Low-temperature Peak Research Articles

Synergistic lubrication effect of graphene oxide and MoS2 nanoparticles in water-based fluid: Experiment and humid-environmental MD simulation study

In this study, a lubricant was synthesized using water-based hybrid nanofluid containing graphene oxide (GO) and MoS2 nanoparticles. Pin-on-disk tribology tests and molecular dynamics (MD) simulations under humid environment were conducted. It was discovered that the GO-MoS2 hybrid nanofluid, at the optimal concentration combination (0.3wt.% GO + 0.1wt.% MoS2), demonstrated a notably enhanced synergistic lubrication effect, resulting in a reduction of approximately 14.6% in the average friction coefficient and 14.4% in the wear rate when compared to the single nanofluid. Through interfacial tribochemical analysis, a protective polycrystalline tribofilm in the thickness of about 18.6nm was formed on metal surface, consisting of ultra-fine GO, MoS2 crystals and amorphous substances derived from the organic matters of nanofluids. Besides, from humid-environmental MD simulation results, there were lower friction force, normal force and peak temperature values in MD model containing both GO and MoS2 nanosheets, meanwhile the lattice mismatch between different nanosheets led to high interlamellar repulsion, further mitigating the pressure and friction. By analyzing the absorption behavior of dispersant molecules, sodium dodecylbenzene sulfonate and triethanolamine molecules partially transferred from nanosheets to Fe surface. Based on the experiment and humid-environmental MD simulation results, the excellent tribological behavior of nanofluid was attributed to the polishing, mending, interlayer sliding effect of nanoparticles and the tribofilm induced by interfacial tribochemistry.

Fire Performance Comparison of Expanded Polystyrene External Thermal Insulation Composites Systems and Expandable Graphite-Modified Surface Covers at Different Scales

Numerous fire disasters have involved thermoplastic expanded polystyrene (EPS) external thermal insulation composite systems (ETICS) on building façades. This study evaluates the flame-retardant efficiency of expandable graphite (EG)-blended EPS ETICS across different scales: micro-scale thermogravimetric (TG) analysis, small-scale bench tests, and large-scale LEPIR 2 tests. TG analysis confirmed EG’s primary role as a physical intumescent, with no significant chemical interactions detected. While EG effectively reduced heat penetration in both small-scale and large-scale fire tests, challenges arose from char layer detachment and oxidation at elevated temperatures (exceeding 540 °C). Despite these limitations, the EG-treated façade exhibited significantly lower peak temperatures compared to the untreated control in the large-scale LEPIR 2 test, with a measured temperature difference of approximately 470 °C. These findings demonstrate the potential of EG to enhance the fire safety of EPS ETICS. The small-scale test bench proved effective for preliminary material screening, providing valuable insights into ignition resistance and flame-retardant properties before proceeding to more resource-intensive large-scale evaluations.

Model of advanced recording system for application in heat-assisted magnetic recording

Heat assisted magnetic recording (HAMR) technology is considered a solution to overcome the limitations of perpendicular magnetic recording and enable higher storage densities. To improve and understand the performance of magnetic writers in HAMR technology, it is crucial to possess a comprehensive understanding of both the magnetic field generated during the writing process and the thermal effects induced by the laser. In this work, we have developed a micromagnetic HAMR model with atomistic parameterization. To demonstrate the applicability of the developed model, it is employed to investigate the Write Current Assisted Percentage (WCAP) measurement which is characterized by the difference in laser current needed to erase a narrow data track with and without assistance of the magnetic field generated by the writer. This value allows us to subsequently consider the strength of the magnetic field from the writer, which is difficult to evaluate experimentally. We study the effect of crucial factors such as the laser current, the frequency of the writing field and the grain size distribution of the recording media on the WCAP. The results reveal that, under a high applied field, a correspondingly elevated WCAP is generated. This observation suggests that the track undergoes erasure to approximately half of its amplitude, achieved through the utilization of a low peak temperature. The comparison between simulation and experimental data demonstrates excellent agreement and acts as a validation of the underlying principle of WCAP. Additionally, we explore theoretically the impact of the writer frequency, and the results suggest that lower frequencies give rise to an increase in WCAP. This implies that lower frequencies allow for a reduction in temperature required to erase the track. The technique is valuable in evaluating and contrasting the magnetic behavior of various write pole configurations, examining the frequency responses of different designs, and comparing different media.

