基于TBC的产业集群与供应链系统集成效应框架模型

以TBC战略为基础,分析了产业集群与供应链系统的集成在战略目标、组织运作、市场整合、知识集成与扩散等方面所产生的效应,构建了一个集成效应框架模型,为产业集群与供应链系统的集成研究提供理论支持和预先分析支持.     

An Overview of Superalloy Research and Development in Korea

The technology level and industry activities in the field of aerospace engineering are very weak compared to Korea's economic size, and the R&D on superalloys is only at the beginning stage. However, various government funded projects are in progress and many companies are ready to participate in gas turbine businesses, and, as a result, the R&D activities in superalloys will be accelerated. This article introduces Korea's current R&D status on superalloys and its future is prospected.     

Deposition of zirconium monoxide glomeruli by laser ablation

 Zirconia is evermore in demand as a thermal barrier coating (TBC) for energy economy and metal protection. Several methods are in use to produce the coatings, including sol-gel, CVD and PVD, however laser ablation, has not been notoriously reported. The present work presents the use of a N₂-SF₆ pulsed laser beam, focused (6 J/cm²) on a metallic zirconium target in a reactor with low pressures of oxygen or helium. Sparks were observed in oxygen atmosphere, which denoted oxidation of laser ablated zirconium. Transmission Electron Microscopy (TEM) and optical interferometric microscopy, identifying small agglomerates of ZrO (cubic phase) studied the crystallographic structure and morphology of the obtained particles. The pyrophorous oxidation phenomenon of ablated Zr droplets is described and interpreted by thermochemical simulations, and the deposited morphology is characterized. Received: 23 March 1998 / Accepted: 30 July 1998     

利用开口矩形波导探头进行热障涂层微波检测的参数优化设计

利用CST微波工作室(computer simulation technology microwave studio)仿真研究用矩形波导作为探头检测热障涂层厚度的可行性,并对波导探头进行仿真计算,分析提离距离对反射系数幅值和相位差的影响.结果表明,在特定的提离距离时利用反射系数的幅值和相位差都可良好地表征涂层的厚度。     

Modification of NiCoCrAlY with Pt: Part Ⅱ. Application in TBC with pure metastable tetragonal(t’) phase YSZ and thermal cycling behavior

A thermal barrier coating system comprising Pt-modified NiCoCrAlY bond coating and nanostructured 4mol.% yttria stabilized zirconia(4YSZ, hereafter) top coat was fabricated on a second generation Ni-base superalloy. Thermal cycling behavior of NiCoCrAlY-4 YSZ thermal barrier coatings(TBCs) with and without Pt modification was evaluated in ambient air at 1100?C up to 1000 cycles, aiming to investigate the effect of Pt on formation of thermally grown oxide(TGO) and oxidation resistance. Results indicated that a dual layered TGO, which consisted of top(Ni,Co)(Cr,Al)_2O_4 spinel and underlying α-Al_2O_3, was formed at the NiCoCrAlY/4 YSZ interface with thickness of 8.4μm, accompanying with visible cracks at the interface. In contrast, a single-layer and adherent α-Al_2O_3 scale with thickness of 5.6μm was formed at the interface of Pt-modified NiCoCrAlY and 4 YSZ top coating. The modification of Pt on NiCoCrAlY favored the exclusive formation of α-Al_2O_3 and the reduction of TGO growth rate, and thus could effectively improve overall oxidation performance and extend service life of TBCs. Oxidation and degradation mechanisms of the TBCs with/without Pt-modification were discussed.     

