Bottom Region Research Articles

Differences in hardness and microstructure of laser cladding M2 coatings

The M2 coatings on medium carbon steel were prepared using a laser cladding process, and the microstructure and microhardness of the coatings were studied. The results show that the microhardness of the coating shows an increasing trend from the coating top to the bonding interface. The microhardness is 694 HV1 at the surface of the coating, which reaches 836 HV1 in the bottom regions of the coating. The wear rate of the coating is 0.32 mm3/N·m, which shows lower wear rate and better wear resistance. The coating microstructure is also different, and the coating consists of overlapping and non overlapping regions. The microstructure of overlapping region is a dendritic solidified crystalline structure encapsulated on α - Fe phase primary crystals with a dispersed carbide. The microstructure of non overlapping zone is composed of columnar crystal zone, basket crystal zone, and dendritic zone from the bottom of the coating to the surface, respectively, with the carbides distributed along the grain boundaries in the form of a network. Near the coating interface, needle-like high-carbon martensite forms in the coating. The carbides in the coating are relatively coarse.

The influence of plating with flat bars around technological cutouts on the stress state of a 37500 tdw chemical tanker

The purpose of this study is to determine the stress states of the plating around the technological cutouts of a 37500 tdw chemical tanker under normal operational conditions, taking into account the efficiency of operational optimization and structural strength increase. This study will assess the stress state in the double bottom region of the ship, which experiences the most significant external loads from hydrostatic water pressure and internal loads from cargo pressure.

Numerical Study of Bottom Shape Effect on the Mixing for Stirred Tank

Abstract In this work, computational fluid dynamics (CFD) was used to investigate the effect of the bottom shape on the flow field and mixing characteristics in an agitated vessel stirred by six-pitched blade turbine (PBT6). The simulation was based on the resolution of the Navier-Stokes equations using standard k-ε turbulence model. Hydrodynamic behavior of the stirred vessel with four types of bottom shapes was investigated, a flat bottom and three different semi-elliptical bottoms. The results show reasonably satisfactory agreement with the experimental data. The CFD simulation also showed that the semi-elliptical bottom shapes had a significant influence on the velocity profiles and on the turbulent kinetic energy distributions of the local flow generated at the bottom region of the vessel.

A Preliminary Numerical Study on the Performance of Cyclone Separators in Supercritical CO2 Solar Power Plants

A combined approach of computational fluid dynamics, the discrete phase model, and the wall erosion model was used to numerically investigate the hydrodynamics, separation efficiency, and erosion rate in cyclone separators for s-CO2 solar power plants. Moreover, the results were compared with those for air and CO2 as carrier phases. The experimental data from the literature were used to validate the numerical model, and it was observed that the simulated gas velocities and wall erosion rate accurately aligned with the experimental measurements. The numerical results reveal that s-CO2 had the largest tangential velocity compared to the other two media; its area-weighted axial velocity of upward flow was the lowest in the middle part of the cyclone body, and varied considerably in the bottom region of the conical section. The particles were all collected at the bottom surface of air and CO2, but the separation efficiency of s-CO2 was 81.51%, due to the poor distribution of the vortex and short circuit. Finally, the erosion rate distribution and averaged surface erosion rate were also analyzed for the three carrier phases.

Double-averaged turbulence statistics of wave current flow over rough bed with staggered arrangement of hemispherical blocks

Double-average turbulence characteristics of combined wave-current flow are studied over a rough bed comprising hemispheres arranged in a staggered pattern with different spacing (p/r = 4, 6, and 8; p = pitch length, r = height). The instantaneous velocity data was collected by Acoustic Doppler Velocimetry for the evaluation of double-average (DA) velocity, turbulence intensity, form-induced intensity, Reynolds stress, and form-induced stresses. The smallest DA velocity was obtained for p/r = 4 at the bottom region, signifying that p/r = 4 offered the maximum resistance to the flow among the tested cases. DA Reynolds stress is decreased for the entire flow depth due to superimposed waves. The advection of momentum-flux of normal stress in stream-wise and bottom-normal directions is increased at the outer layer and decreased at the near-bed region after wave-imposition. Maximum TKE production and diffusion are obtained just above the interfacial sub-layer and the middle of the form-induced sub-layer respectively. The turbulence structure is strongly anisotropic at the bottom region for p/r = 4 and near the outer layer, the tendency towards the return to isotropic state is dominant while with the increase in roughness spacing, a decrease in anisotropy is observed. Furthermore, an increase in wave-frequency decreased the tendency for the return to isotropy at the free surface.

