Defence Metallurgical Research Laboratory, Hyderabad, India.
Defence Metallurgical Research Laboratory, Hyderabad, India.
Ultrasonics. 2018 Nov;90:42-51. doi: 10.1016/j.ultras.2018.05.007. Epub 2018 May 16.
The high temperature strength of directionally solidified Ni-base super alloy CM 247LC strongly depends on the morphology, volume fraction, size and size distribution of γ' precipitate (NiAl) in the FCC γ matrix. The microstructure of the alloy is engineered to achieve the right combination of these parameters that provides the required high temperature strength and creep resistance. The alloy contains high volume fraction of coherent γ' precipitates having near cubic shape. High temperature exposure of gas turbine components made out of the alloy leads to coarsening of the γ' precipitates and broadening of the γ matrix channel. This in turn, adversely affects the high temperature mechanical properties of the alloy. The present study endeavours to non-destructively characterize such detrimental changes in the microstructure that controls the mechanical properties and limits the life of components. The microstructural changes of the fully heat treated alloy exposed at 980 °C for different hours (100-1200) of thermal exposure have been characterized using ultrasonic methods. Changes in microstructural parameters due to different hours of thermal exposure have been correlated with changes in ultrasonic velocity, ultrasonic attenuation coefficient and second order acoustic nonlinearity parameter. It is observed that the change in attenuation is predominantly by absorption of the ultrasonic wave due to dislocation damping in the γ channels. Nonlinear ultrasonic parameter changes with thermal exposure predominantly due to the alteration of dislocation precipitate interaction. A dislocation precipitation interaction model for ultrasonic wave distortion has been used to explain the observed variation in nonlinear parameter. A microstructural parameter has been identified that varies in a similar way as ultrasonic attenuation and second order ultrasonic parameter. It is shown that variations in the acoustic non-linearity parameter follow the trend more closely with the identified microstructural parameter.
定向凝固 Ni 基高温合金 CM 247LC 的高温强度强烈依赖于 FCC γ 基体中γ' （NiAl）析出相的形态、体积分数、尺寸和尺寸分布。该合金的微观结构经过设计，以实现这些参数的正确组合，从而提供所需的高温强度和抗蠕变性能。该合金含有高体积分数的具有近立方形状的相干γ' 析出相。高温暴露于由该合金制成的燃气涡轮组件会导致 γ' 析出相粗化和 γ 基体通道变宽。这反过来又会对合金的高温力学性能产生不利影响。本研究旨在非破坏性地表征控制力学性能和限制部件寿命的微观结构中的这种有害变化。使用超声方法对在 980°C 下暴露不同时间（100-1200 小时）的完全热处理合金的微观结构变化进行了表征。由于不同小时的热暴露导致的微观结构参数的变化与超声速度、超声衰减系数和二阶声非线性参数的变化相关联。观察到衰减的变化主要是由于 γ 通道中的位错阻尼导致超声波的吸收。非线性超声参数随热暴露的变化主要是由于位错析出相相互作用的改变。已使用用于解释观察到的非线性参数变化的位错析出相互作用模型来解释超声波失真的变化。已确定一个微观结构参数，该参数以与超声衰减和二阶超声参数相似的方式变化。结果表明，声非线性参数的变化与所识别的微观结构参数的变化更接近。
