Trial to Develop High strength Nickel-based Alloys possessing. High resistance to both Hot-corrosion and Thermal Fatigue by a Heat Treated Process producing a Composite Structure

本研究的目的是开发具有优良性能的镍基高温合金，如高温强度、抗热腐蚀性、抗热疲劳性等。为此，我们尝试采用一种新的方法，即利用偏析现象获得由含有不同尺寸γ'相的两个区域组成的复合组织。首先，研制了高铬镍基高温合金，并对合金的力学性能和表面稳定性进行了研究。结果表明：（1）尽管Cr含量高达12%（质量分数），但不同合金的抗热腐蚀性能差异较大。合金中Ti/Al成分比越高，耐热腐蚀性能越好。(2)高温抗氧化性在低Ti/Al组成比中获得，这与热腐蚀抗性的情况成反比。该结果表明，存在最佳的Ti/Al组成比以获得优异的抗热腐蚀性和抗氧化性。(3)实验合金在1313 K/137 MPa条件下的持久寿命低于含3%Re合金的CMSX-4，但两种实验合金在1193 K/196 MPa条件下的持久寿命超过了CMSX-4。这一事实表明，超合金。(4)钴在高应力水平下起到增加蠕变断裂寿命的作用，但在低应力水平下不再起作用。(5)具有复合结构的实验合金表现出低的耐热疲劳性，表明合金中的均匀组成对于它们的耐热疲劳性的良好指示是必要的。

The purpose of this research is to develop nickel based superalloys possessing excellent properties, such as high temperature strength, hot-corrosion resistance, thermal fatigue resistance, etc. For this purpose, we tried to employ a new method, which utilized the segregation phenomenon to obtain a composite structure consisting of two regions containing different sizes of the γ' phase. Firstly, high Cr nickel based superalloys were developed, and the mechanical properties and surface stability of the alloys were examined. The results are obtained as follows ;(1) In spite of high Cr content of 12mass%, hot corrosion resistance is different considerably among the experimental alloys. Good hot-corrosion resistance is obtained in a high Ti/Al compositional ratio in alloys. (2) High temperature oxidation resistance is obtained in a low Ti/Al compositional ratio, which is in inverse relation to the case of hot-corrosion resistance. This result indicates that an optimum Ti/Al compositional ratio will exist to obtain an excellent resistance to both hot corrosion and oxidation. (3) The experimental alloys exhibit shorter in creep rupture life in the condition of 1313K/137MPa than CMSX-4 containing 3%Re alloy, but two experimental alloys exceed the rupture life of CMSX-4 in the condition of 1193K/196MPa. This fact shows that a superalloys. (4) Cobalt plays a role to increase creep rupture life at high stress levels but it does not play anymore at low stress levels. (5) The experimental alloys having the composite structure exhibit low thermal fatigue resistance, indicating that homogeneous composition in alloys is necessary for a good indication of the thermal fatigue resistance of them.