Shape-controlled Bose–Einstein condensation

Abstract Size-invariant shape transformation is a geometric technique that allows for a clear separation between quantum size and shape effects by modifying the shape of the confinement domain without altering its size. The impact of shape on the behavior of confined systems is significantly different from that of size, making it an emerging area of research. The recent realization of flat-bottomed optical box traps has further contributed to the study of quantum gases in complex confinement geometries. Here, we propose shape-induced Bose–Einstein condensation at a fixed size, temperature, and density. We investigate the impact of pure quantum shape effects on a non-interacting Bose gas confined within nested square domains, where the shape parameter is defined and controlled by the rotation angle between the inner and outer squares. Our findings reveal that specific heat exhibits an additional low-temperature peak at certain shapes. This work opens new avenues for controlling quantum systems through geometric manipulation and provides insights into the thermodynamic properties of Bose gases under shape-induced quantum effects.

Experimental Study of Conduction Heat Transfer Using Phase Change Material Ice Bag Gel in Bricks

This experiment investigates the heat transfer characteristics of an ice bag gel phase change material (PCM) incorporated within bricks. The study seeks to investigate the performance of ice bag gel as PCM in improving thermal behavior of building material. The experiment consisted of subjecting brick samples with and without ice bag gel PCM to thermal cycles in a semi-automated laboratory setup. The results indicate that ice bag gel PCM incorporated in bricks exhibited minimal changes and better heat transfer as compared to the dry bricks. It was observed that the ice bag gel PCM registered lower peak temperature and slower rates of temperature drop which means their heat storage and release characteristics were efficient. Furthermore, the ice bag gel system produced a steady radiation flux, indicating that it was able to minimize the effects of temperature variations. These results imply that ice bag gel PCM has the potential to be a green and economical option for enhancing thermal comfort and decrease energy consumption in buildings.

Synthesis of thermally stable orange light-emitting phosphors: characterization and investigations of Sm3+-doped CsCaF3 phosphors for solid-state-lighting applications

In this study, we synthesized and characterized pure CsCaF3 and CsCaF3 doped with samarium (Sm3+) ions using a solid-state method. X-ray diffraction analysis was employed to examine the crystal structure, while field emission scanning electron microscopy analyzed the surface morphology of the doped sample. A color coordinate graph was used to calculate the color, with the Commission Internationale de l'Eclairage (CIE) fitting the color of both pure and doped samples. Upon excitation at 405 nm (6H5/2→6F7/2 transition), the doped CsCaF3 emitted an orange light. The CsCaF3:Sm3+ sample (0.8 mol%) displayed 86% color purity and a color temperature of 2191 K, making it suitable for lighting applications. The thermoluminescence (TL) curve of the beta-irradiated CsCaF3:Sm3+ (0.8 mol%) sample showed peaks at 174 °C and 297 °C. Preheating techniques eliminated the low-temperature peak, and the peak temperature of maximal TL intensity (Tm) was 297 °C. The activation energy (Ea) and frequency factor (s) were determined using the peak shape method and varying heating rates. The dosage response of CsCaF3:Sm3+ (0.8 mol%) was examined for potential dosimetry applications.

