Y.Kurata and H.Utsumi (Japan Atomic Energy Research Institute
,
Tokai-mura
,
Naka-gun
,
Ibaraki-ken
,
319-1195
,
Japan)(Tohoku University
,
Sendai
,
980-8579
,
Japan)
金属学报(英文版)
Applicability of the following creep constitutive equations was investigated for normal type creep curves of Ni-18.5Cr alloy and tertiary creep dominant curves of Ni-18.5Cr16W alloy under constant load: the θ projection method describing a creep curse by a sum of two exponential terms, modified θ method describing a primary creep stage by an exponential term and a tertiary creep stage by a logarithmic term, modified Ω method describing a creep curve by a sum of two logarithmic term, 2θ method with only a tertiary creep component and Ω method. The θ, modified θ and modified Ω methods can describe normal type and tertiary creep dominant curves. Tertiary creep dominant curves of Ni-18.5Cr-16W alloy at 900℃ are also described using 2θ and Ω methods. Applicability of the modified θ and modified Ω methods is superior for constant load creep curves because they can predict creep curves up to rupture and rupture life accurately and conservatively.
关键词:
creep equation
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Surface & Coatings Technology
Thermal barrier coatings (TBCs) were obtained using a detonation gun (D-gun) spraying technique on a Ni-base superalloy, M38G. The thermal conductivity of freestanding YSZ coatings and the thermal shock behaviors of TBCs system were studied. The results showed that the D-gun sprayed TBC had a very low thermal conductivity of 1.0-1.4 W/m K, close to that of the plasma sprayed YSZ coatings and much lower than their EB-PVD counterparts. The TBCs exhibited excellent resistance to thermal shock up to 400 cycles of 1050 degrees C to room temperature (forced air cooling) +200 cycles of 1100 degrees C to room temperature (forced water quenching). The damage evolution mode of TBC system during the thermal cycling was discussed in the light of the features of microstructural development and phase changes. (c) 2004 Elsevier B.V. All rights reserved.
关键词:
thermal barrier coatings;detonation gun spraying;thermal conductivity;thermal shock cycling;bond-coat;conductivity;oxidation
Surface & Coatings Technology
During the detonation gun (D-gun) spraying process, the detonation products showed an undesirable dispersion when they were spurted out from the nozzle of the barrel at high velocity and pressure. To resolve this problem, a separation device was designed and constructed in the detonation gun spraying system. The WC-Co coatings were synthesized by the D-gun spraying system with and without using a separation device, respectively. The results showed that the use of the separation device resulted in better properties of the D-gun sprayed WC-Co coatings, e.g., lower the surface roughness, lower the porosity, higher the microhardness, higher the elastic modulus, and higher the interfacial adhesive strength. Also, the tribological performance of the WC-Co coatings was improved. The relationship of surface roughness, microhardness, elastic modulus, adhesive strength, and wear resistance of the WC-Co coatings with porosity was discussed. At the same time, there is an inevitable disadvantage for using the separation device, i.e., the relatively lower effective utility rate of the feedstock powder. Therefore, the separation device is suitable to be applied in occasions of high-performance requirements where increased costs are acceptable. (C) 2008 Elsevier B.V. All rights reserved.
关键词:
Separation device;D-gun spraying;WC-Co coating;Surface roughness;Mechanical property;Wear;dynamic-response;elastic-modulus;microstructure;indentation;parameters;substrate;friction;deposits;titania;tests
Tribology Letters
A WC-Co coating with self-lubricating property was deposited by detonation gun (D-gun) process, using a commercial WC-Co powder doped with a MoS2-Ni powder, under a proper spray condition. It is proved that the MoS2 composition in the feed powder was kept, which is attributed to the protection of Ni around it, and its content is a little higher in the resulting coating. Evaluation on sliding wear property indicates that the MoS2 composition plays an important role in lowering both coefficient of friction and wear rate for the resulting coating, which is confirmed by observations on wear track, as well as X-ray photoelectron spectroscope (XPS) results on worn surface. It suggests that the deposition of WC-Co coating with self-lubricating property by D-gun spray is feasible by controlling lubricant powder and spray conditions, which can exhibit higher sliding wear resistance.
关键词:
ceramics;coatings;hardness;self-lubrication;sliding-wear behavior;carbide grain-size;cermet coatings;cemented;carbides;hvof;microstructure;resistance
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
It is essential to analyze the residual stresses of thick coatings since they seriously affect coatings' performance during their service. It is also important to understand the mechanisms by which the stresses arise, to predict and control the stresses for improving coating properties. Because the Stoney formula is commonly used to relate stress to curvature for thin coatings, a new calculation formula was developed to estimate the residual stresses of thick coatings that represent a comprehensive stress state of the coated specimen. Based on the deduced formula and accurate curvature measurements, the residual stresses of detonation gun (D-Gun) sprayed WC-Co coatings with different thickness were obtained. With increasing the coating thickness, the residual stress changed gradually from the tensile nature to a compressive nature. Meanwhile, the coating was in an approximately stress-free state at the thickness of around 365 mu m. The analysis results emphasized the significance of peening stress in controlling the final stress state of the coated specimen, due to the high spraying velocity and kinetic energy during the D-Gun spraying process. Finally, the effects of residual stress on the mechanical properties of the coating were understood, namely, the compressive stress could significantly improve the coating properties, whereas the tensile stress impaired the coating properties. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
关键词:
Residual stress;D-Gun spraying;WC-Co coating;Peening stress;Mechanical property;particle-velocity;elastic-modulus;(ti,al)n films;microstructure;temperature;deposition;thickness;titania;solids;metals
Surface & Coatings Technology
NiCrAlY coating was deposited on a single crystal Ni-base superalloy by detonation gun spraying. By means of XRD, SEM and EDS, isothermal oxidation behavior of the coatings at 1050 degreesC were studied. The results showed that detonation gun sprayed NiCrAlY coatings held a favorable oxidation resistance. Their oxidation kinetics at 1050 degreesC obeyed the parabolic law. alpha-Al2O3 scale was formed on the coating surface and kept almost intact after oxidation for 300 It. Internal oxidation led to the formation of Al2O3 at the coating/substrate interface, and needlelike (Al, N) compounds appeared in the undersurface area of the substrate. (C) 2002 Elsevier Science B.V. All rights reserved.
关键词:
detonation gun spraying;NiCrAlY coating;isothermal oxidation;alloys;plasma
Materials Transactions
NiCrAlY coatings were prepared by the newly-developed detonation gun spray process. The oxide scale formation and evolution on these coatings during isothermal oxidation in air at 1100 degrees C were investigated. It was found that semi-molten particles, particle debris and pores, are present in the surface layer of the as-sprayed coating. During 100 h oxidation, the particle debris and some semi-molten particles gradually change into oxide mixture consisting of spinel, chromia and nickel oxides. However, after removal of the surface layer of the coating by a grinding treatment, a dense and single-layer alpha-Al2O3 scale forms on the surface of the coating during the oxidation. The mechanisms governing the oxide scale formation and evolution are discussed in terms of atomic diffusion and thermodynamic stability. In addition, thermogravimetric analysis showed that the oxidation rate of the ground NiCrAlY coating at 1100 degrees C is much lower than that of the as-sprayed one. The residual stress in thermally grown oxide scales was investigated using photo-stimulated luminescence spectroscopy.
关键词:
NiCrAlY coating;oxidation;thermally grown oxide;detonation gun spray;thermal barrier coatings;high-temperature oxidation;bond coatings;stress-distribution;spalling failure;behavior;diffusion;systems;tbc;superalloy
