Heat Input Research Articles

A Comparative Study on Laser Cutting Performance with Varying Speeds at 10 M Underwater

Despite the dismantling structures that are submerged to significant depths of water during the decommissioning of nuclear power plants, there is limited research on deep-water laser cutting processes. A self-designed pressurized chamber was used in this study and successfully conducted the world’s first laser cutting experiment in a simulated 10 m water depth environment. laser cutting was performed in a 10 m underwater environment, and the cutting efficiency was compared to that observed in a 1 m underwater environment. Therefore, A 100 mm thickness of 304 stainless steel was successfully cut underwater, and the highest cutting speed of 100 mm/min was achieved. The result indicates that, as the cutting speed increased during underwater laser cutting, both the heat input and the mass flow rate of the assist gas decreased, resulting in a narrower rear kerf width and an ineffective evacuation of the molten metal.

Effect of Process Parameters on the Mechanical Properties of Simultaneous Double-Sided Friction Stir Welding Joints

Currently, conventional single-sided friction stir welding is primarily suitable for joining thin plate aluminum alloys, and its application to thick plates is still challenging in terms of welding efficiency and joint mechanical properties. Simultaneous double-sided friction stir welding (SDS-FSW) is a high-efficiency joining technique specifically developed for welding thick plates. However, there is little research on the influence of SDS-FSW process parameters on the joint mechanical properties. In this study, a 12 mm thick AA6061-T6 aluminum alloy and dual robot welding equipment are used to conduct SDS-FSW experiments exploring the influence of rotational speed ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} and welding speed v on the mechanical properties and microstructure. The results show that when the welding parameters are ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} = 800 r/min and v = 60–80 mm/min, smooth and defect-free thick plate aluminum alloy SDS-FSW joints can be obtained, and the macroscopic morphology of the joints is distributed in a “dumbbell” shape. The grain size in the weld nugget zone increases with increasing welding heat input. The microhardness distribution in the joint displays a “W” shape, and the hardness value of the weld nugget zone can reach 67% to 86% of that of the base metal (BM). The junction between the thermo-mechanically affected zone and the heat affected zone is the weakest region of the joint, with the lowest hardness being approximately 51% of that of the BM. When the welding parameters are ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} = 800 r/min and v = 140 mm/min, the SDS-FSW joint has the highest tensile strength, reaching 78.43% of the BM strength and exhibiting ductile fracture characteristics. This research indicates that acceptable weld strength in thick aluminum alloys can be achieved via the SDS-FSW joining mechanism, highlighting its significant potential for industrial applications.

Single-Loop Triple-Diameter Pulsating Heat Pipes at Reduced Heat Input: A CFD Study on Inner Diameter Optimization

The geometric configuration, particularly the inner tube diameter, plays a significant role in the thermal performance of pulsating heat pipes (PHPs). Previous experimental research has demonstrated that single-loop triple-diameter PHPs (TD-PHPs) outperform single-loop single-diameter PHPs (SD-PHPs) and dual-diameter PHPs (DD-PHPs) in terms of thermal performance under moderate heating input powers ranging from 25 W to 75 W. However, a reduction in heat input from 75 W to 25 W leads to a diminished impact of TD-PHPs on the thermal performance. Therefore, to improve the overall performance of TD-PHPs, this study used two-dimensional transient computational fluid dynamics simulations to identify the optimal inner tube diameters for TD-PHPs at a low heat input by evaluating the thermal resistance of five TD-PHPs with various inner diameters. The findings reveal that the TD-PHP configuration exhibits minimum thermal resistance, with inner diameters of 4.5 mm for the upper arch (the condenser section), 4.0 mm for the wide branch, and 2.5 mm for the narrow branch, primarily due to its full circulation flow pattern. Furthermore, the overall heat transfer performance of the optimal TD-PHP was compared with that of an SD-PHP at low heat inputs (10 and 18 W), indicating that although the optimal TD-PHP shows lower thermal resistance, it does not significantly affect the start-up time.