Exploration of the reactivities of homemade binary pyrotechnics

Understanding the properties of explosives is the basis for investigating and analyzing explosion cases. To date, due to the strict legal control of standard explosives and initiators, homemade pyrotechnics composed of oxidizers and fuels have become popular explosive sources of improvised explosive devices (IEDs) threatening greatly social stability and personal safety. The reactivity of pyrotechnics strongly depends on their intrinsic characteristics and operating conditions, which determine the efficiencies of heat and mass transfer between the reaction zone and the unreacted zone. Herein, the tests of thermodynamics, pressurization characteristics, and combustion propagation behaviors are conducted to explore the effects of oxidizer species, particle size, and loading density on the reactivity of homemade binary aluminum-based pyrotechnics. The results show that the pyrotechnics with potassium chlorate (KClO3) have the strongest reactivity with the highest pressurization rate (dp/dt) and the shortest combustion duration. Compared with their counterparts based on aluminum microparticles(mAl), pyrotechnics consisting of Al nanoparticles (nAl) possess superior reactivity as expected, which results from the relatively short heat and mass transfer distances. The nAl-based pyrotechnics have a low reaction exothermic peak temperature, great heat release, great aluminothermic reaction completeness, and high produced peak pressure with several orders of magnitude higher pressurization rate. Increasing the loading density of the pyrotechnics over a certain value can change the dominant mode of heat transfer from convective to conduction, sharply decreasing the pressurization characteristics and combustion front propagation velocities (vp). The results of theoretical calculations using the NASA-CEA codes show that loading density can alter the reaction process of the pyrotechnics, leading to a decrease in the predicted pressure per unit mass for Al/KNO3 or Al/AP, and an increase for Al/KClO3. For nAl/potassium nitrate (KNO3), the density is between 1.0 and 1.25 g cm−3, across which dp/dt decreases by one order of magnitude from 0.148 to 0.014 MPa ms−1. In addition, vp decreases by three orders of magnitude from 0.040 to 0.078 m s−1. Distinct pressurization behaviors of nAl/AP are observed at a density of 1.5 g cm−3, while the variation in nAl/KClO3 reactivity fluctuates. These results are beneficial for the damage assessment of scenes caused by an explosion and for inversely calculating charge parameters.

MoS2 stabilize Ti3C2 MXene for excellent catalytic effect of thermal decomposition of ammonium perchlorate

Ammonium perchlorate (AP), the most widely used oxidizer in energetic materials, is crucial for studying catalytic thermal decomposition. Newly discovered Ti3C2 MXene and MoS2 demonstrating promising prospects in the field of the pyrolysis catalyst in AP. In this study, we employed a hydrothermal method to anchor nano-sized MoS2 in situ on the surface of Ti3C2 MXene, leading to the fabrication of MoS2-Ti3C2 nanocomposites. Various characterizations indicated that MoS2 was attached to the surface and edges of Ti3C2, thereby enhancing the stability and conductivity. Results revealed that upon the addition of 4 wt% MoS2-Ti3C2, the low-temperature decomposition peak of AP reduced from 331.2 °C to 296.6 °C, while the high-temperature decomposition peak advanced from 427.5 °C to 387.1 °C, showing a superior catalytic effect compared to the individual MoS2 or Ti3C2. Additionally, the catalytic mechanism of MoS2-Ti3C2 on the thermal decomposition of AP may involve enhanced electrical conductivity, facilitating rapid proton transfer (H+), accelerated redox reactions, prompt release of gas products, and thereby expediting the progression of the decomposition reaction. Consequently, it can be anticipated that anchoring MoS2 on the surface of Ti3C2 represents an effective strategy for enhancing the catalytic activity of Ti3C2 MXene towards the thermal decomposition of AP.

