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An optimal annealing process for enhancing the room-temperature fracture toughness of MoSiBTiC alloys was investigated in this study. The alloy with a composition of Mo–5Si–10B–10Ti–10C (at%) was subjected to three annealing conditions to control its microstructure. Quantitative microstructural analysis and mechanical testing revealed that the toughness of the MoSiBTiC alloys increased with the size of the Mo ss phase and decreased with its hardness. Annealing at 1800 °C for 24 h promoted microstructural coarsening but also led to increased solution hardening and reduced ductility of the Mo ss phase. In contrast, annealing at 1600 °C for 100 h improved the ductility of the Mo ss phase by reducing solution hardening, although the coarsening of the Mo ss phase was relatively slow. Based on these findings, a two-step annealing process that combines the benefits of lower-temperature and higher-temperature annealing conditions was proposed to effectively enhance the fracture toughness of MoSiBTiC alloys.

B1-type TiC compounds in equilibrium with metal solid solution phases can possess off-stoichiometry allowing them to exhibit different mechanical properties compared to those containing stoichiometric TiC, which typically decreases the toughness of the material. In this study, the fracture behavior of Mo/(Ti 0.96 ,Mo 0.04 )C 0.67 two-phase alloys was investigated. The load–displacement curves of the Mo/(Ti 0.96 ,Mo 0.04 )C 0.67 two-phase alloys, as measured by four-point bending tests, were similar regardless of the (Ti 0.96 ,Mo 0.04 )C 0.67 volume fraction , whereas the peak stress and fracture toughness increased with increasing volume fraction. These results suggest that (Ti 0.96 ,Mo 0.04 )C 0.67 acts as both a strengthening and toughening phase. Two factors are considered to contribute to its function as a toughening phase: the presence of the Mo phase within the (Ti 0.96 ,Mo 0.04 )C 0.67 grains, and the improvement in the deformability of (Ti,Mo)C x itself owing to its off-stoichiometry.

In this study, the ultrahigh-temperature tensile creep behaviour of a TiC-reinforced Mo-Si-B-based alloy was investigated in the temperature range of 1400–1600 °C at constant true stress. The tests were performed in a stress range of 100–300 MPa for 400 h under vacuum, and creep rupture data were rationalized with Larson-Miller and Monkman-Grant plots. Interestingly, the MoSiBTiC alloy displayed excellent creep strength with relatively reasonable creep parameters in the ultrahigh-temperature range: a rupture time of ~400 h at 1400 °C under 137 MPa with a stress exponent ( n ) of 3 and an apparent activation energy of creep ( Q app ) of 550 kJ/mol. The increasing rupture strains with decreasing stresses (up to 70%) and moderate strain-rate oscillations in the creep curves suggest that two mechanisms contribute to the creep: phase boundary sliding between the hard T 2 and (Ti,Mo)C phases and the Mo ss phase, and dynamic recovery and recrystallization in Mo ss , observed with orientation imaging scanning electron microscopy. The results presented here represent the first full analysis of creep for the MoSiBTiC alloy in an ultrahigh-temperature range. They indicate that the high-temperature mechanical properties of this material under vacuum are promising.

B1-type MX ceramics are composed of transition metals (M) and C, N, and/or O (X) occupying the M and X sites, respectively, and having M – X nearest neighbor (NN) bonds and M – M and X – X next nearest neighbor (NNN) bonds. Substitution of the elements and the formation of structural vacancies in B1-type ceramics change the numbers and strengths of the bonds, leading to novel properties. The change in elastic modulus of off-stoichiometric TiC in equilibrium with a Ti – Mo solid solution phase was experimentally investigated based on the rule of mixtures from the Voigt model. The experimentally obtained values agreed well with the results of density functional theory calculations. The bulk modulus ( K ) of TiC increased from 205.6 to 239.2 GPa as the fraction of Ti sites occupied by Mo increased from 0.11 to 0.33, whereas the Young’s modulus ( E ) and the shear modulus ( G ) remained nearly constant. On the other hand, all three elastic moduli decreased with increasing vacancy fraction at the C sites. These results suggest that the M–X bond strength should be the dominant factor in these moduli and the effect of M–M bond on K is greater than that of G and E .

The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750 °C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [ 01 1 ¯ ] ( 111 ) and [ 11 2 ¯ ] ( 111 ) . These two shear systems share the same glide plane but differ in loading direction. The [ 11 2 ¯ ] ( 111 ) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [ 01 1 ¯ ] ( 111 ) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior.

High-temperature compressive properties of two TiC-added Mo-Si-B alloys with nominal compositions of Mo-5Si-10B-7.5TiC (70Mo alloy) and Mo-6.7Si-13.3B-7.5TiC (65Mo alloy) (at.%) were investigated. The alloys were composed of four constituent phases: Mo solid solution (Mo ss ), Mo 5 SiB 2 , (Mo,Ti)C, and (Mo,Ti) 2 C. The primary phases of the 70Mo and 65Mo alloys were Mo ss and T 2 , respectively. The compressive deformability of the 65Mo alloy was significantly limited even at 1600°C because of the elongated, coarse primary T 2 phase, whereas the 70Mo alloy had good compressive deformability and a high strength in the test-temperature range of 1000–1600°C; the peak stresses were 1800 MPa at 1000°C, 1230 MPa at 1200°C, and 350 MPa at 1600°C. At and above 1200°C, the peak stress values were more than double those of Mo-6.7Si-7.9B, Ti-Zr-Mo, and Mo-Hf-C alloys. The plastic strain in the 70Mo alloy at temperatures lower than the ductile–brittle transition temperature of T 2 was generated by plastic deformation of not only Mo ss but also of (Mo,Ti)C and (Mo,Ti) 2 C. This work indicates that (Mo,Ti)C and (Mo,Ti) 2 C play an important role in determining the high-temperature strength and deformation properties of TiC-added Mo-Si-B alloys.

