Search

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]

• A multiscale model describing the evolution of helium bubbles is established based on the rate equations and the population balance equation. • The model can effectively describe the nucleation and evolution of helium bubbles. • The model contains bubble evolution mechanisms including "migration and coalescence (MC)" and "Ostwald ripening (OR)". • The model allows for independent statistics on the contribution of MC and OR, as well as an explanation of their coupling effects. A multiscale model describing the evolution of helium bubbles in the irradiated materials is established based on the rate equations and the population balance equation. The size distribution of the helium bubbles and the evolution law of the statistical average size and number density of the bubbles with time changing predicted by the model are in good agreement with the experimental statistics. The influence of annealing temperature, annealing time, irradiation energy, irradiation flux, and coarsening mechanisms on the evolution of helium bubbles are numerically simulated and discussed, taking FeCrAl alloy as the irradiated material. The results show that the bubble evolution is dominated by the Ostwald ripening mechanism under high temperature annealing conditions (≥ 1073 K), and the time dependence of the average size and density of helium bubbles is consistent with the existing theoretical results. And the number of shrinking helium bubbles caused by Ostwald ripening is effectively reduced by the bubble coalescence effect, leading to further growth of the proportion of large-sized helium bubbles. Consequently, a Gaussian bubble size distribution has been obtained modeling the coupling of the Ostwald ripening mechanism and the bubble coalescence mechanism. The generation rates of helium and vacancy in the material during irradiation, as well as their ratio, are significant factors that can affect the nucleation and evolution of helium bubbles. [ABSTRACT FROM AUTHOR]

Act as a candidate for heat pipe reactor core, molybdenum‑rhenium (47.5 wt%) alloy possesses excellent mechanical properties at a wide temperature range (from room temperature to recrystallized temperature). Compressions at varied temperatures and strain rates were given to study the microstructural evolutions of Mo-47.5Re alloy. Yield strength is similar in sample compressed at 400 °C with high strain rate (1.67 × 10−1 /s) and the one at room temperature with low strain rate (1.67 × 10−3 /s). However, deformation twins are only observed under room temperature and are absent as temperature rises to 400 °C. Thus. Twinning in Mo Re alloy is much sensitive to temperature. The microstructure of Mo-47.5Re alloy is quite stable even compression at 1200 °C. Although sub-grains increasing after 1200 °C compressions, no recrystallization was detected. In addition, microstructural evolutions of Mo-47.5Re are outstandingly dependent on strain rates at 400 °C, while are much less obviously at 800 °C and 1200 °C. No phase changes are detected, which verifies good structural stability in Mo-47.5Re. • Deformation twins in Mo-47.5Re are carefully characterized under room temperature compression. • Deformation twins in Mo-47.5Re are absent as compressive temperature rises. • The rate-dependent microstructural evolutions are outstanding at 400 °C, while are much less obvious at 1200 °C. [ABSTRACT FROM AUTHOR]

• The self-developed copper-coated FBG demonstrated high viability, repeatability, and stability across a wide temperature range from cryogenic (4.2 K) to elevated levels. • The temperature response of the copper-coated FBG was nearly independent of temperature below around 30 K, facilitating strain measurement without the need for temperature compensation. • The strain sensitivity calibration of the copper-coated FBG proved to be a feasible method, utilizing the thermal deformation of the tested object across a broad temperature range from 939 K to 4.2 K. Preliminary demonstrations show Fiber Bragg Grating (FBG) sensors effectively measure low temperatures, such as in Helium cryostats. These sensors, resistant to electromagnetic interference, offer significant potential for monitoring strain and temperature within superconducting coils and cryogenic structures due to their compact size. Standard FBG sensors are constrained by the thermal expansion coefficient of the polyimide coating, restricting their use as embedded sensors during the heating process of Nb 3 Sn superconducting coils. These sensors are currently unable to endure temperatures exceeding 400 °C, essential for fabricating Nb 3 Sn coils through the wind and react technique. This study explores enhancing the endurance of FBG sensors through magnetron sputtering coating process with copper (thickness of 20 μm), which has a thermal expansion coefficient similar to Nb 3 Sn coils. The results showed improved repeatability and survival for the copper-coated FBG in comparison to the standard polyimide-coated FBG from room temperature up to 939 K. Subsequently, the strain and temperature sensing capabilities of the FBG sensors with copper coating are evaluated using a separately developed controllable conduction cooling system, ranging from room temperature to 4.2 K. The findings in this paper demonstrate that the copper coating significantly enhances the durability of the FBG sensors under high temperatures. Additionally, the strain and temperature sensing characteristics of the sensors remain effective across a broad range from cryogenic to elevated temperatures. The homemade FBGs were independent of temperature below 30 K and responsible for the larger internal thermal strain of Nb 3 Sn magnets during its pre-heat treatment and operation. [ABSTRACT FROM AUTHOR]

In this study, TiO 2W addition improved the oxidation resistance of the Mo–Si–B composite at 1300 °C. The TiO 2 partially dissolved in SiO 2 modified the network structure of the SiO 2 glass and improved its fluidity at the initial oxidation stage. This favored to a continuous scale cover on the surface of the Mo–Si–B composite rapidly. The residual TiO 2W promoted the formation of a passivated multilayer borosilicate scale at current temperature, which could impede the MoO 3 volatilisation and O diffusion at the stable oxidation stage. The SiC W addition, compared to the TiO 2W , especially could ensure the Mo–Si–B–SiC composite withstand a higher temperature such as 1400 °C. Its oxidation and the more intermetallics in the composite could increase the number of active sites of the SiO 2 glass, thereby supplying the borosilicate scale with a relatively sufficient Si element. Thus, the transient oxidation stage was minimised and the initial mass loss was reduced, which indicated a continuous borosilicate scale had formed quickly at the initial stage. Finally, the improved viscosity of the borosilicate due to a lower B/Si ratio, could obviously decreased the oxygen diffusion and enabled the formation of a protective borosilicate layer at or above 1400 °C. [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]