MOFs derived Ni-Mn bimetal nano-catalysts with enhanced hydrogen pump effect for boosting hydrogen sorption performance of MgH2

In the present work, highly effective Ni-MnO binary nanocomposite catalysts were designed and synthesized using a one-pot method from Ni-Mn based bi-metal organic frameworks (MOFs). These nanocomposites were introduced into MgH2 through ball milling as catalysts to enhance the hydrogen storage properties of MgH2. Through varying the Ni/Mn ratio in the bimetal MOFs, it is found that the Ni1Mn1−MOF derived catalyst showed the best promotion effect on MgH2. The MgH2–10 wt.% Ni1Mn1−MOF derivative demonstrated favorable overall performance with the low desorption peak temperature (218.2 °C) with a saturated hydrogen capacity of 6.42 wt.% and rapid hydrogen release/uptake kinetics. It can still reabsorb about 1.15 wt.% H2 within 30 min at a temperature as low as 50 °C. Both performance tests (DSC and TPD) and structural characterizations (XRD, HRTEM, etc.) revealed that the synergistic role of in situ formed Mg6MnO8 and Mg2NiH4/Mg2Ni phases for improving the hydrogen sorption properties of MgH2. Theoretical calculations reveal that Mg6MnO8 destabilizes metal-H bonds in MgH2 and Mg2NiH4, leading to an enhanced “hydrogen pump” effect of Mg2NiH4 for MgH2. This research provides a strategy to rational design and preparation of bimetal MOF derivatives for the development of advanced hydrogen storage materials.

Turbulent Accelerating Combusting Flows with Methane-Vitiated Air Flamelet Model

This work presents a numerical study of a diffusion flame in a reacting, two-dimensional, turbulent, viscous, multicomponent, compressible mixing layer subject to a large favorable streamwise pressure gradient. The boundary-layer equations are solved coupled with both the k–ω and shear-stress transport turbulence models. A compressible extension of the flamelet progress variable method has been proposed and tested for use with large-eddy simulations or Reynolds-averaged Navier–Stokes analyses of the burning of methane in pure air and vitiated air; the latter being particularly relevant in turbine burner scenarios. Effects of the level of detail of the reaction mechanism on the subgrid- and resolved-scale computations are studied. A comparison is made with results obtained using a simplified one-step reaction. The numerical results employing the flamelet model with the more detailed reaction mechanism show faster chemistry, significantly reduced peak temperatures, and stronger sensitivity to pressure. Vitiated air flames are found to be dominated by unstable solutions, resulting in a weak flame with substantially lower peak temperature and impeded development, struggling to persist without quenching.

Ultra-high Prussian blue loading in SPEEK matrix fabricated by one-step electrostatic spraying as proton exchange membranes for fuel cell

Mixed matrix proton exchange membrane is promising for fuel cell application, but maximizing nanofiller loading to enhance performance is significant challenge. This study developed a one-step electrostatic spraying strategy to prepare ultra-high Prussian blue loading (up to 66.7 wt%) in sulfonated poly(ether ether ketone) matrix (PB@SPEEK). By coupling the electrostatic spraying and in situ solvent evaporation densification, SPEEK fills the voids between PB nanoparticles, forming a bicontinuous microstructure in the membrane. The ultra-high PB content of 66.7 wt% enable a fully utilization of its intrinsic properties, resulting in extremely low swelling ratio of 3.4% at 80°C, excellent flexibility of freely folding, and nearly 100% mass retention after 12-hour immersion in Fenton reagent at 60°C. In single-cell tests, the PB@SPEEK mixed matrix membrane shows stable internal resistance due to easily water hydration, therefore achieving excellent low-temperature peak power (1973.9 mW/cm2 at 40 °C and 2078.0 mW/cm2 at 60°C). The strategy developed in this study enables the one-step preparation of large-area, ultra-thin and ultra-high capacity of inorganic nanofiller mixed matrix proton exchange membranes for high-performance fuel cell.

