Bellotti Aurelio, Kim Jin-Yeon, Bishop Joseph E, Jared Bradley H, Johnson Kyle, Susan Donald, Noell Philip J, Jacobs Laurence J
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
J Acoust Soc Am. 2021 Jan;149(1):158. doi: 10.1121/10.0002960.
This study employs nonlinear ultrasonic techniques to track microstructural changes in additively manufactured metals. The second harmonic generation technique based on the transmission of Rayleigh surface waves is used to measure the acoustic nonlinearity parameter, β. Stainless steel specimens are made through three procedures: traditional wrought manufacturing, laser-powder bed fusion, and laser engineered net shaping. The β parameter is measured through successive steps of an annealing heat treatment intended to decrease dislocation density. Dislocation density is known to be sensitive to manufacturing variables. In agreement with fundamental material models for the dislocation-acoustic nonlinearity relationship in the second harmonic generation, β drops in each specimen throughout the heat treatment before recrystallization. Geometrically necessary dislocations (GNDs) are measured from electron back-scatter diffraction as a quantitative indicator of dislocations; average GND density and β are found to have a statistical correlation coefficient of 0.852 showing the sensitivity of β to dislocations in additively manufactured metals. Moreover, β shows an excellent correlation with hardness, which is a measure of the macroscopic effect of dislocations.
本研究采用非线性超声技术来追踪增材制造金属中的微观结构变化。基于瑞利表面波传播的二次谐波产生技术用于测量声学非线性参数β。不锈钢试样通过三种工艺制成：传统锻造制造、激光粉末床熔融和激光工程化净成形。通过旨在降低位错密度的退火热处理的连续步骤来测量β参数。已知位错密度对制造变量敏感。与二次谐波产生中位错 - 声学非线性关系的基本材料模型一致，在再结晶之前的整个热处理过程中，每个试样中的β都会下降。从电子背散射衍射测量几何必要位错（GNDs）作为位错的定量指标；发现平均GND密度和β的统计相关系数为0.852，表明β对增材制造金属中位错的敏感性。此外，β与硬度具有极好的相关性，硬度是位错宏观效应的一种度量。
