OXIDATION RESISTANCE AND MICROSTRUCTURE OF Pt AND PtIr DIFFUSION COATINGS ON Ni BASED SINGLE CRYSTAL SUPERALLOYS BY ELECTROPLATING METHOD

In this study, Pt and PtIr diffusion coatings on Ni based single crystal superalloys were fabricated by an electroplating method followed by an annealing heat treatment process. The microstructure and phase constitution of the coatings were studied by SEM/EDS and XRD methods. The cyclic oxidation test at 1150oC was conducted to investigate the oxidation resistance of the coatings. The results showed that the addition of Ir in the coating led to the formation of α(NiPt2Al) phase and reduced the formation Kirkendall voids in the coating after 100 cycle oxidation test.

Corrosiveness of Palm Biodiesel in Gray Cast Iron Coated by Thermoreactive Diffusion Vanadium Carbide (VC) Coating

Palm biodiesel is a currently used biofuel, principally as an additive or substitute of diesel fuel in vehicular internal combustion engines. In the present work, vanadium carbide (VC) coatings were deposited on gray cast iron (GCI) using the thermoreactive diffusion process (TRD) to evaluate the corrosiveness of palm biodiesel and compare it with gray cast iron corrosion behavior. VC coated and uncoated gray cast iron samples were tested by immersion corrosion tests (291 K and 313 K), cyclic oxidation test (CO), and the electrochemical impedance spectrometry test (EIS). The corrosion test showed the reduction of the corrosion rate for the VC coating when compared to gray cast iron. EIS tests of coated samples showed higher values of polarization resistance when compared with uncoated gray cast iron samples. Results confirmed that while biodiesel was more corrosive than diesel on both coated and uncoated gray cast iron, the VC coating was efficient in protecting the substrate exposed to both fuels.

Oxidation Resistance of Modified Aluminide Coatings

The application of protective aluminide coatings is an effective way to increase the oxidation resistance of the treated parts and prolongs their lifetime. The addition of small amount of noble metals (platinum or palladium) or reactive elements such as: hafnium, zirconium, yttrium and cerium has a beneficial effect on oxidation behavior. This beneficial effect includes an improvement of adhesion of alumina scales and reduction of oxide scale growth rate. Platinum and hafnium or zirconium modified aluminide coating were deposited on pure nickel using the electroplating and CVD methods. The coatings consisted of two layers: an outer, β-NiAl phase and the interdiffusion γ’-Ni3Al phase. Palladium dissolved in the whole coating, whereas hafnium and zirconium formed inclusions on the border of the layers. Samples were subjected to cyclic oxidation test at 1100 °C for 200h. Oxidation resistance of the palladium, Hf+Pd and Zr+Pd modified coatings deposited on pure nickel does not differ significantly, but is better than the oxidation resistance of the non-modified one.

Investigation of Element Effect on High Temperature Oxidation of HVOF NiCoCrAlX Coatings

MCrAlX (M: Ni or Co or both, X: minor elements) coatings have been widely used to protect hot components in gas turbines against oxidation and hot corrosion at high temperatures. Understanding the influence of the X-elements on oxidation behaviour is important in the design of durable MCrAlX coatings. In this study, NiCoCrAlX coatings doped with Y+Ru and Ce, respectively, were deposited on Inconel-792 substrate by HVOF. The samples were subjected to isothermal oxidation test in laboratory air at 9000, 1000, 1100 ºC and cyclic oxidation test between 100 ºC and 1100 ºC with 1 hour dwell time at 1100 ºC. It was observed that the coating with Ce shows a much higher oxidation rate than the coating with Y+Ru under both isothermal and cyclic oxidation tests. Besides, β-depletion due to interdiffusion between coating and substrate was significantly lower with Ru addition. Simulations results using both a moving phase boundary model and an established oxidation-diffusion model show that Ru stabilize β grains which reduces β-depletion of coating due to substrate interdiffusion. This paper presents a comprehensive study of the influence of Ce and Ru on oxidation behaviour including investigation of the microstructure evolution influenced by oxidation time at coating surface and coating-substrate interface combining experiment and simulation results.