Combustion reactivity of sewage sludge hydrochar derived from hydrothermal carbonization via thermogravimetric analysis

Wastewater treatment plant sludge contains a high concentration of organic compounds that can be used to produce fuel viahydrothermal carbonization (HTC). This study investigated the combustion reactivity and kinetic parameters of hydrochars produced to understand the combustion behavior of the solid fuel derived from HTC. The hydrochar was produced at various temperatures ranging from 150 to 300 °C, reaction times ranging from 30 to 150 min, and solid loadings ranging from 10% to 30%. The combustion behavior of sewage sludge (SS) and hydrochar was evaluated using thermogravimetric analysis with a constant air flow rate (100 mL/min) and heating rate (10 °C/min) from ambient temperature to 900 °C. It was observed that the HTC temperature, reaction time, and solid loading influenced the combustion characteristics and kinetics of the hydrochar. Additionally, the hydrochar exhibited higher ignition and burnout temperatures and a lower peak temperature than SS, indicating superior performance and reactivity in combustion. The combustion kinetic analysis also revealed that the hydrochar had a range of lower activation energy (29.12–41.60 kJ/mol) than SS (52.95 kJ/mol). Therefore, hydrochar derived from SS has the potential to be used as a substrate for solid fuel production for future renewable energy sources.

Thermal Evaluation of Bone Drilling with a One-Drill Protocol.

This study evaluates the thermal impact of a one-drill protocol for osteotomy preparation in dental implant surgery. Our findings demonstrate a significant reduction in heat generation compared to traditional sequential drilling, suggesting potential benefits for implant osseointegration and patient comfort. Specifically, the one-drill protocol was associated with lower peak temperatures and a reduced duration of elevated temperatures. These findings suggest that the one-drill protocol may contribute to improved implant stability and reduce the risk of thermal-induced bone damage. While further research is needed to confirm these findings in clinical settings, the results of this study provide promising evidence for the potential advantages of the one-drill protocol in dental implant surgery. Additionally, the one-drill protocol may offer simplified surgical workflows and reduced instrument management, potentially leading to improved efficiency and cost-effectiveness in dental implant procedures.

Numerical study on heat transfer and flow characteristics of symmetric Tesla-type microchannel heat sinks

This study numerically investigates the thermal performance of multi-stage Tesla valve microchannels (TVM) and a symmetric variant (SYMTVM) using single-phase deionized water, with mass flow rates ranging from 0.5459 to 1.6377 g/s. Both designs, particularly under reverse flow, exhibit lower peak temperatures and reduced temperature gradients compared to forward flow. The SYMTVM, characterized by its increased vortices and bifurcations, periodically disrupts and redevelops the thermal boundary layer, enhancing heat transfer efficiency. The TVM exhibits a significantly higher pressure drop than the SYMTVM across all flow conditions, with the reverse flow in TVM reaching up to 2.48 times that of forward flow and exceeding SYMTVM, especially at a peak flow rate of 1.6377 g/s. The performance evaluation criteria (PEC) and thermal resistance criteria (PECTR) demonstrate the superior performance of SYMTVM, with a reduced connection angle between the trunk and helix regions enhancing thermal efficiency. Furthermore, the SYMTVM-Reverse structure with a 30° interconnection angle demonstrates superior performance compared to the conventional rectangular microchannel (RM), achieving a Nusselt number (Nu) that is five times higher than that of the RM and an overall performance up to 2.59 times greater. These results indicate the SYMTVM-Reverse’s high heat transfer efficiency and its capacity to effectively balance thermo-hydraulic performance, even with increased power dissipation.

Insight into evolution characteristics of pyrolysis products of HLH and HL coal with Py-VUVPI-MS and DFT

