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Impulse Excitation Study of Elasticity of Different Precipitated Microstructures in IN738LC at High Temperatures

机译:高温下IN738LC中不同沉淀微结构的弹性脉冲激励研究

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摘要

The elastic modulus of the cast superalloy IN738LC in various heat-treated conditions was determined with multiple specimens for each microstructure using the impulse excitation technique and the resonant frequencies while heating and cooling. Whereas the second and higher order harmonics were also excited in the high temperature range 700-1000 deg C in 50 mm long specimens during controlled heating, analogous specimens 35 mm in length, impacted in similar fashion, did not excite the higher harmonics. Also, the 50 nim long specimens became excited and stayed in the second harmonic over broader temperature ranges during uncontrolled cooling inside the closed furnace. Ail precipitated conditions had nearly similar elastic data, varying from about 200 to 115 GPa, with small deviations, within 5 percent, found among multiple specimens of similar microstructures tested. Specimens with fine nano-size precipitates had a distinctly smaller rate of decrease in elastic modulus with increasing temperature, in contrast to a somewhat larger and nearly similar rate of decrease in specimens with coarse or medium-sized precipitates. This behavior is indicative of a larger average cohesive strength between the atoms and/or between the matrix and the precipitate particles in the former microstructure. The duplex size precipitate microstructure seemed to have both small and large drops in different specimens.
机译:使用脉冲激发技术和加热和冷却时的共振频率,通过多个试样针对每个显微组织确定在各种热处理条件下铸态高温合金IN738LC的弹性模量。尽管在受控加热期间在50 mm长的试样中在700-1000摄氏度的高温范围内也激发了二次谐波和更高次的谐波,但长度类似的35 mm的类似试样却没有激发更高的谐波。同样,在封闭的炉子内部不受控制的冷却过程中,50尼姆长的试样被激发并在更宽的温度范围内停留在二次谐波中。所有沉淀条件都具有几乎相似的弹性数据,范围从约200 GPa至115 GPa,在测试的具有相似微观结构的多个样品中发现的偏差很小,在5%之内。带有细纳米尺寸析出物的样品的弹性模量随温度升高而降低的速率明显较小,而带有粗糙或中等尺寸析出物的样品则具有稍大且几乎相似的降低速率。该行为表明在原子之间和/或在基质与沉淀物颗粒之间的平均内聚强度更大。在不同的样品中,双相尺寸沉淀物的微观结构似乎都有小滴和大滴。

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