High Temperature Oxidation of Al-Alloyed SiMo Cast Iron in CO2-Containing Atmospheres

The SiMo cast iron with 5.45 wt% of Al has been developed for using as an automotive exhaust manifold. Cyclic oxidation test of that alloy and the conventional SiMo cast iron was conducted at 850 oC in 5%CO2+12%O2+83%N2 and 10%CO2+12%O2+78%N2. It was found that oxidation kinetics of the SiMo cast iron alloyed with 5.45 wt% of Al was lower than that of the SiMo cast iron. An X-ray diffraction technique and a scanning electron microscope equipped with energy dispersive spectroscopy were performed for characterisation. Thermal oxide scale on the SiMo cast iron consisted of hematite, magnetite and silica, while it was mainly alumina, additionally with hematite and magnetite, for the SiMo cast iron alloyed with 5.4 wt%. Formation of the alumina promoted oxidation resistance of the later cast alloy.

Oxidition Resistance of Multi-Arc Ion Plating TiN Films

Depositing TiN Film on the surface of 4Cr5MoSiV1 with multi-arc ion plating technology method. And 350°C, 450°C, 550°C and 650 °C short oxidation test and 550 °C cyclic oxidation test. By scanning electron microscopy (SEM) and electron spectrometry (EDS) to analysis micro-structure and phase structure of test samples, study TiN film on oxidation resistance, and utilize indentation method to measure mechanical properties. Results show: In a short time under oxidizing conditions, at 550 °C the TiN film still has a good oxidation resistance. The film still have a sufficient bonding strength below 600 °C.

Formation of Ni Aluminide Coating Containing Reactive Elements by Simultaneous Electrodeposition and Cyclic Oxidation Resistance

A Ni aluminide layer containing Zr or Hf was formed on a Ni specimen by the simultaneous electrodeposition of Al and Zr or Al and Hf using a molten-salt bath. When the simultaneous electrodeposition of Al and Zr was carried out using molten NaCl-KCl containing 3.5 mol%AlF3 and 0.05 mol%ZrF4, the electrodeposited layers were formed in the order of Ni2Al3, NiAl3 and Al from the Ni substrate side. The ZrAl3 particles were uniformly formed in the surface region of the NiAl3 and Al layers. On the other hand, when the simultaneous electrodeposition of Al and Hf was carried out using molten NaCl-KCl containing 3.5 mol%AlF3 and 0.05 mol%HfF4, the electrodeposited layer consisted of Ni2Al3 as the inner layer and NiAl3 as the outer layer were formed with HfAl3 particles uniformly formed in the surface region of the NiAl3 layer. For the sample treated with the simultaneous electrodeposition of Al and Zr, no significant change in the mass gain was observed during the cyclic-oxidation test at 1423 K, suggesting that the sample had a high cyclic-oxidation resistance. Similarly, the sample treated by the simultaneous electrodeposition of Al and Hf had a high cyclic-oxidation resistance. An adhesive scale, having localized inward penetrations consisting of Al2O3 containing ZrO2 or HfO2, was formed on the samples having the high cyclic-oxidation resistance.

In Situ Thermal Gradient Controlled Investigation of Spallation -Experimental Design and Preliminary Results

Based on a coupled numerical and experimental approach, the design and implementation of an in situ thermal-gradient-controlled cyclic oxidation test, dedicated to the investigation of the TGO and TBC spallation, is presented. The influence of the specimen through thickness thermal gradient as well as the benefits of the video real-time monitoring of the cooling phase of an oxidation test is discussed in the case of the spallation of an alumina scale grown on FeCrAl alloys.

Effect of Hf Addition on High Temperature Properties of Ir-Containing Alloy Coatings

In the present study, high temperature properties of Ir-modified and Ir-Hf-modified aluminide coatings on Ni-based single crystal superalloy TMS-82+ were discussed. They were prepared by depositing pure Ir and Ir-Hf alloys on TMS-82+ using magnetron sputtering and EB-PVD, followed by a conventional Al-pack cementation process. The effects of Hf addition on the oxidation resistance and top-coat spallation resistance were investigated. Cyclic oxidation test at 1423K for 1h as one heating cycle revealed that while there is a small difference in oxidation kinetics and spallation lives between Ir and Ir-Hf coatings, drastic difference in surface morphology was observed. After 50 oxidation cycles the Ir-modified aluminide coating showed surface rumpling whereas the Ir-Hf modified aluminide coatings kept the flat surface. It was also revealed that excessive addition of Hf promoted the internal oxidation, resulting in the deterioration of substrates. These results agree with the conventional Pt-modified aluminide coatings and Ni-Al-Hf alloys.