Additive manufacturing of Stellite 6 alloy by laser-directed energy deposition: Engineering the crystallographic texture

Additive manufacturing (AM) of Stellite 6 alloy using laser-directed energy deposition (L-DED) technology was explored. The impact of argon and nitrogen as the shielding gas atmosphere and of the laser processing parameters on the microstructural characteristics of the L-DED manufactured single- and double-layers of the Stellite 6 alloy were studied. The microstructural characteristics and mechanical properties of the additively manufactured Stellite 6 alloy were investigated using electron backscatter diffraction (EBSD) analysis and indentation micro-hardness measurements. Also, the tribological behavior of the processed Stellite 6 were studied under different loading conditions. Based on the observed structural evolution including the phase transformations, optimized process parameters were established for the building of the main structural wall of the Stellite 6 alloy. Subsequently, the optimized set of processing parameters was analyzed in connection to the crystallographic textural majority of the manufactured alloy. The overall homogenous solidification microstructure of the constructed wall was characterized along different sections, i.e., bottom, middle, and top regions. At the bottom, the microstructure was dominated by gradients due to the solidification mechanism and the formation of a combined equiaxed/columnar dendritic structural morphology upon rapid cooling, resulting in a heterogeneous distribution of mechanical strength. The microstructure mainly consisted of columnar dendrites, generating a dominant textural component of 100<013> with a J-index of 1.62 in the matrix. After L-DED, the hardness of the alloy was found increased up to 565 HV, with a mean value of about 430 HV, depending on the geometrical location across the manufactured alloy wall. Also, a superior wear resistance of 4.91 × 10−5 mm3/Nm under a maximum load of 50 N was observed as a result of the enhanced mechanical properties. In fact, these findings substantiate an exciting approach to develop material properties with respect to processing design in which an advanced alloy is manufactured in a single step without particular post-processing.

Experimental investigations on the microstructural evolution and their influence on mechanical, tribological and corrosion performance of wire-arc additive manufactured SS316L structure

The study investigates the feasibility of emerging wire arc additive manufacturing technology to fabricate steel structures. The grain morphology and phase transformation of the WAAM-printed structure have been thoroughly examined and investigated their influence on the mechanical, tribological, and corrosion performance. The structure is characterized by fine equiaxed grains nearer to the cold substrate and coarse columnar grains along the upper regions. The average grain size in the top, middle, and bottom regions of the printed wall is 12.34 ± 5.81 µm, 10.27 ± 2.84 µm, and 4.33 ± 0.89 µm respectively. The higher temperature gradient in the bottom regions led to the ferrite-austenite solidification mode that switched toward the primary austenite solidification mode in the upper layers. The printed parts witness superior mechanical properties with an improved micro-hardness and tensile strength however reduced ductility compared to the conventionally produced steel. The longitudinal direction of the printed parts experienced slightly higher hardness than the transverse. The tribological performance in different regions is investigated under different loading conditions and discovered an improvement in the wear-resistant properties of the fabricated part to its wrought counterpart even at high load conditions. Moreover, comparative corrosion resistance properties of the WAAM and wrought steel were detected with a slightly higher corrosion rate along the upper region in a moderately saline environment with flowing and stagnant conditions. The study detects the dependence of the characteristics properties on the grain morphology and existing phases in different regions of the arc additive-manufactured steel wall.

Influence of tool plunge depth and multiple passes on the microstructure, texture evolution and hardness of age-hardenable aluminium 7075 alloy

In this study, the surface properties of AA7075 were modified through the solid-state friction stir processing technique using a hexagonal-shaped H13 pin. Single pass friction stir processing was conducted at two different shoulder plunge depths at constant tool rotation and linear speeds with the resulting cross-sections being examined using optical macroscopy. Six friction stir processing passes were then carried out intermittently at optimal shoulder plunge depth and the corresponding microstructural evolution along the nugget was investigated using advanced microstructural characterization techniques such as electron backscatter diffraction and high-resolution transmission electron microscopy. Bulk texture examination was conducted using the neutron diffraction method, while hardness measurements were taken using Vicker's hardness testing machine. Single pass friction stir processing conducted at a shoulder plunge depth of 0.25 mm produced defect-free material consolidation with a refined grain structure along the nugget. Minimum grain size averaging 3.78 μm was observed at the top, while slightly increased grain sizes were noticed at the middle and bottom regions of the nugget. After 6 friction stir processing passes, grain size was reduced significantly averaging 1.84 μm at the top, while size at the pin-driven zone exhibited an increasing trend due to heat input and strain rate variations. Both, single-pass and 6 pass specimens exhibited a weaker texture along the nugget due to randomness in grain orientation and the effect of particle-stimulated nucleation mechanism. In the single-pass specimen, hardness decreased along the nugget, with a maximum of 85.2 HV at the top, while 6-pass specimen exhibited an improved hardness of 133.5 HV due to the strengthening caused by grain refinement, precipitates and dislocations.

