材料科学技术（英）
Creep testing was conducted on K40S alloy. The detailed creep deformation and fracture mechanisms under constant load were studied. The results show that the stress exponent ranges between 7 and 14.4 at elevated temperature 973similar to1173 K, and that the activation energy is approximately 449.1 kJ/mol. During creep, the grain boundary sliding cut off primary carbides at the boundary, generating the "O" model cracks. The creep failure mode of K40S alloy is transgranular ductile and cracks originate at the primary carbides. A long carbide and matrix interface is often a preferential path for crack propagation. The creep mechanism is discussed in light of the creep microstructure, the stress exponent and the activation energy.
关键词:
K40S alloy;creep;fracture;crack propagation;activation-energies;superalloy;term
王宝奇
,
谷南驹
,
郭素珍
,
马晓莉
金属学报
利用Bain点阵对应对K-S模型的晶格改建过程进行了严密的数学描述.对于不同的马氏体正方度,提出了计算第一切变、第二切变及晶格调整的计算依据,并给出了普遍的计算公式.以Fe-1.4C和纯铁为例,计算了马氏体相变的点阵畸变.进一步分析表明,K-S模型实质是Bain模型的旋转.计算的结果与实测的取向关系相符合.
关键词:
K-S模型
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null
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Corrosion Science
Arc ion plating had been employed on a cobalt-base superalloy K40S to deposit a NiCrAlYSi coating to improve its oxidation resistance at 1323-1423 K in air. The K40S superalloy had poor oxidation resistance because a non-protective and easy spalling surface oxides scale mixed of Cr2O3 and CoCr2O4 was formed on its surface. After coated with NiCrAlYSi coating, a dense and protective alpha-Al2O3 scale was formed on the coating and excellently improved its oxidation resistance. Inter-diffusion obviously occurred between the coating and the substrate K40S superalloy in oxidation process, which resulted from Co atoms in K40S outwards diffused. A richen Cr and W carbides inter-diffusion layer was formed, which could acted as a diffusion barrier that barred Al atoms in coating inwards diffusion. Though the NiCrAlYSi changed into NiCoCrAlYSi during oxidation process, it still possessed a good oxidation resistance and. had a considerable long-term life. (C) 2008 Elsevier Ltd. All rights reserved.
关键词:
cobalt-base superalloy K40S;NiCrAlYSi coating;arc ion plating;high;temperature oxidation;inter-diffusion;aluminide coatings;cyclic oxidation;alloys
Transactions of Nonferrous Metals Society of China
Fatigue crack propagation behavior of K40S cobalt-base superalloy under ambient atmosphere at 700 degreesC and 900 degreesC was investigated. The detailed fatigue crack propagation and fracture mechanism under the alternating loads were studied. The results show that, there is a defined threshold for K40S alloy at elevated temperatures. The fatigue threshold is 23. 9 MPa . m(1/2) at 700 degreesC and 12 MPa . m(1/2) at 900 V. The significant decrease of the threshold with increasing temperature is associated with the oxidation induced embrittlement at crack tip. Observation on the fatigue fracture surfaces indicates a ductile fracture mechanism related to the fatigue crack growth.
关键词:
cobalt-base superalloy;fatigue crack propagation;fatigue threshold;ductility;growth-behavior;alloy;steel
Materials Letters
Secondary M,C precipitation was investigated in K40S cobalt-base alloy after 100 h aging at 950 degreesC. The results showed that it was closely related to the tungsten-rich zones inherited from the as-cast condition and the degeneration of the primary M7C3 carbide. A direct element reaction, 6M + C --> M6C, in which C comes from the decomposition of the M7C3 carbides, is suggested as the mechanism of secondary M6C precipitation in K40S alloy. (C) 2001 Elsevier Science B.V. All rights reserved.
关键词:
M6C precipitation;aging;M7C3 carbide;superalloy
