定向凝固镍基合金DZ444声学特性的各向异性

选取定向凝固镍基高温合金DZ444不同方向片状试样,利用电子背散射衍射等技术表征晶体取向和微观组织,利用脉冲回波技术分析纵波声速和声衰减系数。结果表明:两声学特性呈各向异性,随着试样平面法向与凝固方向之间夹角φ由0°到45°再到90°,纵波声速由5533m/s增大到6595m/s后又降至5634m/s,而声衰减系数逐渐增大,变化约0.19dB/mm;对信号频谱分析发现,表面回波与一次底波的主频差值、主频幅值差值及表观积分反射系数均逐渐增大,这主要是由微观组织和晶体取向差异造成的。

Anisotropic acoustic properties of directionally solidified nickel-based superalloy DZ444

Directionally solidified nickel-based superalloy DZ444 specimens with different directions were selected.The crystal orientation and microstructure were characterized by electron back-scattered diffraction technique and so on.The longitudinal wave velocity and attenuation coefficient were analyzed by ultrasonic pulse-echo technique.Results show that the above two acoustic properties are anisotropic.With the included angleφbetween the normal direction of the sheet plane and the solidified direction increases from 0°to 45°to 90°,the longitudinal wave velocity increases from 5533m/s to 6595m/s and then decreases to 5634m/s,while the attenuation coefficient shows a monotonic increment of 0.19dB/mm.Further spectrum analysis shows that the main frequency shift,amplitude shift and apparent integral reflection coefficient of the surface echo and the bottom echo present a similar trend with the attenuation coefficient.This is mainly resulted by the difference of microstructure and crystal orientation.