Mechanical Characterization of Tungsten-Titanium-Lanthana alloy: Influence of Temperature and Atmosphere

The target is to evaluate the mechanical behavior of Ti and La2O3 dispersed W alloy, processed by HIP and compare it with a reference pure-W. Tests were performed in both oxidant (air) and inert (vacuum) atmosphere in a temperature range from -196 to 1200 °C

Thermal and mechanical properties of W/Cu composite materials for ITER heat sink applications

One of the main challenges in the development of a fusion power plant is the adequate selection of the materials that will withstand the extreme conditions of temperature, load and radiation. Among those issues, the control of the heat removal by the divertor is critical, hence the highest heat load inside the reactor will be found in it. For this purpose, one solution proposed is a novel optimized water-cooled monoblock divertor consisting of W as plasma facing material and W/Cu composites as the baseline heat sink material. The attraction of these metal matrix composites in fusion applications is twofold: the W matrix provides the necessary strength of the composite at high temperatures, while Cu provides the required high thermal conductivity for efficient heat removal in the cooling system. In this context, the goal of this study is the characterization of W-Cu composite materials produced by means of liquid Cu infiltration of open porous W preforms. In order to achieve it, a new experimental device was set up to test the composites under high vacuum atmosphere while in the temperature range between 273 K and 1073 K. Tensile and fracture tests in three point bending configuration have been conducted in this temperature range and atmosphere. Additionally, micromechanical and physical characterization was also performed by means of micro and nanoindentation and High Temperature X-Ray Diffraction respectively

Mechanical Characterization of Multicrystalline Silicon Substrates for Solar Cell Applications

The possibility of using more economical silicon feedstock, i.e. as support for epitaxial solar cells, is of interest when the cost reduction and the properties are attractive. We have investigated the mechanical behaviour of two blocks of upgraded metallurgical silicon, which is known to present high content of impurities even after being purified by the directional solidification process. These impurities are mainly metals like Al and silicon compounds. Thus, it is important to characterize their effect in order to improve cell performance and to ensure the survival of the wafers throughout the solar value chain. Microstructure and mechanical properties were studied by means of ring on ring and three point bending tests. Additionally, elastic modulus and fracture toughness were measured. These results showed that it is possible to obtain marked improvements in toughness when impurities act as microscopic internal crack arrestors. However, the same impurities can be initiators of damage due to residual thermal stresses introduced during the crystallization process

Mechanical characterization of multicrystalline silicon wafers

The possibility of using more economical silicon feedstock, i.e. as support for epitaxial solar cells, is of interest when the cost reduction and the properties are attractive. We have investigated the mechanical behavior of two blocks of upgraded metallurgical silicon, which is known to present high content of impurities even after being purified by the directional solidification process. The impurities are mainly metals like Al and silicon compounds. Thus, it is important to characterize their effect in order to improve cell performance and to ensure the survival of the wafers throughout the solar value chain. Microstructure and mechanical properties were studied by means of ring on ring and three point bending tests. Additionally, Young’s modulus, hardness and fracture toughness were measured. These results showed that it is possible to obtain marked improvements in toughness when impurities act as microscopic internal crack arrestors. However, the same impurities can be initiators of damage due to residual thermal stresses introduced during the crystallization process

How do Impurity Inclusions Influence the Mechanical Properties of Multicrystalline Silicon?

The purpose of this research is to characterise the mechanical properties of multicrystalline silicon for photovoltaic applications that was crystallised from silicon feedstock with a high content of several types of impurities. The mechanical strength, fracture toughness and elastic modulus were measured at different positions within a multicrystalline silicon block to quantify the effect of impurity segregation on these mechanical properties. The microstructure and fracture surfaces of the samples was exhaustively analysed with a scanning electron microscope in order to correlate the values of mechanical properties with material microstructure. Fracture stresses values were treated statistically via the Weibull statistics. The results of this research show that metals segregate to the top of the block, produce moderate microcracking and introduce high thermal stresses. Silicon oxide is produced at the bottom part of the silicon block, and its presence significantly reduces the mechanical strength and fracture toughness of multicrystalline silicon due to both thermal and elastic mismatch between silicon and the silicon oxide inclusions. Silicon carbide inclusions from the upper parts of the block increase the fracture toughness and elastic modulus of multicrystalline silicon. Additionally, the mechanical strength of multicrystalline silicon can increase when the radius of the silicon carbide inclusions is smaller than ~10 µm. The most damaging type of impurity inclusion for the multicrystalline silicon block studied in this work was amorphous silicon oxide. The oriented precipitation of silicon oxide at grain and twin boundaries eases the formation of radial cracks between inclusions and decreases significatively the mechanical strength of multicrystalline silicon. The second most influencing type of impurity inclusions were metals like aluminium and copper, that cause spontaneous microcracking in their surroundings after the crystallisation process, therefore reducing the mechanical response of multicrystalline silicon. Therefore, solar cell producers should pay attention to the content of metals and oxygen within the silicon feedstock in order to produce solar cells with reliable mechanical properties

