Hot Oxidation Resistance Research Articles

Enhancing hot oxidation resistance of the HVOF-sprayed NiCoCrAlTaY coating by alumina nanoparticles via a modified suspension route

The effect of alumina (Al2O3) nanoparticles on the hot oxidation behavior of NiCoCrAlTaY coating is investigated. High velocity oxygen fuel (HVOF) technique was employed to deposit coatings on a single crystal CMSX-4 Ni-based superalloy. Different amounts of α-Al2O3 nanoparticles (3, 6 and 9 wt%) were added to NiCoCrAlTaY powder via a modified suspension route. By this modification, the Al2O3 nanoparticles were adhered on the surface of the atomized metallic NiCoCrAlTaY powders with a relatively uniform distribution. The composite powder was then sprayed on the superalloy substrate by an industrial HVOF route. The cyclic hot oxidation resistance of the coatings was evaluated at 1100 °C. Results showed that the coating with 6 wt% nano-Al2O3 experienced significantly better oxidation performance. The presence of nano-Al2O3 in the coating accelerated the formation of α-Al2O3 dense oxide layer and, thereby, delayed diffusion of other elements to the surface. Adding more Al₂O₃ nanoparticles up to 9 wt% led to an increase in porosity and surface roughness of the coating which decreased oxidation resistance.

Hot Oxidation Resistance of a Novel Cast Iron Modified by Nb and Al Addition for Exhaust Manifold Applications

Hot Oxidation Resistance of a Novel Cast Iron Modified by Nb and Al Addition for Exhaust Manifold Applications

A study of the dependence on the Co and Ni proportions of the oxidation at elevated temperature of TaC-strengthened {Ni and Co}-based cast superalloys

Cobalt and nickel may play antagonist roles on the microstructures and high temperature properties of cast chromium-rich superalloys containing the same tantalum and carbon molar fractions. Since such alloys may be considered for uses at temperature levels as high as 1200 °C, the whole range of base compositions was explored with six model quaternary alloys with Ni and Co contents varying from 0 to 100% of the remaining elements, the 25 wt%Cr, 0.4 wt%C and 6 wt%Ta being deducted. The interdendritic carbide network of the as-cast microstructures is made of chromium carbides and tantalum carbides for the Ni-richest alloys and of TaC only for the Co-richest ones. {170 h, 1200 °C}-exposure carried out in laboratory air led to important morphology deterioration for the two Ni-richest alloys but limited fragmentation of the TaC in the four Co-richest alloys. At the same time, the most of the alloys more or less well behaved in oxidation, except the two Co-richest alloys for which the too hindered volume diffusion of chromium did not sustain the chromia-forming behavior. Notably the Ni-free cobalt-based alloys suffered from starts of catastrophic oxidation in several surface locations. The quaternary alloy bases allowing taking benefit of the best compromise between hot oxidation resistance and possibly good mechanical behavior at elevated temperature was the model alloys with 14–28 wt%Ni.

Corrosion and Oxidation Behavior of a Fe-Al-Mn-C Duplex Alloy.

The low-density steels represent a topic of great interest within the scientific world because of the great demand from the steel market of increasingly lighter materials, also featured by an optimal mix of the mechanical properties. In this work, the corrosion and hot oxidation resistance of a Fe-15%Mn-9.5%Al-6.5%Ni-1%Cr-0.43%C were analyzed and related to the microstructural features. The material behavior was analyzed both in the as-cast and in the heat-treated state. For the corrosion test, the experimental plan was fulfilled using four different concentrations of HCl and four temperatures. In the case of hot oxidation resistance, the exposure time and the temperature effects were evaluated. The corrosion resistance in HCl was comparable to the stainless steel, and the iso-corrosion curves showed excellent resistance of the 1300 °C solution-treated material, especially at low temperatures, but it is also good at high temperatures due to the hot oxidation.

Increasing the Wear Resistance of Metallic Materials by applying Thermochemical Treatments

Wear is defined as mechanical or physical damage to a contact surface by another as a result of a relative movement. The structure of the steels has a great influence on abrasion resistance, so that certain thermo-chemical treatments applied to steels, besides the structural changes, are also aimed at changes in the chemical composition in the superficial layers as a result of diffusion with certain elements. A highly used thermo-chemical treatment is the aluminization, especially as a process for increasing the wear resistance, of the hot oxidation resistance, in order to replace the expensive refractory alloys with heating resistance up to 800-1000 °C with cheaper materials.

