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首页> 外文OA文献 >Oxidation and the Effects of High Temperature Exposures on Notched Fatigue Life of an Advanced Powder Metallurgy Disk Superalloy
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Oxidation and the Effects of High Temperature Exposures on Notched Fatigue Life of an Advanced Powder Metallurgy Disk Superalloy

机译：高温粉末冶金圆盘高温合金的氧化和高温暴露对缺口疲劳寿命的影响

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Oxidation and the effects of high temperature exposures on notched fatigue life were considered for a powder metallurgy processed supersolvus heat-treated ME3 disk superalloy. The isothermal static oxidation response at 704 C, 760 C, and 815 C was consistent with other chromia forming nickel-based superalloys: a TiO2-Cr2O3 external oxide formed with a branched Al2O3 internal subscale that extended into a recrystallized - dissolution layer. These surface changes can potentially impact disk durability, making layer growth rates important. Growth of the external scales and dissolution layers followed a cubic rate law, while Al2O3 subscales followed a parabolic rate law. Cr- rich M23C6 carbides at the grain boundaries dissolved to help sustain Cr2O3 growth to depths about 12 times thicker than the scale. The effect of prior exposures was examined through notched low cycle fatigue tests performed to failure in air at 704 C. Prior exposures led to pronounced debits of up to 99 % in fatigue life, where fatigue life decreased inversely with exposure time. Exposures that produced roughly equivalent 1 m thick external scales at the various isotherms showed statistically equivalent fatigue lives, establishing that surface damage drives fatigue debit, not exposure temperature. Fractographic evaluation indicated the failure mode for the pre-exposed specimens involved surface crack initiations that shifted with exposure from predominately single intergranular initiations with transgranular propagation to multi-initiations from the cracked external oxide with intergranular propagation. Weakened grain boundaries at the surface resulting from the M23C6 carbide dissolution are partially responsible for the intergranular cracking. Removing the scale and subscale while leaving a layer where M23C6 carbides were dissolved did not lead to a significant fatigue life improvement, however, also removing the M23C6 carbide dissolution layer led to nearly full recovery of life, with a transgranular initiation typical to that observed in unexposed specimens.
机译：对于粉末冶金处理的超固溶热处理的ME3圆盘高温合金，考虑了氧化和高温暴露对缺口疲劳寿命的影响。在704°C，760°C和815°C下的等温静态氧化响应与其他氧化铬形成的镍基高温合金一致：TiO2-Cr2O3外部氧化物与分支的Al2O3内部亚尺度形成，并延伸到重结晶的溶解层中。这些表面变化可能会影响磁盘的耐用性，从而使层的生长速度变得重要。外部水垢和溶解层的生长遵循立方速率定律，而Al2O3子水垢遵循抛物线速率定律。在晶界处溶解的富含Cr的M23C6碳化物溶解，以帮助维持Cr2O3的生长，其深度约为氧化皮厚度的12倍。通过在空气中704°C失效时进行的缺口低循环疲劳测试，检查了先前暴露的影响。先前暴露导致疲劳寿命中高达99％的明显扣款，其中疲劳寿命与暴露时间成反比。在各种等温线处产生的外部鳞片大致相等于1 m厚的暴露，显示出统计上相等的疲劳寿命，从而确定表面损伤是驱动疲劳消耗的原因，而不是暴露温度。断口评估表明，预先暴露的试样的破坏模式涉及表面裂纹萌生，随着暴露的发生，其从主要的单个晶间萌生转变为跨晶传播，转变为裂纹外氧化物的多次萌生。 M23C6碳化物溶解导致表面的晶界减弱，部分原因是晶间裂纹。去除氧化皮和副氧化皮，而保留一层溶解有M23C6碳化物的层并不能显着改善疲劳寿命，但是，去除M23C6碳化物溶解层也可以使寿命几乎完全恢复，而典型的跨晶引发是在未暴露的标本。

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