Flow Strength Measurements of Additively Manufactured and Wrought 304L Stainless Steel up to 200 GPa Stresses

Magnetically-driven, shockless-compression experiments were performed to peak stresses approaching 200 GPa on both a direct energy deposition, additively manufactured (AM) and conventionally, wrought-processed 304L stainless steel to compare their thermodynamic and constitutive responses. Velocimetry measurements were used to infer the response of the 304L stainless steel samples during shockless-compression and release from peak stress. A self-consistent, inverse Lagrangian analysis technique was used to determine the isentrope of each sample to peak compression, while a wave profile analysis method was used to estimate the flow strength, shear modulus, and bulk modulus from the unloading from peak stress. The thermodynamic response of both stainless steels were similar and consistent with current equation of state (EOS) formulations up to 200 GPa. The flow strength, shear modulus, and bulk modulus measurements were also similar between stainless steel variants. The flow strength measurements in the AM material showed evidence of more sample-to-sample variability, particularly at pressures above 100 GPa. This was hypothesized to result from the large grain size imparted during printing. The flow strength and shear modulus measurements of both stainless steels deviated from current calibrations of the Steinberg-Guinan-Cochran and Preston-Tonks-Wallace constitutive models. The bulk modulus values extracted for both stainless steels deviated from those predicted by a Vinet EOS fit to the extracted isentropes, particularly at pressures above 100 GPa. This was found to result from the assumption of linearity of the bulk modulus with pressure in the Vinet model. The observed response of the 304L stainless steel shows a quadratic dependence of the bulk modulus with pressure, which is hypothesized to result from the formation of martensite during loading.