Low Dilution Rates Research Articles

Impact of Heat Input on the Cladding of Super Austenitic Stainless Steel Through the Gas Tungsten Arc Welding Process on ASTM A516 Grade 70 Steel

The cladding process reduces manufacturing costs by depositing super austenitic stainless steel onto low-carbon steel. Arc welding techniques, especially gas tungsten arc welding (GTAW), are commonly used for this purpose. This study evaluates the influence of heat input on cladding performance. Macroscopic analysis showed good fusion of the weld beads to the base metal with no defects. Higher heat input resulted in a lower dilution rate due to increased reinforcement. A microstructural analysis of the heat-affected zones revealed similar characteristics, with martensite formation attributed to cooling conditions. Increased microhardness was observed at the interface between the cladding and base metal, corroborating the microstructural findings. Additionally, a significant enhancement in corrosion resistance was noted in the deposited layers. This research contributes to optimizing cladding processes, ensuring better material performance in industrial applications.

Recycling potential of Cupriavidus necator for life support in space: Production of SCPs from volatile fatty acid and urea mixture

The International Space Station currently requires four annual replenishments for food supply, a practice that won't be feasible for deep space missions due to the greater distances. Based on the design of closed ecological life support systems, two waste streams were identified: urea from the crew urine, volatile fatty acids (VFAs) from a first stage of anaerobic digestion of waste. The objective of this study was to assess the ability of bacterium Cupriavidus necator to produce single cell protein on urea and VFAs. Thus, the effect of carbon sources (glucose vs VFAs) and the dilution rate on the biomass composition was determined in continuous cultures. Complete transformation of the carbon source into protein-rich biomass was achieved up to 78 % cell dry weight (CDW). For both carbon sources, the protein content increased from 55.0 %CDW to 78 %CDW with a decrease in the dilution rate. Conversely, the nucleic acid and polyhydroxyalkanoate contents decreased with the dilution rate from 8.8 %CDW to 4.8 %CDW and 9.8 %CDW to 0.6 %CDW respectively. Working at a low dilution rate seems to be a good way to maximize protein content while minimizing unwanted nucleic acids and polyhydroxyalkanoates.

Achieving excellent properties of laser tailor-welded thin Al-Si coated press-hardened steel joint via controlling dilution rate

In laser tailor welded traditional 25 μm thick Al-Si coated press-hardened steel (PHS), a lot of ferrite was easily formed in the weld, so filling with expensive high-alloys wire is usually necessary. In this work, a new thin Al-Si coated PHS with 18 μm thickness was laser tailor welded, and a cheap low alloy wire was attempted to fill into the weld to via control the dilution rate. At a high dilution rate of 94%, the weld contained a ferrite fraction of 38%, resulting in the fracture occurring in the weld during tension and bending. At a medium dilution rate of 85%, the ferrite fraction in the weld decreased to 18%, obtaining excellent tensile and bending properties. The tensile strength and elongation of the joint reached 1528 MPa and 5.6%, respectively, with fracture being in the base metal (BM). The maximum bending load and displacement were 1291 N and 7.0 mm, respectively, and cracks initiated and propagated in the BM. This is attributed to the small amount of ferrite and stress concentration in the narrow weld. At a low dilution rate of 76%, the ferrite reduced to 6%, and the bending cracks initiated and propagated in the BM. However, the tensile specimen fractured in the weld, which should be related to the relatively low C concentration and the stress concentration at the weld toe due to the weld reinforcements.

High-solid digestion – A comparison of completely stirred and plug-flow reactor systems

