Microstructure and orientation effects on microcompression-induced plasticity in nanoporous gold

Understanding the plastic deformation of nanoporous metals requires a detailed examination of their small-scale microstructural features. In this work, we present a computational study of micropillar compression in single crystal nanoporous gold (NPG) using crystal plasticity. This approach enables a systematic investigation of three key microstructural effects, including ligament size ( 50 ≤ l ≤ 400 nm ), solid fraction ( 0 . 2 ≤ φ ≤ 0 . 3 ), and initial crystal orientation ([001] and [ 1 ̄ 11 ] ), on the plastic response far beyond yielding. After validation against experimental data, the study reveals that, in line with the ’smaller is stronger’ trend, besides the yield strength, the strain hardening rate also increases as ligament size decreases. Moreover, the strain hardening rate follows a power-law scaling with solid fraction, similar to the yield strength. The analysis of two distinct crystal orientations presents findings contrasting with previous assumptions. While the yielding onset remains orientation-independent, as expected, an increase in the strain hardening rate emerges for the harder [ 1 ̄ 11 ] orientation with continued compression. An effect that becomes more pronounced with increasing solid fraction and decreasing ligament size. Under these conditions, harder orientations also amplify local stress heterogeneity. Notably, the stress distribution in NPG is nearly twice as wide as that observed in the single crystal bulk material ( φ = 1 . 0 ). Compared to the crystal plasticity approach, traditional isotropic plasticity predicts more uniform local stress fields.