Dislocation exhaustion and ultra-hardening of nanograined metals by phase transformation at grain boundaries

Abstract

The development of high-strength metals has driven the endeavor of pushing the limit of grain size (d) reduction according to the Hall-Petch law. But the continuous grain refinement is particularly challenging, raising also the problem of inverse Hall-Petch effect. Here, we show that the nanograined metals (NMs) with d of tens of nanometers could be strengthened to the level comparable to or even beyond that of the extremely-fine NMs (d ~ 5 nm) attributing to the dislocation exhaustion. We design the Fe-Ni NM with intergranular Ni enrichment. The results show triggering of structural transformation at grain boundaries (GBs) at low temperature, which consumes lattice dislocations significantly. Therefore, the plasticity in the dislocation-exhausted NMs is suggested to be dominated by the activation of GB dislocation sources, leading to the ultra-hardening effect. This approach demonstrates a new pathway to explore NMs with desired properties by tailoring phase transformations via GB physico-chemical engineering.

Morphology engineering induces the increase of FeP/CoP heterointerface density for efficient alkaline water splitting driven by interfacial dual active sites

“…5(b) and (c) demonstrate that FeP/CoP NMs exhibit the lowest Tafel slope (70.4 mV dec −1 for HER; 44.5 mV dec −1 for OER) among all as-obtained FeP/CoP samples, verifying that the HER process driven by FeP/CoP NMs obeys the Volmer–Heyrovsky kinetics mechanism, enabling efficient H 2 generation. 35–38 The Nyquist plot (in Fig. S10a, ESI†) shows that the charge transfer resistance ( R ct ) of FeP/CoP NMs is 138 Ω, which is 331 Ω and 1962 Ω lower than that of FeP/CoP MOs and FeP/CoP MRs, respectively, corroborating that the FeP/CoP NMs have the fastest electron transfer speed with the help of rich heterogeneous interfaces.…”

“…S10a, ESI †) shows that the charge transfer resistance (R ct ) of FeP/CoP NMs is 138 O, which is 331 O and 1962 O lower than that of FeP/CoP MOs and FeP/CoP MRs, respectively, corroborating that the FeP/CoP NMs have the fastest electron transfer speed with the help of rich heterogeneous interfaces. [38][39][40][41][42] And FeP/CoP NMs shown in Fig. S10b (ESI †) also own the lowest R ct value (42 O) for the OER, meaning that the FeP/CoP NMs show a superior OER dynamic mechanism.…”

Flexible-in-rigid polycrystalline titanium nanofibers: a toughening strategy from a macro-scale to a molecular-scale

“…On the other hand, decreasing the crystal size could decentralize the loaded tension on abundant nanocrystals and restrict the stress-induced crevice propagation along the grain boundaries, which is known as the Hall–Petch effect. 24 Both the TEM images (Fig. 2d and Fig.…”

Phase Engineering and Synchrotron-Based Study on Two-Dimensional Energy Nanomaterials

“…SR-XRD can also be used to discover the c-axis lattice thermal expansion caused by the Jahn−Teller effect of anatase titanium dioxide (TiO 2 ) at high temperatures, as seen by Foo et al 168 Additionally, SR-XRD data of Fe−Ni alloys during thermal treatment, as analyzed by Wu et al, have been used to trace the variation of dislocation density. 169 The modified Williamson− Hall method revealed that the density of dislocations was dramatically decreased from 1.2 × 10 15 m −2 to 4.1 × 10 13 m −2 after annealing at 300 °C for 1 h, resulting in a significant increase in material hardness.…”