Search

Mo-12Si-8.5B alloy with layered Mo 2 TiAlC 2 (a new MAX phase) additions, in order to improve its fracture toughness, were prepared by hot pressing. The composition analysis combined with microstructure features revealed that after hot pressing sintering, the Mo 2 TiAlC 2 does not decompose but still maintains the layered structure and exhibits a good interface bonding with the matrix. The grain size of Mo-12Si-8.5B alloys was apparently refined by Mo 2 TiAlC 2. The mechanical properties suggested that the Mo 2 TiAlC 2 phase affects the hardness of Mo-12Si-8.5B alloy mainly through grain refinement. As the amount of Mo 2 TiAlC 2 increased, the compressive strength and flexure strength of alloys improved nonlinearly which is caused by the relatively low strength of Mo 2 TiAlC 2 and stress release due to its basal plane sliding, the enhanced strength was attributed to the particle strengthening and fine grain strengthening. The Mo 2 TiAlC 2 phase exhibits a remarkably toughening effect on Mo-12Si-8.5B alloy. The fracture toughness of Mo-12Si-8.5B-2%Mo 2 TiAlC 2 alloy increased by about 52% compared with the Mo 2 TiAlC 2 free alloy. Except for the fine-grain toughening caused by Mo 2 TiAlC 2 particles, the improvement of fracture toughness of Mo-12Si-8.5B alloy by Mo 2 TiAlC 2 is mainly caused by the crack deflection, the steps formed by Mo 2 TiAlC 2 fracture and basal plane (0001) sliding of Mo 2 TiAlC 2. • The layered Mo 2 TiAlC 2 MAX phase was firstly added to Mo-12Si-8.5B alloy. • Mo 2 TiAlC 2 shows a good interface bonding with matrix and refine the grain size. • Compressive and flexure strength improved nonlinearly with Mo 2 TiAlC 2 increasing. • The Mo 2 TiAlC 2 exhibits a remarkably toughening effect on Mo-12Si-8.5B alloy. [ABSTRACT FROM AUTHOR]

Nozzle materials always withstand ultra-high temperatures (above 2000 °C) in space propulsion and other fields, which results in complex physical-chemical phenomena under actual operating conditions. The ablation mechanism and microstructural evolution of W-3Re-xHfC alloys were investigated to simulate the actual service conditions. Results show an outstanding ablation resistance. The linear ablation rate of the W 3Re matrix is 6.67 μm/s, the W-3Re-0.5HfC, W-3Re-5HfC and W-3Re-10HfC alloys are 2.93 μm/s, 2.23 μm/s and 2.26 μm/s, respectively. The linear ablation rates of W-3Re-0.5HfC, W-3Re-5HfC, and W-3Re-10HfC alloys decreased by 66%, 67%, and 67% compared with the W 3Re matrix, respectively. Thermochemical oxidation of the W 3Re matrix and HfC was the primary ablation mechanism of W-3Re-xHfC alloys. This work contributes to the design and improving the ablation resistance of W Re alloy applications in extreme environments. • Adding HfC particles significantly improves the ablation properties of W- 3Re alloy. • The ablation distance is shortened or the ablation time is prolonged, the worse ablation resistance • HfC and HfO 2 particles have high melting points, which nail the matrix grains and improve improving ablation resistance. • Thermochemical oxidation of the W- 3Re matrix and HfC particles is the primary ablation mechanism. [ABSTRACT FROM AUTHOR]

• Helium ion-irradiation responses in Mo-Re alloys at room temperature were evaluated via micro-pillar compression. • Orientation-dependent irradiation-induced hardening is obvious in low Re Mo-Re alloys, while is weak on high Re alloys. • Irradiated pillars with [1 0 0] orientation all shows higher flow stresses than pillars with [1 1 0] orientation after yield. Helium ion-irradiation responses in molybdenum (Mo) and molybdenum-rhenium (Mo-Re) alloys at room temperature were evaluated via micro-pillar compression. Irradiation-induced hardening is closely dependent on orientation in Mo-Re alloys with low Re content, while is weak orientation-dependence on high Re alloys. Irradiated pillars with [1 0 0] orientation all shows higher flow stresses than pillars with [1 1 0] orientation after yield, which is distinguishing from pillars before irradiation that has been shown in our previous work. High density of dislocation loops and helium bubbles after irradiation at room temperature induces severe hardening in Mo. Voids / small loops induced by irradiation lead to less hardening in Mo-Re alloy than in Mo. No precipitation is observed in all samples, which may be attributed to low irradiated temperature and implantation energy. [ABSTRACT FROM AUTHOR]

Mo 42Re alloy, as a high-temperature structural and functional material, has broad application prospects in the nuclear industry. In this study, the hot deformation behavior of Mo 42Re alloy was systematically investigated using hot compression tests and electron backscatter diffraction (EBSD) techniques in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1. The results showed that the flow stress of Mo 42Re alloy exhibited a strong dependence on temperature and strain rate. The strain rate sensitivity index (m -value) was high under the conditions of 1350–1450 °C and 0.001 s−1. With increasing deformation temperature and decreasing strain rate, dynamic recrystallization (DRX) was significantly promoted, and the recrystallized volume fraction increased from 2.79% at 1200 °C/1 s−1 to 20.3% at 1500 °C/0.001 s−1. Meanwhile, the occurrence of and DRX effectively reduced the grain reference orientation deviation (GROD) gradients and kernel average misorientation (KAM) levels within the grains. This study revealed the mechanisms of microstructural evolution during hot deformation of Mo 42Re alloy, providing important guidance for optimizing its thermomechanical processing parameters. • The Mo 42Re alloy exhibits pronounced strain-rate sensitivity at 1350 -1450 ℃ and 0.001 s -1 strain rate. • Elevating the deformation temperature and lowering the strain rate significantly enhance DRX fraction. • Raising temperature and lowering the strain rate promote DRV and DRX, reducing GROD gradients and KAM levels. [ABSTRACT FROM AUTHOR]

W–3Re alloys reinforced with various HfC particles contents (0 wt%, 0.5 wt%, 1 wt%, 5 wt%, 10 wt%) were fabricated using spark plasma sintering (SPS) at 2050 °C for 10 min. Microstructure, Vickers hardness and high temperature compression properties of the sintered W-3Re- x HfC alloys were investigated. Spherical HfC nanoparticles and micron scale clusters are distributed at the grain boundaries of the W–Re matrix. These nanoscale HfC particles pin dislocations and grains boundary as well as refine grain, thus enhancing the strength of composites. Furthermore, the HfC-W interfaces are well bonded semi-coherently without apparent interfacial gaps. The high temperature strength and micro-hardness of sintered composites are significantly increased with an increase of HfC contents. The micro-hardness of W–3Re alloy was 659.4 HV when 10 wt % HfC was added, which is enhanced up to 92.5 % compared with matrix. Its compressive strength is 850 MPa, increased by ~286 % compared with that of W–Re matrix. Quantitative analysis indicates that the main strength mechanisms are grain refinement, Orowan strengthening and interfacial thermal mismatch strengthening, which are influenced significantly by the HfC contents. This study provides new insights into composites performance optimization, reinforcement designs and strengthening mechanisms of particles reinforced W matrix alloys. [ABSTRACT FROM AUTHOR]