High-solid digestion (HSD) for biogas production is a resource-efficient and sustainable method to treat organic wastes with high total solids content and obtain renewable energy and an organic fertiliser, using a lower dilution rate than in the more common wet digestion process. This study examined the effect of reactor type on the performance of an HSD process, comparing plug-flow (PFR) type reactors developed for continuous HSD processes, and completely stirred-tank reactors (CSTRs) commonly used for wet digestion. The HSD process was operated in thermophilic conditions (52 °C), with a mixture of household waste, garden waste and agricultural residues (total solids content 27–28 %). The PFRs showed slightly better performance, with higher specific methane production and nitrogen mineralisation than the CSTRs, while the reduction of volatile solids was the same in both reactor types. Results from 16S rRNA gene sequencing showed a significant difference in the microbial population, potentially related to large differences in stirring speed between the reactor types (1 rpm in PFRs and 70–150 rpm in CSTRs, respectively). The bacterial community was dominated by the genus Defluviitoga in the PFRs and order MBA03 in the CSTRs. For the archaeal community, there was a predominance of the genus Methanoculleus in the PFRs, and of the genera Methanosarcina and Methanothermobacter in the CSTRs. Despite these shifts in microbiology, the results showed that stable digestion of substrates with high total solids content can be achieved in both reactor types, indicating flexibility in the choice of technique for HSD processes.

Microstructure, corrosion resistance and high temperature oxidation properties of AlCrFeNiCu high-entropy alloy coating by high-speed laser cladding

AlCrFeNiCu high-entropy alloy (HEA) coating was prepared on Zirconium (Zr) rod by high-speed laser cladding (HSLC) technique. The effect of different laser power and scanning speed on the forming quality of the coating was studied. When the specific energy density was in the range of 3.0–3.2 J/mm2, the AlCrFeNiCu HEA coating with good adhesion to the substrate, low dilution rate (small heat affected zone) and no cracks were obtained. The phase structure, microstructure, microhardness, corrosion resistance and high temperature oxidation resistance of the coating were tested and analyzed. The results show that the AlCrFeNiCu HEA coating is composed of 76.9 % BCC phase and 23.1 % FCC phase, in which the BCC phase is mainly composed of disordered BCC phase rich in Cr and Fe elements and ordered B2 phase rich in Al and Ni elements, and the FCC phase is rich in Cu elements. Due to the rapid cooling of HSLC, the coating structure gradually changes from columnar crystal to equiaxial crystal from bottom to top. The hardness of the coating is as high as 805 HV, which may be caused by the solution strengthening effect, lattice distortion effect and slow diffusion effect of HEA. In 3.5 % NaCl solution and 0.1 mol/L KOH solution, the self-corrosion current density of the coating is 4.209 × 10−8 A/cm2 and 4.331 × 10−8 A/cm2, respectively. The passivation film on the surface of the coating is composed of a variety of oxides, and the oxygen vacancy density of the passivation film in the two solutions is 2.552 × 1020 cm−3 and 5.794 × 1020 cm−3, with fewer pitting pits on the surface. The structural integrity of the coating can be maintained after 60 min oxidation at 1200 °C. The oxidation process follows the growth kinetics curve, and the surface oxides mainly comprise FeAl2O4, Al2O3 and Cr2O3. AlCrFeNiCu HEA coating improves the corrosion resistance and high temperature oxidation resistance of the Zr-4 alloy.

Microstructure and hardness of CoNiCrFeTix high-entropy alloy coatings prepared by laser cladding: Combining experimental and molecular dynamics simulation

Laser cladding technology offers several advantages over alternative coating methods, including rapid cooling, low dilution rate, and effective metallurgical bonding between the coating and matrix. However, there is limited understanding regarding the microstructures and properties of laser-cladded high-entropy alloy (HEA) coatings. Thus, our research aims to investigate the characteristics and performance of CoNiCrFeTix (x = 0.1, 0.3, 0.5, 0.7) HEA coatings, produced through laser cladding, on Q235 steel substrates We employ molecular dynamics (MD) simulation and experimental techniques to examine the impact of Ti element content on the structure and hardness of the cladding layer. The MD simulation accurately reproduces the melting and nucleation processes of crystal structures, providing insights beyond what is observable through experiments alone. Our results reveal that the cladding layer is predominantly composed of an FCC phase, with an increasing presence of a BCC phase as the Ti content rises. Correspondingly, experimental observations confirm that the CoNiCrFeTix HEA coating primarily consists of the FCC phase, while FeCr, Ni2Ti, and Co2Ti phases emerge with higher Ti content.The cladding layer exhibits a characteristic dendritic (DR) structure, where the interdendritic (ID) region expands as Ti content increases. Additionally, we conducted surface hardness testing on the cladding layer. The hardness of the cladding layer increases with the increase of Ti content, and the increase in Ti content enhances the stability of the dislocation density in the cladding layer.

