Outer Surface Layer Research Articles

Improving the strength-ductility synergy and surface properties of NiFe29Cr21CuMo-based alloy laser welding subsequent deep cryogenic treatment and vacuum plasma WC20Cr3C2NiX coating

The novel research work focused on enhancing the mechanical properties and joining strengths of laser welding (LW) procedures on a sample of NiFe29Cr21CuMo-based alloy. Moreover, the surface properties and microstructure were improved by vacuum plasma spraying the WC20Cr3C2NiX coating (vacuum plasma spray coating (VPSC)) and deep cryogenic treatment (DCT). Based on temperature, two DCTs (DCT-(L)–(H)) were carried out: −180°C and 250°C on twin boundaries structure, NiFeCr phase, CrMo structure, and µ-austenite lattice structure was observed of the inner surface layer. The plasma spray WC20Cr3C2NiX coating technology was used to improve the outer layer and residual stress. The DCT and VPSC process investigations using electron backscatter diffraction demonstrated unambiguously that the inner and outer surface layer of the µ′(Ni–Fe2Cr3), Fe–CrC, β′-Fe2Cr4, CrCoMn structure, and twin boundary's structure were present. Heat inputs on plasma spray coating samples were more affected in the inner and outer surface layer to the formation of strong crystallographic NiCr phase, β′-Ni/Cr, and CrC/Mn structure. Moreover, the CrMn structure, Fe(AsO4) phase, and NiFeBCr phase abruptly increased the hardness value of DCT-(L) samples of the outer surface. The DCT-(H)–VPSC method yielded a hardness value of 18% highly present. Peak profile investigation revealed the various ranges: 0 to −600 µm for LW + DCT-(H) coating samples, 225–350 µm for LW + DCT-(L) coating samples, and −100 to −200 µm for LW + DCT-(L)–(H) coating. Electrochemical analysis employing potential dynamic polarization was used to assess each sample's corrosion resistance. The corrosion resistance and surface characteristics of DCT and VPSC were superior.

Systematic analysis of the gallium ions and structure-directing agents in the preparation of NiW HDS catalysts over mixed oxides of Al2O3-TiO2

In this study, we prepared Al2O3-TiO2 (AT) mixed oxides to synthesize NiW catalysts for sulfur removal reactions. The AT support samples were prepared with various surfactants. Additionally, gallium atoms (2.4 wt%) were introduced as an additive to coat the outer surface layers of AT support that lacked Al3+ or Ti2+ cations. Characterization results showed substantial differences in textural properties, chemical composition, and surface acidity. The x-ray Photoelectron Spectroscopy (XPS) and High-Resolution Transmission Electron Microscopy (HR-TEM) results demonstrated that the NiW/AT-L-Ga sample has a better combination of dispersion, sulfidation, and promotion among materials. The sulfided NiW/AT-L-Ga catalyst had the highest catalytic activity. After incorporating Ga, XPS observed that the activity could be associated with an increase in the NiWS active phase; however, including a surfactant in the synthesis of the support allowed an increase in the amount of NiWS phase. The active phase was modeled considering the HR-TEM results for the slab length, revealing the atoms at the border susceptible to promotion.

Enhanced interlaminar structure and dynamic mechanical properties of Tectona grandis fiber (TGF)/polypropylene fiber (PPF)/carbon nanotube (CNT) nano composite prepared solid dipping coating process

Abstract The interlaminar structure and dynamic mechanical properties of Tectona grandis fiber (TGF), polypropylene fiber (PPF), and carbon nanotube (CNT) nano composite were investigated in the current study. In order to improve the mechanical characteristics and microstructure, the present investigations used T. grandis fiber and polypropylene fiber (inorganic–organic) materials mixed with nano composite and epoxy resin. Strong bonding strength and high wear resistance were created by the silane characteristics during the coating process for the outer surface layers. Since CNT nanomaterials were directly reflected onto the outer surface, the microstructure analyses amply demonstrated that hexagonal lattice structure and crystallisation development were detected in the inner surface layer. In order to increase high stiffness and bonding strength, storage modulus and loss modulus values were applied to all composite materials, and the TGF/PPF/CNT composite materials’ hardness value was developed at 112 HV. The tensile strength of TG/PP composite was 46.7 MPa, while that of TGF/PPF/CNT composite was 57.4 MPa. Studies on wear resistance showed unequivocally that the TGF/PPF/CNT composite reduced wear and friction.

The influence of UV radiation on the properties of GFRP laminates in underwater conditions

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed.