Selective Degradation of Polyethylene Terephthalate Plastic Waste Using Iron Salt Photocatalysts.

Plastic pollution poses a significant challenge to environmental conservation. Efficient recycling of plastic is a key strategy to address this issue. Polyethylene terephthalate (PET), commonly found in plastic bottles, represents a substantial portion of plastic waste. Consequently, the efficient degradation and recycling of PET is crucial for the sustainable development of society. However, the implementation of methods for PET depolymerization and recycling typically necessitates alkaline/acidic pre-treatment and significant energy input for heating. Here, we propose a gentle, and highly efficient photocatalysis approach for selectively degrading PET plastic waste into terephthalic acid (TPA) in high yield (up to 99%) using cost-effective iron salts. Notably, this method achieved excellent selectivity with high TON and TOF values, applying oxygen or air as environmentally friendly oxidants. In addition, the solvent can be recycled without compromising the TPA yield, and large-scale reactions can be performed smoothly.

The Effective Elastic Thickness of the Lithosphere Reveals Tectonic Process and Lithospheric Rheology of the Eurasian Basin

ABSTRACTWe obtained the effective elastic thickness of the lithosphere (Te) in the Eurasian Basin using the fan‐shaped wavelet method. For ultraslow spreading ridges, the magmatic heat input is insufficient to form continuous quasisteady‐state magma lenses along the axis, resulting in significant variability in the rheological strength of the lithosphere. We suggested that the tectonic inheritance resulted in the different lithospheric rheology of WVZ and SMZ, consequently leading to distinct tectonic‐magmatic activities. The SMZ with less magmatic activity has a weaker lithosphere than that of the EVZ with extensive magmatism. We propose that the lithospheric rheology and thermal structure of ultraslow spreading ridge may be influenced not by the amount of magma supply but by the mode of magma emplacement.

Direct laser active brazing of 316Ti to alumina

AbstractThis work addresses the challenges in brazing thermohydraulic sealings involving dissimilar materials, specifically 316Ti stainless steel and alumina, which have significantly different coefficients of thermal expansion (CTEs) and elastic constants. Traditional brazing methods require complex interlayers or extensive metallization steps, leading to issues such as dimensional changes, braze voids, and inadequate corrosion resistance due to prolonged high‐temperature exposure. A novel laser‐based brazing technique utilizing a diode laser is introduced to create high‐quality, localized joints while preserving the integrity of the parent materials. The study systematically optimizes laser process parameters using finite‐element modeling and the Taguchi method to achieve the desired bead geometry and thermal stress distribution with minimal heat input. Comparative analysis between laser active brazing (LAB) and conventional furnace brazing was conducted through metallography, shear testing, and autoclave testing. Results indicate that LAB parameters significantly affect bead thickness and shear strength, with laser‐brazed joints demonstrating superior quality and stability post‐autoclave testing compared with furnace‐brazed joints. The thermodynamic and kinetic aspects of the brazing process were also analyzed. In conclusion, the LAB method for brazing 316Ti to alumina proves to be a successful and efficient alternative, with joint properties meeting or exceeding those of traditional furnace brazing.

Heterogeneous interfaces of aluminum bronze/Inconel 718 dissimilar alloys under different wire arc directed energy deposition sequences

Abstract The layer-by-layer deposition strategy of additive manufacturing makes it ideal to fabricate dissimilar alloy components with varying functionality, which has promising application potential in a large number of industrial areas. In this study, two components composed of ERCuAl-A2 aluminum bronze (CuAl9) and Inconel 718 nickel-based superalloy were fabricated with different deposition orders by wire-arc directed energy deposition. Subject to changes in heat input and thermophysical properties of the substrate, the transition region of the deposited Cu–Ni component with the bottom half of CuAl9 and the top half of Inconel 718 is narrow and serrated. This region features a laminated intermetallic compound layer due to the convection and rapid cooling in the molten pool. In contrast, the Ni–Cu component deposited in the opposite order exhibits a 2 mm gradient transition zone. Within this region, a large number of diverse precipitates were found as well as regional variations in grain size due to the multi-layer partial remelting. Both two components show strong bonds and their tensile specimens tested along the vertical direction always fracture at the softer CuAl9 side. Excellent tensile properties along the horizontal direction were obtained for Cu–Ni (Ultimate tensile strength: 573 MPa, yield stress: 302 MPa, elongation: 22%), while those of Ni–Cu are much lower due to the existence of the solidification cracks in the transition zone. The results from this study provide a reference for the additive manufacturing of Cu/Ni dissimilar alloy components, as well as their microstructure and mechanical properties control.