Airlift bioreactor–based strategies for prolonged semi-continuous cultivation of edible Agaricomycetes

Submerged cultivation of edible filamentous fungi (Agaricomycetes) in bioreactors enables maximum mass transfer of nutrients and has the potential to increase the volumetric productivity of fungal biomass compared to solid state cultivation. These aspects are paramount if one wants to increase the range of bioactives (e.g. glucans) in convenient time frames. In this study, Trametes versicolor (M9911) outperformed four other Agaricomycetes tested strains (during batch cultivations in an airlift bioreactor). This strain was therefore further tested in semi-continuous cultivation. Continuous and semi-continuous cultivations (driven by the dilution rate, D) are the preferred bioprocess strategies for biomass production. We examined the semi-continuous cultivation of T. versicolor at dilution rates between 0.02 and 0.1 h−1. A maximum volumetric productivity of 0.87 g/L/h was obtained with a D of 0.1 h−1 but with a lower total biomass production (cell dry weight, CDW 8.7 g/L) than the one obtained at lower dilution rates (12.3 g/L at D of 0.04 and vs 13.4 g/L, at a D of 0.02 h−1). However, growth at a D of 0.1 h−1 resulted in a very short fermentation (18 h) which terminated due to washout (the specific D exceeded the maximum growth rate of the fungal biomass). At a D of 0.04 h−1, a CDW of 12.3 g/L was achieved without compromising the total residence time (184 h) of the fermentation. While the D of 0.04 h−1 and 0.07 h−1 achieved comparable volumetric productivities (0.5 g/L/h), the total duration of the fermentation at D of 0.07 h−1 was only 85 h. The highest glucan content of cells (27.8 as percentage of CDW) was obtained at a D of 0.07 h−1, while the lowest glucan content was observed in T. versicolor cells grown at a D of 0.02 h−1.Key points• The highest reported volumetric productivity for fungal biomass was 0.87 g/L/h.• Semi-continuous fermentation at D of 0.02 h−1 resulted in 13.4 g/L of fungal biomass.• Semi-continuous fermentation at D of 0.07 h−1 resulted in fungal biomass with 28% of total glucans.

Rapid preparation of nanocrystalline high-entropy alloy coating with extremely low dilution rate and excellent corrosion resistance via ultra-high-speed laser cladding

Ultra-high-speed laser cladding (UHSLC) not only offers an efficient solution to the limitations of conventional laser cladding but also aligns with the contemporary objectives of material conservation and efficiency enhancement in metal protective coatings. This study investigates the fabrication of CrFeCoNiMo0.2 high-entropy alloy (HEA) coatings using UHSLC and traditional laser cladding (TLC) methods. Key aspects such as macroscopic forming quality, element distribution, dilution rate, grain morphology, hardness, and electrochemical corrosion properties of both UHSLC and TLC coatings are thoroughly examined. Notably, UHSLC-produced coatings, with their significantly reduced thickness ranging from 100 to 300 μm, demonstrate an impressively low substrate dilution rate compared to the 2–3 mm thickness of TLC coatings. The rapid solidification inherent in UHSLC leads to smaller grain sizes in the coating, resulting in enhanced hardness. Moreover, the UHSLC coating exhibits superior corrosion resistance, characterized by a lower maintaining-passivity current density in 1 mol/L H2SO4 and a higher self-corrosion potential relative to TLC coatings. This work presents a novel approach, employing high-efficiency and low-cost laser-cladding technology, to minimize dilution in the matrix and improve the coating properties of HEAs.

