A New Strategy to Prevent The Undesirable High Temperature Fatigue Reduction due to Cellular Formation in Microstructurally-Controlled Ni-Base Superalloys : -For Refurbishment and Recoating Technology-

近年来，工业燃气涡轮机发电厂已成为许多国家的主要基本负荷电源。这些应用需要高度可靠的长期负载机器，可以使用廉价的可用燃料运行。毫无疑问，在极其恶劣的条件下，对服役中的热段部件进行维修、重涂和翻新将是不久的将来不可避免的技术。然而，这些技术还没有确定的方法。本工作的主要目的是从材料相关性的角度对镍基高温合金的组织控制修复和涂层技术有一个基本的认识，首先研究了单晶镍基高温合金CMSX-4和定向凝固合金CM 247 LC的组织变化。在室温下对这些合金进行塑性应变以模拟几种服役损伤后，再热处理作为通常的损伤过程， ...更多信息 在1080 ~ 1300℃的高温下进行锗的回收。一个显着的变化，微观结构，或细胞的形成，被发现发生，这取决于再热处理温度。其次，在电液疲劳试验机上，在950℃、10 Hz频率、完全保留加载比的空气中，研究了不同应变场和材料中的显微偏析对疲劳性能的影响。实验表明，一旦形成蜂窝状结构，疲劳强度就会显著降低，这表明蜂窝状结构对涂层的重涂和翻新技术具有重要作用，最后提出了减少和防止上述不良影响的方法。疲劳试验发现，采用表面改性技术或防护涂层可能是一种很有前途的方法。控制涂层的合金成分也是减少有害影响的有效方法。少

Recently industrial gas turbine power plants have been the major baseload source of power for many countries. These applications require a highly reliable, long-term load mechine which can operate using cheap, available fuels. Nobody doubts that repair, recoating and refurbishment of the hot section components in service under extremely sever condition will be inevitable technology in very near future. Nevertheless, there has been no established method for these technologies yet. Main objective in this work is to get basic understandings on the refurbishment and rcoating technology of microstructurally-controlled Ni-base superalloys, from a viewpoint of material relaibility.At first the microstructural changes in a single crystal Ni-base superalloy, CMSX-4, and a directicnally-solidified alloy, CM247LC, are shown in this work. After a plastic straining at room temperature into these alloys to simulate several kinds of in-service damages, the re-heat treatments as a usual course of dama … More ge recovery process was performed at elevated temoeratures ranged from 1080℃ to 1300℃. A siginificant change in microstructure, or cellular formation, was found to occur, depending on the re-heat treatment temperature. It was also found that the change was quite anisotropic, being influenced by the strain field and the microsegregation in the material.Next the effect of the carried out at 950℃ in air at a frequency of 10 Hz under fully-reserved loading ratio, by means of an electro-hydraulic fatigue testing machine. The experiments indicated that once the cellular formation was reached, the fatigue strength was remarkably reduced : an indication of a serious role of the cellular formation was reached, the fatigue strength was remarkably reduced : an indication of a serious role of the cellular formation for recoating and refurbishment technology.Finally the method to reduce and prevent the above undesirable effect is shown. It was found by the fatigue tests that the application of the surface modification technique, or protective coating might be a promising method. It was suggested that the control of alloy composition of the coating could also be a useful technique to reduce the harmful effects. Less