Thermal Stress Resistance Research Articles

Fabrication of Burner Rig and Testing of Thermal Barrier Coatings

This research explores the design and fabrication of burner rig to test Thermal Barrier Coatings (TBCs) aimed at enhancing the longevity and performance of gas turbines. Gas turbines, commonly used in aviation and power generation, face extreme operating conditions with high temperatures and thermal gradients that can lead to significant component damage. TBCs, ceramic coatings applied to engine components, play a crucial role in providing thermal insulation and mitigating thermal fatigue, oxidation, and thermal shock. The study involved designing a burner rig, modeled in Solid Works and fabricated from mild steel, to replicate the high temperature environment of gas turbines. The experimental setup was enhanced by the precise machining of components like the aluminum alloy 6061 substrate, achieved through EDM wire cutting. The study demonstrates how factors such as material selection, bond coat and topcoat thickness, porosity, and thermal cycling significantly influence TBC performance. Testing with the burner rig showed that TBCs can greatly enhance engine efficiency and lifespan by providing robust thermal insulation. Advanced monitoring techniques, including infrared thermography and acoustic emission testing, were employed to evaluate the behavior of TBCs under thermal cycling. The findings underscore the need for balancing thermal insulation with thermal stress resistance to maximize coating performance. This research serves as a foundation for further advancements in TBC materials and testing methodologies, with the goal of enhancing the operational efficiency, longevity, and environmental sustainability of gas turbine engines.

Plant growth promoting properties of Methylobacterium brachiatum B0021T and its influence on the growth and short-term thermal stress resistance of Lactuca sativa L

Abstract The paper describes the investigation of the effect of inoculation by Methylobacterium brachiatum B0021T on both the growth lettuce plants and their resistance to short-term thermal stress which was made for the first time. The ability of strain B0021T to synthesize indole derivatives, siderophores, to solubilize insoluble phosphates was revealed. It was shown that inoculation of lettuce plants by strain B0021T improved of shoot growth and development, formation of the root system. It had a positive effect on the work of the photosynthetic apparatus, and also increased resistance to short-term temperature stress in vegetation experiments. The obtained results indicate the potential of using the studied strain to improve the yield of agricultural crops, as well as to protect plants from unfavorable environmental conditions.

Dietary Thymol Supplementation Promotes Antioxidant Responses and Thermal Stress Resistance in Rainbow Trout, Oncorhynchus mykiss.

Rainbow trout fingerlings were fed, in triplicate, diets supplemented with 0 (CTL), 50 (50 TM), 100 (100 TM), 200 (200 TM), 400 (400 TM) and 800 (800 TM) mg/kg of thymol, followed by 48 h of thermal stress. Growth performance and humoral immunological parameters showed no significant responses to dietary thymol concentrations. Fish fed 50-400 mg/kg thymol diets had significantly higher survival after heat stress. Plasma cortisol, glucose, hepatic glutathione peroxidase, glutathione reductase and erythrocyte catalase significantly increased after thermal stress, whereas total plasma antioxidant capacity, ascorbate, and hepatic/erythrocyte reduced-glutathione significantly decreased. There were significant elevations in plasma ascorbate and hepatic glutathione reductase in the 50 TM, 100 TM and 200 TM groups; plasma total antioxidant capacity in the 100 TM and 200 TM groups; hepatic glutathione peroxidase in the 200 TM group; and hepatic-reduced glutathione in the 100 TM, 200 TM and 400 TM groups, compared to CTL. The highest hepatic superoxide dismutase and lowest hepatic malondialdehyde were observed in the 100 TM group before heat stress. These parameters significantly increased after thermal stress in the treatment groups, except in the 100 TM and 200 TM groups. Hepatic catalase showed no significant difference among the treatment groups before thermal stress. Hepatic catalase significantly increased after heat stress in all treatment groups, except in the 100 TM group. Erythrocyte superoxide dismutase significantly increased in the 100 TM group before heat stress, whereas erythrocyte malondialdehyde significantly decreased in the 100 TM and 200 TM groups after thermal stress. Based on the results, 100 mg/kg of thymol can promote antioxidant power and thermal stress resistance in rainbow trout.

