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

该项目是为了通过晶界和界面结构开发超高温抗热和抗氧化材料而进行的。取得的主要结果如下：1.研究成果。Ni-Fe合金晶界氧化及氧化诱发脆性研究：研究了Ni-Fe合金晶界结构对晶界氧化的影响。我们发现晶间氧化优先发生在随机晶界，而低Σ符合晶界如Σ3、Σ11、Σ19具有良好的抗氧化性。将晶界工程应用于控制多晶Ni-Fe合金的氧化脆化，综合考虑了晶界特征分布(GBCD)和晶界密度(晶粒度)。为此目的的最佳晶界微结构的存在已被预测。晶界组织对力学性能和晶界…的影响纳米晶镍的脆化：我们发现，纳米晶镍的显微硬度不仅随着符合界面频率的增加而降低，而且随着符合界面相互连接的三重点的增加而降低。此外，我们还证实了通过控制GBCD和晶粒度可以改善晶界偏析诱发的脆性。控制碳化硅氧化脆化的研究：研究了掺杂(镁、铝、磷)对β-碳化硅晶界组织的影响。我们通过控制掺杂成功地改变了β-碳化硅中的GBCd。此外，我们还用一些在不同温度和氧分压下氧化的试件，在室温下通过三点弯曲试验评价了氧化脆性。研究发现，降低β-碳化硅中的随机晶界频率和晶粒度，可以有效地改善其氧化脆性。较少

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