Papers by Keyword: Diffusion Coating

Abstract: In the recent search nickel superalloy Inconel 600 was coated with Zr-modified aluminide diffusion coating using pack cementation technique. Diffusion coating was done in a single step utilizing a conversion reaction of 10% Al, 2% ZrO₂, 4% NaCl, and 84 percent Al₂O₃ (wt. percent ) and a simultaneous aluminizing-zirconizing process. The diffusion coating operations were performed in an argon environment at 1050 °C for 10 hours. The test of the isothermal oxidation in dry air was performed on the Inconel Alloy 600 (IA600) without and with Zr-modified aluminide coating for 800-1000 °C. The oxidation kinetic of IA600 and its coated system was found to follow the parabolic law. The activation energy is 243 kJ/mol. for the coated system and 457 kJ/mol. for the uncoated system. XRD analysis show that oxide phases are formed on an uncoated IA600 surface during most of the oxidation exposure conditions are NiO, Cr₂O₃, Fe₂O_3, NiCr₂O₄ and NiFe₂O_4, , whereas alumina scale is the major oxide that is obtained on the surface of coated samples.

Abstract: The technology of diffusion saturation of austenitic steels by chromium and nickel in the medium of low-melting liquid metal melts is shown. The saturation temperature was up to 1050°C, and the duration was up to 8 hours. It was found that it is the most effective to apply coatings according to the technological scheme: pre-carburization-diffusion metallization – final carburization. It was found that the coating consists of 4 layers. The surface layer has a thickness of up to 5 mkm and a microtuberance of up to 19500 MPa. The second layer, up to 12 mkm thick, has a microhardness of up to 7500 MPa. The third, up to 50 mkm thick, has a microhardness of 2300 MPa. In the fourth layer, up to 150 mkm thick, the microhardness gradually decreases from 2300 MPa to the microhardness of the base. At the same time, the total thickness of the coatings is up to 200 mkm.

Abstract: Reformer materials are exposed to severe operating conditions at high temperature in aggressive catalyzer and combustion atmospheres. Therefore, materials used for the construction of the reformer reactor have to possess appropriate high temperature resistance. Diffusion coatings improve the high temperature resistance of materials by enrichment of the alloy surface with thermodynamically stable oxide formers. Beside conventional mono-element diffusion coatings (e.g. Al coating), multi-element diffusion coatings can be developed in a single process step. In this work we developed Al diffusion and Al-Si and Al-Si-RE (RE: reactive element Y, Ce) co-diffusion coatings on a low cost austenitic 18Cr10Ni-steel. The high temperature resistance of coated and uncoated 18Cr10Ni-steel, 20Cr31Ni-steel and 23Cr18Fe-Ni base alloy was tested in catalyzer and combustion atmosphere under cyclic operation conditions.

Abstract: The paper reviews the advantages of diffusion coating and the parameters deciding an optimum coating performance. Furthermore, innovative coating approaches are presented which have a significant potential beyond existing diffusion coating solutions.

Abstract: High-cycle-fatigue (HCF) fracture mechanism of nickel-based superalloy IN 792 coated with Pt-modified aluminide outward-diffusion coating is studied with focus on the influence of coating cracks. It is found that cracking of the diffusion coating prior to HCF tests has little influence on the fatigue limit of specimens with thin coating (50 μm) but lowers the fatigue limit of specimens with thick coating (70 μm). By fractographic analysis, three types of fractural modes are established according to their crack initiations: internal, external and mixed. While external fractural mode is related to the propagation of existing cracks in the coating, internal facture initiates often at Ti-Ta-W-rich carbides and/or topological-close-packed (TCP) phases and grainboundaries in the superalloy. Increasing the thickness of diffusion coating or the amplitude stress promotes the fractural mode transition from internal/mixed to external. The influence of precracking of coatings on the HCF fracture mechanism can be qualitatively explained by its influence on the stress intensity factor.

Abstract: The effects of diffusion temperature and time on the mechanism of the surface layers formation during low activity vapour phase aluminizing process on a Ni-base superalloy CMSX4 single crystal was experimentally investigated. The coating morphology of as aluminized samples grown along the substrate [100] and [110] directions of the substrate crystal was analysed by means of SEM, EDS and EBSD techniques. The presence of three layers, where β-NiAl differently combines to γ’, γ and TCP phases, was always observed. The β-NiAl phase in particular displayed two different morphologies and textures depending on the interface movement mechanism generating this phase at its external/internal interface. The presence of secondary precipitated phases within the coating layer, their composition and morphology, helped to understand the coating development process. The surface layer formation mechanism was found to be slightly temperature-dependent.

Abstract: High temperature low cycle fatigue behaviour of cast nickel-based superalloy Inconel 738LC in as-received condition and coated with an Al-Si diffusion layer was studied. The Al-Si protective layer was deposited on the gauge section of cylindrical specimens using the slurry technique. Fatigue tests were performed on cylindrical specimens under total strain control in symmetrical cycle at 800 °C in air. The coating has a beneficial effect on fatigue life in the low amplitude domain. The stress response of the coated material is higher for high amplitudes in comparison with the uncoated one. Fracture surfaces and sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Abstract: CBN diffusion coating on the ball nose end mills made of AISI-M35 high speed steel (HSS) has been produced thermo-chemically. The microstructure and component depth profiles of the CBN diffusion layer have been studied by scanning electron microscopy and energy dispersive X-ray spectrometry. The results on laboratory cutting tests of ball nose end mills made of AISI-M35 HSS with and without complex CBN diffusion coating are also introduced in the paper. The relationship between wear kinetics and tool life has been established. It was shown that under the used cutting conditions the tool life of the mills with the coating was a factor of 1.6 higher than that of the mills without the coating. The higher tribological stability of the coating in cutting process was supported by metallographic observations of the worn surfaces using scanning electron microscopy.

Abstract: Cylindrical specimens of Inconel 713LC in as-cast condition and with Al diffusion coating by the CVD technique were cyclically strained under total strain control at 800 °C. Hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The coating has a beneficial effect on the Manson-Coffin curve while the fatigue life is reduced in the Basquin representation. The stress response of the coated material is lower in comparison with the uncoated one. Sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Abstract: Hard coatings show various tribological behaviors against different contact materials (counter-faces) during dry sliding depended on their microstructure, surface morphology and encountered tribological systems and condition. In this work, the tribological and wear mechanisms of vanadium carbide (VC) and vanadium nitrocarbide (V(N,C)) layers were examined against WC/Co cemented tungsten carbide pin during pin-on-disk sliding wear testing. The V(N,C) layer was produced by a duplex surface treatment involving the gas pre-nitrocarburising followed by thermo-reactive diffusion (TRD) vanadizing technique. The coating layers were characterized by a cross sectional and morphological examination methods and X-ray diffraction analysis to identify damages of the coating’s surface. Wear mechanisms were determined by SEM microscope in BSI and SE mode accompanied by EDS analysis. Results revealed that the surface morphology of the V(N,C) coating consist of dense and smooth layer in comparison with the VC coating surface which reveals a non-uniform structure with chasms. It was determined that the activation of tribo-chemical system and oxidizing of the coating layer together with minor plastic deformation are the dominant wear mechanism in the V(N,C) coated steel. In the case of the VC coating, combination of abrasive wear and adhesion of pin material to coating and vice versa are the major impairing mechanisms.