Antioxidant and Longevity-Related Properties of the Ethyl Acetate Fraction of Cnidium officinale Makino in Caenorhabditis elegans.

Reactive oxygen species (ROS) are produced from energy metabolism and may cause diseases or cell death. Antioxidation refers to the suppression of ROS production and is considered beneficial in preventing diseases. This study aimed to examine the antioxidative effects of Cnidium officinale Makino (COM) extracts and fractions using Caenorhabditis elegans as an experimental model. The COM ethanol extract was fractionated according to polarity. The results showed that the ethyl acetate fraction of COM showed powerful radical scavenging activities and increased the activities of superoxide dismutase (SOD) and catalase in C. elegans in a concentration-dependent manner. Moreover, the ethyl acetate fraction reduced the ROS production rate in C. elegans and increased the cell survival rate, suggesting oxidative and thermal stress resistance. In addition, the SOD-3::green fluorescent protein (GFP) expression level in the transformed cells of C. elegans (CF1553) increased, suggesting oxidative stress resistance. Similarly, the HSP-16.2::GFP expression level increased, suggesting thermal stress resistance. In conclusion, the ethyl acetate fraction of COM demonstrated the strongest antioxidative effects, indicating that it may help extend longevity.

Evaluating perovskite solar panels for thermal stability and inclination performance through finite element modelling

This paper presents a foresight simulation of perovskite solar modules, focusing on their behavior under different wind velocities and the thermal effects of varying solar irradiance conditions. Despite the burgeoning interest in Perovskite solar panels (PSPs) due to their lower material costs and promising efficiencies, there exist significant research gaps, particularly in the interaction between wind flow and thermal variations, as well as the performance dynamics under distinct wind velocities. To address these gaps, Finite Element Modelling (FEM) simulations were conducted to analyze the thermal stability and wind stress resistance of PSPs, employing a structural design analogous to commercial silicon PV panels. The simulations revealed that the implementation of a cooling system effectively lowered the average temperature of the perovskite layer by a factor of 2.46, significantly reducing the risk of thermal degradation. Additionally, wind stress simulations demonstrated a direct proportionality between the vertical pressure on the panels and their inclination angles, suggesting that lower angles could minimize wind-induced damage while considering daily solar azimuth. The study’s outcomes contribute to the understanding of PSPs’ mechanical and thermal resilience, proposing an optimized design approach for enhanced durability and efficiency in real-world applications. However, the segregation of thermal and wind flow simulations suggests an area for further integrated studies to fully comprehend the simultaneous effects of environmental factors on PSP performance.

Enhanced thermal shock resistance of gradient high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Ce2O7/YSZ thermal barrier coatings

High-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Ce2O7 (LECO) has been verified as a potential candidate for thermal barrier coatings (TBCs). In this work, two different structured LECO coatings were constructed and the thermal shock behavior was systematically investigated. In the classical double-layered LECO coating (D-LECO), the cracks initially originated from the edge and completely exfoliated from substrate after failure. To strengthen the thermal stress resistance of the coating, a gradient multilayered LECO/YSZ coating (M-LECO) was designed with five ceramic sub-layers. The thermal shock life of M-LECO was greatly enhanced by approximately 4 times. Unlike the typical TBCs, the delamination first appeared at an annular region on the surface, located away from the center and edge. Besides, the spalling only occurred in the topmost LECO layer with a thickness loss of less than 5%. After failure, the underneath coating could still provide efficient thermal protection to substrate. The better thermal shock resistance of M-LECO was mainly attributed to the fine gradient structure of the coating and the intrinsic property of high-entropy LECO. The microhardness and fracture toughness in M-LECO were strengthened layer by layer along the thickness direction, alleviating the thermal stress accumulation in the coating and greatly improving the cracking resistance of the interface. Moreover, the high-entropy effect and sluggish diffusion effect of LECO improved its sintering resistance, thereby enhancing the thermal shock resistance of M-LECO. Such design not only fully utilizes the unique thermo-physical properties of high-entropy ceramics, but also effectively solves the problem of weak adhesion between the LECO and the substrate during thermal shock.