Previously, we isolated jacalin-related lectins termed PPL2, PPL3 (PPL3A, 3B and 3C) and PPL4 from the mantle secretory fluid of Pteria penguin (Mabe) pearl shell. They showed the sequence homology with the plant lectin family, jacalin-related β-prism fold lectins (JRLs). While PPL3s and PPL4 shared only 35%–50% homology to PPL2A, respectively, they exhibited unique carbohydrate binding properties based on the multiple glycan-binding profiling data sets from frontal affinity chromatography analysis. In this paper, we investigated biomineralization properties of these lectins and compared their biomineral functions. It was found that these lectins showed different effects on CaCO3 crystalization, respectively, although PPL3 and PPL2A showed similar carbohydrate binding specificities. PPL3 suppressed the crystal growth of CaCO3 calcite, while PPL2A increased the number of contact polycrystalline calcite composed of more than one crystal with various orientations. Furthermore, PPL4 alone showed no effect on CaCO3 crystalization; however, PPL4 regulated the size of crystals collaborated with N-acetyl-D-glucosamine and chitin oligomer, which are specific in recognizing carbohydrates for PPL4. These observations highlight the unique functions and molecular evolution of this lectin family involved in the mollusk shell formation.

TiC was added to Mo-Si-B alloys using a conventional Ar arc-melting technique, and the phase equilibria, microstructure evolution, and high-temperature strength at 1673 K (1400 °C) were investigated. The primary phase changed to Mo solid solution (Mo ss ), Mo 5 SiB 2 (T 2 ), or TiC depending on the composition. Following the primary phase solidification, a Mo ss  + TiC, Mo ss  + T 2 , or Mo ss  + T 2  + TiC + Mo 2 C eutectic reaction took place as the secondary solidification step. In some alloys, Mo ss  + T 2  + TiC and Mo ss  + T 2  + Mo 2 C eutectic reactions were present as higher-order solidification steps. After annealing at 2073 K (1800 °C) for 24 hours, Mo ss , T 2 , TiC, and Mo 2 C coexisted stably with microstructural coarsening. The coarsening rate was much faster in an alloy with no TiC dispersion, suggesting that TiC has a strong pinning effect on the grain boundary and interface migration. Compression tests conducted at 1673 K (1400 °C) revealed strength properties of almost all the alloys that were better than those of the Mo-Hf-C alloy (MHC). Alloy densities were 9 g/cm 3 or less, which is lighter than pure Mo and MHC (≥10 g/cm 3 ) and competitive with Ni-base superalloys. TiC-added Mo-Si-B alloys are promising candidates for ultrahigh-temperature materials beyond Ni-base superalloys.

We determined the primary structures of jacalin-related lectins termed PPL3s (PPL3A, 3B, and 3C, which are dimers consisting of sequence variants α + α, α + β, β + β, respectively) and PPL4, which is heterodimer consisting of α + β subunits, isolated from mantle secretory fluid of Pteria penguin (Mabe) pearl shell. Their carbohydrate-binding properties were analyzed, in addition to that of PPL2A, which was previously reported as a matrix protein. PPL3s and PPL4 shared only 35–50% homology to PPL2A, respectively; they exhibited significantly different carbohydrate-binding specificities based on the multiple glycan binding profiling data sets from frontal affinity chromatography analysis. The carbohydrate-binding specificity of PPL3s was similar to that of PPL2A, except only for Man3Fuc1Xyl1GlcNAc2 oligosaccharide, while PPL4 showed different carbohydrate-binding specificity compared with PPL2A and PPL3s. PPL2A and PPL3s mainly recognize agalactosylated- and galactosylated-type glycans. On the other hand, PPL4 binds to high-mannose-and hybrid-type N-linked glycans but not agalactosylated- and galactosylated-type glycans.

Nacreous layers of pearl oyster are one of the major functional biominerals. By participating in organic compound-crystal interactions, they assemble into consecutive mineral lamellae-like photonic crystals. Their biomineralization mechanisms are controlled by macromolecules; however, they are largely unknown. Here, we report two novel lectins termed PPL2A and PPL2B, which were isolated from the mantle and the secreted fluid of Pteria penguin oyster. PPL2A is a hetero-dimer composed of α and γ subunits, and PPL2B is a homo-dimer of β subunit, all of which surprisingly shared sequence homology with the jacalin-related plant lectin. On the basis of knockdown experiments at the larval stage, the identification of PPLs in the shell matrix, and in vitro CaCO3 crystallization analysis, we conclude that two novel jacalin-related lectins participate in the biomineralization of P. penguin nacre as matrix proteins. Furthermore, it was found that trehalose, which is specific recognizing carbohydrates for PPL2A and is abundant in the secreted fluid of P. penguin mantle, functions as a regulatory factor for biomineralization via PPL2A. These observations highlight the unique functions, diversity and molecular evolution of this lectin family involved in the mollusk shell formation.