Direct numerical simulation for lid-driven cavity under various Reynolds numbers in fully staggered grid

Finite difference method in a fully staggered grid is applied to solve the incompressible Navier–Stokes equation with direct numerical simulations. Without a turbulent or transient model, lid-driven cavity simulations are conducted with various Reynolds numbers from 102 to 106. The fluid property is fixed, and a lid velocity is changed to set the Reynolds number condition. Time steps are adjusted to keep the consistency of Courant number conditions. Simulation results are compared with the experimental measurements for a Reynolds number of 104 condition, in which the result shows relatively larger values of non-dimensional root mean square (RMS) compared to the other Reynolds number conditions. Vertical and horizontal velocity components show comparably higher RMS distributions around a downstream eddy region and above a bottom surface region, respectively, when the Reynolds number is 104. Time-averaged and RMS distributions show reasonable agreement with the experimental results, and a velocity spectral analysis shows the Kolmogorov spectrum of −5/3 slope for all velocity components. Taylor–Görtler-like (TGL) vortices are observed clearly in the downstream jet region. When the Reynolds number increases, the size of the TGL vortical structure in the spanwise direction decreases and numerous small-scale vortices occur.

Research on Simulation of Coating Fusion and Solidification Process in Electro-Spark Deposition

As a surface-strengthening technology, electro-spark deposition (ESD) is widely used in the strengthening and repair of key components of high-end equipment. In this paper, a fusion and solidification model of ESD coating is established. The method of heat–fluid–solid interaction is adopted to simulate the material’s flow and fusion process in the droplet dropping into the molten pool. The distribution law of the coating-matrix material inside the coating was studied. Through the heat transfer between the molten material and the matrix material, the condensation and solidification process of the coating-matrix material is simulated, the temperature change in the coating area during the solidification process is analyzed, and the solidification law of the molten material is studied. The results show that the deposition time reaches 80 μs, and the content of electrode material at the bottom of the molten pool reaches 4.5%. The content of electrode material in the upper region of the material gushing out of the molten pool is higher than that in the bottom region. The material outside the molten pool solidifies first, and the molten material in the molten pool gradually solidifies from the bottom up; the shape of the solidification interface is similar to the boundary of the molten pool. Through the single-point deposition experiment of electro-spark deposition, the surface morphology of the deposition point was observed. The depth of the concave part of the contour can reach 16 μm. The difference between the two contour curves in the horizontal direction is not much; the error of the diameter is about 4%. The element distribution of the surface and the section of the deposition point are analyzed. The diffusion distance in the depth direction of the coating is about 4μm, and the transverse diffusion distance inside the coating is 364 μm. The error is 7.6% compared with the experimental results. The cross-section structure of the deposition point was observed, and the error between the experimental results and the simulation results in diameter is about 11%. It was found that the material distribution in the sedimentary area is basically consistent with the simulation results, and the simulation results are verified from the side.

Parameter design of the compressed air energy storage salt cavern in highly impure rock salt formations

Compressed air energy storage (CAES) salt caverns are suitable for large-scale and long-time storage of compressed air in support of electrical energy production and are an important component for realizing renewable energy systems. In this paper, the use of sediment voids in highly impure rock salt formations for CAES is proposed. The interaction between the insoluble sediment and the cavern wall is analyzed. A geomechanical model is established to optimize the design parameters of CAES salt caverns. The simulation results show that as the cavern height increases, the displacement decreases in the bottom sediment region and increases in the waist. As the internal air pressure increases, the safety factor increases, while the volume shrinkage and displacement decrease. The plastic zone and the strength utilization rate decrease, and the safety factor increases with increasing pillar width. Based on the above results, the long cylindrical cavern is recommended to have a height in the range of 260–280 m and a diameter of 80 m. The minimum internal air pressure is 10–12 MPa, and the maximum internal air pressure is 16–18 MPa. The pillar widths between caverns are approximately 2.0–2.5 times the cavern diameter. In this study, for a single cavern with a diameter of 80 m and a height of 260–280 m, the upper free volume (excluding sediment) and the lower sediment filled volume of a single cavern are approximately 4.6–5.0 × 105 m3 and 7.2–7.8 × 105 m3, respectively. The sediment voids used for storing compressed air increase by at least approximately 3.6 × 105 m3, which is approximately 0.8 times the upper free cavern volume. The results show that the CAES salt cavern in highly impure rock salt is feasible and has great potential.