Compatibility study of high density polyethylene grade 80 gas pipe with synthetic polyglycol-based brake oil

High Density Polyethylene (HDPE) is one attractive technical option for the transportation and distribution of natural gas and hydrocarbons given the advantages in long-term mechanical strength, lifespan, maintenance costs and resistance to chemical aging. This study investigates the compatibility of extruded pipe material from copolymerized HDPE-80 with DOT 3 brake fluid. Machined standard specimens from inner (IL) and outer (OL) pipe layers are aged in commercial synthetic polyglycol-based oil for 7 days at laboratory conditions. The percent mass changes are +2.2% and +1.9% respectively for IL and OL pipe surfaces. These results are in the same range of published sorption data for other oils and fuels. Stress-strain parameters (E, σ y, σ CD, σ f, ε y, Δ ε CD, ε f) and fracture work are established and thoroughly discussed for both pipe sides. For IL, the reduction of E, σ y and ε f are respectively 28.0%, 13.9% and 22.7%, while for OL they are 22.6%, 7.7% and 25.1%. Globally, it is concluded that strength properties degradation in DOT 3 oil is more important for IL compared to OL. There is an important loss of ductility for both pipe sides. Ageing caused IL crystallinity ( Xc) to increase while OL showed inverse results probably because of frozen anti-oxidants in the outer surface layers following water quenching during extrusion. Before and after ageing, the as-received OL is found to be more resilient to oxidation than corresponding IL, as higher OIT parameters are also shown in the case of crude oil compatibility investigations. DOT 3 brake oil seem to accelerate the degradation of HDPE-80 thermal stability with a higher intensity for IL.

Tuning enhanced dielectric properties of (Sc3+–Ta5+) substituted TiO2 via insulating surface layers

In this study, we achieved significantly enhanced giant dielectric properties (EG-DPs) in Sc3+–Ta5+ co-doped rutile-TiO2 (STTO) ceramics with a low loss tangent (tanδ ≈ 0.05) and high dielectric permittivity (ε′ ≈ 2.4 × 104 at 1 kHz). We focused on investigating the influence of insulating surface layers on the nonlinear electrical properties and the giant dielectric response. Our experimental observations revealed that these properties are not directly correlated with the grain size of the ceramics. Furthermore, first-principles calculations indicated the preferred formation of complex defects, specifically 2Ta diamond and 2ScVo triangular-shaped complexes, within the rutile structure of STTO; however, these too showed no correlation. Consequently, the non-Ohmic properties and EG-DPs of STTO ceramics cannot be predominantly attributed to the grain boundary barrier layer capacitor model or to electron-pinned defect-dipole effects. We also found that the semiconducting grains in STTO ceramics primarily arise from Ta5+, while Sc3+ plays a crucial role in forming a highly resistive outer surface layer. Notably, a significant impact of grain boundary resistance on the nonlinear electrical properties was observed only at lower co-dopant concentrations in STTO ceramics (1 at%). The combination of low tanδ values and high ε′ in these ceramics is primarily associated with a highly resistive, thin outer-surface layer, which substantially influences their non-Ohmic characteristics.

Microstructure and corrosion resistance of 23Cr9Ni4Mo2Mn filler duplex stainless steel 2205 fabricated by wire arc additive manufacturing with subsequent severe shot peening and Ni58Cr20Fe5Mo10 plasma spray coating

In the current study, 23Cr9Ni4Mo2Mn (FeAs) filler and duplex stainless steel 2205 materials were used in multi-layer deposition processes for wire arc additive manufacturing (WAAM) process. The WAAM samples were prepared with WAAM coated (WAAM-C) and Post-shot peening coated WAAM (PSPC-WAAM) in order to improve the microstructure and surface properties. The severe shot peening process and Ni58Cr20Fe5Mo10 plasma spray coating was increase the corrosion resistance and outer layer strength, whereas different types of structure were observed in the WAAM-DSS plates: Solid phase martensite (SPM), acicular austenite phase (AAS), FeCr2O4, martensite-austensite phase (MAP) and multi-phase ferrite structure. The severe shot peening procedure and Ni58Cr20Fe5Mo10 plasma spray coating samples were clearly visible in the Electron Backscatter Diffraction (EBSD) analyses, which also showed that the outer and inner surface layers of the samples contained CrFe2O4, NiFe2O4 cubic ferromagnetic oxide, and BiFeO3 phase. Direct mixing of the 23Cr9Ni4Mo2Mn filler with the base materials produced a homogenous structure with a high bonding strength. Bi1<001>, Bi2<111>, and Bi3<110> of the BiFeO3 crystal structure were discovered in the inner surface layer according to the PSPC-WAAM sample of angle 0–1800 texture results, whereas the WAAM-C sample of the outer layer revealed that As1<001>, As2 < 100>, and As3 < 111> of the α-martensite structure were exposed at the outer surface layer. PSPC-WAAM had a 6 % increase in hardness over WAAM-C in both the inner and outer surface regions. Hardness value of PSPC-WAAM was 286 HV on NiCr bulk structure demanded, whereas ferrite secondary phase of WAAM-C have increased the hardness value at 224 HV compared to the base materials. Both the PSPC-WAAM and WAAM-C samples achieved improved corrosion resistance and strong surface bonding. The WAAM, WAAM-C, and PSPC-WAAM samples were the subject of potential dynamic experiments, AFM and wear properties.

