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Increasing the proportion of bainite and martensite phases is one of the effective ways to enhance the toughness of medium-carbon low-alloy steel(42CrMo). In this paper, the surface heat treatment of 42CrMo steel is carried out by using a laser heat source to achieve complete austenitization, then with electromagnetic induction heating for several times to implement insulation, and eventually to promote bainite phase transformation. In conjunction with the temperature history curves, OM, SEM, and EBSD are used to characterize the bainite morphology and percentage of bainite via different parameters of the hybrid process. The results demonstrate that the hybrid process combined with twice electromagnetic induction heating can yield a considerable proportion of bainite phase in 42CrMo steel. The resulting duplex structure, consisting of bainite and a minor fraction of martensite, exhibits a significant increase (81.1%) in tensile strength, while maintaining similar impact toughness. The elongation after fracture only has a slight reduction of 5.5% compared to that of the substrate. This innovative process provides a practical alternative to traditional bainite isothermal treatment method which must perform in a heat treatment furnace. Therefore, it is presented as a promising solution for enhancing the mechanical properties of medium-carbon low-alloy high strength steels.

ABSTRACTA comprehensive control methodology has been developed to address challenges such as temperature fluctuations, inconsistent depth penetration, and compositional integrity variations during laser-induction hybrid strengthening performed with consistent power parameters. This approach synergistically integrates a fuzzy controller and a decoupling compensator. In the initial part of this study, a temperature field model was utilized to investigate the effects of different process factors on temperature profiles. The analysis of step response data facilitated the development of mathematical models that delineate the correlation between the input factors and output responses. Subsequently, a decoupling compensation technique was used to reduce the coupling effects between temperature and its rate of change. A fuzzy controller was then developed to reduce the system's reliance on mathematical models, hence improving the accuracy of the control strategy. The results indicate that the application of fuzzy PI control and the implementation of decoupling compensation, the control strategy successfully improves the performance of the controller by minimizing parameter interactions. This strategy also incorporates real-time adjustment of PI parameters. Compared to conventional PI control, this method offers improved response speed and reduced overshoot. The laser-induction hybrid strengthening technique ensures superior temperature control, maintaining steady-state temperature precision within a 1% tolerance.

Element segregation and texture control are two prominent challenges for Inconel 718 repairing via laser cladding. Hence, the electromagnetic field was introduced in the laser cladding of Inconel 718 in this paper. The effect of thermal-electromagnetic convection, magnetic torque, and electromigration induced by electromagnetic field on element segregation and texture of Inconel 718 was studied. Results show element segregation is suppressed due to thermal-electromagnetic convection and electromigration. More Nb and Ti are solid-dissolved into the γ matrix. The average fraction of the Laves phase reduces from 6.44 % to 4.04 %, while the morphology of the Laves phase is modified from long-chain-like to discrete wormlike and exhibits smaller size, owing to modified element segregation. Moreover, magnetic torque drives the rod crystal to rotate with the applied electromagnetic field and thereby the long axis of the rod crystal deviates from direction. The maximum multiple of uniform density decreases from 7.54 to 2.97. This study provides a promising method to weaken texture and element segregation in laser additive manufacturing.

The effective welding of a 6 mm thick TA2 pure titanium medium-thickness plate was achieved by laser–arc hybrid welding (LAHW) with helium–argon mixed shielding gas. Conducted research on the influence of helium–argon mixed shielding gas on plasma and arc characteristics during welding, and its further impact on the microstructure, internal porosity defects, tensile properties, and corrosion resistance of welded joints was explored. The study demonstrated that under the shielding gas with 75% helium, the arc width narrowed significantly from 6.96 mm to 2.61 mm, achieving a 63% reduction, which enhanced the concentration of arc heat flux density. Achieved a well-formed weld with no surface spatter and significantly reduced the internal porosity rate from 3.02% to 0.47%, which is an 84% decrease. Tensile fractures are located in the base material, all exhibiting plastic failure. The corrosion resistance of the welded joint initially increased and then decreased with the increase of helium content in the shielding gas, peaking at 75% helium content.