To achieve a comprehensive understanding of the influence of chemical structure on the evolution characteristics of coal pyrolysis products, pyrolysis reaction of two kinds of low rank coal (Huolinhe and Huangling coal) were investigated with pyrolysis-vacuum ultraviolet photoionization mass spectrometry (Py-VUVPI-MS). The soft ionized mass spectral detection can provide evolved information of original pyrolysis product. The chemical structure of coal samples was characterized by solid-state 13C NMR, indicating HLH coal with more branched chain and longer aliphatic chain structure. The bond dissociation enthalpies (BDE) of β-Cal-Cal and β-Cal-O within model compounds were obtained with density functional theory. The difference of peak temperature with maximum evolution was collected to investigate the effect of the chemical environment on evolution behavior of pyrolysis products. The results reveal that branched and long aliphatic side-chains can reduces BDE of β-Cal-Cal and β-Cal-O, resulting in the lower peak temperature of pyrolysis products derived from HLH coal. Substituent groups (such as alkyl and hydroxyl groups) attached on the aromatic rings can reduce peak temperatures. Moreover, the effects of the different substituted position on the aromatic ring of the methyl group presented on differences of the BDE. An increase in aromatic ring size correlates with a certain degree of reduction in BDE for β-Cal-Cal; consequently, peak temperature of pyrolysis products with larger aromatic rings is lower. The pyrolysis behavior of coal were discussed based on the experimental observations and theoretical calculation, which are beneficial to understand the reaction route and mechanism of coal pyrolysis.

Multi-Fidelity Modelling of the Effect of Combustor Traverse on High-Pressure Turbine Temperatures

As turbine entry temperatures of modern jet engines continue to increase, additional thermal stresses are introduced onto the high-pressure turbine rotors, which are already burdened by substantial levels of centrifugal and gas loads. Usually, for modern turbofan engines, the temperature distribution upstream of the high-pressure stator is characterized by a series of high-temperature regions, determined by the circumferential arrangement of the combustor burners. The position of these high-temperature regions, both radially and circumferentially in relation to the high-pressure stator arrangement, can have a strong impact on their subsequent migration through the high-pressure stage. Therefore, for a given amount of thermal power entering the turbine, a significant reduction in maximum rotor temperatures can be achieved by adjusting the inlet temperature distribution. This paper is aimed at mitigating the maximum surface temperatures on a high-pressure turbine rotor from a modern commercial turbofan engine by conducting a parametric analysis and optimization of the inlet temperature field. The parameters considered for this study are the circumferential position of the high-temperature spots, and the overall bias of the temperature distribution in the radial direction. High-fidelity unsteady (phase-lag) and conjugate heat transfer simulations are performed to evaluate the effects of inlet clocking and radial bias on rotor metal temperatures. The optimized inlet distribution achieved a 100 K reduction in peak high-pressure rotor temperatures and 7.5% lower peak temperatures on the high-pressure stator vanes. Furthermore, the optimized temperature distribution is also characterized by a significantly more uniform heat load allocation on the stator vanes, when compared to the baseline one.

Friction stir welding of AA2024-T3 and SS304 alloys: microstructural analysis, microhardness evaluation, and tensile performance

This study examines the feasibility of friction stir welding (FSW) for dissimilar butt joints formed between 3 mm thick 2024-T3 aluminum alloy and AISI 304 stainless steel. It explores the impact of operational parameters, particularly traverse speeds of 20 and 40 mm min−1, a fixed tool rotation speed of 450 rpm, a tool pin offset of 1.5 mm, and a tool shoulder diameter of 18 mm, on microstructure, microhardness, and tensile strength. A traverse speed of 40 mm min−1 resulted in a lower peak temperature of 257.75 °C, while optimal conditions at a speed of 20 mm min−1 led to peak temperatures of 356.5 °C. This higher temperature facilitated material deformation, improved flow, enhanced mixing, and contributed to grain refinement, with an average grain size of 4.2 μm. Vickers microhardness tests revealed a maximum hardness of 339 Hv at a traverse speed of 40 mm min−1 and 413 Hv at 20 mm min−1. The ultimate tensile strength (UTS) reached 338 MPa, resulting in a joint efficiency (JE %) of 76.81% for the weld performed at optimal conditions.

