• Journal of Welding and Joining
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• v.26 no.5
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• pp.36-42
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• 2008

Carbon nanotube (CNT) aluminum composite coatings were built up through kinetic spraying process. Deposition behavior of CNT aluminum composite on an aluminum 1050 alloy substrate was analyzed based on deposition mechanism of kinetic spraying. The microstructure of CNT aluminum composite coating were observed and analyzed. Also, the electrical resistivity, bond strength and micro-hardness of the CNT aluminum composite coatings were measured and compared to kinetic sprayed aluminum coatings. The CNT aluminum composite coatings have a dense structure with low porosity. Compared to kinetic sprayed aluminum coating, the CNT aluminum composite coatings present lower electrical resistivity and higher micro-hardness due to high electrical conductivity and dispersion hardening effects of CNTs.

• Corrosion Science and Technology
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• v.6 no.1
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• pp.18-23
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• 2007

DLC coatings have been deposited onto substrate of STS 316L and Ti alloy using r.f. PACVD (plasma-assisted chemical vapor deposition) with a mixture of $C_{6}H_{6}$ and $SiH_{4}$ as the process gases. Corrosion performance of DLC coatings was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) and surface analysis (scanning electron microscopy). The electrolyte used in this test was a 0.89% NaCl solution of pH 7.4 at temperature $37^{\circ}C$. The porosity and protective efficiency of DLC coatings were obtained using potentiodynamic polarization test. Moreover, the delamination area and volume fraction of water uptake of DLC coatings as a function of immersion time were calculated using electrochemical impedance spectroscopy. This study provides the reliable and quantitative data for assessment of the effect of substrate on corrosion performance of Si-DLC coatings. The results showed that Si-DLC coating on Ti alloy could improve corrosion resistance more than that on STS 316L in the simulated body fluid environment. This could be attributed to the formation of a dense and low-porosity coating, which impedes the penetration of water and ions.

• Corrosion Science and Technology
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• v.6 no.3
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• pp.120-127
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• 2007

In any developing nation major investment goes for infrastructure and it is not exception in India. Good numbers of buildings, bridges, shopping malls, car parks etc. are coming up with steel for sustainable development. Thus protecting the structures from corrosion are the challenges faced by professionals for all types of steel structures. About 3% of GDP is accounted for loss due to corrosion. To combat this up to date corrosion map is called for as the country has wide variation of climatic zones with vastcoastline. Logically organic paint system can be prescribed based on the corrosion rate on bare steel with respect to environment. Present paper will emphasis on the study conducted on two types of structural steel coated with organic paint located in twomarine environment having been exposed for three years, Test coupons made from steels both bare and coated are deployed at two field stations having marine (Digha) and industrial marine (Channai) environments. Various tests like AC impedance DC corrosion, polarisation, salt spray test, $SO_2$ chamber and Raman spectroscopy were carried out both in laboratory on fresh as well as coupons collected from exposure sites. Rust formed on the bare and scribed coated coupons are investigated. It is found that normal marine environment at Digha exhibits higher corrosion rate than polluted marine environment in Channai. Rust analysis indicates formation of ${\propto}$-FeoOH protects or reduces corrosion rate at Channai and formation of non-protective ${\gamma}$-FeoOH increases corrosion rate at Digha. The slower corrosion rate in Channai than at Digha is attributed due to availability of $SO_2$, in the environment, which converts non‐protective rust ${\gamma}$-FeoOH to protective rust ${\propto}$-FeoOH. While comparing the damage on the coated panels it is found that low alloy structural steel provides less damage than plain carbon steel. From the experimentations a suitable paint system specification is drawn for identical environments for low medium and high durability.

• Corrosion Science and Technology
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• v.21 no.3
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• pp.230-241
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• 2022

Austenitic stainless steel has been widely used because of its good corrosion resistance and mechanical properties. However, intergranular corrosion can occur if the alloy is welded or aged. The objective of this study was to determine intergranular corrosion behaviors of austenitic medium carbon (0.05 wt%) and low carbon (0.02 wt%) stainless steel aged at several conditions. Alloys were evaluated according to ASTM A262 Practice A, ISO 12732 DL-EPR (double loop-electrochemical potentiokinetic reactivation) test, and ASTM A262 Practice C. The degree of sensitization and intergranular corrosion rate were obtained. The relationship between the degree of sensitization and the intergranular corrosion rate showed a very large fluctuation. Such behavior might be related to whether two-dimension tests or three-dimension tests were performed. On the other hand, regardless of carbon content of alloys, when the intergranular corrosion rate increased, the degree of sensitization also increased. However, the DL-EPR test showed a higher sensitivity than the Huey test for differentiating the intergranular corrosion property at a low intergranular corrosion rate, while the Huey test had a higher sensitivity than the DL-EPR test for distinguishing the intergranular corrosion property at a high intergranular corrosion rate.

