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]

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]

The hot compression behavior of sintered W-3Re-5HfC alloy was investigated using the Gleeble1500D thermo-mechanical simulator at deformation temperatures and strain rates from 1200 °C to 1500 °C and 0.001 s−1 to 1 s−1, respectively. The microstructural evolution and flow behavior were studied. The microstructural observations reveal that the original grains are initially squashed, and then refined, which can be attributed to the occurrence of dynamic recovery and continuous dynamic recrystallization. Moreover, the electron backscattered diffraction analysis demonstrates a typical fibrous texture at low temperatures and high strain rates, which gradually transforms into the plate-like texture with the increase of temperature and decrease of strain rate. Based on the experimental results, arrhenius constitutive equations and an artificial neural network (ANN) model were developed for the characterization and prediction of the high-temperature deformation behavior in the W-3Re-5HfC alloy. The results indicate that the ANN model is more efficient in predicting the hot compressive behavior of W-3Re-5HfC alloy than the constitutive equations. The correlation coefficient and average absolute relative error in constitutive equations are found to be 0.99299 and 4.09%, respectively, whereas the corresponding values in the ANN model are found to be 0.99892 and 0.99%. In order to meet the performance requirements of different high-temperature structure parts, thermal deformation of W-3Re-5HfC alloy is needed to obtain the required microstructure and mechanical properties. ANN model provide theoretical basis for reducing deformation defects, saving process design time and obtaining machining parts with excellent microstructure. • The hot deformation behavior be predicted by Arrhenius model and artificial neural network model. • Dynamic evolution of coarse grains can be controlled by DRV and DRX. • A typical fibrous texture at low temperature and high strain rate • Artificial neural network model has higher accuracy in predicting the hot deformation behavior. [ABSTRACT FROM AUTHOR]