The Effect of Laser Power on the Microstructure and Wear Resistance of a Ni3Al-Based Alloy Cladding Layer Deposited via Laser Cladding

A coating prepared via laser cladding has the advantages of a high-density reinforced layer, a low matrix dilution rate, and combination with matrix metallurgy. In this study, Ni3Al-based alloy cladding layers with Cr7C3 were prepared via laser cladding, and the corresponding microstructures and wear resistance were studied in detail. The results show that the Ni3Al-based cladding layer prepared using laser cladding technology had good metallurgical bonding with the matrix, and there were no pores, cracks, or other defects on the surface. The microstructures of the laser cladding layer were mainly γ′-Ni3Al, β′-NiAl, and in situ C7C3. As the laser power increased, the heat input increased, resulting in an increase in the dilution rate. Simultaneously, the carbide size in the laser cladding layer increased. With the increase in laser power, the hardness of the laser cladding layer of the Ni3Al-based alloy decreased, and the wear resistance of the laser cladding layer first strengthened and then weakened. When the laser power increased to 2.0 kW, the wear rate of the laser cladding layer decreased to 0.480 × 10−5 mm3/N·m. When the laser power increased to 2.4 kW, the wear rate of the laser cladding layer increased to 0.961 × 10−5 mm3/N·m, which was twice the rate at 2.0 kW. This could be attributed to small Cr7C3 particles, which could not effectively separate the wear pairs, resulting in more serious adhesive wear. Large Cr7C3 particles caused the surface of cast iron material with lower hardness to be damaged, which suffered more serious particle wear. The generation of short rod-shaped carbides should be avoided because, in the process of friction and wear, carbides with these shapes are easy to break, thus leading to crack initiation.

Enhancement mechanisms of self-lubricating Ti3SiC2 ceramic doping in CoCrFeNi high-entropy alloy via high-speed laser cladding: Tribology and electrochemical corrosion

High-entropy alloys (HEAs) are renowned for their superior mechanical properties and corrosion resistance, positioning them as promising materials in the realm of wear and corrosion-resistant applications. In this study, CoCrFeNi HEA coatings were fabricated utilizing the high-speed laser cladding (HLC), and the effects of adding Ti3SiC2 self-lubricating phase on the microstructure, wear resistance, and electrochemical corrosion performance of CoCrFeNi HEA coatings was investigated. The results show that CoCrFeNi HEA coatings synthesized via HLC exhibit an impressively low dilution rate of <0.1 %, while concurrently ensuring a robust metallurgical bond with the substrate. CoCrFeNi coating has an FCC simple solid solution structure. Upon the addition of Ti3SiC2, the composite structure comprises FCC, Ti3SiC2, and TiC phases. The friction coefficients (COFs) of CoCrFeNi coating and the coatings with 3, 6, and 9 at.% Ti3SiC2 content are 0.684, 0.628, 0.429, and 0.426, respectively. Predominantly, the wear mechanisms observed encompass abrasive wear, adhesive wear, and oxidative wear. Intriguingly, when the Ti3SiC2 content reaches 6 at.%, a contiguous self-lubricating layer forms within the wear track, leading to a notable reduction in COF and a marked enhancement in wear resistance. In electrochemical corrosion evaluations, the coatings demonstrated polarization resistances of 11,400, 9923, 9654, and 6125 Ω·cm2, respectively. While Ti3SiC2 exhibits commendable passivation capabilities, an elevated Ti3SiC2 content can expedite corrosion processes by fostering a potential difference battery formation on the coating surface.

Switching from wet to dry anaerobic digestion of food waste with different dilution times under no mechanical mixing condition

Previous research on anaerobic digestion of food waste has primarily focused on either wet or dry anaerobic digestion (AD), typically accompanied by continuous mechanical mixing. However, the necessary dilution rates and the extent of mixing required have yet to be addressed. In this study, we investigated switching from wet to dry AD of food waste without mechanical mixing, employing different dilution rates. Lab-scale anaerobic reactors were operated with dilution rates of 10, 5, and 2 times during Phases I (0–56 days), II (57–121 days), and III (122–209 days), respectively. The methane production rates were not significantly different (p > 0.05) across the dilution rates decreased from 10 to 2 times. Remarkably, the methane production in the anaerobic reactors exhibited fluctuations due to variations in feeding, with the methane production rate ranging from 2.0 to 2.7 g CH4-COD/(L d), without mechanical mixing, as the solids content transitioned from wet to near-dry digestion conditions (15 %, food waste). The distribution of sludge volatile solids concentrations remained uniform in the reactor, even at high solids concentrations of up to 15 %. A dynamic microbial community response to changes in dilution rates, with a shift from aceticlastic to hydrogenotrophic methanogenesis pathways. Syntrophic acetate oxidization bacteria (the genus Syner-01 (4.2–8.9 %) and f_Synergistaceae (3.6–4.2 %)) were highly enriched as switching from wet AD to dry AD. The study's findings provide crucial operational insights for anaerobic food waste treatment, potentially resulting in decreased water usage and operational costs, particularly in scenarios with low dilution rates and without mechanical mixing.

