Constitutive structural parameter c _b for the work‐hardening behavior of laser powder‐bed fusion, additively manufactured 316L stainless steel

Abstract

The mechanical behavior of additively manufactured (AM) 316L produced by laser powder-bed fusion (LPBF) process is now assessed using a workhardening model that is derivative from the Kocks-Mecking (K-M) relationship. A constitutive parameter c b for the microstructure is derived that is representative of the work-hardening behavior, as determined by the plastic strain ε p between the yield point σ y and ultimate strength σ u. The varied mechanical response that can be representative of AM metal behavior, as associated with surface irregularities and build direction, can be evaluated with this approach. Results are presented for the mechanical behavior of a 316L stainless steel as evaluated through uniaxial tensile test measurements.

A constitutive structural parameter c b for the work hardening behavior of additively manufactured Ti‐6Al‐4V

“…Here, the value of σ* is unique to the AM alloy under consideration. In addition, the result for Ti‐6Al‐4V AM is similar to the trend reported 9 for 316L wherein the c b value for the wrought alloy is found at the lower bound computed for the LPBF AM material where plasticity is at its greatest.…”

“…Consistent with the comments in the literature cited for data sampling, Table 1 data do not evidence large effects for build orientation or the machined versus as‐printed surface finish of LM samples. A similar result was found 9 for LPBF 316L AM tensile bars, that is, the effect of anisotropy diminished as the cross‐section thickness increased in value. These results are consistent with an analysis of thicker samples wherein the surface roughness effect is minimized.…”

“…31—a hot drawn Ti‐6Al‐4V wire is found 8 at a slightly lower σ* value of 0.65. In comparison, a different σ* value of 0.51 ± 0.06 was reported 9 for LPBF 316L AM samples. The trend is similar for Ti‐6Al‐4V and 316L, in that although the constituent plasticity behaviors are directly associated with the unique microstructure, the AM samples for an alloy system appear to rest on a constitutive c b versus ε p curve.…”

“…The tensile samples that have a 5‐mm diameter and 25‐mm gage length are tested with a load frame crosshead speed of 2.5·10 −2 mm·s −1 . In another SLM synthesis of Ti‐6Al‐4V, conditions for the Zone‐I melting of Ti‐6Al‐4V are considered 9 where the mechanical behavior of fully dense SLM Ti‐6Al‐4V is evaluated in tension (although the surface condition and specimen orientation are not reported for sample no. 20 that is listed in Table 1).…”

“…Several measurable parameters from tensile experiments are used to determine a constitutive formulation for the softening factor c b that include the plastic strain ε p from the yield point σ y to the strength σ u at the instability. The Morris Jr. model was later developed to assess the mechanical behavior of drawn wires from Ti alloys 8 across a wide range of strain rate and to characterize the tensile behavior 9 of 316L LPBF AM material. A survey of the literature on Ti‐6Al‐4V AM material is now undertaken to explore the utility of this model to distinguish between the tensile behaviors of SLM and EBM materials 10–17 .…”