For the compression of an elastic sphere with radius of R, Hertzian theory predicts the

relationship between applied load F and compression depth δ as [26] (2) where E * is the reduced Young’s modulus of the sphere. In this paper, E * is fitted from the load versus compression depth relation in the elastic regime by AZD1390 nmr Equation 2. For different twin spacing, the value of E * keeps almost the same as 287.4 GPa. It is seen that the elastic response of nanosphere under compression is determined mainly by the local elastic properties under indenter. Therefore, for a given loading direction, the change of twin spacing does not affect the overall elastic response of nanosphere. And the reduced modulus is much larger than the theoretical prediction 153 GPa of the bulk single crystal material in <111 > direction [27]. In nanowires and nanoparticles, improved

elastic modulus and yield stress have also been observed [5, 13]. However, the introduction of TBs plays an important role in plastic deformation. The first load-drop, as marked by arrows in Figure 2, indicates the appearance of initial yield. The local peak load corresponding to the first load-drop may be considered as the yield load. It is found that, when the twin spacing decreases from 5.09 to 1.25 nm, the yield load increases from 0.28 to 0.62 μN. In the further development of plasticity, the compression load of the twinned selleck chemicals llc nanosphere is significantly larger than that of the twin-free nanosphere for the same compression depth. The highly serrated load-compression response is indicative of dislocation activities inside the deformed nanospheres. www.selleck.co.jp/products/Gefitinib.html To estimate the influence of TBs qualitatively, the strain energy stored in nanospheres up to a given compression depth (δ/R = 53.3%) is also shown in Figure 3. It is found that, the strain energy of twinned nanospheres increases clearly as the twin spacing decreases, reaching its maximum at the twin spacing of 1.88 nm, and then declines with further decreasing

twin spacing. Such characteristics are similar to those in nanotwinned polycrystalline materials [4, 9]. Figure 3 Strain energy of the deformed nanosphere as a function of twin spacing up to δ / R  = 53.3%. In order to understand the underlying strengthening mechanisms, we examine the atomistic structures in plastic stage for several samples, as shown in Figure 4. For a twin-free nanosphere, the plastic deformation begins with the nucleation of partial click here dislocations from the contact edge, and the dislocations then glide on 111 slip planes. Without experiencing obstacles from TBs, most partial dislocations easily glide to the opposite surface and annihilate here, forming surface steps. This process exhausts nucleated dislocations in nanosphere and reduces dislocation density, corresponding to the dislocation starvation mechanism.