Microcrack nucleation in thermal barrier coating systems

Crack nucleation in thermal-barrier coating (TBC) systems subjected to a monotonic cooling process is studied. The TBC system is modeled using the finite element method, where cracks are represented as discrete discontinuities across continuum elements using the partition-of-unity method. The numerical implementation used for crack nucleation is based on an algorithm where, at insertion of a discontinuity, the traction response is derived from a cohesive zone model that has been modified to (i) behave like an initially rigid cohesive model, and to (ii) ensure smoothness of the traction-separation law at zero crack opening. Accordingly, an adequate convergence behavior of the numerical formulation can be warranted in boundary value problems of systems with relatively complex geometries. In the present numerical study, a comparison is made between TBC systems composed of different constitutive models. The fracture patterns and evolutions of the overall crack growth resulting from the simulations clearly illustrate the importance of accounting for the effects of plasticity in the bond coating and anisotropy in the top coating. The computed fracture profile is in good correspondence with experimental observations reported in the literature.     

On stresses induced in a thermal barrier coating due to indentation testing

Instrumented indentation has been suggested as a method to determine interfacial fracture toughness of thermal barrier coatings. However, in a previous experimental study we showed that the results are ambiguous. In this work, we investigate the experimental results by numerical simulations incorporating the material microstructure. In the numerical simulations, based on finite element analyses, the stress fields that are associated with the loading and unloading of the indenter are investigated. By comparing these stress fields to the damage observed in the experimental study, including crack path and interfacial delaminations, we explain key findings from the experimental observations. Our results suggest that indentation testing of multilayered coated structures might not induce the delamination in the overall weakest interface and therefore the test results must be evaluated with care.     

Effect of atmosphere composition on the oxidation behavior of MCrAlY coatings

In the present work the effect of atmosphere composition on the growth rate and adherence of the alumina scales was studied using free‐standing MCrAlY‐coatings and TBC‐specimens with MCrAlY‐bondcoats. The exposures comprised isothermal and cyclic exposures in laboratory air and Ar‐H₂‐H₂O at 1100 °C. It is shown that minor Zr‐addition to the bondcoat results in enhanced scale growth and internal oxidation. This effect is independent of the atmosphere composition. As a consequence of the rapid oxide formation the times to TBC failure on the Zr‐containing bondcoat in both atmospheres were much shorter compared to those with Zr‐free bondcoat. In the latter case the formation of a thin compact alumina TGO was slower in H₂/H₂O than in air resulting in significantly longer TBC‐lifetime in the former atmosphere.     

Parameters affecting TGO growth rate and the lifetime of TBC systems with MCrAlY‐bondcoats

In the present work different parameters which affect the oxide growth on MCrAlY‐bondcoats have been studied, in an attempt to find a reliable way to define the critical oxide thickness to failure of an EB‐PVD thermal barrier coatings (TBC). It was found that the variation of selected parameters such as oxidation temperature, surface roughness, and bondcoat thickness certainly alters the thermally grown oxide (TGO) growth rate. However, simultaneously the morphology, composition, and/or microstructure of the oxide are changed, which can affect the critical TGO thickness to failure in a TBC system. In contrast, the variation of the oxygen partial pressure of the oxidizing atmosphere led to different TGO growth rates without significantly changing the oxide morphology and composition. Comparing the TGOs grown at different rates in the specimens exposed to high pO₂ and low pO₂ atmospheres, it was estimated that at failure the oxide scales in both specimens have reached a similar critical thickness.     

An investigation on hot corrosion behavior of YSZ-Ta2O5 in Na2SO4 + V2O5 salt at 1100 °C

This study compares the hot corrosion performance of yttria stabilized zirconia (YSZ), and YSZ-Ta₂O₅ (TaYSZ) composite samples in the presence of molten mixture of Na₂SO₄ + V₂O₅ at 1100 °C. For YSZ, the reaction between NaVO₃ and Y₂O₃ produces YVO₄ and leads to the transformation of tetragonal ZrO₂ to monoclinic ZrO₂. For TaYSZ, minor amounts of NaTaO₃, TaVO₅ and Ta₉VO₂₅ are formed as the hot corrosion products with only traceable amounts of YVO₄. Due to the synergic effect of doping of zirconia with both Y₂O₃ and Ta₂O₅, the TaYSZ sample has a much better hot corrosion resistance than YSZ.