Deformation mechanism of WC single crystals under nanoindentation: Effects of surface defects and orientation on pop-in and hysteresis

Toy nanoindentation model and incipient plasticity

A toy model of two dimensional nanoindentation in finite crystals is proposed. The crystal is described by periodized discrete elasticity whereas the indenter is a rigid strain field of triangular shape representing a hard knife-like indenter. Analysis of the model shows that there are a number of discontinuities in the load vs penetration depth plot which correspond to the creation of dislocation loops. The stress vs depth bifurcation diagram of the model reveals multistable stationary solutions that appear as the dislocation-free branch of solutions develops turning points for increasing str…

Nanoindentation-Induced Phase Transformation in Silicon

Nanoindentation-induced phase transformation in silicon has been studied. A series of nanoindentations were made with the sharp diamond Berkovich tip. During nanoindentations, maximum load ranged from 2000 $μ$N to 5000 $μ$N, with a 1000 $μ$N/sec loading rate. Slow unloading rate at 100$μ$N/sec was chosen to favor the formation of the crystalline end phases, high pressure phase (Si-III and Si-XII). Fast unloading rate at 1000$μ$N/sec was used to obtain amorphous phase. The phase transformation was examined by Raman spectroscopy and plan-view transmission electron microscopy (TEM). HPP have been…

Grain boundary effect on nanoindentation: A multiscale discrete dislocation dynamics model

Nanoindentation is a convenient method to investigate the mechanical properties of materials on small scales by utilizing low loads and small indentation depths. However, the effect of grain boundaries (GB) on the nanoindentation response remains unclear and needs to be studied by investigating in detail the interactions between dislocations and GBs during nanoindentation. In the present work, we employ a three-dimensional multiscale modeling framework, which couples three-dimensional discrete dislocation dynamics (DDD) with the Finite Element method (FEM) to investigate GB effects on the nano…

自离子辐照对晶体铁纳米压痕诱导塑性的影响：一项实验与计算联合研究

Self-ion irradiation effects on nanoindentation-induced plasticity of crystalline iron: A joint experimental and computational study

该研究结合纳米压痕、EBSD实验与MD、3D-DDD多尺度模拟，揭示5 MeV Fe2+自离子辐照下高纯铁的位错形核、塑性突跳与硬化机制。

Discrete Dislocation Dynamics Simulations of Nanoindentation with Pre-stress: Hardness and Statistics of Abrupt Plastic Events

The yield surface in crystal plasticity can be approached from various directions during mechanical loading. We consider the competition between nanoindentation and tensile loading towards plastic yielding. For this purpose, we develop a two-dimensional discrete dislocation model that is then utilized to investigate the hardness and pop-in event statistics during nanoindentation of single crystal under tensile pre-stress. Indentation is performed by using cylindrical (circular in 2D) indentation with varying radius and under both displacement and load control. Tensile in-plane stress, varying …

Bending, Nanoindentation and Plasticity Noise in FCC single and poly crystals

We present a high-throughput nanoindentation study of in-situ bending effects on incipient plastic deformation behavior of polycrystalline and single-crystalline pure aluminum and pure copper at ultra-nano depths (<200nm). We find that hardness displays a statistically inverse dependence on in-plane stress for indentation depths smaller than 10nm, and the dependence disappears for larger indentation depths. In addition, plastic noise in the nanoindentation force and displacement displays statistically robust noise features, independently of applied stresses. Our experimental results suggest th…