Quasicrystals (QCs) possess rotational symmetries forbidden in the conventional crystallography and lack translational symmetries. Their atoms are arranged in an ordered but non-periodic way. Transmission electron microscopy (TEM) was the right tool to discover such exotic materials and has always been a main technique in their studies since then. It provides the morphological and crystallographic information and images of real atomic arrangements of QCs. In this review, we summarized the achievements of the study of QCs using TEM, providing intriguing structural details of QCs unveiled by TEM analyses. The main findings on the symmetry, local atomic arrangement and chemical order of QCs are illustrated.

Poor mechanical properties of copper (Cu) hinder its applications as structural materials. Developing bioinspired-laminated structure is among the most promising strategies for obtaining modern structural materials with excellent combination mechanical properties. To explore the possibility of enhancing mechanical properties of Cu, herein, we fabricated boron nitride nanosheets/copper (BNNSs/Cu) composites with a bioinspired laminated structure, achieved by ball milling and spark plasma sintering (SPS). Their mechanical properties were investigated. The results indicate that their tensile strength and toughness are both larger than those of pure Cu: the addition of 0.3 vol% of BNNSs improves the tensile strength from 187 MPa to 216 MPa and the elongation from 41% to 56%, respectively. The enhancement of ductility is due to the unique lamellar distribution of BNNSs in composites, which resulted in retarding cracks propagation; the strengthening effect of BNNSs is determined by the moderate interfacial bonding strength and possible agglomeration of BNNSs. Graphical Abstract

Copper matrix composites (CMCs) were prepared by blending Cu particles with boron nitride nanosheets (BNNSs) and then by consolidating the blended particles using spark plasma sintering (SPS). The relative density of the compacts was over 99%, and an intact interface was formed between Cu and the BNNSs. Within the range of the BNNS content studied, its introduction improved microhardness and wear resistance. With the introduction of 0.2 vol% BNNSs, the friction coefficient reduced from 0.15 to merely 0.07, and the wear resistance improved by over 100%. This makes the CMCs reinforced with BNNSs promising materials in applications such as bearings.

MoAlB ceramic coatings were prepared on a 316 steel surface by atmospheric plasma spraying with different arc power levels. The phase composition, microstructure and wear resistance of coatings against GCr15 and Si₃N₄ counterparts were studied. The MoAlB ceramic decomposed and was oxidized to form MoB and Al₂O₃ during plasma spraying. With the increase of the arc power, MoAlB experienced more decomposition, but the coatings became denser. When the arc power increased from 30 to 36 kW, the wear rates of coatings against GCr15 and Si₃N₄ balls reduced by 91% and 78%, respectively. The characterization of wear tracks shows that when against GCr15 counterparts, the main wear mechanisms are abrasive and adhesive wear, and when against Si₃N₄ counterparts, fatigue and abrasive wear are dominant. The refinement of wear resistance by increasing arc power can be attributed to the improvement of density and adhesive strength among splats.