Yoshitaka Kojima

Microstructure and mechanical properties of ductile Ni3AI-type compound in Fe-(Ni, Mn)-AI-C systems rapidly quenched from melts

By the rapid quenching technique, nonequilibrium Ni3Al-type compounds with high strength and hardness as well as large elongation have been found in Fe-Ni-Al-C and Fe-Mn-Al-C systems. This formation region is limited to about 7 to 55 wt pct Ni, 3 to 9 wt pct Al and 0.8 to 2.4 wt pct C for Fe-Ni-Al-C and to about 7 to 65 wt pct Mn, 3 to 9 wt pct Al and 0.8 to 2.4 wt pct C for Fe-Mn-Al-C. The Ni3Al-type compound has fine grains of about 1 to 10 μm in diam. Their Vickers hardness and yield strength increase with increase in the amounts of carbon, aluminum or nickel and the highest values attain about 665 DPN and 1690 MPa for Fe-Ni-Al-C and 600 DPN and 1740 MPa for Fe-Mn-Al-C. Elongation increases with decrease in carbon or aluminum and attains about 11 pct for Fe-20 wt pct Ni-6 wt pct Al-1.2 wt pct C and 28 pct for Fe-20 wt pct Mn-8 wt pct Al-1.6 wt pct C. The good strength and ductility of the Ni3Al-type compounds remain unchanged on tempering for 1 h until heated to about 750 K. Further, it has been found that the addition of chromium, molybdenum or cobalt is effective for the improvement of mechanical properties and thermal stability of the compounds. Thus, the use of materials containing Ni3Al-type compounds may be attractive for fine gage high-strength wire or plate applications.

ZrO2 and Cu functionally gradient materials prepared by a dynamic ion mixing process

Abstract ZrO2-Cu films have been prepared as functionally gradient materials (FGM) which change continuously from Cu to ZrO2. Partially stabilized ZrO2 (PSZ) and the PSZ-Cu FGM films were prepared on a Cu substrate by a dynamic ion mixing process. Oxygen ion irradiation was essential for the FGM formation of the PSZ-Cu films, because films deposited without oxygen ion irradiation were easily peeled from the substrate during the deposition steps. The electron beam deposition rates of Cu and ZrO2 were individually controlled. The FGM structures were analysed by X-ray photoelectron spectroscopy and transmission electron microscopy. Cu and PSZ crystal grains were finely mixed in the FGM layers. The thermal resistance of the FGMs was examined by a heat test in which the film surface was heated by an Ar + H2 plasma jet. No cracks were observed on the PSZ-Cu FGM surfaces after the test. However, for PSZ film (without the FGM layer) on the Cu substrate, cracks were seen.

Evaluation of the Accuracy of Young’s Moduli of Thermal Barrier Coatings Determined on the Basis of Composite Beam Theory

The Young’s modulus of thermal barrier coating (TBC) is an important mechanical property as it is required for calculating the parameters of material mechanics in the TBC system. In this study, we investigated the accuracy of the Young’s modulus of TBC calculated using the composite beam theory. Generally, both the Young’s modulus and the thickness of TBC are approximately one order of magnitude lower than those of the substrate. Consequently, the Young’s modulus of the TBC calculated on the basis of the composite beam theory is considerably sensitive to experimental errors. In order to improve the accuracy of the composite beam method, methods that make use of coating strain, substrate strain, or deflection were compared. The methods with low sensitivity to experimental errors were determined through sensitivity analysis. Further, the effectiveness of the methods with low sensitivity was confirmed experimentally.

Thermal Diffusivity Measurement for Thermal Spray Coating Attached to Substrate Using Laser Flash Method

Ceramic-based thermal barrier coatings are used as heat and wear shields of gas turbine blades. There is a strong need to evaluate the thermal conductivity of coating for thermal design and use. The thermal conductivity of a bulk material is obtained as the product of thermal diffusivity, specific heat capacity, and density above room temperature in many cases. Thermal diffusivity and thermal conductivity are unique for a given material because they are sensitive to the structure of the material. Therefore, it is important to measure them in each sample. However it is difficult to measure the thermal diffusivity and thermal conductivity of coatings because coatings are attached to substrates. In order to evaluate the thermal diffusivity of a coating attached to the substrate, we have examined the laser flash method with the multilayer model on the basis of the response function method. We carried out laser flash measurements in layered samples composed of a CoNiCrAlY bond coating and a 8YSZ top coating by thermal spraying on a Ni-based superalloy substrate. It was found that the procedure using laser flash method with the multilayer model is useful for the thermal diffusivity evaluation of a coating attached to a substrate. # 2011 The Japan Society of Applied Physics

