► Diffusion bonding experiment between W and EUROFER97 using V interlayer. ► Investigations of the microstructure of the bonded materials especially at bond interfaces. ► Influence of intermetallic ...phases formed between EUROFER97 and V on the local hardness. ► Investigations of the mechanical properties of bonded specimens including tensile and Charpy impact tests.
Diffusion bonding is selected to join W to EUROFER97 for the manufacturing of some components in the fusion technology. A direct bonding does not seem feasible due to the high interfacial residual stress induced by the large mismatch of the coefficient of thermal expansions of both materials to be bonded. To reduce the residual stress, a V plate with a thickness of 1mm was introduced as an interlayer. The diffusion bonding was conducted at 1050°C for 1h. The uniaxial applied compression stress was calculated considering the 5% allowable creep deformation on the EUROFER97’s side. Investigations on bonded specimens showed defect free interfaces. Microstructure alterations were detected just at the EUROFER97/V interface. A very hard layer assumed to be a σ phase with a thickness of about 4μm was found on the EUROFER97’s side along the bond interface. A 6μm carbide layer containing V2C with also a high hardness value was identified on the V interlayer’s side. The impact toughness of the bonded specimens was low, however comparable to that of tungsten especially if the specimens were tested at RT. Tensile test at 550°C showed a relatively high tensile strength of bonded specimens, which achieved about 50% of the tensile strength of EUROFER97.
► Thermal stability of microstructures and its influences on mechanical properties. ► Investigations of inelastic behaviors of Hastelloy C-22 at elevated temperatures. ► Optimization of diffusion ...bonding parameters using a diffusion bonding model. ► Influences of surface impurities on the diffusion bonding quality. ► Verification of the optimized bonding parameters through bonding experiments.
The paper presents an optimization of diffusion bonding processes of Hastelloy C-22 based on the coupling of experiments and model simulations for manufacturing of micro heat exchangers for chemical applications. A systematic work is begun with experimental investigations of the influences of the bonding temperature on microstructures and mechanical properties of the material to be bonded. Based on these, the optimal bonding temperature is determined. To predict the remaining bonding parameters, a diffusion bonding model is used. The mechanical properties used as input parameters are provided by tensile and creep tests. The experimental investigations and model calculations yielded an optimized parameter set of 1050°C, 26MPa and 3.6h for a given surface roughness. This is verified by diffusion bonding using sheet material for various compression stresses, bonding durations and surface roughness. Bonding with this parameter set is successfully conducted, which in turn resulted in a sound bonding seam. The tensile strength was comparable to that of the base material and the toughness was higher than 50% of that of the base material.
Due to its advantages, tungsten is selected as armor and structural material for use in future fusion power plants. To apply tungsten as structural material, a joint to EUROFER97 is foreseen in ...current divertor design for which the diffusion bonding is considered in this work. The joining must have acceptable strength and ductility without significant change in microstructures. So far, numerous diffusion bonding experiments without and with post bonding heat treatment (PBHT) are performed at 1050°C for various bonding duration. For the bonding processes without PBHT, the bonding seams obtained are defect free and have a very high tensile strength. However they are brittle due to a thin layer of FeW intermetallic phase and metal carbides. For the bonding processes with PBHT, the bonding specimens fail at the bonding seam.
Vacuum-soaked biomass gasification is a method being developed to replace fossil fuels in a safe, simple, and reliable manner. The biomass gasification process demands high temperatures in the region ...of 800–1000 °C, yet even when applying vacuum pressure and soaking the biomass, the experimental results of the gasification temperature can be maintained properly. Cyclone and heat exchanger system, the reactor's syngas exit temperature, which is typically 600 °C, and may be lowered to under 50 °C. The heat exchanger's temperature profile indicates that 8 m are the most practical/ideal length. The heat exchanger's effectiveness is almost perfect (0.99) and higher than in earlier experiments (0.43–0.55). The use of an open-water jacket improves the performance of the heat exchanger by lowering the LMTD by 33.60% and lowering the heat transfer rate by 24.55%. Open-water life jackets do not significantly improve effectiveness.