Experimental analyses of solidification phenomena in an ice-based thermal energy storage system

Latent thermal energy storage devices can efficiently store surplus thermal energy during off-peak hours. The system's phase change material (PCM) improves energy storage capacity and isothermal properties. Most PCMs have weak thermal conductivity, which hampers heat transfer. Thus, the present analysis involves an insight into the heat transfer characteristics and thermal performance of a vertical tube-in-tank cold storage system. The objective of this investigation is to gain a better understanding of the significance of buoyancy-driven convection within the side bulk region during the discharging of water as PCM in the heat exchanger. A series of experiments are conducted to investigate the effect of varying the initial bulk temperature on the rate of PCM solidification. The effects of three distinct initial bulk temperatures which are 20 °C, 15 °C, and 5 °C on the solidified mass fraction, thermal performance, and heat transfer rate at various radial and axial locations in PCM are examined. It is seen that PCM experienced a varying cooling rate with varying axial height and is found to be the highest in the bottom region. PCM temperature decreases from top to bottom under the cases of 20 °C and 15 °C, respectively. In contrast, a narrow-ranged thermocline layer is observed under 5 °C bulk temperature, making uniform temperature distribution within the bulk. The influence of bulk natural convection prevails in the later stages of the discharging process under 5 °C bulk, whereas it predominantly exists during the initial stages of solidification under bulk temperatures of 20 °C and 15 °C.

Numerical Simulations and an Updated Parameterization of the Breaking Internal Solitary Wave Over the Continental Shelf

AbstractThe breaking of internal solitary waves (ISWs) over slope‐shelf topography induces energy dissipation and enhances mixing. In this work, high‐resolution, laboratory‐scale simulations are employed to investigate the instability mechanisms and dissipation of ISWs. We find that the increasing nonhydrostatic pressure during deformation contributes to an adverse pressure gradient, which induces plunging flow for overturning. Shear instability and convective instabilities trigger wave breaking. Wave‐induced vortexes induce strong shearing and enhance the dissipation of energy by 1–2 orders of magnitude larger than that which occurs under stable conditions. Furthermore, based on laboratory results, we evaluate two commonly used parameterizations (Pacanowski &amp; Philander, 1981, https://doi.org/10.1175/1520-0485(1981)011&lt;1443:povmin&gt;2.0.co;2, i.e., PP81; Klymak &amp; Legg, 2010, https://doi.org/10.1016/j.ocemod.2010.02.005, i.e., KL10) in coarser‐resolution global ocean models by modifying the horizontal resolution from 100 grids every wavelength to approximately 30. The results show that PP81 and KL10 can both improve the estimation of the energy loss, but can only depict strong shear within the pycnocline and bottom boundary regions, respectively. Finally, an updated parameterization is presented that can effectively describe the strong shear in two regions during wave breaking. The flow field and dissipation are more consistent with the laboratory results using the new parameterization. This study improves the understanding of the mixing parameterizations in simulating the continuous processes of strong internal wave breaking.

Benincasa hispidas-inspired pore-gradient aerogel with integrated water and thermal management for highly efficient solar vapor generation and water purification

Engineering the pore structure of evaporator to effectively integrate water and thermal management is critical for efficient solar-driven interfacial vapor generation. Here, inspired by the unique structure of Benincasa hispidas, a bioinspired pore-gradient aerogel was fabricated for the first time. Experiments and numerical simulations reveal that the unique anisotropic porous structure of aerogel, which consists of small-pores at top region and large-pores at bottom region, enabling it to maximize the heat gains from the sunlight and localize the generated heat while provide adequate water supply concurrently. Under solar illumination (1 kW m−2), the fabricated aerogel can achieve a high evaporation rate of 2.49 kg m−2h−1, and the calculated energy efficiency is approximately 96.3 %, which is comparable to most of state-of-the-art evaporators. Additionally, with this aerogel employed, effective purification toward various undrinkable water can be achieved. This work derives from nature, providing us a design blueprint to integrate water and thermal management in a bulky material, and it is expected to advance one step further toward the design and practical application of high-performance solar evaporators.

