Grain Boundary and Interface Architecture for Ultra-High Temperature Materials -Occurrence of Super-Heat Resistance and Oxidation Resistance-

本项目旨在通过晶界和界面结构来开发超高温耐热抗氧化材料。主要研究结果如下：Ni-Fe合金晶界氧化及氧化致脆性的研究：研究了Ni-Fe合金晶界组织对晶间氧化的影响。我们发现晶间氧化优先发生在随机边界，而低-Σ重合边界如Σ3， Σ11， Σ19具有优异的抗氧化性。利用晶界特征分布（GBCD）和晶界密度（晶粒尺寸），将晶界工程应用于控制多晶Ni-Fe合金的氧化致脆。为了达到这一目的，已经预测了最佳晶界微观结构的存在。晶界显微组织对纳米晶镍力学性能和晶界段的影响：我们发现纳米晶镍的显微硬度不仅随着符合边界出现频率的增加而降低，而且随着符合边界相互连接的三相点的增加而降低。另外，我们还证实了晶界偏析引起的脆性可以通过控制晶界密度和晶粒尺寸来改善。碳化硅氧化脆的控制研究：研究了掺杂剂（Mg、Al、P）对β-碳化硅晶界组织的影响。通过控制掺杂剂，我们成功地改变了β-碳化硅的GBCD。此外，我们还利用一些在不同温度和氧分压下氧化的试样，在室温下进行了三点弯曲试验，评估了氧化引起的脆性。研究发现，减小随机边界的频率和晶粒尺寸可以有效地改善β-碳化硅的氧化脆。少

This project was conducted for development of heat- and oxidation-resistant materials at ultra-high temperatures through grain boundary and interface architecture. Main results obtained are as follows.1. A study on grain boundary oxidation and oxidation induced brittleness in Ni-Fe alloy : The effect of grain boundary structure on intergranular oxidation was investigated in a Ni-Fe alloy. We have found that intergranular oxidation preferentially takes place at random boundaries, while low-Σ coincidence boundaries such as Σ3, Σ11, Σ19 possess excellent oxidation resistance. Grain boundary engineering was applied to controlling oxidation induced embrittlement in polycrystalline Ni-Fe alloy by taking account of the grain boundary character distribution (GBCD) as well as the grain boundary density (grain size). The presence of an optimal grain boundary microstructure for this purpose has been predicted.2. Effect of grain boundary microstructure on mechanical property and grain boundary seg … More regation induced embrittlement in nanocrystalline nickel : We have found that the microhardness in nanocrystalline nickel decreases not only with increasing the frequency of coincidence boundaries but also with increasing triple points at which the coincidence boundaries are interconnected. In addition, we have confirmed that the grain boundary segregation induced brittleness can be improved by controlling the GBCD and the grain size.3. A study on Control of oxidation induced embrittlement in Silicon Carbides : The effect of dopants (Mg, Al, P) on the grain boundary microstructure was studied in β-silicon carbide. We have succeeded in changing the GBCD in β-silicon carbide by controlling dopants. In addition, we have evaluated oxidation induced embrittlement by 3-point bending test at room temperature using some specimens oxidized at different temperatures and oxygen partial pressures. It has been found that the oxidation embrittlement in β-silicon carbide can be effectively improved by decrease in the frequency of random boundaries and the grain size. Less