Insecticide resistant mosquitoes remain thermal stress resistant, without loss of thermal plasticity

A major component of mosquito's climate change response is their heat tolerance, and any ability to rapidly adjust to extreme environmental conditions through phenotypic plasticity. The excessive use of insecticides for the control of major mosquito species leads to resistant populations, however it is largely unclear if this concurrently impacts thermal stress resistance and their potential to adjust tolerance via phenotypic plasticity. Culex pipiens pipiens, Culex pipiens molestus and Aedes albopictus populations obtained from the same region were subjected for 12 generations to selection trials to larvicides Diflubenzuron (DFB) and Bacillus thuringiensis subsp. israelensis (Bti) to develop insecticide resistance. Adults emerging from the selected populations were acclimated at different temperatures and the upper and lower critical thermal limits (CTmax and CTmin) were estimated using dynamic thermal assays. In addition, the supercooling points (SCPs) of non-acclimated adults of resistant and control populations were determined. Our results revealed marked differences in thermal response among the three species, the different acclimation regimes and sexes. Aedes albopictus was more resistant in high than low temperatures compared to both Culex pipiens biotypes. Culex forms responded similarly to heat but differently to cold stress. In both forms, females responded better than males to all thermal stressors. Acclimation at higher and lower temperatures improves CTmax and CTmin values, respectively in both insecticide resistant and control populations of all three species. Overall, selection to insecticides did not affect the thermal performance of adults. Hence, insecticide-resistant mosquito populations perform similarly to untreated ones and are capable of readily adapting to new environmental changes rising concerns regarding their geographic range expansion and disease transmission globally.

Microencapsulated Lactobacillus Powder: An Approach to Produce Probiotics Resistant to Different Stress Conditions

Microencapsulated probiotics may be an effective method of producing stable preparations that retain functional properties for nutraceutical applications. Morphology, thermal and mechanical stress resistance, storage, and release stability of bacteria in simulated gastrointestinal fluid were examined. The survival rates after different treatments were significantly higher when Lactobacillus spp. was microencapsulated, in comparison with freeze-dried cells. Notably, encapsulated samples exhibited optimal protection under gastrointestinal conditions, with survival rates of 25% at 100° C, 41% at 70% relative humidity for 20 days, and 32% after exposure to a mechanical force of 3 tons. Conversely, non-encapsulated samples failed to survive under gastrointestinal conditions following thermal, mechanical, and storage treatments. Consequently, the study highlights those key probiotic properties, such as thermal, humidity, mechanical stress, and pH tolerance, that were retained to a significant extent through microencapsulation.

Exploitation of Ekoli Edda clay for 33KVA porcelain insulator production

Exploitation of Ekoli Edda clay to devise 33KVA porcelain insulator was done to ascertain the appropriateness of available local raw materials for porcelain insulators production. Ekoli Edda clay was used to formulate eleven samples (A to K) with other materials after characterization and formed using jigger jolleying machine. The properties scrutinized after sintering at 14000C signified that samples A - K had linear shrinkage ranging 7.5% to 2.5% with compressive strength ranging 21.14MPa to 30.84MPa respectively. The study uncovered that samples A - K as declared above had water absorption ranging from 3.06% - 1.21% with matching values of 1.092% - 0.011% succeeding glazing respectively. The apparent porosity indicated that samples A - K had 3.10% - 1.29% with resultant values of 1.331% - 0.031% after glazing, while bulk density result confirmed that samples A - K had 1.94g/cm3 - 3.03g/cm3. Flash over voltage results exposed that samples A - K had 30 KVA - 37 KVA with matching thermal stress resistance result ranging from 20 - 8 numbers of cycles correspondingly. It was discovered that the higher the percentage of Ekoli Edda clay in the recipe of the porcelain insulators, the higher the linear shrinkage, porosity, thermal stress resistance and water absorption while the lower the compressive strength, bulk density and flash over voltage of the porcelain insulators. On the other hand, sample K endow with the most encouraging result when reflecting on the properties affirmed above. Consequently, sample K is recommended for mass production of 33KVA porcelain insulator. It was noted that with 100% local raw materials, 33KVA porcelain insulator of global standard can be produced locally. Hence, exploitation of the local content for mass production of the porcelain insulators will not only lessen the cost or stop their importation, but it will also create employment opportunity, enhance and broaden the wealth of the nation.