Facile preparation of Fe-Beta zeolite-supported transition metal oxide catalysts and their catalytic performance for the simultaneous removal of NOx and soot

Diesel engine exhaust comprises nitrogen oxides (NOx) and soot particles, which cause serious air pollution. However, owing to the contradictory nature of NOx reduction and soot oxidation, a trade-off exists in the simultaneous removal of NOx and soot. Consequently, catalytic technology has become a hot research topic. This study prepared MOδ/Fe-Beta (M=Fe, Co, Ni, Mn, Cu) catalysts through incipient wetness impregnation using Fe-Beta as the support and explored the catalytic performance of the above catalysts. The results exhibited the good performance of the prepared catalysts. The introduction of Mn resulted in a lower peak temperature of soot combustion for the catalyst, and slightly decreased deNOx performance of Fe-Beta. The soot combustion temperature was as low as 422 °C, and the temperature window for 80% NO conversion was 164–423 °C. The interaction between MnOδ and zeolite can regulate the acid sites and produce sufficient active oxygen species for the catalyst. The catalytic activity of the MnOδ/Fe-Beta catalyst is due to its strong redox property, appropriate number of acid sites and sufficient number of active oxygen species. In addition, the catalyst had good stability and water and sulfur resistance, therefore it had great potential for future application in simultaneous removal of NOx and soot from diesel engine exhaust.

Experimental and numerical investigation on the combustion behavior of densified wood: Differences among wood species and impact of char oxidation

Densified wood (DW) is a novel structural material with promissing application potential in construction industry due to its excellent mechanical performance. However, it could also be a disastrous fuel contributing to the development of fires. This work experimentally and numerically investigated the combustion behavior of DW. The differences among wood species (fir, pine and oak) and their char oxidation impacts are emphasized. The experimental results indicate that DW has a 44.7 K lower pyrolysis peak temperature on average, a 32.2 % lower peak mass loss rate, and a 8 % higher residual mass ratio than natural wood (NW) in N2 due to the delignification process. The hemicellulose and cellulose pyrolysis are endothermic in N2 but exothermic in air. Wood pyrolysis has an additional char oxidation reaction in air. The higher density of DW leads to longer times for ignition and flaming combustion. DW presents a higher heat release rate and average 4.7 MJ kg−1 higher effective heat of combustion of char. Two parallel pyrolysis reaction schemes based on ambiance are proposed, which well-predict the microscale characterizations but fail to represent the combustion behavior. An optimized mode was developed by adding a continuous char oxidation reaction to the N2 reaction scheme, which best predicts the combustion behaviors.

Interfacial microstructure and mechanical property of dissimilar resistance spot welded joint of TC4 titanium alloy and 316L stainless steel with nickel interlayer

Dissimilar materials of TC4 titanium alloy and 316L stainless steel were joined by means of resistance spot welding with nickel interlayer in different thicknesses. A significant enhancement in terms of nugget morphology quality with less defects was achieved for the welded joints with nickel interlayer compared with that without interlayer. With increasing the nickel interlayer thickness from 50 μm to 300 μm, the effective nugget diameter increased gradually from ∼4.8 mm to ∼5.2 mm, which was lower than that of the interlayer-free welded joint being ∼5.9 mm. A thinner intermetallic compound layer with dual-layered structure features with thickness of ∼11 μm was formed at the nugget/titanium interface in the welded joint with nickel interlayer compared with that of the interlayer-free welded joint, meanwhile an intermetallic compound layer with thickness of ∼3 μm was formed at the nugget/stainless steel interface, which exhibited serrated structure features. The introduction of nickel interlayer in the welded joint could suppress the formation of the brittle Ti–Fe intermetallics such as Fe2Ti, and facilitate the formation of TiNi, Ti2Ni and TiNi3. A more homogeneous current density distribution and a lower peak temperature (1809 °C) during welding were achieved via employing nickel interlayer. With increasing nickel interlayer thickness from 0 μm to 300 μm, the tensile shear load of welded joints experienced an increased tendency first and then decreased, meanwhile the maximum tensile shear load of 3.7 kN was obtained with the interlayer thickness of 200 μm, which was 61% higher than that of the interlayer-free welded joint.