Development of Microstructured Carbon Coatings by Substrate-Catalytic CVD

Carbon nanostructured films were synthesized by chemical vapor deposition (CVD) on H18 stainless steel (AISI 440C) sheets with an H2/CH4/N2 gas mixture at various substrate temperatures. During the synthesis, the iron and chromium oxide layer was formed between the steel and carbonaceous layer. The carbon films exhibited wall-like and spherical morphologies and structures, as characterized by scanning electron microscopy and Raman spectroscopy. It was found that the synthesis temperature affects the microsphere density and, therefore, also in the electrochemical behavior. The electrochemical behavior of nanostructured carbon coatings strongly depends on the CVD deposition conditions. The best corrosion resistance (Rp = 11.8 MΩ·cm2, Icorr = 4.4 nA·cm−2) exhibits a nanostructured carbon sample with a moderate amount of sp2-C-rich carbon microspheres CμSs synthesized at 700 °C. The corrosion resistance of the nanostructured carbon coating is better than raw stainless steel.

Unravelling the Fe Effect on the Corrosion of Chromium Coatings: Chemical Composition and Semiconducting Properties

A model trivalent chromium-based electroplating bath doped with different concentration of Fe was used to obtain the different metallic coatings. The impact of the Fe was investigated on the Cr layer and on its native passive film by a detailed characterisation using X-ray Photoelectron Spectroscopy (XPS), Angle Resolved XPS and Auger Electron Spectroscopy. Moreover, the semiconducting properties of their oxide layers were explored by Mott-Schottky and the corrosion performance by the linear polarisation resistance and kinetics of the oxide formation. Results revealed not only a homogeneous Fe distribution into the Cr layer but also the presence of an iron-chromium duplex oxide layer for concentrations ≥ 100 mg/L Fe in the bath. The Mott-Schottky analysis showed a p-n junction for such coatings due to the presence of an iron oxide layer on the top of a chromium oxide one which increases the total amount of point defects (charge carrier density) and drastically affects their corrosion resistance (the polarisation resistance decreased by one order of magnitude and their oxide layer showed slower kinetics and a higher passivation current). In contrast, coatings with a single chromium oxide layer showed a p-type semiconducting behaviour as well as the best corrosion performance.

Microstructure Investigation, Hot Tensile and Hot Corrosion of IN600 to Nimonic 75 heterogeneous Connection in Spot Welding

Nimonic 75 and Inconel 600 alloys are the Nickel-based superalloys which are used in manufacturing gas turbine components. In the current research, a superalloy Ni-based Nimonic sheet and Inconel 600 were used, joint by resistant spot welded (RSW) machine at currents of 2, 4, and 6 kA, pressure of 5 and 7 bar, and times of 0.6, 0.9 and 1.2. Non- destructive inception methods and light and scanning electron method (SEM) and light optic microscope (LOM) were used to evaluate joints' quality. Shear and micro-hardness test was used to check the mechanical properties of the joint. The findings indicate that the most appropriate welding connection of inhomogeneous points at the current of 4 kA was the holding time 0.9 second and electrode force 7bar. The analysis of microstructure consisted of 3 welding zones which are affected by heat and the base metal. The warm corrosion scanning microscope test results at 600 °C and 800 hours confirmed that the existence of a chromium oxide layer on the surface of the superalloy, which has the main role in protecting the piece in the output temperature.

Metallographic Documentation of the Degradation of Iron and Nickel Based Alloys in HCl and H2S Containing Environments, between 480 – 680 °C

Corrosion behavior of the alloys 1.7386 (P9), 1.4462, 1.4841, 1.4959 (Alloy 800HT) and 2.4816 (Alloy 600) was tested for 24, 72 and 240 h between 480 – 680 °C. The testing gas atmosphere contained 3.8 vol. % HCl, 200 ppm H2S and CO, CO2 and N2. It simulated conditions present in a thermal cracking process for post-consumer plastics. Samples were analyzed by metallography, SEM/EDX and XRD after corrosion experiments. Additionally, their mass loss during the test was evaluated. A multilayered structure of corrosion products grew on the samples during the corrosion experiments. The composition of the corrosion products depended not on the material, but on the testing temperature. At 680 °C chromium sulphide formed the outer layer, followed by a chromium oxide layer. Below these two layers a chlorine containing layer was observed. At 480 °C mainly nickel sulphide was detected, besides chromium oxide and iron- and chromium chloride. Especially at higher testing temperatures FeCl2 was not observed directly on the samples, but as colorless crystals at the colder parts of the testing equipment. At 680 °C the mass loss of the samples decreased with increasing nickel content. However, this effect changed entirely at lower testing temperatures. At 480 °C 1.7386 and 2.4816 showed nearly the same mass losses.

Formation of a Calcium Phosphate Layer with Immobilized Cobalt Chromite Nanoparticles on Cobalt−Chromium Alloy by a Laser-Assisted Biomimetic Process

The biocompatibility and osteoconductivity of metallic biomaterials can be achieved by calcium phosphate (CaP) coating. We recently developed a laser-assisted biomimetic (LAB) process for rapid and area-specific CaP coating on several materials. In the present study, the LAB process was applied to cobalt–chromium (Co−Cr) alloy, a metallic biomaterial widely used in orthopedic and dental applications. The LAB process was conducted by irradiation of unfocused pulsed laser light onto the substrate immersed in supersaturated CaP solution. The LAB-processed substrate formed CaP on the irradiated surface within only 5 min and was coated with a micron-thick CaP layer within 30 min by the effects of laser-induced surface modification and heating. Ultrastructural analysis with transmission electron microscopy revealed that the resultant CaP layer was integrated with the underlying substrate through two intermediate layers, an upper chromium oxide layer and a lower Co-rich (Cr-deficient) alloy layer. The CaP layer was loaded with a large number of cobalt chromite (CoCr2O4) nanoparticles. The results obtained offer new insights into the mechanism of CaP coating in the LAB process and future applications of LAB-processed Co−Cr alloys.

The Oxidation of Metal Alloy Foils in the Presence of Water Vapor

Water vapor can be detrimental to the elevated temperature oxidation resistance of alloys that rely on the formation of a protective chromium oxide layer. The resulting degradation can be significant, particularly when such alloys are in the form of light gauge sheet and strip. Long-term test results will be presented for commercially available wrought austenitic stainless steels and nickel-base superalloys exposed at 1300°F and 1400°F in environments containing various levels of water vapor.