Self-passivating W-Cr-Y alloys: characterization and testing

The use of self-passivating tungsten alloys for the first wall armor of future fusion reactors is advantageous concerning safety issues in comparison with pure tungsten. Bulk W-10Cr-0.5Y alloy manufactured by mechanical alloying followed by HIP resulted in a fully dense material with grain size around 100 nm and a dispersion of Y-rich oxide nanoparticles located at the grain boundaries. An improvement in flexural strength and fracture toughness was observed with respect to previous works. Oxidation tests under isothermal and accident-like conditions revealed a very promising oxidation behavior for the W-10Cr-0.5Y alloy. Thermo-shock tests at JUDITH-1 to simulate ELM-like loads resulted in a crack network at the surface with roughness values lower than those of a pure W reference material. An additional thermal treatment at 1550 °C improves slightly the oxidation and thermo-shock resistance of the alloy

Melt infiltrated Tungsten-Copper composites as advanced heat sink materials for plasma facing components of future nuclear fusion devices

The exhaust of power and particles is regarded as a major challenge in view of the design of a magnetic confinement nuclear fusion demonstration power plant (DEMO). In such a reactor, highly loaded plasma facing components (PFCs), like the divertor vertical targets, have to withstand both severe high heat ux loads and considerable neutron irradiation. Existing divertor target designs make use of monolithic tungsten (W) and copper (Cu) material grades that are combined in a PFC. Such an approach, however, bears engineering difficulties as W and Cu are materials with inherently different thermomechanical properties and their optimum operating temperature windows do not overlap. Against this background, W-Cu composite materials are promising candidates regarding the application to the heat sink of highly loaded PFCs. The present contribution summarises recent results regarding the manufacturing and characterisation progress of such W-Cu composite materials produced by means of liquid Cu melt infiltration of open porous W preforms. On the one hand, this includes composites manufactured by infiltrating powder metallurgically produced W skeletons. On the other hand, W-Cu composites based on textile technologically produced fibrous reinforcement preforms are discussed

Microstructural and mechanical characteristics of W-2Ti and W-1TiC processed by Hot Isostatic Pressing

It has been demonstrated that mechanical alloying and subsequent consolidation by hot isostatic pressing (HIP) is a successful route to produce dispersion strengthened W alloys with properties satisfying the design requirements of particular plasma facing components in the fusion reactor. However, the presence of the alloying element as a phase filling large interstices between W particles appears to reduce the mechanical properties of these alloys. In order to limit this phase separation induced by the HIP treatment and the detrimental effects on the mechanical properties, the enhancement of the mechanical alloying process, and the effect of a postconsolidation heat treatment in an reducing atmosphere, have been investigated

Influence of high aluminium content on the mechanical properties of directionally solidified multicrystalline silicon

The purpose of this research is the mechanical characterisation of multicrystalline silicon crystallised from silicon feedstock with a high content of aluminium for photovoltaic applications. The mechanical strength, fracture toughness and elastic modulus were measured at different positions within the multicrystalline silicon block to quantify the impact of the segregation of impurities on these mechanical properties. Aluminium segregated to the top of the block and caused extensive micro-cracking of the silicon matrix due to the thermal mismatch between silicon and the aluminium inclusions. Silicon nitride inclusions reduced the fracture toughness and caused failure by radial cracking in its surroundings due to its thermal mismatch with silicon. However, silicon carbide increased the fracture toughness and elastic modulus of silicon

On the thermal stability of the nanostructured tungsten coatings

Tungsten is a candidate to be used as plasma facing materials in future fusion nuclear reactors. There, the material has to withstand large radiation fluxes and thermal loads. Nowadays, nanostructured tungsten (NW) seems to exhibit a better radiation-resistance than the coarse grained. However, the thermal stability of NW is still an open question. On these bases, the thermal stability of NW coatings is studied in the temperature range from 1000 to 1473 K. For this purpose, Samples were isothermally annealed in vacuum at temperatures from 298 to 1473 K. The morphological and microstructural properties of the samples were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-Ray diffraction (XRD), respectively. For T 100 K, nanostructures start to grow in a bimodal fashion with activation energy of 0259 eV, reaching a submicron-sized threshold at T approximate to 1473 K