Optimizing aquaculture-scale common carp artificial reproduction: a novel approach to sperm cryopreservation using large-volume containers and elevated thawing temperatures

IntroductionThe successful cryopreservation of common carp sperm is crucial for its application in aquaculture and selective breeding programs. This study investigates the efficacy of cryopreserving sperm in large containers (5 mL) with a low dilution rate (1:1) in three different cryoprotective media and thawing in different conditions.MethodsThe developed method utilizes a low-ionic (hypotonic) cryoprotective medium, freezing with a controlled cooling rate, and high-temperature sperm thawing (60°C). The investigation employs a detailed spermatozoon motility assessment.ResultsPost-thaw motility of 32.3% ± 14% and initial curvilinear velocity of 89 ± 20 μm/s across 30 males were observed. Principal component analysis of sperm kinematic characteristics revealed distinct populations of sperm cells exhibiting varying responses to cryopreservation. The developed method achieved successful fertilization comparable to that of the non-frozen control group using sperm from a single cryotube (2.5 mL, approximately 50 * 109 spermatozoa) to fertilize 200 g of eggs (1:120,000 egg:spz).DiscussionThis novel approach demonstrates an effective cryopreservation protocol for common carp sperm in large-volume cryo-containers in combination with low-ionic cryomedia and high thawing temperature, providing methods well-suited for fisheries practices and selective breeding programs. Future studies of the biological properties of different sperm subpopulations in post-thaw sperm samples can contribute to a deeper understanding of sperm biology, improve cryopreservation techniques, and enhance the success rates of assisted reproductive technologies.

A Two-Stage Cascade for Increased High-Value Product Accumulation in Chlamydomonas asymmetrica

Cascade systems are used in the large-scale production of astaxanthin, facilitating a successful value-added process despite high accumulating costs. However, their application to other high-value products (HVPs), like lutein, β-carotene, chlorophylls, and fatty acids, remains unexplored. This study investigates Chlamydomonas asymmetica in chemostatic cultures, focusing on the impact of light and dilution rate. A two-stage cascade system is designed, combining high-light growth with low-light pigment accumulation. The results show potential for productivity improvement. Notably, the spacetime yield (STY) of Chlorophyll a increased by 20.96%, reaching 2.73 g·L−1·d−1 at the lowest dilution rate. Lutein maintains a consistent concentration of 22.34 mg·g−1, while β-carotene achieves a maximum STY of 3.60 mg·L·d−1. A cascade modification with a hollow fiber membrane significantly enhances HVP concentrations—Chlorophyll b, Lutein, Chlorophyll a, β-carotene, EPS, and GLA increase 27.23%, 38.95%, 31.88%, 86.19%, 128.7%, and 57.71%, respectively. STY improvements for these HVPs range from 1.78% to 82.96%. This study offers insights into C. asymmetica’s response and proposes a cascade modification for enhanced HVP production and downstream processing efficiency.

