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

Abstract

The mechanical behavior of Ti‐6Al‐4V produced by additive manufacturing processes is assessed as based on a model derived from the Kocks–Mecking relationship. A constitutive parameter cb is derived from a linear Kocks–Mecking relationship for the microstructure that is characteristic of the work hardening behavior. The formulation for cb is determined by considering the plastic strain between the strengths at the proportional limit and the plastic instability. In this way, the model accommodates the variation in work hardening behavior observed when evaluating material as produced and tested along different orientations. The modeling approach is presented and evaluated for the case of Ti‐6Al‐4V additively manufactured materials as tested under quasi‐static uniaxial tension. It is found that different test specimen orientations, along with postbuild heat treatments, produce a change in the microstructure and plasticity behavior which can be accounted for in the corresponding change of the cb values.

On the Onset of Plasticity: Determination of Strength and Ductility

“…Here, strength can be denoted (Jankowski, 2023a) by the proportional limit σ p , or an offset yield strength σ d that marks the transition between Stage 3 and 4 work hardening. These predicted trends in work hardening, as shown in Figure 3, can now be assessed for a set of mechanical property data (Jankowski & Yee, 2023a;Jankowski, et al, 2020;Jankowski, 2021;Jankowski & Yee, 2023b) of additively manufactured Ti-6Al-4V. A relationship is explored between the softening coefficient c b3 and the yield strength σ y .…”

“…Despite these limitations, the approach of using a softening coefficient (c b i ) for the stages of work hardening provides a straightforward means to define the useful plasticity of a material as, e.g., it may change due to a consequence of synthesis method as well as post-processing conditions. This approach of determining c b ivalues has proven to be a successful path to differentiate the effect of process parameters in the evaluation of additively manufactured (AM) alloys such as 304L (Jankowski & Yee, 2023a), 316L (Jankowski et al, 2020), Ti-6Al-4V (Jankowski, 2021), and Al 6061 (Jankowski & Yee, 2023b). The analysis of the formalisms further developed (Jankowski, 2023a) to detail the inter-relationships between σ(ε) and Θ(σ) reveal insight to the onset of plastic deformation, as typically referred to as Stage 3 of the Kocks-Mecking Θ(σ) behavior.…”