Разом з режимами обробки, властивостями матеріалу деталі та порошку та інш., від якості «фокусування» газопорошкового струменя (ГПС) в зону дії лазерного випромінювання цілком та повністю залежить продуктивність, якість та економічні показники лазерного газопорошкового наплавлення (ЛГПН), швидкого виготовлення виробів по технології направленого лазерного плавлення та легування поверхні виробів. На жаль, в літературі майже не висвітлено етапи та методи проектування систем подачі ГПС в зону дії сфокусованого лазерного випромінювання, прості методи вимірювання його параметрів та контролю. Розробка методики проектування та створення систем подачі ГПС в зону дії сфокусованого лазерного випромінювання, які задіяні при реалізації процесів ЛГПН та простих методів контролю параметрів ГПС. При досягнені поставленої мети (крім евристичних) використовуються чисельні методи векторної оптики, газової динаміки та методи обробки відеозображень. Розроблені оригінальні системи для реалізації ЛГПН, що забезпечують підвищення продуктивність операції, яка виконується за рахунок зменшення масових витрат порошкового матеріалу. Встановлено, що в просторі проектування, багатоканальні системи подачі ГПС в зону дії сфокусованого лазерного випромінювання (в порівнянні з одноканальними або коаксіальними системами) забезпечують підвищення продуктивності операції, яка виконується (особливо при обробці поверхонь, які лежать під кутом до горизонту) та дозволяють подавати в зону обробки порошкові суміші різного хімічного складу.

Warpage deformation inevitably occurs when laser powder bed fusion (LPBF) is applied on an overhanging structure. An effective support added to the system can mitigate warpage and improve the accuracy of formed parts. Four types of support structures are designed, and sheet tensile specimens and overhanging structures with different support structures are fabricated in this study. The tensile failure behavior and warpage suppression ability of different support structures are investigated, with the relation of the support influence to the design of support structure analyzed. The results show that the support with reinforcement can effectively restrain warpage deformation of the overhanging structure. During the process of tension, the main failure area of the support structure is located on the top of the support structure, close to the overhanging solid body. Increasing the change ratio of the support cross-sectional area is helpful to improve the constraint ability of the support. This design provides a new method for accurate forming of overhanging structures via LPBF and evaluating the restrain ability of support structures.

This paper analyzes the OBL strategy’s impact on optimizing the GWO algorithm and identifies three shortcomings. the specific limitations of the OBL optimization approach. To address these three shortcomings and enhance both global optimization and local exploration capabilities of GWO, this paper introduces a follow-controlled opposition learning strategy. then, the paper analyzes the control parameter C of the grey wolf algorithm to investigate its impact on global optimization and local exploration. Based on these properties, a new control parameter C is proposed. The proposed learning strategy and control parameter C are introduced into the traditional grey wolf algorithm to obtain the FCGWO algorithm. Finally, this paper conducts a comparative analysis of the FCGWO algorithm in comparison to other meta-heuristic algorithms, as well as the enhanced grey wolf algorithm, utilizing 23 benchmark test functions and 2 engineering problems. The results indicate that FCGWO effectively avoids the shortcomings of the traditional OBL, while also outperforming other algorithms significantly in terms of solution quality.

Calcium sulfoaluminate (CSA) cement, as a type of low-carbon cement, can contribute to further reduction in carbon emissions with carbonation technologies. However, the detailed microstructure development of CSA cement during the carbonation process has been rarely analyzed. In this paper, wet carbonation was applied to CSA cement to investigate the microstructure evolution of carbonation products and carbon absorption capacity of CSA cement by means of pH measurement, X-ray diffraction (XRD) measurement, thermogravimetric (TG) measurement, Fourier-transformed infrared spectroscopy (FT-IR) measurement and scanning electron microscope measurement. During the carbonation process, the formed ettringite product and the dicalcium silicate clinker were carbonated immediately to generate calcium carbonate crystals, silica gel and aluminum hydroxide (AH3) gel. With the trend of pH increasing first and notably decreasing later, the coupling interaction between the hydration and carbonation reactions of CSA cement was revealed. From the XRD and TG results, three types of calcium carbonate crystal forms (calcite, vaterite and aragonite) were detected, and the content of calcium carbonate increased with the increase in carbonation time. FT-IR analysis further confirmed the existence of calcium carbonate, silica gel and AH3 gel with their characteristic vibrations. Moreover, the microstructure of carbonation products with different morphologies was observed. The application of wet carbonation to CSA cement provides a more comprehensive insight to the carbonation mechanism of this low-carbon cement.

