Deformation-Controlled Design of Metallic Nanocomposites

Abstract

Achieving the theoretical strength of a metallic alloy material is a demanding task that usually requires utilizing one or more of the well-established routes: i. decreasing the grain size to stop or slow down the dislocation mobility, ii. adding external barriers to dislocation pathways, iii.altering the crystal structure, or iv. combining two of the previous discrete strategies, i.e., implementing crystal seeds into an amorphous matrix. Each of the outlined methods has clear limitations, hence further improvements are required. We present a unique approach that envelops all the different strength-building strategies together with a new phenomenonphase transition. We simulated the plastic deformation of a Zr-Nb nanolayered alloy using molecular dynamics and ab initio methods, and observed the transition of Zr from HCP to FCC, and then to BCC during compression. The alloy, which was prepared by magnetron sputtering, exhibited near-theoretical hardness (10.8 GPa) and the predicted transition of the Zr structure was confirmed. Therefore, we have identified a new route for improving the hardness of metallic alloys.

Phase Engineering of Nanostructural Metallic Materials: Classification, Structures, and Applications

“…The crystalline nanolayers interacted intensely in the confined layer-space below 10 nm, which might induce phase transformation and the formation of near-coherent interfaces. 12 8c). 153 The reported multiple-sandwiched architecture had a more coarsely grained austenitic interior and an SNDP-CC surface comprising alternating austenite and martensite nanolayers with thicknesses of 5−7 nm.…”

“…148−151 The distinct crystalline phases constituting the SNDP-CC alloys with different crystallographic structures or orientations facilitate phase-transformation-induced strengthening in the confined nanoscale space through the release of deformation energy. 12 Therefore, interfacial compatibility and phase stability play significant roles in the deformation behavior of SNDP-CC materials. Xin et al reported an SNDP-CC magnesium alloy obtained via ultrafast spinodal decomposition at a low temperature (Figure 8a).…”

“…Nanolamellar composites are common SNDP-CC materials owing to their easy preparation. The crystalline nanolayers interacted intensely in the confined layer-space below 10 nm, which might induce phase transformation and the formation of near-coherent interfaces . Yavas et al.…”

“…The third category of supra-nano-dual-phase materials is alloys comprising different crystalline phases with sizes below 10 nm. The interfacial mismatch between crystalline phases could have additional strengthening effects that suppress the softening phenomenon caused by GB migration, GB sliding, or grain rotation in the nanograined materials. − The distinct crystalline phases constituting the SNDP-CC alloys with different crystallographic structures or orientations facilitate phase-transformation-induced strengthening in the confined nanoscale space through the release of deformation energy . Therefore, interfacial compatibility and phase stability play significant roles in the deformation behavior of SNDP-CC materials.…”

“…The ultrafine structural units of supra-nano materials, which are expected to affect the short- and medium-range orders of the overall material, can be manipulated through phase engineering in a controllable manner. Many extraordinary properties have been achieved via the design of supra-nano structuring, such as in the cases of a supra-nano-dual-phase (SNDP) glass–crystal Mg-based alloy with a near theoretical strength (3300 MPa), a lamellar supra-nano-dual-phase Zr/Nb alloy with a near theoretical hardness (10.8 GPa), and highly active Al–Mn–Ru catalysts. , In this context, the supra-nano phase is defined as the nanophases with a size of less than 10 nm. The size of a supra-nano phase is comparable to that of the flow units of the amorphous phase, and the strengthening effects correlating to the strong suppression of shear localization are achieved through the fragmentation and rotation of these supra-nano particles in the front of shear bands .…”