Review on High-Energy Beam Based Processing Technologies for Fabrication of Small Modular Reactor

The development of small modular reactors (SMRs) has attracted significant attention owing to the increasing interest in energy security and carbon neutrality worldwide. An SMR is an advanced nuclear reactor with a power capacity of up to 300 MWe per unit. To fabricate the SMR, innovative manufacturing technologies such as powder metallurgy hot isostatic pressing (PM-HIP), electron beam welding (EBW), and diode laser cladding (DLC) were introduced to reduce the fabrication cost and time. Particularly, this replaced arc-based welding and cladding with high-energy beam-based EBW and DLC. The EBW could provide one pass welding for extremely thick specimens. In addition, in the case of using the DLC, only one layer cladding was acceptable for corrosion protection owing to its low dilution rate. However, studies on the innovative manufacturing technologies were less reported because of technology security. In this study, recently reported research articles regarding the EBW and DLC were reviewed. In particular, local vacuum and reduced pressure electron beam studies were discussed by comparing their the arc welding results. Process parameter studies on the DLC were also reviewed to introduce appropriate optimized conditions for the industry application.

Comparing electrochemical pitting behavior and passive films of Fe-Cr-B alloy coatings manufactured via high deposition rate and conventional laser directed energy deposition

This study conducted a comparative analysis of the microstructural features and electrochemical pitting performance of high deposition rate laser directed energy deposition (H-LDED) and conventional laser directed energy deposition (LDED) Fe-Cr-B alloy coatings. It aimed to reveal the impact of process-induced microstructural differences on pitting performance. The microstructure of both coatings consists of a Fe-rich matrix phase and (Fe, Cr)2B phase. In comparison to LDED coatings, H-LDED coatings offer advantages due to their rapid solidification, resulting in significantly finer microstructure, reduced microelement segregation, and significantly lower dilution rates. However, H-LDED coatings exhibit higher porosity (0.06 %) compared to LDED coatings (0.02 %). Under identical chemical composition conditions, the thickness, structure, and composition of the passive film in both coatings are similar, indicating that microstructural differences have minimal impact on passive film formation. In cases of consistent coating thickness, dilution rate emerges as the most significant factor influencing corrosion resistance, while porosity plays a prominent role under uniform coating chemical composition conditions. In summary, the advantages of H-LDED coatings encompass high deposition efficiency and low dilution rates, allowing for the production of thin coatings that meet service requirements.

Effect of heat treatment on microstructure and properties of additively manufactured aluminum bronze-steel bimetallic structures

To achieve improved microstructure and mechanical properties, the bypass current metal inert gas welding (BC-MIG) with forced cooling was firstly utilized in the additive manufacturing of aluminum bronze-steel bi-metallic structures. Microstructure and mechanical properties, including tension strength, residual stresses, and hardness distribution, were studied with and without post-heat treatment. The results show that a sound metallurgical bonding interface was formed without any defect due to the low dilution rate from bypass coupled arc and high molten solidification rate from forced cooling, and the diffusion zone thickness was below 1.5 μm. Moreover, the as-fabricated microstructure displayed significant hierarchical heterogeneity due to uneven deformation of grains. After heat treatment, the sample exhibited reoriented grains and homogenized microstructure. Concurrently, dislocation density and residual stress reduced and achieved a uniform distribution recrystallization within the aluminum bronze alloy region and dislocation climb and slip phenomena within the steel portion. Consequently, the heat-treated specimen in the welding direction exhibits a 36.3% decrease in YS (249 MPa) and an 11% decrease in UTS (493 MPa), while the EL (65%) experiences a significant increase of 58.5%. In the building direction, the heat-treated specimen shows a 17.8% decrease in YS (124.6 MPa) and an 2.88% decrease in UTS (508.8 MPa), while the EL (55.8%) experiences an increase of 26.8%.

A Review of the Laser Cladding of Metal-Based Alloys, Ceramic-Reinforced Composites, Amorphous Alloys, and High-Entropy Alloys on Aluminum Alloys

As one of the lightest structural metals, the application breadth of aluminum alloys is, to some extent, constrained by their relatively low wear resistance and hardness. However, laser cladding technology, with its low dilution rate, compact structure, excellent coating-to-substrate bonding, and environmental advantages, can significantly enhance the surface hardness and wear resistance of aluminum alloys, thus proving to be an effective surface modification strategy. This review focuses on the topic of surface laser cladding materials for aluminum alloys, detailing the application background, process, microstructure, hardness, wear resistance, and corrosion resistance of six types of coatings, namely Al-based, Ni-based, Fe-based, ceramic-based, amorphous glass, and high-entropy alloys. Each coating type’s characteristics are summarized, providing theoretical references for designing and selecting laser cladding coatings for aluminum alloy surfaces. Furthermore, a prediction and outlook for the future development of laser cladding on the surface of aluminum alloys is also presented.