Expression, not sequence, distinguishes miR-238 from its miR-239ab sister miRNAs in promoting longevity in Caenorhabditis elegans.

MicroRNAs (miRNAs) regulate gene expression by base-pairing to target sequences in messenger RNAs (mRNAs) and recruiting factors that induce translational repression and mRNA decay. In animals, nucleotides 2-8 at the 5' end of the miRNA, called the seed region, are often necessary and sometimes sufficient for functional target interactions. MiRNAs that contain identical seed sequences are grouped into families where individual members have the potential to share targets and act redundantly. A rare exception seemed to be the miR-238/239ab family in Caenorhabditis elegans, as previous work indicated that loss of miR-238 reduced lifespan while deletion of the miR-239ab locus resulted in enhanced longevity and thermal stress resistance. Here, we re-examined these potentially opposing roles using new strains that individually disrupt each miRNA sister. We confirmed that loss of miR-238 is associated with a shortened lifespan but could detect no longevity or stress phenotypes in animals lacking miR-239a or miR-239b, individually or in combination. Additionally, dozens of genes were mis-regulated in miR-238 mutants but almost no gene expression changes were detected in either miR-239a or miR-239b mutants compared to wild type animals. We present evidence that the lack of redundancy between miR-238 and miR-239ab is independent of their sequence differences; miR-239a or miR-239b could substitute for the longevity role of miR-238 when expressed from the miR-238 locus. Altogether, these studies disqualify miR-239ab as negative regulators of aging and demonstrate that expression, not sequence, dictates the specific role of miR-238 in promoting longevity.

In Situ Cross-Linking Strategy to Enable Highly Stable Perovskite Solar Cells.

The perovskite solar cells (PSCs) have achieved great success in power conversion efficiency due to their excellent optoelectrical properties of perovskite. However, the instability of PSCs severely impedes their commercialization. Recently, in situ cross-linking strategy has been proposed to mitigate stability issues of PSCs, enabling highly efficient and stable PSCs. Here, the critical factors that lead to the degradation of PSCs are first outlined. Then, a comprehensive review of in situ cross-linking strategy in perovskite to enhance the moisture, thermal, illumination, and bending stress resistance properties of PSCs is presented. Furthermore, the detailed mechanism underlying these advantageous effects is discussed pertaining to crystallization regulation, immobilization of ions, water resistance, and release of unfavorable stress. Finally, the current challenges and further development trends of in situ cross-linking strategy in PSCs and extension to other optoelectronic devices are prospected.

Thermal Stress Resistance for the Structure of MEMS-Based Silicon Differential Resonant Accelerometer

Due to material mismatch, silicon differential resonant accelerometers (SDRA) experience unpredictable thermal stress that is challenging to account for. An SDRA with a stress-isolated frame that is co-faced with the sensitive structural layer is shown in this study. Analytical construction is used to create the stress transmission model of SDRA, which incorporates the equivalent stiffness of a stress-isolated frame. It offers a technique to balance the scale factor of the device with thermal stress resistance. Then, from -40°C to 85°C, the proposed SDRA devices’ temperature behavior with and without a stress-isolated frame were examined theoretically, numerically, and experimentally. The measured temperature sensitivities of the device with the stress-isolated structure were around -1.15Hz /°C, 0.19mg/°C, and 37.23ppm /°C for the frequency, bias, and scale factors, respectively. The bias instability of the novel device is 0.72μg. Under the identical experimental conditions, each of these metrics outperformed the device without stress isolation by one to two orders of magnitude, demonstrating the efficiency of the novel stress-isolated structure.