Thermal Cycle Properties of Plasma Sprayed Oxidation-Resistant Metallic Coatings

Thermal cycle resistance of Ni-20Cr, Ni-50Cr and CoNiCrAlY coatings produced by air plasma spraying was investigated according to Japanese Industrial Standard Testing method for thermal cycle resistance of oxidation resistant metallic coatings (JIS H 8452: 2008). The specimens were exposed to a cyclic heating and cooling regimen comprised of up to 100 cycles of 10 hours heating to 1000 °C or 1093 °C in air followed by cooling. The thermal cycle resistance of oxidation-resistant metallic coatings was found to depend strongly on testing temperature and on the chemical composition of the coating materials. In thermal cycle testing at 1000 °C, no remarkable failure was observed in any specimen. However, in thermal cycle testing at 1093 °C, spalling was observed over the entire surface of the Ni-20Cr coating, although the Ni-50Cr and the CoNiCrAlY coatings exhibited excellent thermal cycle resistance even upon exposure to 100 thermal cycles. The CoNiCrAlY coating showed mass gain with increasing number of thermal cycles due to preferential oxidation between thermal spray particle splats. Furthermore, the failure behavior of specimens was investigated in detail by SEM, XRD, EPMA, etc.

Fe-Si Thermal Spray Coating for Fire Side Corrosion and Erosion Protection in Coal-Fired Boiler

Fe-Si intermetallic thermal spray powders have been developed for sulfidation corrosion and erosion protection for furnace walls in pulverized coal fired boiler. In this paper, evaluation of corrosion and erosion resistance of developed coatings was performed. The corrosion test results showed that the developed coatings almost equal corrosion resistance to conventional corrosion resistant coatings under the low NOX boiler condition. Erosion test results also indicated that Fe-20Si-1B using atmospheric plasma spraying showed higher erosion resistance than the conventional coatings.

304 The Influence of Long Term Operation on Delamination Behavior of Thermal Barrier Coatings under Thermo-mechanical Fatigue.

1 緒 言 燃料価格の上昇および環境問題などから,発電効率の 向上が強く求められている.ガスタービンの高効率化に は高温化が効果的であるものの,クリープ強度に対する 材料の制限から,遠心力が作用するタービン動翼の信頼 性を維持するべく,冷却の強化を図る必要がある. 近年,冷却強化の手法の一つとして,熱伝導率の低い セラミック皮膜を動翼表面に施工することで,内部冷却 翼の温度を低減する熱遮蔽コーティング (TBC, Thermal Barrier Coatings) の適用が主流となりつつある. TBCはすでに運用中の翼に施工することも可能であ り,耐食耐酸化性向上も期待できることから,その適用 範囲は今後さらに拡大することが予想される.しかしな がら,TBCの損傷挙動を定量的に評価するには,まだ不 透明な点も多い.1) 従来 TBCに関する研究は,皮膜の性質に関する内容 とはく離強度に関する内容に大別されてきた.膜質につ いて Fujiiらは,高温曝露に伴う焼結によりセラミック層 の気孔率が減少するとともに熱伝導率が増加する挙動を LMP (Larson-Miller Parameter) を用いて整理する手法を 提案している.2)TomimatsuらはEB-PVD (Electron Beam Enhanced Physical Vapor Deposition) により製膜した TBCを対象として,レーザー光を用いた皮膜内の残留応 力測定手法を提案するとともに,高温曝露に伴い残留応 力の値が増加することを報告している.3)また脇らはセラ ミック層の残留応力を応力開放法により求めるとともに, 繰り返し負荷下での皮膜の変形特性を示している.4), 5) 一方強度については,西野らが TBCの施工により等 温下での低サイクル疲労寿命が低温で短寿命,高温で長 寿命となることを示し,これはボンド層の延性の温度依 存性に起因すると説明している.6)しかしながらガスター ビンの高温部品には,Fig. 1に示すように起動・停止に 熱機械疲労下における熱遮蔽コーティングのはく離挙動 吉 竹 茂 飯 尾 哲 史 船 尾 淳 喜 関 原 傑 有 川 秀 行 市 川 国 弘 Delamination Behavior of Thermal Barrier Coatings under Thermo-Mechanical Fatigue

Development of Materials and Coating Processes for High Temperature Heavy Duty Gas Turbines

This paper describes materials developed for the first stage nozzle and all stages turbine disc, and the new coating processes of the first stage bucket for high temperature, heavy duty gas turbines.A cobalt base casting superalloy (30Cr-10Ni-7W-0.2Nb-0.15Zr-0.2Ti-bal.Co), having high creep rupture strength and ductility, was used for the first stage nozzle and 12Cr forging material, having high creep rupture strength, was used for all stages turbine disc of the high temperature, heavy duty gas turbine, the H25. To increase hot corrosion properties of the first stage bucket, MCrAlY was applied on the bucket external surfaces by a low-pressure plasma-spray coating technique. A procedure of chemical vapor deposition for Al coating on the bucket internal cooling paths was also established for future high temperature gas turbines.Copyright