Showing 9 results for Oxidation
M. Ozve Aminian, J. Hedjazi, Y. Kharazi,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: In this research, the oxidation behaviour of high Aluminum heat resistant steel (%25Cr,%20Ni,%8Al) hasbeen evaluated at the temperature range of (1000-1300ºC).The results showed that there was no countinous healinglayer on the surface of the alloy when Al increased up to %5.5 and the oxidation resistance of steel decreased due toformation of spinel oxides on the surface.By increasing the aluminum amount to %8, only Al oxide formed due to decreasing carbon potential of thealloy,homogenity of elemental concentration in matrix and no diffusion of oxygen through oxide–metalinterface,therefore it has superior oxidation resistance. Meanwhile,oxidation tests showed that the weight gain of thesteel at high temperature oxidation even at 1300ºC was too low.
S. Noori, J. Khalil-Allafi,
Volume 12, Issue 2 (6-2015)
Abstract
The effect of anodic oxidation of a NiTi shape memory alloy in sulfuric acid electrolyte on its surface
characteristics was studied. Surface roughness was measured by roughness tester. Surface morphology was studied
using optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion behavior was specified by
recording Potentiodynamic polarization curves and measuring the content of Ni ions, released into a SBF solution
using atomic absorption spectroscopy (AAS). Fourier transformation infrared radiation (FT-IR) and energy dispersive
spectroscopy were employed to verify the biocompatibility of the anodized and bare alloys after submersion in SBF. It
was shown that anodic oxidation in sulfuric acid significantly increases corrosion resistance and biocompatibility. This
layer improves corrosion resistance and Ni ion-release resistance by impeding the direct contact of the alloy with the
corrosion mediums i.e. Ringer and SBF solutions. The TiO2 oxide layer also decreases the releasing of Ni ions in to
SBF solution
A. Mohsenifar, M. R. Aboutalebi, S. H. Aboutalebi,
Volume 12, Issue 3 (9-2015)
Abstract
Hot dip aluminizing was carried out on the low carbon steel rod under optimized conditions. The aluminized
samples were further oxidized at 1000̊C in air atmosphere at two different times of 20 and 60 minutes. Microstructure
study and phase analysis were studied by scanning electron microscopy and X-ray diffraction methods, respectively.
The characterization of the coating showed that, Fe2
Al5
has been the major phase formed on the surface of specimen
before heat treatment. Following the oxidation of the coating at high temperature, Al
2O3
was formed on the surface of
coating while Fe
2
Al5
transformed into FeAl and Fe
3
Al which are favorable to the hot corrosion resistance of the
coating. Corrosion resistance of aluminized samples before and after heat treatment was evaluated by rotating the
samples in the molten aluminum at 700 ̊C for various times and the dissolution rate was determined. The obtained
results showed that by oxidizing the coating at high temperature, the corrosion resistance of the samples in molten
aluminum improves significantly.
M. Divandari, M. Mehrabian,
Volume 14, Issue 3 (9-2017)
Abstract
This paper investigates the difference between thickness of zinc-based alloys oxide films in dynamic condition using the oxide-metal-oxide (OMO) sandwich method and static condition by theoretical calculations. In dynamic condition, the thickness of the oxide film in the OMO sandwich sample was characterized by scanning electron microscopy (SEM). In the static condition, the thickness and type of the oxide films were studied based on thermodynamic and kinetic estimations. The results showed that the oxide film thickness in molten Zn4Al and ZA27 alloys using OMO sandwich method was estimated to be in the range of 70-200 nm and 30-100 nm, respectively. However, the thickness of oxide films in the static oxidation based on the theoretical calculations, regardless of melt chemical composition, were about 2-5 nm.
R. Latifi, S. Rastegari, S. H. Razavi,
Volume 16, Issue 4 (12-2019)
Abstract
In the present study, Zirconium modified aluminide coating on the nickel-base superalloy IN-738LC was first created by high activity high temperature aluminizing based on the out-of-pack cementation method. Then, Zr coatings were applied to simple aluminide coatings by sputtering and heat treatment in order to study the effect of Zr on the coating microstructure and oxide spallation. Microstructural studies were conducted by using scanning electron microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and x-ray diffraction (XRD) microanalysis. The results indicated that zirconium modified aluminide coating, like aluminide coating, has a two-layer structure including a uniform outer layer of NiAl and an interdiffusion layer in which zirconium is in a form of solid solution in the coating. Furthermore, the 300nm Zr-coated NiAl demonstrated an excellent scale adhesion, a slow oxidation rate and lower amounts of some other elements such as Ti and Cr in its oxide layer leading to a pure aluminide oxide layer.