Examination of Microstructure, Mechanical Properties, and Fatigue Strength in a Wire Arc Additively Manufactured Material Comprising Dissimilar Materials: AISI 316L Stainless Steel and Carbon Steel

This study provides a comprehensive investigation into the microstructure, hardness, tensile strength, and bending fatigue behavior of a Wire Arc Additively Manufactured (WAAM) component composed of dissimilar materials—Carbon Steel (CS) and 316L stainless steel. Microscopic analysis reveals distinct microstructural characteristics, such as equiaxed ferrite grains in WAAM CS and a coarse columnar structure with delta-ferrite phases in WAAM 316L. A macroscopic phase map indicates a predominantly Body-Centered Cubic (BCC) structure near the interphase, suggesting element migration between CS and 316L due to high heat input. Higher magnification scans highlight martensitic structures on both sides of the interphase, with the CS side exhibiting larger grain sizes. Hardness assessment along the built direction shows a peak hardness of 407 HV near the interphase on the 316L side, contrasting with the CS side's average interphase hardness of 316 HV due to larger grain sizes. The yield strength of both WAAM CS and WAAM dissimilar material was consistently measured at 392 MPa. In comparison, WAAM 316L exhibited a slightly lower yield strength of 359 MPa. Notably, WAAM 316L demonstrated the highest tensile strength among the materials, reaching 656 MPa. Meanwhile, WAAM CS displayed a robust tensile strength of 503 MPa, and the WAAM dissimilar material exhibited a yield strength of 520 MPa. In terms of elongation, WAAM CS and WAAM 316L showcased values of 44.9% and 49.6%, respectively. On the other hand, WAAM dissimilar material exhibited a somewhat lower elongation of 20.4%, suggesting a different mechanical behavior in terms of ductility. Bending fatigue tests on WAAM 316L, WAAM CS, and the dissimilar material reveal a fatigue limit of approximately 225 MPa for WAAM 316L, 210 MPa for WAAM CS, and approximately 210 MPa for the dissimilar material. In the low-cycle and medium-cycle regimes, the dissimilar material exhibits slightly superior fatigue strength, potentially due to its marginally higher static strength. Notably, consistent fractures on the CS side during fatigue tests underscore a recurring behavior in the dissimilar material.

A many-body quantum model is proposed as the mechanism responsible for accelerating rates of heat uptake by oceans as anthropogenic heat inputs rise

Abstract A recent many-body quantum approach to thermal radiation (1) reveals that the energy capacitance of heated water is about twice its heat capacitance, due to energy stored as local hybrid pairs of photons coupled resonantly to local matter excitations, with pair density weighted by mass density. Energy exchange between photons and localised dipole excitations inside water at steady temperature T, occurs at sites where a hybridisation potential within the Hamiltonian couples local oscillation modes to “free” photon modes. Photon modes in both directions are phase retarded at exit sides of a hybrid site. Optically sharp variations with frequency in the index of refraction n(f) and photon density of states follow. Exit spectral intensities at equilibrium temperature T carry quantum information on the energy density of matter excitations coupled to photons, while occupied hybrid sites are the source of all “free” photons and internal spectral intensities. The matter excitations coupled locally to photons are distinct from those that define specific heat, but in water both arise from molecular oscillations. The energy capacitance CEX(T) of hybrid pairs depends on mass density and is independent of heat capacitance CHT(T) which sets temperature T. CEX(T) is sensitive to T and doubles as a capacitance of energy and of “quantum information”. Expressions for CEX(T) are derived from first principles and applied to water. The density of occupied hybrids is amplified near surfaces by photons reflected off the surface, which create new hybrid pairs, but not extra heat. Energy capacitance CEX(T)+CHT(T) sets dT(t)/dt prior to a new equilibrium state emerging, after input heating rate dQ/dt is switched. Rising atmospheric intensities then raise T, dQ/dt, CEX(T) and CHT(T). The times available to cool overnight are fixed, so that a rising capacitance, adds to energy stored at an accelerating rate. 


