Increase in Oxidation Resistance of MAR M-509 via LA-CVD Aluminizing

Due to their excellent mechanical properties, Co-based alloys are one of the main candidates to replace Ni-based alloys in high temperature application. Knowledge about oxidation resistance of Co-based alloy MAR M-509 and the extent of its aluminizing on its oxidation resistance is limited. Therefore, in the present study, an aluminide layer was manufactured by low activity chemical vapor deposition (LA-CVD) on MAR M-509. Aluminized and uncoated alloys were investigated in terms of oxidation kinetics and oxidation resistance during isothermal and cyclic oxidation at 1000 and 1100 °C. Material in the as-cast and after exposure was analyzed using scanning electron microscopy (SEM), thermogravimetry (TG) and glow-discharge optical emission spectrometry (GD-OES). Obtained results allowed for elucidating of degradation mechanism including nitridation process of carbides for MAR M-509. It was found that aluminizing of MAR M-509 significantly decreases its oxidation kinetics by the factor of 2.5 and 1.5 at 1000 and 1100 °C respectively. Moreover, the suppression of identified degradation mechanism in case of aluminized alloy was found until occurrence of breakaway oxidation of the aluminide layer. It was also proposed that further increase in oxidation resistance can be successively achieved by an increase in aluminide layer thickness.

Nondestructive Methodology for Identification of Local Discontinuities in Aluminide Layer-Coated Mar 247 during Its Fatigue Performance

In this paper, the fatigue performance of the aluminide layer-coated and as-received MAR 247 nickel superalloy with three different initial microstructures (fine grain, coarse grain and column-structured grain) was monitored using nondestructive, eddy current methods. The aluminide layers of 20 and 40 µm were obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 and 12 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of MAR 247 nickel superalloy and the coating were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). It was found that fatigue performance was mainly driven by the initial microstructure of MAR 247 nickel superalloy and the thickness of the aluminide layer. Furthermore, the elaborated methodology allowed in situ eddy current measurements that enabled us to localize the area with potential crack initiation and its propagation during 60,000 loading cycles.

Aluminide Thermal Barrier Coating for High Temperature Performance of MAR 247 Nickel Based Superalloy

In this paper, mechanical properties of the as-received and aluminide layer coated MAR 247 nickel based superalloy were examined through creep and fatigue tests. The aluminide layer of 20 µm was obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of the layer was characterized using the scanning electron microscopy (SEM) and X-ray Energy Dispersive Spectroscopy (EDS). It was found that aluminide coating improve the high temperature fatigue performance of MAR247 nickel based superalloy at 900 °C significantly. The coated MAR 247 nickel based superalloy was characterized by the stress amplitude response ranging from 350 MPa to 520 MPa, which is twice as large as that for the uncoated alloy.

High Temperature Corrosion Behaviour of Aluminide-Coated Cast Iron for an Exhaust Manifold Application

To reduce the pollution emission from vehicles, an improvement on the combustion process is expected, leading to increased exhaust gas temperature. As a result, the development of new materials for an exhaust manifold used at higher temperatures is required. A cost-effective cast iron exhaust manifold treated by aluminising pack cementation was developed in the present work to combat the high temperature corrosion. Its kinetics under cyclic oxidation in N2–12%O2–10%H2O at 850 °C was parabolic with the rate constant (kp) of 5.66 × 10−12 g2 cm–4 s–1, about two orders of magnitude lower than that of the bare cast iron, which indicated the protectiveness of the applied coating. These results relate to the protective alumina formation for the aluminised cast iron and the formation of the less protective iron oxides for the bare cast iron after oxidation, as evidenced by the XRD and Raman spectroscopy results. The addition of 10% water vapour to N2–12%O2 thickened the aluminide layer from 344 μm for the sample oxidised in dry atmosphere to 409 μm for the sample oxidised humidified one. It accelerated the oxidation rate of the aluminised cast iron as the kp value increased by 8.5 times, and also increased the hardness of the aluminised surface, as it was 364 HV for the sample exposed to dry atmosphere and 420 HV for the sample exposed to humidified one. The latter result implied the possibility of the hydrogen dissolution into the metal surface. The roles of hydroxyl ion and dissolved hydrogen on the oxidation and evolution of the aluminide layer after exposure to water vapour were proposed.

Electron Microscopy Characterization of the High Temperature Degradation of the Aluminide Layer on Turbine Blades Made of a Nickel Superalloy

The effects of exposure to overheating (temperature above 1000 °C) on the degradation (modification) of layers of coatings (coatings based on aluminum) of uncooled polycrystalline rotor blades of aircraft turbine jet engines were investigated under laboratory conditions. In order to determine the nature of the changes as well as the structural changes in the various zones, a multi-factor analysis of the layers of the coating, including the observation of the surface of the blades, using, among others, electron microscopy, structural tests, surface morphology, and chemical composition testing, was carried out. As a result of the possibility of strengthening the physical foundations of the non-destructive testing of blades, the undertaken research mainly focused on the characteristics of the changes occurring in the outermost layers of the coatings. The obtained results indicate the structural degradation of the coatings, particularly the unfavorable changes, become visible after heating to 1050 °C. The main, strongly interacting, negative phenomena include pore formation, external diffusion of Fe and Cr to the surface, and the formation and subsequent thickening of Fe-Cr particles on the surface of the alumina layer.

Process and High-Temperature Oxidation Resistance of Pack-Aluminized Layers on Cast Iron

Pack aluminizing of spheroidal graphite cast iron with different aluminizing temperature and time was studied. Results showed that the thickness of aluminized layer increased with the increasing temperature and time. The optimized process parameters are as follow: the aluminizing packed temperature is 830 °C and the time is 3 h. The aluminized layer consisted of the inner FeAl and the outer Fe2Al5. Some graphite nodules were observed in the aluminide layer after aluminizing. The mass gain of the aluminized cast iron was 0.405 mg/cm2, being 1/12 of the untreated substrate after oxidation. The high temperature oxidation resistance can be improved effectively by pack aluminizing, even though there were graphite nodules in the aluminide layer.