Exploring advanced phycoremediation strategies for resource recovery from secondary wastewater using a large scale photobioreactor

This study aimed to investigate the operation of a 1000L microalgae-based membrane photobioreactor system in a greenhouse for continuous secondary wastewater treatment using Desmodesmus sp., a green microalgae strain originally isolated from a German sewage plant. The research spanned both summer and winter seasons, seeking to comprehend key trends and optimization strategies. Maintaining low cell concentrations in the photobioreactor during periods of light inhibition proved advantageous for nutrient uptake rates. Effective strategies for enhancing algae-based wastewater treatment included cell mass recycling, particularly during periods of high light availability. In comparison to conventional continuous cultivation methods, employing cell recycling and high dilution rates during times of abundant light, alongside using low cell concentrations and dilution rates during light inhibition, resulted in an 80 % and 10 % increase in overall biomass productivity during summer and winter, respectively. Furthermore, nitrogen/phosphorus (N/P) removal rates exhibited a 23 % improvement during winter, while remaining unchanged in summer.

Influence of process and heat input on the microstructure and mechanical properties in wire arc additive manufacturing of hot work tool steels

The present study demonstrates the suitability of wire arc additive manufacturing (AM) for hot work tool steel processing. Different arc welding techniques and energy inputs were applied and systematically compared to determine the deposition characteristics, microstructure and mechanical properties. All AM deposits show a sound visual appearance and full density without macroscopic imperfections, i.e. cracking. By adhering to a pre-defined interpass strategy, the cold metal transfer process can be used to achieve higher weld beads with lower dilution and faster build-up rates than the metal active gas process. The microstructure of the AM parts is comparable for all process configurations and consists of an α/α′-matrix with a finely dispersed vermicular and polygonal δ-ferrite network; no notable amount of retained austenite could be measured, but it could be observed by transmission electron microscopy embedded within the laths. Intensive precipitation of multiple molybdenum-based precipitates is observed along the interface matrix to δ-ferrite. In contrast, iron-based precipitates are predominantly found inside and at the boundaries of the laths of the matrix. Similarities are also evident in the mechanical properties, resulting in an average hardness of 380–390 HV1 and absorbed impact energy of 10–12 J at room temperature. High yield strength values of 1000–1100 MPa and ultimate tensile strength of 1200–1400 MPa were obtained. No significant differences in the measured mechanical properties could be noted regarding the specimen orientation, indicating the isotropy of the properties.

Optimization of the Forming Quality of a Laser-Cladded AlCrFeNiW0.2 High-Entropy Alloy Coating

Laser cladding is an effective surface strengthening method widely used in the surface treatment of extreme operating components such as gas turbines, aviation engines, and nuclear facilities. However, traditional cladding layers struggle to meet the diverse application needs of extreme working conditions due to their single cladding material and poor forming quality. Therefore, this article selected the new-type high-entropy alloy as the coating material and optimized its laser cladding process parameters in order to obtain an AlCrFeNiW0.2 high-entropy alloy coating with an excellent forming quality. It was found that as the laser power increased from 300 to 1800 W, the AlCrFeNiW0.2 high-entropy alloy coating transitioned from the incomplete or near-melted state to the fully and over-melted state gradually, while the coating showed the opposite trend of change as the laser scanning speed increased from 0.002 to 0.008 m/s. And when the laser power was 1000 W, the scanning speed was 0.005 m/s, and the spot diameter was 0.003 m, the AlCrFeNiW0.2 high-entropy alloy coating with a low dilution rate (9.95%) had no defects such as pores and cracks, and achieved good metallurgical bonding with Q235 steel substrate, demonstrating excellent forming quality. These could provide valuable theoretical and technical guidance for optimizing the laser cladding process and forming quality of new-type high-entropy alloy coatings.