Systematic Research on Hig-Strength and High Performance Ni-Base Superalloy Coatings for Advanced Gas Turbines.

开展了镍基高温合金的高温机械疲劳（TMF）和等温低周疲劳（ILCF）强度及其防护涂层的合作研究。通过对裂纹萌生、断口形貌和位错组织的观察，讨论了基体合金和涂层对TMF和ILCF寿命的影响。本文还讨论了TMF与ILCF之间的关系。结果表明：(1)基体合金对TMF寿命和ILCF的影响较大。与传统的多晶合金相比，单晶和定向凝固合金及其涂层普遍表现出最优异的性能。(2)位错组织的观察表明，TMF和ILCF在镍基高温合金中的控制和变形机制存在本质上的差异。因此，用ILCF试验再现和估计镍基高温合金的TMF破坏在原则上是不合理的。(3)与基体相比，镍基高温合金涂层在非相状态下的TMF寿命明显降低。裂纹密度的研究表明，这是由于涂层薄膜在TMF试验中达到最大拉伸应变的温度下延展性较低，导致严重的裂纹。因此，对镍基高温合金涂层进行TMF寿命预测，不仅要了解基体，还要了解涂层本身。(4)对于涂层的TMF失效，应注意ILCF试验的结果，这些结果可能会给我们提供一些误导性的信息：例如，涂层显著降低了非相条件下的TMF寿命，尽管900℃时ILCF寿命有所提高。少

Collaborative research, which cover the themo-mechanical fatigue (TMF) and isothermal low-cycle fatigue (ILCF) strengths of Ni-Base superalloys and the protective coatings at elevated temperatures, has been carried out. Based on the observations of the crack initiation, the fracture surface and the dislocation structures, the effects of the substrate alloy and the coating on the TMF and ILCF lives are presented in this paper. The correlation between the TMF and ILCF are also discussed.The results obtained by the collaborative research are summarized as follows :(1) The TMF lives, as well as the ILCF, were strongly dependent of the substrate alloys. The single crystal and directionally-solidified alloys and their coatings generally exhibited the most excellent properties, compared with those of the traditional pollycrystalline alloy.(2) The observation of dislocation structures indicated that the controlling and deformation mechanisms were intrinsically different between TMF and ILCF in … More the Ni-base superalloys. Accordingly, it must be unreasonable in principle to reproduce and to estimate the TMF failure of the Ni-base superalloys by the ILCF tests.(3) Remarkable reductions in the TMF life of the Ni-base superalloy coatings under the out-of-phase condition was found to occur, compared with that of the substrate. It was shown by the investigation of the crack density that this was due to the low ductility of the coating film at the temperatures at which the maximum tensile strain was reached in the TMF tests, resulting in severe crackings. Hence, it is essential for the TMF life prediction of Ni-base superalloy coatings to get understandings not only on the substrate but also the coating film.(4) Regarding as the TMF failure of the coatings, attention should be paid to the results by ILCF tests which can provide us a somewhat misleading information : e.g., the TMF lives under the out-of-phase condition were significantly reduced by the coating, although the ILCF one at 900℃ was improved. Less