TiAl合金高温疲劳小裂纹与长裂纹扩展行为

Behavior of small and long fatigue crack propagration of TiAl alloy at elevated temperature

摘要:

本研究利用原位观察疲劳试验方法研究了变形TiAl合金在650℃下的三维小裂纹扩展行为,利用传统疲劳裂纹扩展试验方法研究了合金在650～800 ℃温度范围内的长裂纹扩展行为。结果显示,650℃下,变形TiAl合金的三维小裂纹在低于长裂纹扩展门槛值的区域依然能够扩展,并且扩展速率高于长裂纹；试样棱边平直横向加工刻痕是合金三维小裂纹萌生的主要位置之一,小裂纹在扩展过程中发生偏折并在偏折处合并,合金的疲劳寿命对试样表面的不规则条状加工缺陷不敏感；在650～800 ℃温度范围内,合金的疲劳长裂纹稳态扩展速率对温度变化不敏感,裂纹扩展过程均显示解理断裂,裂纹扩展门槛值受韧脆转变温度影响,韧脆转变温度以下温度的门槛值较低。

Abstract:

Three-dimensional small crack propagation behavior of deforming TiAl alloy at 650℃ is studied by in-situ observation fatigue testing, and then long crack propagation behavior of the alloy in temperature range from 650℃ to 800℃ is studied by fatigue crack propagation tests. It shows that, the three-dimensional small cracks can still grow even though in the stress intensity factor region that below the long crack propagation threshold value, furthermore, the growth rates of small cracks are higher than long cracks in this region; The sample edge straight horizontal manufacturing nick is one of the main positions of three-dimensional small crack initiation of the alloy. Small cracks merge at the position of bends that occur during the fatigue testing. The fatigue life of the alloy is not sensitive to irregular strip manufacturing defects on the surface of the sample; The steady propagation rates of long fatigue cracks of the alloy are not sensitive to temperature changes in temperature range from 650℃ to 800℃. All the long crack propagation processes exhibit the cleavage fracture. Crack propagation threshold values are related to ductile-brittle transition temperature, the temperatures below the ductile-brittle transition temperature have lower threshold values.