Small size strength dependence on dislocation nucleation

From “Smaller is Stronger” to “Size‐Independent Strength Plateau”: Towards Measuring the Ideal Strength of Iron

“…During the collapse, the spherical nanoparticle evolved into a pancake-like plate (Figure 1c). This deformation character is significantly different from the compress of nanosphere Si particles, which only demonstrate gradually local surface damage near the contact point and no such catastrophical failure [30].…”

Crystal Engineering for Mechanical Strength at Nano-Scale Dimensions

“…An increase in mechanical toughness has been attributed to nano-scale silicon crystal thin films, nanospheres, and nanopillar type materials [61] mentioned at the beginning of the current report [2,4]. Valiev et al [22][23][24] have described a full range of strength and related material properties that are improved at nano-scale dimensions.…”

“…The measurements were compared to a tensile strength of 13.4 GPa reported for an iron "whisker". The method of testing relates to measurements reported for silicon nanospheres of comparable dimensions, also oxide film encased, and interpreted using a Hertzian nanoindentation basis [2]. Very importantly, an inverse dependence of strength on crystal size was found.…”

“…The current measurements cover on a log/log basis the size dependence of strength based on the following effective length scales: the average grain diameter for conventional 0.15 wt % carbon mild steel and other decarburized [9], IF (interstitial-free) iron [10], and ball-milled iron [11] materials; the lamellar spacing for eutectoid (pearlitic) iron-Fe 3 C (iron carbide) wire [12,13]; and, the subgrain boundary spacing for the topmost hypereutectoid wire material measurement [14], which strength level falls coincidentally at the previously estimated value of E/30. One might also note that the solid and dashed curves beginning from largest length scale follow a (1/ ) 1/2 dependence beginning from different levels of the σ 0 value specified in Equation (2). At its smallest size, the solid inverted-triangle and open-circle points at smallest size give indication of transition from a (1/ ) 1/2 dependence for Equation (2) to a (1/ ) dependence for Equation (1); see the drawn-in top-right-triangle of unit slope based on the length scale.…”

“…Previous indication had been given by Langford for a possible (1/ ) dependence for other pearlitic wire results [20]. Admittedly, however, the highest strength result obtained in [14] was obtained in a relatively more complicated situation and the subgrain spacing was taken in that report as the effective grain size to fit a raised H-P dependence in Equation (2). Under the condition of such severe drawing, the Fe 3 C carbide phase, that anyway is thermodynamically unstable, was found to dissolve in a carbon-supersaturated ferrite phase that then evolved into a final stabilized columnar, nano-scale, subgrain boundary structure with segregated carbon, thus producing the present suggested changeover to a (1/ ) dependence of the resultant strength.…”