Effect of heat input on microstructure and mechanical properties of AA6061 alloys fabricated by additive friction stir deposition

Heat input (HI) is the major factor that affects the surface quality, microstructure and mechanical properties of the deposition during the additive friction stir deposition (AFSD) process. Effect of HI on the microstructure and mechanical performance of the AFSDed AA6061 has been in-depth explored via adjusting the values of traverse speed (v) and layer thickness (t). Results indicate that deposition with a higher HI promotes the material flow behavior as well as the plastic deformation, which effectively enhances the grain refinement and structural uniformity, and avoids the formation of defects. Meanwhile, TEM results confirm that the enhanced HI leads to the formation of a higher volume fraction of the finer precipitations (Mg2Si and AlFeSi phases), which assists in suppressing abnormal grain growth phenomenon and improves the bonding strength of the deposition. As HI decreases, the transfer efficiency of materials clearly reduces because of the incompletely softened materials, causing less plastic deformation and poor interlayer bonding strength of the deposition. The deposition with the lowest HI displays the worst tensile properties with the lowest micro-hardness (107 HV0.5), YS (273 MPa) and UTS (303 MPa).

Effect of heat input on the microstructure and performance of dissimilar welded joint between Q345B low-alloy steel and 2205 duplex stainless steel

Q345B/2205 dissimilar steel multi-layer multi-pass welded joints were prepared using gas metal arc welding (GMAW). The effects of heat inputs on the microstructures and properties of welded joints were studied. The morphology and composition distribution of Q345B base metal near the fusion line were investigated. The results showed that the welded joints under different heat inputs were all present “carbon depleted zone” and “carburized zones” on both sides of the Q345B base metal and transition layer interface. The microstructure of the “carburized zones” was composed of martensite phase and granular bainite phase. It was found that only the welded joints with heat inputs of 1.765 kJ/mm and 2.860 kJ/mm met the usage requirements. The corrosion behavior and characteristics of the welded joint with a heat input of 1.765 kJ/mm in a 3.5 wt % NaCl solution were investigated intensively. During the soaked process of 14 days, the total impedance value of the welded joint showed first increasing and then decreasing. The maximum value of 8.7 kΩ cm2 was obtained on the 5th day. As the soaked time increased, the corrosion products of the welded joint underwent the formation, thickening, cracking and detachment, which was the main reason of the change in the corrosion resistance. The research results of this article have significant implications for the application of low-alloy steel and stainless steel welded joints in engineering.

Autothermal hydrogen release from liquid organic hydrogen carrier systems

A typical feature that the LOHC technology shares with other types of chemical hydrogen storage is that the release of hydrogen from the carrier requires an input of heat. In many use cases where waste heat from external sources is not available (e.g. in heavy-duty mobility), this is seen as a major drawback. In this paper, we show that autothermal LOHC dehydrogenation offers a very attractive way to overcome this drawback. In detail, we demonstrate autothermal hydrogen release from dicyclohexylmethane using diphenylmethane oxidation to benzophenone as source of heat. The full storage cycle involves benzophenone hydrodeoxygenation to dicyclohexylmethane, dicyclohexylmethane dehydrogenation to diphenylmethane, and diphenylmethane oxidation to benzophenone. We studied both the individual reaction steps using pure feedstocks and the integral cycle in which the intermediates and by-products of each reaction remain in the system for the subsequent reaction step. Although no efforts have yet been made to develop special catalyst materials for this purpose, the results with the applied commercial hydrodeoxygenation (Pd/C), dehydrogenation (Pt on alumina) and partial oxidation (VOx/TiO2) catalysts are already very promising. The storage cycle can be closed with high selectivity and with only minor total oxidation losses. The proposed concept of autothermal LOHC dehydrogenation offers the potential to increase the amount of useable hydrogen from a given amount of charged hydrogen carrier by up to 30%.

