  
Phase Composition ◽  
Corrosion Behavior ◽  
Layer Structure ◽  
Energy Dispersive Spectrometer ◽  
Oxide Films ◽  
Optical Microscope ◽  
X Ray Diffraction ◽  
Parabolic Law ◽  
Incoloy 800 ◽  
Kinetics Of

The corrosion behavior of Incoloy 800 as the receiver tube materials in a solar tower field exposed to a mixed molten nitrate salts (KNO3: 40wt.%, NaNO3: 60wt%) at 560°C, has been investigated by several methods. After Incoloy 800 specimens were immersed respectively in molten salts at 560°C for different times (5h, 10h, 20h, 30h, 40h, 60h, and 80h), the weight-loss of specimens were test, the morphology of oxide films on the Incoloy 800 specimens were observed by Optical microscope (OM) and Scanning electron microscopy (SEM), the phase composition of the oxide film were investigated by X-ray diffraction (XRD) and Energy dispersive spectrometer (EDS). The experimental results revealed that the corrosion kinetics of the tested alloy agreed with the parabolic law at 560°C, and the corrosion rate is 91.5μm/year. The analysis of the phase composition shows the oxide films had a duplex layer structure with Fe2O3in the outer layer, andγ-(Fe,Ni) and Cr2O3in the inner layer.

Effect of Y2O3 on Microstructure and Oxidation Behavior of Aluminide Coating on Ni-Based Superalloy

2015 ◽  
Vol 1095 ◽  
pp. 603-607 ◽  
Author(s):  
Yin Qun Hua ◽  
Zhen Rong ◽  
Kang Min Chen ◽  
Yun Xia Ye ◽  
Wen Hui Wu ◽  
...  
Keyword(s):  
Rare Earth ◽  
Oxidation Behavior ◽  
Aluminide Coating ◽  
Rare Earth Oxide ◽  
X Ray Diffraction ◽  
Aluminide Coatings ◽  
Lower Temperature ◽  
Α Al2o3 ◽  
Surface Morphologies ◽  
Kinetics Of

The oxidation behavior of Ni-based superalloy GH586 which is treated by pack-cementation aluminizing was investigated. Scanning electron microscope and X-ray diffraction were used to analyze the microstructure of aluminide coatings and the surface morphologies of the oxide scales. Results show that the main phase of the aluminide coatings was NiAl. The aluminide coating can be formed at lower temperature due to the addition of rare earth oxide in the mixture powders. The thickness of aluminide coating at 900°C was about 110μm, and another aluminide coating with rare earth oxide Y2O3 at 800°C was about 38μm. The oxidation kinetics of aluminized specimens approximately followed a parabolic oxidation law at 1000°C. The morphology of the oxidation scales was primarily θ-Al2O3 with minor α-Al2O3. The scales of the coatings with rare earth oxide Y2O3 after oxidation was more dense.

Wear Kinetics of Steels with Diffusion Coatings in Rolling Friction

2020 ◽  
Vol 56 (1) ◽  
pp. 50-58
Author(s):  
P. V. Kaplun ◽  
V. A. Honchar ◽  
T. V. Donchenko
Keyword(s):  
Rolling Friction ◽  
Diffusion Coatings ◽  
Kinetics Of

scholarly journals Stable and Metastable Phase Equilibria Involving the Cu6Sn5 Intermetallic

2021 ◽  
Author(s):  
A. Leineweber ◽  
M. Löffler ◽  
S. Martin
Keyword(s):  
Phase Equilibria ◽  
Electron Backscatter Diffraction ◽  
Metastable Phase ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heat Treated ◽  
Ordered Phases ◽  
Backscatter Diffraction ◽  
Kinetics Of

Abstract Cu6Sn5 intermetallic occurs in the form of differently ordered phases η, η′ and η′′. In solder joints, this intermetallic can undergo changes in composition and the state of order without or while interacting with excess Cu and excess Sn in the system, potentially giving rise to detrimental changes in the mechanical properties of the solder. In order to study such processes in fundamental detail and to get more detailed information about the metastable and stable phase equilibria, model alloys consisting of Cu3Sn + Cu6Sn5 as well as Cu6Sn5 + Sn-rich melt were heat treated. Powder x-ray diffraction and scanning electron microscopy supplemented by electron backscatter diffraction were used to investigate the structural and microstructural changes. It was shown that Sn-poor η can increase its Sn content by Cu3Sn precipitation at grain boundaries or by uptake of Sn from the Sn-rich melt. From the kinetics of the former process at 513 K and the grain size of the η phase, we obtained an interdiffusion coefficient in η of (3 ± 1) × 10−16 m2 s−1. Comparison of this value with literature data implies that this value reflects pure volume (inter)diffusion, while Cu6Sn5 growth at low temperature is typically strongly influenced by grain-boundary diffusion. These investigations also confirm that η′′ forming below a composition-dependent transus temperature gradually enriches in Sn content, confirming that Sn-poor η′′ is metastable against decomposition into Cu3Sn and more Sn-rich η or (at lower temperatures) η′. Graphic Abstract

In-situ stabilization of silver nanoparticles in polymer hydrogels for enhanced catalytic reduction of macro and micro pollutants

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Luqman Ali Shah ◽  
Rida Javed ◽  
Mohammad Siddiq ◽  
Iram BiBi ◽  
Ishrat Jamil ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Thermo Gravimetric Analysis ◽  
Activation Parameters ◽  
Reduction Reaction ◽  
Gravimetric Analysis ◽  
X Ray Diffraction ◽  
In Situ Stabilization ◽  
Hybrid Hydrogels ◽  
Kinetics Of

AbstractThe in-situ stabilization of Ag nanoparticles is carried out by the use of reducing agent and synthesized three different types of hydrogen (anionic, cationic, and neutral) template. The morphology, constitution and thermal stability of the synthesized pure and Ag-entrapped hybrid hydrogels were efficiently confirmed using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). The prepared hybrid hydrogels were used in the decolorization of methylene blue (MB) and azo dyes congo red (CR), methyl Orange (MO), and reduction of 4-nitrophenol (4-NP) and nitrobenzene (NB) by an electron donor NaBH4. The kinetics of the reduction reaction was also assessed to determine the activation parameters. The hybrid hydrogen catalysts were recovered by filtration and used continuously up to six times with 98% conversion of pollutants without substantial loss in catalytic activity. It was observed that these types of hydrogel systems can be used for the conversion of pollutants from waste water into useful products.

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