Ultrasound attenuation was measured in nickel specimens of about 30 mm diameter prepared using the high pressure torsion technique. The cold working process produced an equivalent shear strain increasing from zero at the center up to 1000% at the edge of the specimen. The fragmentation of the grains due to multiple dislocations led to an ultrafine microstructure with large angle grain boundaries. The mean value of the grain size distribution gradually decreased from ∼50 μm at the center to 0.2 μm at the edge. Laser pulses of 5 ns were employed for the excitation of broadband ultrasound pulses covering the spectral range of 0.1-150 MHz. The ultrasound pulses were measured from the opposite side of the specimen by means of an optical interferometer and a piezoelectric foil transducer in two experimental setups. The features of the detected signal forms are discussed. The absolute value of the attenuation decreases from the center to the edge of the specimen showing nearly linear frequency dependence. The variation of the phase velocity was measured in a 6 mm-thick high pressure torsion nickel sample, revealing a velocity increase from the center to the edge.

中文翻译：

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严重塑性变形镍中超声波的衰减。

在使用高压扭转技术制备的约 30 毫米直径的镍样品中测量超声衰减。冷加工过程产生了等效剪切应变，从中心的零增加到试样边缘的 1000%。由于多位错导致的晶粒破碎导致具有大角度晶界的超细微观结构。晶粒尺寸分布的平均值从中心的~50 μm 逐渐减小到边缘的 0.2 μm。5 ns 的激光脉冲用于激发覆盖 0.1-150 MHz 光谱范围的宽带超声脉冲。在两个实验装置中，通过光学干涉仪和压电箔换能器从样品的另一侧测量超声脉冲。讨论了检测到的信号形式的特征。衰减的绝对值从样品的中心到边缘减小，显示出几乎线性的频率依赖性。在 6 毫米厚的高压扭转镍样品中测量相速度的变化，显示从中心到边缘的速度增加。