Xiang Zan

Mechanical properties and microstructural change of W-Y2O3 alloy under helium irradiation.

A wet-chemical method combined with spark plasma sintering was used to prepare a W–Y2O3 alloy. High-temperature tensile tests and nano-indentation microhardness tests were used to characterize the mechanical properties of the alloy. After He-ion irradiation, fuzz and He bubbles were observed on the irradiated surface. The irradiation embrittlement was reflected by the crack indentations formed during the microhardness tests. A phase transformation from α-W to γ-W was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Polycrystallization and amorphization were also observed in the irradiation damage layer. The W materials tended to exhibit lattice distortion, amorphization, polycrystallization and phase transformation under He-ion irradiation. The transformation mechanism predicted by the atomic lattice model was consistent with the available experimental observations. These findings clarify the mechanism of the structural transition of W under ion irradiation and provide a clue for identifying materials with greater irradiation resistance.

Effects of zirconium element on the microstructure and deuterium retention of W–Zr/Sc2O3 composites

Dense W and W–Zr composites reinforced with Sc2O3 particles were produced through powder metallurgy and subsequent spark plasma sintering (SPS) at 1700 °C and 58 MPa. Results showed that the W–1vol.%Zr/2vol.%Sc2O3 composites exhibited optimal performance with the best relative density of up to 98.93% and high Vickers microhardness of approximately 583 Hv. The thermal conductivity of W–Zr/Sc2O3 composites decreased initially and then increased as the Zr content increased. The moderate Zr alloying element could combine well with Sc2O3 particles and W grains and form a solid solution. However, excess Zr element leads to agglomeration in the grain boundaries. W–1vol.%Zr/2vol.%Sc2O3 composite had a good deuterium irradiation resistance very closing to pure tungsten compared with the other Zr element contents of composites. Under 500 K, D2 retention and release of them were similar to those of commercial tungsten, even lower between 400 K to 450 K. Pre-irradiation with 5 keV-He+ ions to a fluence of 1 × 1021 He+/m2 resulted in an increase in deuterium retention (deuterium was implanted after He+ irradiation), thereby shifting the desorption peak to a high temperature from 550 K to 650 K for the W–1vol.%Zr/2vol.%Sc2O3 composite.

Microstructure and performance of rare earth element-strengthened plasma-facing tungsten material.

Pure W and W-(2%, 5%, 10%) Lu alloys were manufactured via mechanical alloying for 20 h and a spark plasma sintering process at 1,873 K for 2 min. The effects of Lu doping on the microstructure and performance of W were investigated using various techniques. For irradiation performance analysis, thermal desorption spectroscopy (TDS) measurements were performed from room temperature to 1,000 K via infrared irradiation with a heating rate of 1 K/s after implantations of He+ and D+ ions. TDS measurements were conducted to investigate D retention behavior. Microhardness was dramatically enhanced, and the density initially increased and then decreased with Lu content. The D retention performance followed the same trend as the density. Second-phase particles identified as Lu2O3 particles were completely distributed over the W grain boundaries and generated an effective grain refinement. Transgranular and intergranular fracture modes were observed on the fracture surface of the sintered W-Lu samples, indicating some improvement of strength and toughness. The amount and distribution of Lu substantially affected the properties of W. Among the investigated alloy compositions, W-5%Lu exhibited the best overall performance.

Numerical Simulation and Experimental Research of the Hydrostatic Extrusion Process of Pure Tungsten

A finite element model (FEM) of the hydrostatic extrusion (HE) process with pressure load model is established in this paper. On this basis, the hot hydrostatic extrusion process of sintered pure tungsten under different temperatures (T), extrusion ratios (R) and die angles (α) are simulated by introducing the Johnson-Cook constitutive relation for material flowing behavior. The simulation results show that there is a negative correlation between the extrusion pressure (P) and T, a positive correlation between P and lnR. And during the increase of the α value, the P value decreases first and then increases. The die angle corresponding to the minimum P is different under different extrusion ratio. Furthermore, a tendency of internal cracking during the process can be found when the R value is relatively small. Based on the simulation results, the experiment of hot hydrostatic extrusion of sintered pure tungsten is carried out. The microhardness, microstructure and mechanical properties of the tungsten before and after the process are investigated. The results show that after the hot hydrostatic extrusion, the grain size of the tungsten is subdivided, the hardness is improved obviously and the mechanical properties is remarkable.

Fabrication of W-Cu/Lu2O3 Composites with High Strength and Electrical Conductivity Prepared by Electroless Plating and Powder Metallurgy

W–Cu (0, 0.25, 0.75, 1.5, and 3 wt.%)/Lu2O3 composite materials were prepared through electroless plating with simplified pretreatment method and powder metallurgy. The phases and morphologies of the W–Cu/Lu2O3 composites were characterized by X-ray diffraction, field emission scanning electron microscopy and energy dispersive spectroscopy. The relative density, microhardness, electrical conductivity, and bending strength of the sintered samples were examined. The experimental results show that W–Cu composites with uniform structures can be obtained with pretreated W using the simplified method, followed by electroless Cu plating. The microstructure and properties of the composites were significantly affected by the addition of Lu2O3 nanoparticles, resulting in high electrical conductivity and strength. The electrical conductivity of W–Cu/1.5 wt.% Lu2O3 composites reached 63.3%, which is higher than the national standard value of 50.71%. The bending strength of W–Cu/1.5 wt. % Lu2O3 reached 1306.7 MPa, which is 65.41% higher than the national standard. These results may be attributed to the uniform distribution of refined particles with Lu2O3 content increased to 1.5 wt. %.

Chemical Synthesis and Oxide Dispersion Properties of Strengthened Tungsten via Spark Plasma Sintering

Highly uniform oxide dispersion-strengthened materials W–1 wt % Nd2O3 and W–1 wt % CeO2 were successfully fabricated via a novel wet chemical method followed by hydrogen reduction. The powders were consolidated by spark plasma sintering at 1700 °C to suppress grain growth. The samples were characterized by performing field emission scanning electron microscopy and transmission electron microscopy analyses, Vickers microhardness measurements, thermal conductivity, and tensile testing. The oxide particles were dispersed at the tungsten grain boundaries and within the grains. The thermal conductivity of the samples at room temperature exceeded 140 W/m·K. The tensile tests indicated that W–1 wt % CeO2 exhibited a ductile–brittle transition temperature between 500 °C and 550 °C, which was a lower range than that for W–1 wt % Nd2O3. Surface topography and Vickers microhardness analyses were conducted before and after irradiations with 50 eV He ions at a fluence of 1 × 1022 m−2 for 1 h in the large-powder material irradiation experiment system. The grain boundaries of the irradiated area became more evident than that of the unirradiated area for both samples. Irradiation hardening was recognized for the W–1 wt % Nd2O3 and W–1 wt % CeO2 samples.