基于双模式超声换能器的选择性激光熔化316L制件弹性常数无损表征研究

Nondestructive characterization of elastic constants for 316L parts by selective laser melting based on dual-mode ultrasonic transducer

选择性激光熔化技术(SLM)可以快速成型任意结构的金属零件,但其制件的内部组织和材料性能与传统制件有着显著区别。基于双模式超声换能器对SLM 316L不锈钢制件的不同方向弹性常数及其分布进行表征研究。首先通过设计并制备高性能双模式超声换能器,搭建超声弹性常数分布测量系统。对SLM制备的316L不锈钢试样依次进行纵波和两个正交横波声速测量,获得同位置处不同方向弹性模量和泊松比。通过不同成型方向的声速测量,发现SLM制件在堆积z方向熔化层内呈现显著区别,表现出明显的各向异性。而y-z平面内弹性常数分布表征表明,杨氏模量E13大于E12,泊松比σ13小于σ12,且制件各熔化层弹性常数分布规律相似。此外,还讨论了加工过程中扫描速度和扫描间距等工艺参数对弹性参数的影响。选择性激光熔化制件弹性常数的有效无损表征将为增材制件内部质量控制和工艺改善提供技术基础。

Selective laser melting(SLM)can be used for rapid forming of metal parts with arbitrary structure,but the internal structure and material properties of the parts are significantly different from traditional parts.The elastic constants and their distribution in different directions of SLM 316 L stainless steel parts are characterized based on a dual-mode ultrasonic transducer.Firstly,a measurement system of ultrasonic elastic constant distribution is built by designing and fabricating a high-performance dual-mode ultrasonic transducer.The longitudinal wave and two orthogonal shear wave velocities of 316 L stainless steel samples prepared by SLM are measured successively,and the elastic modulus and Poisson′s ratio in different directions at the same position are obtained.Through the measurement of sound velocity in different forming directions,it is found that SLM parts show significant difference in the melted layer in the z direction of stacking,showing obvious anisotropy.The distribution of elastic constants in the y-z plane shows that Young′s modulus E13 is greater than E12,and Poisson′s ratioσ13 is less thanσ12,and each melted layer of the part has similar elastic constant distribution rule.In addition,the influences of main process parameters such as scanning speed and hatch space on the elastic constants are also discussed.The effective nondestructive characterization of elastic constants of selective laser melting parts will provide a technical basis for internal quality control and process improvement of additive manufacturing parts.