CFD-DEM investigation of flow and heat transfer characteristics in a directly irradiated fluidized bed

The directly irradiated fluidized bed reactor has gained widespread attention due to its strong heat and mass transfer performance. However, there is still a lack of in-depth understanding of the gas–solid flow characteristics, heat transfer mechanisms, and flow pattern evolution in the fluidized bed. To address this, the computational fluid dynamics-discrete element method (CFD-DEM) was employed in this study to investigate the correlation between the flow pattern and the heat transfer path. The simulation results show that increasing the superficial gas velocity from the minimum fluidization velocity (umf) to 1.4umf induces a circulation pattern that significantly reduces the overheating phenomenon, resulting in a 40.52% decrease in the maximum particle temperature and a 74.59% decrease in the temperature standard deviation. The particle temperature increases in the top heat-collecting region, followed by thermal conduction and convection transferring the energy to low-temperature particles and fluid in the near-wall and bottom regions. As the superficial gas velocity increases, the proportion and frequency of particles entering the heat-collecting region increase, resulting in a more uniform temperature distribution within the bed. Taking into account factors such as heat transfer characteristics and fluidization energy consumption, a fluidization velocity of 1.6umf is recommended as the optimum operating condition for particles in this work, as it ensures a uniform temperature distribution within the bed and minimizes convective and radiative losses.

ORAL REHABILITATION IN A TOTAL EDENTULOUS PATIENT WITH INFLAMMATORY FIBROUS HYPERPLASIA: case report

Inflammatory fibrous hyperplasia or fissured epulis is a very common lesion in patients who use maladapted removable prostheses. It consists of a connective tissue overgrowth as a response to constant trauma in a specific area. Clinically, it is presented as an exophytic process or a well-defined elevation. It is generally, sessile-based and asymptomatic. Its consistency varies from firm to flaccid, with smooth surface or occasionally ulcerated, and its color is similar to the adjacent mucosa or erythematous. The most recommended treatment is surgical removal, however there are other methods such as cryotherapy, micro-abrasion and laser therapy. The aim of this work is to describe the stages of diagnosis and treatment, from the surgical technique for removing inflammatory fibrous hyperplasia to the patient's rehabilitation, with new prostheses. This is a case report of a 79-year-old female patient who attended the clinic at Faculdade Patos de Minas (FPM) reporting dissatisfaction with the loss of lip support and the aesthetics of her complete denture prosthetics. During the clinical examination, a nodular tissue growth was identified in the bottom region of the anterior maxillary vestibule’s sac. As a proposed treatment, an excisional biopsy was performed, confirming the diagnosis of inflammatory fibrous hyperplasia through histopathological analysis. After healing, new prostheses were produced, intending to meet the patient's requirements. The present study is expected to emphasize the importance of a thorough clinical examination, so that all changes in the patient are identified and, when necessary, perform a biopsy and histopathological analysis. In summary, it is essential to adjust or produce new prosthetic parts to prevent tissue trauma or cause negative consequences. The patient's postoperative period was uneventful, with favorable healing, and after the new prosthetic devices were put in place, function and aesthetics were restored.

Microstructure gradient formation in electron-beam melting powder-bed fusion of a gamma-prime Ni-based superalloy

Microstructure gradient is formed during the additive manufacturing of Ni-based superalloy Haynes® 282® via electron-beam melting powder-bed fusion (EB-PBF) process. The precipitation of secondary phases occurs owing to EB-PBF in-situ heat treatment as consequence of high temperature powder bed pre-heating and multiple melting and re-heating thermal cycles, which can be summarised as a carbide precipitation heat treatment at 1000–1025 °C/8 h, aging between 875 and 975 °C/30 h, followed by a slow cooling step. Relatively large precipitates formed inter- and intragranularly with M3B2 boride and gamma-prime (γ') have sizes of approximately 5 μm and 110 nm, respectively, at the bottom of the build. The size of the precipitates decreases along the build direction. In the top region, the precipitate sizes of boride and γ' are 1 μm and 50 nm, respectively. MC carbide with a size of <1 μm precipitated throughout the build. A good correlation is observed in terms of the γ' size to hardness with average values of 350 HV at the bottom and 400 HV at the top. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL.) values at the bottom and top regions are 1080 ± 40 MPa, 805 ± 25 MPa, and 20 ± 5%; and 1105 ± 20 MPa, 825 ± 15 MPa, and 25 ± 5%, respectively. Overall, EB-PBF Haynes® 282® exhibits higher UTS and YS but lower EL than those of the as-received wrought alloy (950 ± MPa, 650 ± 15 MPa, and 40 ± 5%, respectively).

