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 T₂ 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.

We report for the first time the effect of temperature on the mechanical properties of (Ta_1/3Ti_1/3Zr_1/3)C carbide. Flexural strength and fracture toughness were investigated using the three-point bending technique in argon. Using commercially available carbide powders with an equimolar ratio and performing spark plasma consolidation at 1973°C, we obtained a bulk single-phase medium-entropy carbide ceramic with the lattice parameter a= 4.458 Å. The flexural strength and fracture toughness at room temperature reached on average 700 MPa and 3.2 MPa m^1/2, respectively. At 1800°C, local decomposition of the medium-entropy carbide took place as a structure with a local chemical gradient was observed after high-temperature tests, which increased fracture toughness by 30% (to 4.4 MPa m^1/2).

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 $[01\overline{1}](111)$ and $[11\overline{2}](111)$ . These two shear systems share the same glide plane but differ in loading direction. The $[11\overline{2}](111)$ 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 $[01\overline{1}](111)$ 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.

The room-temperature fracture toughness of ZrC-added Mo–Si–B alloys prepared using an arc-melting technique was investigated. The constituent phases of the heat-treated alloys were mainly molybdenum solid solution (Moss), Mo5SiB2 (T2), and ZrC, with a small amount of Mo2B in a few alloys. Four-point bending tests with a Chevron-notch were performed, and the average fracture-toughness values ranged from 12.4 to 20.3 MPa(m)1/2 depending on alloy composition. Here, the effects of the volume fractions of the constituent phases and the continuity of Moss on the fracture toughness are discussed. The fracture toughness improved with an increase in the volume fractions of the Moss and ZrC phases. Alloys with a higher Moss continuity exhibited higher fracture toughness, for example, the fracture toughness of 64.5Mo–3.2Si–6.5B–12.9Zr–12.9C (mol.%) was 19 MPa(m)1/2; the alloy contained a >95%-continuous Moss phase, even though it also contained 16 vol.% T2 and 23 vol.% ZrC.