Disclosing Connection Links between Microstructure and Mechanical Performance in Pulsating Current Gas Tungsten Arc Welding of Hastelloy B-2 Superalloy

In this study, welding a Ni-Mo-based superalloy (Hastelloy B-2) was examined in order to characterize the microstructure and mechanical performance of joints along with assessing the effects of current intensity on the microstructure and mechanical responses of different weld zones. The gas tungsten arc welding (GTAW) process was used to weld the samples using ERNiCrMo-2 filler metal. The pulsed current GTAW process was used to weld the superalloy sheets of thickness of 1 mm with background current (Ib) of 20 A and 40 A and peak current (Ip) of 80 A and 60 A. Tensile and Vickers microhardness tests were conducted to evaluate the effect of pulsed current on mechanical properties of the welds along with chemistry and microstructure characterizations. Finally, the fracture surfaces after the tensile test were studied using SEM fractography analysis. The results indicated that increasing Ib and decreasing Ip led to low heat input and high cooling rate resulting in a high thermal gradient. This caused microstructure transition from the columnar dendrites to the coaxial ones in the weld zone; molten metal convection in the fusion zone led to fine grains in the weld zone during welding time. Moreover, a significant decrease in the amount of molybdenum carbides at the interdendritic regions of the weld metal was observed under these conditions. The tensile strength of the weld metal was higher than that of the base metal resulting in the fracture of all welds from the base metal. Additionally, the microhardness results indicated a significant increase for the weld metal compared to both heat-affected zone (HAZ) and base metal. The higher mechanical properties of the weld metal is attributed to the increase in background current and decrease in peak current leading to a fine grain microstructure. Fractography following the tensile test showed a completely ductile fracture.

Low-Cost Cascade Thermoacoustic Electric Generator for Energy Harvesting

The cascade thermoacoustic heat engine has garnered significant attention for its ability to convert various heat sources into acoustic power without the challenges of acoustic streaming. By integrating it with a commercial loudspeaker, it can be further developed into a novel, low-cost thermoacoustic electric generator. This study aims to design and evaluate a thermoacoustic electric generator capable of producing several watts of electricity. The system consists of a cascade thermoacoustic engine, comprising a standing-wave and a traveling-wave unit, coupled with a B&C 6PS38 loudspeaker in a linear configuration. Atmospheric air is used as the working fluid, and standard market components, such as PVC and steel pipes, are proposed to minimize costs. Unlike traditional thermoacoustic generators, this system uses commercially available loudspeakers and a linear configuration, offering a cost-effective solution for low-wattage power generation, free from the issue of acoustic streaming. This makes it suitable for small-scale, distributed energy systems. The numerical simulation tool DeltaEC is employed to design and assess the system's performance. The optimal configuration is 4 meters long, with the standing-wave and traveling-wave units centrally positioned. Operating at a frequency of 74.56 Hz, the system generates 90.18 W of electrical power with a total heat input of 1046.74 W and an external load resistance of 19.77 ohms. This corresponds to a heat-to-acoustic efficiency of 18.41%, an acoustic-to-electric efficiency of 68.98%, and an overall heat-to-electric efficiency of 8.62%. The study also emphasizes the importance of operating conditions and impedance matching between the cascade engine and the loudspeaker. These findings represent progress toward developing an affordable thermoacoustic generator for energy recovery and other applications.