Microstructure, hot oxidation resistance and damping capacity of Al- alloyed cast iron

Ductile cast iron was developed by adding Aluminium (up to16 wt%Al). Effects of aluminium on microstructure, hardness, oxidation resistance at high temperature and damping capacity of cast iron were studied. Adding Al up to 4.0 wt% raised degree of graphitisation. More than 4.0 wt% up to 13.8 wt%Al showed precipitation of hard carbides. Hardness was increased significantly by increasing Al due to formation of intermetallic compounds. More than 5.8 wt%Al showed a higher oxidation resistance due to formation of complex Fe-Al oxide, acted as a protective and adherent scale. Damping capacity of 2.6 and 4.0 wt%Al was increased as the volume fraction of graphite increased as well as the change of graphite from spheroidal to compacted ones. Damping capacity of 16 wt%Al was enhanced due to high ferrite (86%) containing graphite. However, decreasing of ferrite and disappearing of graphite as well as presence of carbides highly deteriorated damping capacity of 5.8, 9, 12.8 and 13.8 wt%Al cast iron.

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.

Ni–SiC composite plated under a modulated current

Abstract Ni–SiC composite coatings were plated under a modulated current in order to control coating properties including ceramic content, hardness, ductility, internal stresses and hot-oxidation resistance. Composites with SiC gradient distribution were deposited from a Watts-type bath by reducing the current density from 8 to 3 A dm −2 . When a pulse regime with a frequency of 0.05 Hz was used, the composite possessed a combination of enhanced hardness and higher ductility together with lower internal stresses. The best resistance to hot-corrosion at 800 and 1000 °C was obtained for the composite deposited in pulse-reverse regime and containing 17 vol% of SiC.

Electocomposites with SiC content modulated in layers

Nickel electrochemical composites using different sublayers were deposited from a Watts bath containing, in addition, SiC particles of 1 and 5 μm in dispersion. The layers differed both in the incorporated particle content and in their size, resulting from varying the regimes of bath stirring. A ductile underlayer with 0.7–1.1 vol.% of SiC was deposited from the non-agitated bath. Under non-intensive air agitation, an intermediate sublayer with 9.2–11.8 vol.% of the fine dispersed inclusions was obtained. When the most intensive agitation was maintained in the electrolyte, which also containing an additive of silanamine, the upper sublayer was plated with 12.6 vol.% of the dispersed phase. Compared with other layers, the latter contained a lot of the coarser particles and showed an enhanced hot-oxidation resistance. The hardness and internal stresses, the chemical corrosion rate, the morphology and surface profile of each sublayer were investigated.

Influence of yttrium and method of fabrication on the oxidation behaviour of FeCrAl alloys at high temperature in air

The oxidation behaviour of three industrial FeCrAl alloys was studied. Two of the products examined were FeCrAl alloys, one being fabricated by powder metallurgy while the third one was a FeCrAlY alloy. In particular, we have shown that, at high temperature, yttrium may have a detrimental effect on the hot oxidation resistance of this type of alloy. Powder metallurgy does not seem to improve the high temperature behaviour of FeCrAl alloys as stated by the manufacturer.

High-temperature oxidation of aluminum electroplated Fe-Mn alloys

Austenitic Mn-Al alloys (20–32 W/O Mn, 7–10 Al, 2–3 Si, 1C) were found to have satisfactory oxidation resistance up to 950°C under isothermal conditions in air. Surface enrichment of aluminum is a necessary condition for obtaining an almost pure alumina scale for uses at higher temperatures. Four different Mn-steels were Al-coated by the Capuano electroplating process. In all the steels there was an increase in the hot-oxidation resistance. The best results were obtained with steels containing both Al and Si, and this for temperatures up to 1100°C. No spalling was noticed during rapid cooling of the test pieces. Silicon was found to act as a diffusion barrier to outward iron diffusion. It appears that there is formation of a pure, thin film of alumina from the matrix which interacts with the aluminum diffusing from the superimposed, coating for the formation of good bonds.