Solid-state diffusion bonding is a selected joining technology to bond divertor components consisting of tungsten and EUROFER97 for application in fusion power plants. Due to the large mismatch in ...their coefficient of thermal expansions, which leads to serious thermally induced residual stresses after bonding, a thin vanadium plate is introduced as an interlayer. However, the diffusion of carbon originated from EUROFER97 in the vanadium interlayer during the bonding process can form a vanadium carbide layer, which has detrimental influences on the mechanical properties of the joint.
For optimal bonding results, the thickness of this layer and the residual stresses has to be decreased sufficiently without a significant reduction of material transport especially at the vanadium/tungsten interface, which can be achieved by varying the diffusion bonding temperature and duration. The investigation results show that at a sufficiently low bonding temperature of 700°C and a bonding duration of 4h, the joint reaches a reasonable high ductility and toughness especially at elevated test temperature of 550°C with elongation to fracture of 20% and mean absorbed Charpy impact energy of 2J (using miniaturized Charpy impact specimens). The strength of the bonded materials is about 332MPa at RT and 291MPa at 550°C. Furthermore, a low bonding temperature of 700°C can also help to avoid the grain coarsening and the alteration of the grain structure especially of the EUROFER97 close to the bond interface.
Earlier basic investigations revealed that diffusion bonding between tungsten and RAFM-steel at a relalively low temperature using a thin low-activation vanadium interlayer having a CTE between that ...of the parent materials can significantly reduce the residual stresses and produce defect-free bond interfaces. The joint has a high strength as well as sufficient ductility and toughness especially at the test temperature of about 550 degreesC. To apply this knowledge in fusion power plants, particularly in divertors, an acceptable lifetime of such structural joints is required, since they are exposed to high thermomechanical cyclic loading. To simulate the possible operational conditions of a He-cooled divertor, diffusion-bonded specimens are loaded by thermal cycling in a temperature range between 350 degreesC and 500 degreesC and a constant tensile stress based on the calculation of the internal pressure of the divertor thimble. The aim of this experimental work is to check the resistance of the diffusion-bonded W/EUROFER97 against ratcheting during thermomechanical loading and analyze the evolution of microstructures of the joint especially along the bond interfaces.
The dual-coolant lead-lithium (DCLL) blanket concept, which is considered as a candidate for fusion power plants and possibly for a demonstration reactor (DEMO), is being investigated within the ...framework of the European Power Plant Physics and Technology (PPPT) study. One of major issues of the DCLL concept development is the design of the flow channel inserts (FCIs), which are essential for the reduction of magneto-hydrodynamic (MHD) pressure losses. Due to the tight schedule for the short-term PPPT DEMO, a low-temperature DCLL concept with a liquid metal outlet temperature below 500 °C has been proposed. This allows the use of a simpler type of FCI (taking into account the LM corrosion issues), e.g. Eurofer-Alumina-Eurofer sandwich FCI, instead of the SiCf/SiC version for high temperature case, the production thereof is challenging. This paper discusses the technological study on manufacturing of some FCI design variants and post-examination of the samples.
The design of fusion plasma-facing components is challenging, as their materials have to meet rigorous requirements in terms of low activation and high-temperature strength. At the same time, ...sufficient ductility is required even in the low-temperature range. Unfortunately, these properties are not found in conventional materials. To solve this problem, a hybrid material that combines the high strength of one material with the high ductility of the other material was developed. This paper presents the hybrid material, which consists of thin tungsten and vanadium layers. This hybrid material was produced by means of diffusion bonding at relatively low temperature in a vacuum chamber. Microstructural investigations and nanoindentation tests indicated no cracks, no delamination, and no brittle intermetallic phases along the bond interfaces. Investigations of the mechanical properties of the hybrid material by instrumented Charpy impact tests revealed a relatively low ductile-to-brittle transition temperature (DBTT) at 124°C (compared to the DBTT of polycrystalline tungsten of >441°C) with an absorbed Charpy impact energy of 4.53 J kleinst (KLST)-specimen. Additionally, the tested Charpy impact specimens were found to be not fractured thoroughly even at room temperature.
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