To research viscosity fitting model of stable nano-lithium bromide solution (nano-LiBr), the stability of the nano-LiBr and the dynamic viscosity of LiBr were measued by Ultraviolet-visible spectroscopy (UV-vis) and rotational viscometer respectively. Two LiBr with different additives were measured, i.e., LiBr with dispersant (E414) and LiBr with dispersant + copper oxide nanoparticles (CuO). The ranges of measuring temperature were from 25°C–60°C, the concentrations of LiBr were from 50%–59%, the volume fractions of the dispersants were from 0%–4%, and the fractions of nanoparticle volume were from 0%–0.05%. Results indicated that the nano-LiBr with E414 had good stability. The viscosity of the LiBr decreased when temperature increased, and increased when LiBr concentration and dispersant amount were increased. It is also found that the viscosity was directly proportional to the volume fraction of the nanoparticles. This study also showed that the higher the concentration of the base fluid was, the more significant increase of the viscosity was. An empirical viscosity model of stable nano-LiBr with a maximum error of 13% was developed.

Applying rock-filled gabion to buildings in cold regions with mountainous climates has multiple potentials, such as utilizing rock resources, improving building sustainability and saving building energy. Therefore, it is necessary to analyze the thermal performance of gabion buildings. Based on the CFD method, this paper establishes a numerical model of buildings with gabion enclosure structures, analyzes the influence of the gabion structure on the external convective heat transfer coefficient (CHTC), wind pressure, air infiltration, room temperature and building load, and further uses the building energy consumption simulation method to analyze the heat load of gabion buildings. The results showed that the adverse impact of climate on the building thermal performance is significantly diminished by the gabion. Under different weather conditions, the CHTC, the maximum wind pressure difference on the exterior surface, and the air infiltration rate are reduced by different rates. Further, the room base temperature increases throughout the heating season, and the maximum heat load and the cumulative heat load of the building are, respectively, reduced by 10.6% and 24.8%. This work revealed that the gabion is an eco-friendly and adaptive measure to improve thermal performance and indoor thermal comfort.

Diamond/copper composite coating is promising for wear-resistant applications, owing to the extreme hardness of the diamond reinforcement. Ti-coated diamond/copper composite coatings with various laser powers were successfully fabricated employing the novel manufacturing technology of supersonic laser deposition (SLD). Ti-coated diamond, which was able to enhance the wettability between diamond and copper, was prepared at the optimal parameters via salt bath. Nano-spherical titanium carbides were uniformly distributed on the diamond’s surface to generate a favorable interface bonding with a copper matrix though mechanical interlocking and metallurgical bonding during impact. Furthermore, the results showed that the transition layer acted as a buffer, preventing the breakage of the diamond in the coating. SLD can prevent the graphitization of the diamonds in the coating due to its low processing temperature. The coordination of laser and diamond metallization significantly improved the tribological properties of the diamond/copper composite coatings with the SLD technique. The microhardness of the diamond/copper composite coating at a laser power of 1000 W reached about 172.58 HV0.1, which was clearly harder than that of the cold sprayed copper. The wear test illustrated that the diamond/copper composite coating at a laser power of 1000 W exhibited a low friction coefficient of 0.44 and a minimal wear rate of 11.85 μm3·N−1·mm−1. SLD technology shows great potential in the field of preparing wear-resistant hard reinforced phase composite coatings.

Tungsten carbide based cemented carbides, often simply termed hardmetals, are established forefront materials for tools, structural components, and wear parts with stringent requirements. Several of the technological applications in which they are used include exposure to chemically aggressive media. Under these conditions, failure induced under applied load may be accelerated; and consequently, the service life may be decreased. Within this context, this work addresses the influence of corrosion-induced damage on the mechanical integrity and load-bearing capability of hardmetals at different length scales, i.e., from 100s nanometers to 1000s microns. Experimental data acquired by means of nanoindentation, pyramidal, and spherical indentation, as well as sliding contact (micro- and nanoscratch) techniques, are presented. The attained results allow for identifying guidelines for the microstructural design of these materials under combined consideration of corrosion and mechanical contact as service-like conditions. Discussion of the reported findings includes a critical analysis of corrosion effects on the evolution of microstructure-property-performance interrelations for the materials under consideration.

The lubricant behaviour at elevated temperatures was investigated by conducting pin-on-disc tests between P20 tool steel and AA7075 aluminium alloy. The evolutions of coefficient of friction (COF) at elevated temperatures showed three distinct stages: stage I (low friction stage), in which boundary lubrication was prevalent and the coefficient of friction was low; stage II (transient stage), in which the lubricant film thickness decreased to a critical value and the coefficient of friction increased rapidly; and stage III (breakdown stage), in which the lubricant was completely removed from the interface and the coefficient of friction was equal to its value under dry sliding conditions. In the present work, 2 types of water-graphite based lubricants were studied by pin-on-disc tests under different contact conditions. The effects of tooling and workpiece temperature determined from the experimental results were investigated in this paper and a comparison with an oil-graphite based lubricant was conducted.