Thermal stress durability and optical characteristics of a promising solar air receiver based black alumina ceramics

In solar thermal technology, solar receiver materials with high solar absorptivity and photocatalytic efficiency have recently become a mandatory requirement for promoting and maximizing the released thermal and electrical energy. This paper presents a detailed study of the optical performance and thermal stress durability of the promising solar receiver material, black Al2O3/CuO ceramics. Different Al2O3/CuO ceramics with different CuO content (10–40 wt%) were obtained by the pressureless sintering method. Optical properties such as solar absorbance and reflectance, band gap energy and photoluminescence are inclusively investigated. The thermal stress resistance of the obtained ceramic receivers is simulated using the finite element modeling (FEM) method at different temperatures. Results indicated that adding and increasing the content of CuO to Al2O3 has a significant role in transforming alumina from a non-solar light-absorbed material to a solar absorber material with high absorptivity in the Ultraviolet–Visible-Near Infrared (UV-VIS-NIR) spectrum. Composite with 40 wt% CuO has recorded the maximum absorbance of 75% in the visible light region. Moreover, Al2O3/CuO ceramics gave multiple graded band-gaps in the range of (1.6–5 eV). Composites with high wt% of CuO have the most increased photocatalytic activity and light emissivity efficiency. Thermal stress analysis of the different ceramics showed outstanding stress durability with uniform heat distribution. Hence, black Al2O3/CuO ceramics can be considered ideal solar absorber materials with high sustainability and durability at high temperatures.

The Effect of N95 Mask on Peripheral Oxygen Saturation and Heart Rate among Indian Medical Professionals: A Quasi-experimental Study

Introduction: Among all face masks, N95 masks have been recommended for medical professionals involved mainly in patients with severe respiratory illnesses. Studies showing a decrease in peripheral oxygen saturation (SpO2 ) and an increase in heart rate after N95 mask usage have already created panic/ concern among medical professionals. On the contrary, a few studies have shown no such negative impact of N95 mask usage, thereby urging scientific communities to investigate/ explore these contrasting results. Aim: To study the effect of wearing an N95 mask continuously for three hours on SpO2 and heart rate specifically in Indian medical professionals. Materials and Methods: This was a quasi-experimental study conducted for a period of 2 months from June 15, 2022, to August 15, 2022, at Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly, Uttar Pradesh, India, with a total of 105 healthy Indian medical professionals aged 18-40 years (55 males, 50 females) (12 study participants dropped from the study midway). In each participant, SpO2 and heart rate were recorded first without a mask (M0) and then with a mask (M3) after three hours of routine work in the hospital. Using Mystat statistical software (version 12.0), results were expressed as mean±Standard Deviation (SD), and Student’s paired t-test was used to compare the pairs of means. Results: Among the 105 eligible participants, 93 successfully completed the study, whereas 12 participants were excluded (dropout rate=11.42%). The study included 55 males (52.38%) and 50 females (47.61%) with an age range of 18-40 years and a mean age of 30.2±6.4 years. The SpO2 levels statistically showed a highly significant decrease after three hours of wearing an N95 mask (96.5±0.83% in M0 vs. 93.98±0.6% in M3). Similarly, the heart rate statistically showed a highly significant increase after three hours of using an N95 mask (73.45±3.6 in M0 vs. 89.6±6.1 beats/min in M3). Conclusion: The authors highlighted lower SpO2 levels and an increase in heart rate after three hours of N95 mask usage specifically in Indian medical professionals and thereby appeal to develop/upgrade the N95 mask by lowering its humidity, thermal stress, and breathing resistance.

