Meso-scale dislocations and friction of shape-complementary soft interfaces

The interface between two surfaces patterned with complementary shapes such as arrays of ridge–channel structures or pillars accommodates relative misorientation and lattice mismatch by spontaneous production of dislocation arrays. Here, we show that the relative sliding of such an interface is accomplished by dislocation glide on the interfacial plane. An exception is the singular case where the lattices are perfectly matched across the sample dimension, in which case sliding is accompanied by motion of edge-nucleated defects. These are meso-scale analogues of molecular sliding friction mechanisms between crystalline interfaces. The dislocations, in addition to the long-range elastic energy associated with their Burgers vectors, also cause significant out-of-plane dilation, which props open the interface locally. For this reason, the sliding friction is strongly pressure dependent; it also depends on the relative orientation of the patterns. Sliding friction can be strongly enhanced compared with a control, showing that shape-complementary interfaces can be engineered for strongly enhanced pressure- and orientation-dependent frictional properties in soft solids.

Twinning in Czochralski-Grown 36°-RY LiTaO3 Single Crystals

The origin of twinning during the Czochralski (CZ) growth of 36°-RY lithium tantalate (LiTaO3) single crystals is examined, and it is shown that lineages composed of dislocation arrays act as an initiation site for twinning. Two types of lineages expand roughly along three different {12¯10} planes and two different {11¯00} planes. The former lineages and some latter lineages are composed of two types of mixed-dislocations with different Burgers vectors, while the other lineages are composed of only one type of edge-dislocation. All the dislocations have the Burgers vector of ⟨12¯10⟩ type with the compression side at the +Z side. Twin lamellae on {101¯2} are generated at a lineage during the CZ growth. We have hypothesized that dislocations in the lineage with b = 1/3⟨12¯10⟩ change their extension direction along a slip plane of {101¯2}, and they dissociate into pairs of partial dislocations with b = 1/6⟨22¯01⟩and 1/6⟨02¯21¯⟩ forming twin lamellae on {101¯2}.

Crystal Orientation Analysis on Stress Corrosion Cracking Facets in Austenitic Stainless Steels

Quasi-cleavage facets have been detected in the stress corrosion cracking fracture of type 304 and type 316 austenitic stainless steels under an environment containing chloride. Their morphology and crystal orientation were analyzed. In both steels the cold-worked material (CW) showed higher crack propagation rate than annealed one (ST), where the variation of the propagated crystal planes of the CW was higher than that of the ST, and the {111} facet was detected in the CW. Then the CW reveals higher possibilities to choose a low energy crack path rather than the ST. The rearrangement and multiply of {111} dislocation arrays may introduce the {111} transgranular cracking in the CW, and the combining duplex {111} slip operations may result in the {110} facet.

New insights into the role of dislocation engineering in N-type filled skutterudite CoSb3

The critical role of dislocation arrays, introduced by a liquid phase compaction process, on electron and phonon transport behavior is thoroughly elucidated.