M. Ghasemian Safaei, Dr. S. Rastegari, R. Latifi,
Volume 17, Issue 2 (6-2020)
Abstract
In this study, Si-modified aluminide coating on nickel-base superalloy IN-738LC was prepared using a pack cementation method with various powder compositions at 1050 °C for 6 h. The cyclic oxidation test was conducted at 1000 °C followed by cooling at room temperature for 200 h and 20 cycles. The effect of powder composition and the way of cooling on the coatings microstructure and oxidation behavior were studied. Investigations carried out using a scanning electron microscope (SEM), EDS analysis, and XRD. Microstructural observations revealed that the coating thickness of 293 and 274 µm was achieved in the case of using pure Al and Si powder and alloyed Al-20wt.%Si one in the packed mixture, respectively. It was also found that utilizing pure Al and Si powder with NH4Cl as an activator in the pack led to the formation of silicide coating, owing to the higher diffusion of Si, which showed superior cyclic oxidation performance.
Sasan Ranjbar Motlagh, Hosein Momeni, Naser Ehsani,
Volume 18, Issue 1 (3-2021)
Abstract
In this study, the effect of annealing treatment on microstructure and mechanical properties of Nb-10Hf-1Ti wt.% produced by Spark Plasma Sintering (SPS) was investigated. Scanning electron microscope (SEM), optical microscopy, X-ray diffraction analysis, hardness, and uniaxial tension test were used. Annealing treatment was carried out in a vacuum of 10-3 Pa at 1150 °C for 1, 3, 5, and 7 hours and in an argon atmosphere at 1350 °C for 5 hours. Internal oxidation and subsequent hafnium oxide formation causes the hardening of the C103 alloy and drastically increases hardness and tensile strength. Although HfO2 particles formed in the grain boundary cause brittleness and cleavage fracture of samples. Volume fraction, particle size, and mean interparticle spacing of oxides significantly change by annealing and subsequently the mechanical properties are affected. The SPSed sample at 1500 ℃ is softened by annealing at 1150 ℃ for 5 hours and its hardness and yield strength are reduced from 303 Hv to 230 Hv and 538 MPa to 490 MPa respectively. While annealing at 1350 ℃for 5 hours increases hardness and yield strength increases to 343 Hv and 581 MPa.
Alireza Mirak,
Volume 18, Issue 2 (6-2021)
Abstract
In the present study, the early stages of the surface oxidation and fluoridation of liquid AZ91D and AM60B alloys under ultra-high purity (UHP) argon, dry air, and air mixed with two different protective fluorine-bearing gases were studied. The chemical composition, morphology and thickness of the surface films formed inside the trapped bubbles were characterized by SEM and EDS analyses. It is found that the molten AM60B alloy is more sensitive to impurities under UHP argon gas than AZ91D alloy. Under dry air atmosphere, the entire surface of molten AZ91D alloy is covered with an oxide layer and thinner thickness than the surface film formed on AM60B alloy which has a rough surface exhibiting granular growth in later stages of oxidation. The EDS analyses show that film chemistry is mainly composed of Mg, Al, and O elements. Under fluorine-bearing gas/air mixtures with either SF
6 or HFC-R134a at 3.5%vol., a fresh surface film formed with a flat and dense morphology of a uniform thickness composed of mixed Mg, F, Al, and O elements. It is observed that there is a lower O:F intensity ratio in the surface film formed on the molten AZ91D alloy under 1,1,1,2-tetra-fluoroethane (HFC-R134a) mixed with dry air compared to the AM60B alloy under both air/ R134a and air/SF
6 mixtures which shows a higher fluorine concentration in the surface film a leading to a better oxidation resistance
.
Amirhossein Kazemi, Arash Fattah-Alhosseini, Maryam Molaei, Meisam Nouri,
Volume 19, Issue 2 (6-2022)
Abstract
In this study, for the first time, the Forsterite (Mg2SiO4) nanoparticles (NPs) with the size of about 25 nm were added to the phosphate-based electrolyte, and the characteristics and properties of the obtained plasma electrolytic oxidation (PEO) coating on AZ31 Mg alloy was investigated. The results of the potentiodynamic polarization measurements revealed that after one week of exposure to simulated body fluid (SBF) solution, the coating with Mg2SiO4 NPs possessed 12.30 kΩ cm2 polarization resistance, which was more than two times greater than that of the coating without NPs. The thicker coating layer, lower wettability, and also presence of Mg2SiO4 NPs inside the pores were responsible for enhanced corrosion protection in the Mg2SiO4 NPs incorporated coating. After three weeks of immersion in SBF solution, the in-vitro bioactivity test results indicated the ability of the NPs-containing coating to form apatite (Ca/P ratio of 0.92) was weaker than the coating without NPs (Ca/P ratio of 1.17). This could be attributed to the lower wettability of the coating with NPs and supports that the addition of the nanoparticles is not beneficial to the bioactivity performance of the coating.