Failure Analysis of Burst Tube Caused by Corrosion Thinning of the Tube Wall of Boiler Economizer

Abstract A boiler economizer is in continuous operation during several burst pipes. Burst tubes are located near the elbow below the weld, and the weld on both sides of the tube wall is thinning seriously. There is a flue gas formation vortex in the furnace chamber; the outer wall of the tubes is thicker ash, and fins and tubes are corroded to varying degrees. This study employed meticulous macroscopic observation, precise chemical composition analysis, detailed metallography, advanced scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to determine the causes of the coal economizer tube burst and tube wall thinning, ensuring the accuracy of the findings. The chemical composition, microstructure, and grain size of the base material met the requirements of the relevant standards. The heat-affected zone and weld seam show the Widmannstatten structure, a superheated tissue caused by excessive heat input during welding. The outer wall of the pipe corrosion is more serious, resulting in serious wall thinning, and ultimately, the pipe bursts, unable to withstand the pressure inside the pipe. It was eventually determined that the cause of the pipe burst was that the operating temperature of the economizer was close to the dew point, and the flue gas contained sulfur dioxide, sulfur trioxide, and hydrogen chloride that met water vapor at that temperature to form acid. Acid on the outer wall of the pipe was caused by flue gas dew point corrosion, seriously causing the pipe wall to thin. When the pipe wall is thinned to a certain extent due to corrosion, it cannot withstand the pressure inside the pipe, and rupture will occur.

Study on heat transfer and flow of molten pool during the deposition process of laser wire additive manufacturing

In the laser wire additive manufacturing process, the molten pool acts as the critical link between the wire and the deposited part. The heat transfer and flow behavior within the molten pool predominantly determine the quality of the final deposition. Under laser power ranging from 2400 to 3000 W, traverse speeds between 0.01 and 0.04 m/s, and wire feeding speeds from 0.03 to 0.08 m/s, three distinct flow states—single-swirl, double-swirl, and no-swirl—were observed with increasing heat input. Under the optimum process parameters, the molten pool with stable temperature distribution and orderly flow was obtained. In multilayer deposition, the implementation of a laser decay strategy mitigates steep temperature gradients, diminishes the Marangoni effect within the molten pool, and effectively reduces both heat accumulation and lateral flow. Consequently, the flow mode transitions from no-swirl to swirl, and the maximum flow velocity decreases by 40%.

Achieving microstructural homogeneity in the stir zone across thick AA6061 welds using self-reacting bobbin tool friction stir welding

This study focuses into strategizing the usage of self-reacting bobbin tool friction stir welding (SRBT-FSW) to obtain consistent microstructural homogeneity along the thickness of AA6061 aluminium alloy (AA) thick plates during welding. The SRBT-FSW technology, distinguished by its dual-shoulder design, represents a significant step forward in FSW by eliminating the requirement for a backing anvil and promoting balanced heat distribution. This study seeks to address the issues of maintaining uniform microstructural characteristics throughout the weld zone, which is crucial for the mechanical performance and durability of welded joints in structural applications. The experimental study entails the systematic welding of AA6061 plates of 6 mm thickness using a self-reacting bobbin tool under a fixed processing condition. Electron backscatter diffraction (EBSD) was used to characterize the grain structure and phase distribution over the weld. Mechanical parameters like as tensile strength and hardness were determined to establish correlations between microstructure and mechanical performance. The results demonstrated that SRBT-FSW significantly enhances microstructural homogeneity across the weld zone, leading to improved mechanical properties. In the Bottom Zone (BZ), a refined grain structure with an average grain size (AGS) of 3.53 µm and a random or weak texture was observed, contributing to enhanced hardness and mechanical performance, with an ultimate tensile strength (UTS) of 220 MPa. In contrast, the Top Zone (TZ) exhibited a coarser AGS of 4.33 µm with a pronounced {111} crystallographic texture, resulting in a slightly lower UTS of 205 MPa. The Middle Zone (MZ), influenced by the greater heat input from both the TZ and BZ, showed an intermediate AGS of 3.99 µm, predominantly oriented along the {101} plane, and achieved a UTS of 194 MPa, with a slight reduction in ductility. This study highlights the potential of self-reacting bobbin tool friction stir welding as a reliable method for making high-quality, homogeneous welds in thick aluminium plates and paving way for their wider application in the aerospace, automotive, and shipbuilding industries, where homogeneous microstructural qualities are of significant importance.