Laser cladding is a promising surface modification technology to fabricate high-performance parts. However, defects such as porosity, cracks and residual tensile stress are easily produced in laser cladding, leading to significant property reduction and poor reliability. In this study, laser cladding with multidimensional high-frequency vibration was investigated. The effects of multidimensional high-frequency vibration on the improvement of microstructure and mechanical properties were analyzed and discussed based on the vibration-assisted laser cladding experiments. In addition, a numerical model was conducted to help understand the significance of the vibration on flow field and temperature field. Results show that 3D vibration led to the primary dendrite spacing reduction from 11.1 to 6.8 μm, microhardness increase from 199 to 221 HV0.2, and a nearly 110% improvement in the elongations. The findings of this study confirmed the significant benefits of multidimensional high-frequency vibration applied in laser cladding and provided a basis to uncover the underlying mechanisms of multidimensional vibration on the rapid melting and solidification.

NOx emission reduction from gas boilers has become a key issue in improving air quality. Combustion air humidification technology is gradually being used to reduce NOx emissions. However, the NOx emission reduction effect of gas boilers at a higher combustion air humidity has been studied less. A flue gas with low NOx emissions and a waste heat recovery system using combustion air humidification technology are proposed in this study. In the ultra-low NOx mode, the effect of high combustion air humidity on NOx emission reduction and efficiency of the gas boiler were studied experimentally. In the waste heat recovery mode, the effects of the heat network backwater temperature on the NOx emission reduction and system efficiency were studied experimentally. Results showed that an increase in air humidity can significantly reduce the NOx concentration formed by combustion. The ultra-low NOx mode reduces NOx emissions from 130mg/m3 to 23.3 mg/m3 and affects the boiler efficiency slightly. In the waste heat recovery mode, NOx emissions can be reduced to 39.9mg/m3 when the backwater temperature of the heat network is 55 °C. This condition improves the efficiency to 93.8%. The analysis results provide suggestions for the selection of the operation modes. [ABSTRACT FROM AUTHOR]

Hot corrosion is one of the crucial failure modes of Ni-based superalloy components operating at high temperatures, which inevitably affects the subsequent mechanical properties of the alloys. In this research, damaged Inconel 718 alloy components with a pre-made trapezoid groove are repaired using laser additive manufacturing technique, and the change mechanisms of the microstructure and tensile properties of the repaired Inconel 718 alloy due to the hot corrosion in the salt mixture of 87.5 wt.% Na2SO4 + 5 wt.% NaCl + 7.5 wt.% NaNO3 at 650 °C for different durations are investigated. The results show that oxidation and Cr-depletion occur on the repaired components due to the hot corrosion, and the corrosion products are mainly composed of Cr2O3, Fe3O4, and Ni3S2. The tensile strength and elongation of the as-repaired specimens are 736.6 MPa and 12.5%, respectively. After being hot corroded for 50 h, the tensile strength increases to 1022.9 MPa and elongation decreases to 1.7%. However, after being hot corroded for 150 h, both tensile strength and elongation of the repaired specimens drop to 955.8 MPa and 1.2%, respectively. The mechanical performance alteration is highly related to thermal effects instead of the molten salt attack.

The hot-wall heat exchanger (HWHE) has been widely used in thermal engineering fields such as ceiling radiant heating/cooling, refrigerator condenser, solar heat collection, and high-temperature heat recovery. However, the numerical simulation normally used for heat transfer prediction in HWHE is usually not as convenient as the analytic solutions in engineering applications. In this paper, a new heat transfer mathematical model of HWHE-based on analytic solutions was developed, which could be much faster to obtain the heat transfer properties of HWHE. The proposed model was validated under four conditions with literature values, which showed that the deviations of heat flux are 2.53%, 0.99%, 2.12%, and 1.96%, indicating its accuracy is satisfied. The model was then used to analyze the thermal property of HWHE. The results show the thermal resistance caused by panel with heat convection and conduction accounts for 96.54% of HWHE thermal resistance, and the thermal resistance caused by heat convection on the surface of panel is 74.43%. The analyzation results also show that adding aluminum foil around pipes could decrease HWHE thermal resistance by 5.11%. Besides, the influence of pipe diameters, pipe distance, pipe heat conductivity, side wall heat conductivity, and convective heat transfer coefficient on the heat transfer performance of HWHE was analyzed. The research in this paper can be used for fast prediction and optimization of heat transfer in HWHE.