When subjected to an exterior stimulus, equivalent to, mechanical loading [1], thermal heating [2], [3], laser surprising [4], electron or ion beam irradiation [5], [6], a crystalline construction might endure twinning which impacts the bodily and chemical properties of the supplies [7], [8], [9], [10], [11], [12]. For instance, it was reported twinning has yielded enhanced mechanical power [13], [14], good ductility [15], higher fatigue resistance [1], [16], [17], glorious electrical conductivity [18], [19], nice radiation injury tolerance [20], [21], notable mild emission [22], and improved catalytic exercise [23]. Understanding the twinning mechanism is indispensable for the design of purposeful supplies.
Based on the classical pathways of twinning, the successive motion of adjoining densely packed atomic planes, e.g., {111} of a face-centered-cubic (FCC) crystal construction, results in formation of a twin embryo [24], [25]. In deformation twinning, numerous unconventional mechanisms are incessantly noticed, equivalent to random activation of partial dislocation, simultaneous activation of partial dislocations [26], or a shuffle mechanism [27]. In distinction to deformation twinning, transformation twinning induced by exterior stimuli aside from mechanical loading is just not properly studied. In our earlier work, using excessive spatiotemporal decision TEM, we discovered that the nucleation of twinning in FCC nanocrystals might be achieved by way of a swap motion-directed twinning mechanism, during which the atomic preparations of two adjoining atomic layers change [26]. With a stronger electron beam depth (8×103e–Å−2s−1), the nanocrystals can rework amongst extra numerous constructions [28], leading to numerous transformation pathways and constructions in twinning or de-twinning processes. Nonetheless, the underlying formation mechanism of advanced twinned constructions, equivalent to fivefold twinning, stays unclear.
On this work, we research FCC lead (Pb) nanoparticles as a mannequin system to discover the transformation twinning extending our earlier research of transformation twinning by way of swap movement. Possible because of the low soften temperature of Pb, it’s simpler to set off the transformation twinning by way of managed electron beam depth. To seize the quick transformation, we used a complicated aberration-corrected TEM geared up with a high-speed Thermo Fisher Scientific Ceta digicam at 40 fps. At a bigger electron present density (8×103 e–Å−2s−1), we instantly noticed for the primary time that single twins might be shaped not solely by way of swap movement but in addition by way of the destruction and restore of the crystal construction. Atomic deviations from equilibrium positions turn out to be intertwined with the tendency for crystallization, leading to pressure accumulation and elimination, which propels the propagation of dual boundaries. For the transformation from a bi-crystal twinning to fivefold twinning, the twinning is accompanied by the decomposition of grain boundaries, interface migration, and pressure elimination. Detwinning is the reverse technique of the three steps, however not in sequence. These discoveries deepen our comprehension of transformation twinning and lay a theoretical basis for comprehending and designing purposeful twinning supplies.