Experimental study to check the efficacy of adding organic additives on engineering properties of lime mortar

Lime has been crucial part of early construction works, used for centuries. Old structures made with lime as mortar have shown exceptional performance in their lifetime, however some of them need repair and restoration. In India, historical structures have been built using animal and plant extracts to enhance the building properties of mortar. This study suggests the possible interaction of organics like jute, jaggery, and egg with lime, to simulate the mortar used in old structures. Jaggery has been added after its fermentation in 10%, 12.5%, and 15% percentages. Raw jute fibre has been used after chopping and incorporated in three different percentages i.e., 1%, 1.5%, and 2%, and percentages for egg are as 4%,6%,8%. Physical properties of these mortars are evaluated using tests like water absorption, carbonation etc., while for mechanical properties compressive strength and split tensile testing has been performed. In addition, wetting and drying cycles has been imposed to check the durability component of the mortars. Results reveal that mortar with jaggery as additive performs better in compression, jute-based mortar has the best tensile strength, and egg-based mortar has the least water affinity. At the same time, the wetting and drying test shows that lime-based mortar have good thermal stress resistance.

Геропротекторная активность транс-коричной кислоты, выделенной из шлемника байкальского (Scutellaria baicalensis)

Trans-cinnamic acid is a phenolic compound with a wide range of bioactive properties, including antioxidant and antibacterial effects. It also has high potential in the food and cosmetic industries. We aimed to isolate trans-cinnamic acid from the Baikal skullcap (Scutellaria baicalensis) and study its geroprotective activity on Caenorhabditis elegans nematodes used as a model organism.
 Our study objects included the S. baicalensis root culture and its extract, trans-cinnamic acid isolated from the extract, and C. elegans nematodes. Trans-cinnamic acid was isolated by high-performance liquid chromatography. The acid’s geroprotective activity was studied by evaluating its effect at concentrations of 10, 50, 100, and 200 μmol/L on the lifespan, stress resistance, and reproductivity of C. elegans. For the lifespan study, the nematodes were cultivated at 20°C for 61 days. To assess their resistance to oxidative stress, 15 μL of 1M paraquat was added to each well of the plate. Thermal stress resistance was determined by raising the temperature to 33°C. For the reproductivity study, the nematodes were cultivated in the S-medium with the addition of Escherichia coli OP50 and trans-cinnamic acid at required concentrations for 72 h.
 The maximum increase in lifespan (9.8%) was observed in the nematodes treated with 50 μmol/L of trans-cinnamic acid. Under oxidative stress, all the concentrations of trans-cinnamic acid increased the survival of nematodes, while under thermal stress, trans-cinnamic acid reduced the percentage of surviving nematodes. At a concentration of 100 μmol/L, trans-cinnamic acid increased the nematodes’ reproduction by 1.48 times.
 Based on our data, trans-cinnamic acid isolated from S. baicalensis can be recommended as a bioactive compound with geroprotective activity. However, further research is needed on other model organisms with detailed toxicity studies.

Influence of Ti3AlC2 addition on water vapor resistance of low‐carbon Al2O3–C refractories

AbstractAl2O3–C refractories are potential candidates for use in gasifiers, and they are Cr2O3‐free. However, the oxidation of the carbon species and ceramic phases within the high‐temperature water vapor environment may deteriorate the integrity of the working lining. Ti3AlC2 has been verified as an effective antioxidant for Al2O3–C refractories in air. In this study, the structural transformation of Ti3AlC2 during heat treatment and the water vapor resistance of Ti3AlC2‐containing Al2O3–C refractories are investigated. The results show that the oxidation of Ti3AlC2 and Si in the matrix contributes to the in situ formation of a multilayer core–shell structure of TiC–AlTi2O5–Al6Si2O13. These structural evolutions improve densification and stimulate pore size refinement, which enhances the mechanical properties and thermal stress resistance of the specimens. In particular, the refined pore size contributes to the significantly improved water vapor resistance at high temperatures.

Effects of edge-seal design on the mechanical and thermal performance of vacuum-insulated glazing