• Journal of Welding and Joining
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• v.34 no.3
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• pp.61-68
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• 2016

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

• Korean Journal of Materials Research
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• v.20 no.1
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• pp.37-41
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• 2010

Creep tests were conducted under a condition of constant stress on two aluminum-based alloys containing particles: Al-5% Mg-0.25% Fe and Al-5% Zn-0.22% Fe. The role of grain boundary sliding was examined in the plane of the surface using a square grid printed on the surface by carbon deposition and perpendicular to the surface using two-beam interferometry. Estimates of the contribution of grain boundary sliding to the total strain, $\varepsilon_{gbs}/\varepsilon_t$ reveal two trends; (i) the sliding contribution is consistently higher in the Al-Mg-Fe alloy, and (ii) the sliding contribution is essentially independent of strain in the Al-Mg-Fe alloy, but it shows a significant decrease with increasing strain in the Al-Zn-Fe alloy. Sliding is inhibited by the presence of particles and its contributions to the total strain are low. This inhibition is attributed to the interaction between the grain boundary dislocations responsible for sliding and particles in the boundaries.

• Korean Journal of Materials Research
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• v.14 no.2
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• pp.101-109
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• 2004

The influences of solidification rates and carbon contents on the formation of the $\delta$-ferrite were studied by directional solidification in modified 12%Cr-l %Mo steels. Directional solidification experimental results showed that solidification microstructure depended on solidification rate and carbon content and chromium equivalent. The length of the mushy zone increased and the dendrite arm spacings decreased as the solidification rate increased. The volume fraction of the 8-ferrite decreased with increasing the solidification rate and carbon content. The volume fraction of the ferrite showed much higher at low solidification rates with planar and cellular interfaces than that at high solidification rates with dendritic interface. It is expected that macro-segregation of C causes lower C content at the lower solidification fraction in the directionally solidified sample, where lower C results in higher volume fraction of the ferrite. In order to estimate solidification microstructure in modified 12Cr-l%Mo steels, various solidification conditions, such as solidification rate, cooling rate, segregation, alloy composition, should be considered.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.4
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• pp.342-349
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• 2009

This study investigated the growth characteristics of carbon nanotubes (CNTs) by changing a period of annealing time and a $C_{2}H_{2}/H_2$ flow ratio at temperature as low as $450^{\circ}C$ with inductively coupled plasma chemical vapor deposition. The 1-nm-thick Fe-Ni-Co alloy thin film served as a catalyst layer for the growth of CNTs, which was thermally evaporated on the 15-nm-thick Al underlayer deposited on the 50-nm-thick Ti diffusion barrier. The annealing at low temperature of $450^{\circ}C$ brought about almost no granulation of the catalyst layer, and the CNT growth was not affected by a period of annealing time. A study of changing the flow rate of $C_{2}H_{2}$ and $H_2$ showed that as the ratio of the $C_{2}H_{2}$ flow rate to the $H_2$ flow rate was lowered, the CNTs were grown to be longer With further decreasing the flow ratio, the length of CNTs reached the maximum and then became shorter. Under the optimized gas flow rates, we successfully synthesized CNTs with a uniform length over a 4-inch Si wafer at $450^{\circ}C$.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.29-36
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• 1991

Pressurized Water Reactor (PWR) pressure vessels are made of forged low alloy steel plates internally clad with an austenitic stainless steel by welding to improve anti-corrosion properties. They display a characteristic behavior of dissimilar metal weld interface during post weld heat treatment (PWHT) and service at high temperature and pressure. In this Study, Metallugical structure of weld interface of SA 508 Class 3 forged steel clad with 309L, Austenitic stainless steel after PWHT was investigated. To estimate the width of the carburized/decarburized bands quantitatively, a model for carbon diffusion was proposed and a theoretical equation was derived.

• Journal of the Korean institute of surface engineering
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• v.48 no.3
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• pp.110-114
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• 2015

The effect of hot-dip aluminizing on the corrosion of the low carbon steel was studied at $650-850^{\circ}C$ for 20-50 h in $N_2/0.5%\;H_2S$ gas. The aluminized steel consisted primarily of the Al topcoat and the underlying Al-Fe alloy layer. Aluminizing drastically improved the corrosion resistance by forming the ${\alpha}-Al_2O_3$ surface scale. Without aluminizing, the steel formed nonadherent, fragile, thick scales, which consisted of FeS as the major phase and iron oxides such as FeO, $Fe_3O_4$ and $Fe_2O_3$ as minor ones.