Use of ultrasound to identify microstructure-property relationships in 316 stainless steel fabricated with binder jet additive manufacturing

In the present study, stainless steel 316 L (SS316L) and stainless steel 316 infiltrated with bronze (SS316 +bronze) samples fabricated with binder jet additive manufacturing were characterized through ultrasonic testing, optical microscopy, and mechanical testing. Attenuation and wave speed values obtained from ultrasonic testing were connected to grain size and porosity, where attenuation was positively correlated, and wave speed was inversely correlated, with porosity. Wave speed also increased as grain size increased. The SS316L sample contained interconnected pores and larger grains near the center of the sample compared to isolated pores and smaller grains near the surfaces, leading to competing influences in the measured wave speed. Uniaxial tension testing of specimens machined from the SS316L and SS316 +bronze blocks showed lower tensile strength and ductility with increased porosity and grain size, which were indicated by the ultrasonic signals. Tensile strength and ductility were inversely correlated to attenuation and standard deviation of wave speed. This study provides a demonstration of the use of ultrasonic testing to detect relative microstructural and mechanical property variances in binder jetted metal alloys.