Although vacuum-insulated glazing (VIG) has been proposed as a promising solution towards developing energy-efficient buildings, VIGs have not become popular in the market due to several technical challenges including the complexity of the fabrication process. In particular, the edge-seal is a key component that significantly affects the thermal insulation and mechanical performance, and the development of edge-seal with adequate thermal insulation, mechanical strength, and reasonable processing cost is essential to overcome such technical issues in VIG. For this purpose, effects of edge-seal design parameters on the VIG performance should be identified. In this research, we analyzed the edge-seal for thermal transport as well as structural stresses to study the effects, and then identified and evaluated the material mixes for the edge-seal requirements. The finite element simulations showed the significance of VIG corner calculation on overall thermal transmittance and the importance of seal conductivity below 1 W/m.K. The experiments with the flexible seals with different ratios of fine glass powder demonstrated that the measured shear strength values for the seal with less than 30% glass powder were more than 10 times larger than the calculated shear stress values. Based on these simulation and experimental results, a flexible sealant was developed using a proprietary mix of ceramic materials that meets the requirements of the designed VIG edge-seal, including structural as well as thermal stress resistance and a low conductivity. Moreover, the sealant is self-curing under atmospheric conditions, and thus it does not require costly inline process of laser curing or oven baking.

A high-strength Ni–Cr–W based superalloy prepared by laser powder bed fusion: printability, microstructure and tensile properties

The Ni–Cr–W based Haynes 230 alloy, is considered to have important applications in the hot-end components of aerospace engines due to its excellent high-temperature properties and oxidation resistance. However, Haynes 230 alloy presents a high hot-cracking tendency during the laser powder bed fusion (LPBF) process. In this study, a novel composition optimized Ni–Cr–W superalloy based on Haynes 230 alloy was fabricated by the LPBF method. The metallurgical defects, microstructure and tensile properties at room temperature (RT) of the LPBF Ni–Cr–W based superalloy printed under different volume energy densities (VEDs) were systematically researched. The results show that the novel Ni–Cr–W superalloy presents excellent processability, and a near-fully dense specimen without any metallurgical defects was obtained under optimal VED of 83.33 J/mm3. However, solidification cracks also occurred in the samples with higher VEDs (exceeding 100 J/mm3). The main reason is the increase of thermal stress and liquid-feeding resistance as VED increases. The rapid scanning speed and steep temperature gradient during the LPBF lead to the occurrence of the multi-scale heterogeneous microstructures, including the epitaxial columnar grains with a mixing of {100} and {110} crystallographic alignment along the building direction (BD) and cellular substructures entangled with high-density dislocation. The cellular substructure strengthening and solution strengthening are the dominant factors for the excellent ultimate tensile strength (1100 MPa), yield strength (850 MPa), and ductility (29.3%) of the LPBF alloy at RT. With the increase of VED, the yield strength of the LPBF alloy decreases. The main reason is the reduction of cellular substructure strengthening. The ultimate tensile strength of the LPBF alloy at 1000 °C reaches 200 MPa, which is superior to that of the LPBF Haynes 230.

Modification of Co–Cr alloys to optimize additively welded microstructures and subsequent surface finishing

Cobalt chromium alloys are often used in turbine and plant construction. This is based on their high thermal and mechanical stress resistance as well as their high wear resistance to corrosive and abrasive loads. However, cobalt is a cost-intensive material that is difficult to machine. Moreover, increasingly complex structures and the optimisation of resource efficiency also require additive manufacturing steps for the production or repair of components in many sectors. Concerning inhomogeneity and anisotropy of the microstructure and properties as well as manufacturing-related stresses, a lot of knowledge is still necessary for the economic use of additive welding processes in SMEs. As a result of the high stresses on the components and requirements for a high surface quality, a complementary use of additive and machining manufacturing processes is necessary. Thereby, Co–Cr alloys are extremely challenging for machining with geometrically defined cutting edges because of their low thermal conductivity combined with high strength and toughness. An approach to solve this problem is to refine and homogenise the microstructure. This is achieved by modifying the alloy with elements zirconium and hafnium, which are added up to a maximum of 1 wt.-%. A reduction of the process forces and stresses on the tool and work piece surface is also achievable via hybrid milling processes. There are already studies on the combined use of additive and machining manufacturing processes based on laser technology. However, knowledge based on powder and wire-based arc processes is important, as these processes are more widespread. Furthermore, the effects on the surface zone of additively manufactured components by hybrid finish milling have not yet been a subject of research. The results show that the structural morphology could be significantly influenced with the addition of zirconium and hafnium.