Dissimilar unbeveled aluminum to steel butt joint achieved by laser-arc hybrid welding-brazing

In this study, unbeveled butt joints of 2 mm thick steel and aluminum plates were welded using a laser-arc hybrid process. The influence of welding speed and wire feed speed on joint weld formation, microstructures, and mechanical properties were investigated. The results indicate that using a laser-arc hybrid heat source enables good weld formation of steel/aluminum dissimilar metals without groove preparation, even under high welding speed conditions. The steel side interface formed Fe₂(Al,Si)₅ near the steel and Fe(Al,Si)₃ near the aluminum. As the welding heat input decreased, the thickness of the intermetallic compounds gradually reduced. With an increase in welding speed or wire feed speed, the tensile strength of the joint first increased and then decreased, reaching a maximum of 104.47 MPa. Cracks propagated rapidly along the intermetallic compound region, resulting in brittle fracture characteristics. The three-point bending test showed a maximum longitudinal bending angle of 53.82° and a maximum transverse bending angle of 36.54°.

Forming control and the relationship between microstructure and mechanical property in TIG-assisted friction stir welded joint of Ti-6Al-3Nb-2Zr-1Mo titanium alloy

In this paper, T-joints of Ti-6Al-3Nb-2Zr-1Mo titanium alloy were joined with friction stir welding, and microstructure evolution and forming mechanism were studied. The effect of using tungsten inert gas welding to heat additionally the FSW was investigated. Results show a strong effection microstructure of stir zone (SZ) due to the temperature gradient and fast cooling rate. The top and middle sections of SZ have a basketweave microstructure, while there is duplex microstructure at the bottom. When welding at 750 rpm-50 mm/min, the maximum tensile strength of the joint is similar to that of the base metal (BM). As the heat input increases, grain coarsening occurs, which reduces the joint tensile strength and the ability to plastically deform. The fracture mode changes from mixed fracture to ductile one. When TIG-assisted heat source is 20 mm in front of the tool and the power input is in 600 W, the temperature field produced is relatively uniform, which has a positive effect on the weld.

Optimizing Heat Transfer in Heat Pipes Using Hybrid Nanofluids With Multi‐Walled Carbon Nanotubes and Alumina

ABSTRACTThis study investigates the thermal performance of heat pipes using hybrid nanofluids composed of multi‐walled carbon nanotubes (MWCNT) and aluminum oxide (Al2O3) nanoparticles. The aim was to assess the effects of nanoparticle concentration (0.1%–0.5%), filling ratio (60%–90%), heat input (50–80 W), and inclination angle (0°–90°) on thermal resistance and heat transfer coefficient (HTC). Hybrid nanofluids were prepared using ultrasonic homogenization, and their stability was confirmed by zeta potential analysis, showing a reduction from −60 to −48 mV over 30 days. Experimental results revealed that the thermal resistance decreased with increasing filling ratio and inclination angle, reaching a minimum of 0.80 K/W at a 90° angle, 90% filling ratio, and 80 W heat input. Similarly, the overall HTC increased with these parameters, peaking at 2250 W/m2 K under the same conditions. At a 0.5% nanoparticle concentration, the HTC improved by up to 40% compared with conventional fluids. The thermal conductivity of the hybrid nanofluid also rose significantly, from 0.7 W/m K at 30°C to 1.5 W/m K at 90°C, outperforming distilled water. These findings highlight the potential of hybrid nanofluids to enhance heat pipe efficiency, particularly in high‐power applications, by optimizing nanoparticle concentration, filling ratio, and inclination angle.