Microstructure Evolution of Boundaries with different Angles in Single Crystal Ni-base Superalloy during High Temperature Oxidation Process
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摘要: 选取镍基单晶高温合金中晶界角度分别为5.4°, 12.3°, 25.7°的小角度和大角度晶界试样, 经标准热处理后, 在1 100 ℃下恒温氧化100, 500, 1 000 h, 研究了氧化过程中不同角度晶界的组织演化。结果表明: 不同角度晶界试样氧化100 h后, 合金表层分成了外氧化膜、无γ′相区和γ′相减少区三个区域, 不同角度晶界试样的无γ′相区和γ′相减少区都形成了少量的内氧化微孔; 氧化500 h后, 不同角度晶界试样上形成的内氧化微孔数量明显增加, 而且随着晶界角度增加, 晶界上的内氧化微孔沿晶界方向的尺寸增大, 逐渐形成狭长的微孔通道; 氧化1 000 h后, 随着晶界角度增加, 晶界上的内氧化微孔尺寸继续增大, 25.7°晶界试样的晶界上形成了连续的内氧化微孔通道, 一直延伸到γ′相减少区, 并通过晶界在晶体内部形成了内氧化区。Abstract: The single crystal Ni-base superalloy samples with low angle boundaries and high angle boundaries were selected. The grain boundary angles of three samples were 5.4°, 12.3° and 25.7°, respectively. The microstructure evolution of samples with different boundary angles and after standard heat trestment was studied in 1 100 ℃ high temperature oxidation process. The results show that the surface of nickel single crystal superalloy with different grain boundary angles was divided into three areas: outer oxide film, γ′-free layer and γ′-reduced layer, after oxidation for 100 h and there was a little internal oxidation micropores in the γ′-free layer and γ′-reduce layer. The number of micropores for three samples all increasd after oxidation for 500 h. The size of micropores increased along the grain boundaries with the increase of the grain boundary angle and the micropores grew up and formed a long and narrow channel. After oxidation for 1 000 h, the size of micropores continued to increase along grain boundaries with the increase of the grain boundary angle. A consecutive internal oxidation micropore channel was formed in the sample with 25.7° angle and extend into the γ′-reduced layer and a internal oxidation layer was formed inside the single crystal.
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