Ultimate Strength of Metals

We present a theoretical model that predicts the peak strength of polycrystalline metals based on the activation energy (or stress) required to cause deformation via amorphization. Building on extensive earlier work, this model is based purely on materials properties, requires no adjustable parameters, and is shown to accurately predict the strength of four exemplar metals (fcc, bcc, and hcp, and an alloy). This framework reveals new routes for design of more complex high-strength materials systems, such as compositionally complex alloys, multiphase systems, nonmetals, and composite structures.

Figure 1

Reference average values of grain boundary energy from DFT [25] compared to predicted values from heat of fusion at zero kelvin.

Figure 2

Aggregate experimental ($x$) and simulation ($o$) data for exemplars of fcc (Cu) [9, 10, 13, 14], bcc (Ta) [13, 28, 29], and hcp (Zn) [13, 30] crystal structures, and an alloy (Ni-W) [26], the maximum shear strengths predicted using the amorphization model (red line), and corresponding Hall-Petch best fit (blue lines) from Cordero et al. [13] or from our fit to literature data (black line). Lines are solid or dashed to indicate regions where they are applicable (i.e., the mechanism with the lowest stress required to activate) or not applicable, respectively.

Figure 3

Comparison of predicted ($x$ axis) and measured ($y$ axis) maximum shear strength for several metals. On the left are the predictions from the amorphization model presented here, while on the right are predictions from a model of crystal shear. The corresponding equations used to calculate predicted strengths are shown at the lower right of each plot.