Optimum process parameters of IN718 alloy fabricated by plasma arc additive manufacturing using Taguchi-based grey relational analysis

The process parameters of IN718 alloy fabricated by plasma arc additive manufacturing (PAAM) were evaluated by Taguchi-based grey relational analysis, and the microstructure and mechanical properties of the PAAM alloy were analyzed to verify the optimized process parameters. The results show that the influence of each process parameter on the dilution ratio and forming coefficient is consistent. Based on the results of Taguchi-based grey relational analysis, the optimized process parameters for PAAM IN718 alloy are plasma arc current 115 A, scanning rate 1000 mm/min, powder feeding rate 16 g/min, and shielding gas flow 800 L/h. The plasma arc current and powder feeding rate play primary roles in the dilution rate and forming coefficient of PAAM IN718 alloy. With the optimized process parameters, the forming and internal crack of the PAAM IN718 alloy is controlled. The microstructure of PAAM IN718 alloy is dominated by temperature gradient and constitutional supercooling, which is sequentially transformed from cellular crystal in the bottom region to coarse columnar dendrite and equiaxed crystal in the top region. Laves phase exhibits a concentration gradient that gradually increases from top to bottom on the cross-section from the range 11.3–18.6 vol%. Due to the solid solution strengthening of Nb/Mo elements and dispersion strengthening by γ″ phase, the microhardness and tensile strength of PAAM alloy after full heat treatment reach about 500 HV and 1284 MPa, respectively. These are satisfactory mechanical properties compared to other additive manufactured IN718 alloys, and PAAM is suitable to prepare IN718 alloy to obtain favorable microstructure and mechanical properties.

Managing the inevitable microstructural and property heterogeneity in powder bed fusion Ti-6Al-4V parts via heat treatment

This study investigates the effects of the commonly-observed microstructure heterogeneity from the metal electron beam powder bed fusion (PBF-EB) processes and how it evolves following the associated heat treatment (HT), on the tensile behaviour of Ti-6Al-4V alloy. A strain gradient crystal plasticity finite element (CPFE) method is employed using physically-based dislocation mechanics to capture the microstructure-sensitive size effect. Microstructural characterization is performed using electron backscatter diffraction (EBSD) of the as-built and post-HT specimens, with measurements of grain morphology, phase, and texture extracted from the bottom and top regions of specimens, used to construct the CPFE models. The dual-phase CPFE model represents α (hcp) and β (bcc) basket-weave morphology, typical in Ti-6Al-4V, with accurate PBF-induced texture definitions defined directly from the measured EBSD data. Key microstructural features exhibiting a gradient include lath width and phase fraction. The effects of as-built microstructural gradient in a single component include an increase of lath width by 43 %, and the beta phase fraction, from bottom to top. The CPFE models successfully predict the effect of HT and microstructural gradient on tensile response, specifically yield stress and initial hardening rate. The role of dislocation density and the associated influence of lath width on yield stress are empirically correlated for the structure-property design of PBF-EB metals. This study also demonstrates the homogenising effect of the heat treatment; effectively eradicating the microstructural gradient observed in as-built specimens.

Study on creep-fatigue life of ODS-Cu as heat sink in divertor PFU

In fusion devices, the actively cooled W-monoblocks of the PFUs (Plasma Facing Units) are installed in the divertor to protect the vacuum vessel and magnets against neutron flux in the bottom region of the vessel. Copper alloy is considered to be the ideal heat sink material due to its high thermal conductivity and sufficient mechanical strength, in which ODS (oxide dispersion-strengthened)-Cu is selected as a candidate. With the increasing of operating parameters, such as higher heat flux (∼20 MW/m2, H-mode) and longer pulse (up to 2.00 h) in EU-DEMO [1], the heat sink structure will undergo thermal creep induced by high temperature, stress and long holding time, which accelerates fatigue failure and could potentially be a very critical issue for the long-term safe operation of the fusion reactor. In this paper, an ITER-like monoblock with ODS-Cu as heat sink was studied for its creep fatigue life under DEMO operation conditions. The temperature distribution and stress/strain results of ODS-Cu were determined using finite element analysis. The investigation shows that high temperature creep occurs at the heat sink. Based on a damage accumulation model, the predicted life of the PFUs for the divertor are investigated at different operating modes. The analysis provides theoretical feasibility for selecting ODS-Cu as a heat sink material. The effect of stress relaxation on creep behavior during thermal stress cycle was also demonstrated and this was compared with the same for CuCrZr.