Kozhushko Victor V, Paltauf Günther, Krenn Heinz, Scheriau Stephan, Pippan Reinhard
Institute of Physics, Karl-Franzens-University of Graz, Universitätsplatz 5, 8010 Graz, Austria.
NDT E Int. 2011 May;44(3):261-266. doi: 10.1016/j.ndteint.2010.12.002.
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.
在使用高压扭转技术制备的直径约为30毫米的镍试样中测量了超声衰减。冷加工过程产生的等效剪切应变从试样中心处的零增加到边缘处的1000%。由于多重位错导致的晶粒破碎产生了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处的约50μm逐渐减小到边缘处的0.2μm。采用5ns的激光脉冲激发覆盖0.1 - 150MHz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式换能器从试样的另一侧测量超声脉冲。讨论了检测到的信号形式的特征。衰减的绝对值从试样中心到边缘减小，呈现出近似线性的频率依赖性。在一个6毫米厚的高压扭转镍样品中测量了相速度的变化，结果表明从中心到边缘速度增加。