Surface nano-crystallisation and mechanical properties of Ti[sbnd]Ta composite materials after surface mechanical grinding treatment

Surface mechanical milling generates gradient nano-structure surfacial layers that enhance the mechanical properties of titanium (Ti)–tantalum(Ta) composites for medical implants. Herein, the effect of surface mechanical grinding treatment (SMGT) on the surface nano-crystallisation of TiTa laminated composites was investigated in terms of micro-structure and Coherent Scattering Regions (CSRs) size using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A strengthening effect was verified using a micro-hardness tester and tensile testing machine, and the fracture mechanism was analysed through fracture observation. The experimental results showed that gradient nano-structures were formed on the surface of the TiTa laminated composites after SMGT, with the smallest CSRs size of the outer surface layer of approximately 13.3 ± 0.4 nm. The plastic deformation mechanism of the TiTa laminated composites during SMGT was a dislocation cutting mechanism. The micro-hardness and tensile strength of the TiTa laminated composites increased after SMGT up to 440 HV and 1097.528 MPa, respectively. The fracture mechanism of the TiTa laminated composites after SMGT was a combination of ductile fracture and quasi-cleavage fracture mechanisms. After SMGT, the TiTa laminated composite performed well and exhibited excellent potential for use in biomaterials.

Critical accretion rates for rapidly growing massive Population III stars

Efforts to understand the origin and growth of massive black holes observed in the early Universe have spurred significant interest in the evolution and fate of rapidly accreting primordial (metal-free) stars. Here, we investigate the evolution of such Population III (PopIII) stars under variable accretion rates, focusing on the thermal response and stellar structure, the impact of the luminosity wave encountered early in the pre-main sequence (pre-MS) phase, and the influence of accretion on their subsequent evolution. We employ the Geneva stellar evolution code and simulate ten models with varying accretion histories, covering a final mass range from 491 M⊙ to 6127 M⊙. Our findings indicate that the critical accretion rate delineating the red and blue supergiant regimes during the pre-MS evolution is approximately 2.5 × 10−2 M⊙ yr−1. Once core hydrogen burning commences, the value of this critical accretion rate drops to 7.0 × 10−3 M⊙ yr−1. Moreover, we also confirm that the Kelvin–Helmholtz timescale in the outer surface layers is the more relevant timescale for determining the transition between red and blue phases. Regarding the luminosity wave, we find that it affects only the early pre-MS phase of evolution and does not directly influence the transition between red and blue phases, which primarily depends on the accretion rate. Finally, we demonstrate that variable accretion rates significantly impact the lifetimes, surface enrichment, and final mass of the PopIII stars, as well as the time they spend in the red phase. Our study provides a comprehensive understanding of the intricate evolutionary patterns of PopIII stars subjected to variable accretion rates.

Durable superhydrophobic coatings for stainless-steel: An effective defense against Escherichia coli and Listeria fouling in the post-harvest environment

Increasing concerns revolve around bacterial cross-contamination of leafy green vegetables via food-contact surfaces. Given that stainless-steel is among the commonly used food-contact surfaces, this study reports a coating strategy enhancing its hygiene and microbiological safety through an antifouling approach via superhydrophobicity. The developed method involves growing a nickel-nanodiamond nanocomposite film on 304 stainless-steel via electroplating and sequential functionalization of the outer surface layer with nonpolar organosilane molecules via polydopamine moieties. The resultant superhydrophobic stainless-steel surfaces had a static water contact angle of 156.3 ± 1.9° with only 2.3 ± 0.5° contact angle hysteresis. Application of the coating to stainless-steel was demonstrated to yield 2.3 ± 0.6 log10 and 2.0 ± 0.9 log10 reductions in the number of adherent gram-negative Escherichia coli O157:H7 and gram-positive Listeria innocua cells, respectively. These population reductions were shown to be statistically significant (α = 0.05). Coated stainless-steel also resisted fouling when contacted with contaminated romaine lettuce leaves and maintained significant non-wetting character when abraded with sand or contacted with high concentration surfactant solutions. The incorporation of superhydrophobic stainless-steel surfaces into food processing equipment used for washing and packaging leafy green vegetables has the potential to mitigate the transmission of pathogenic bacteria within food production facilities.

Creation of a methodology for determining the moisture diffusion coefficient within vacuum drying of fruits

As the drying zone deepens, outer surface layer of the product does not have time to be moistened, due to a small amount of moisture coming from the inside. It becomes dry, its temperature rises. The intensity of moisture transfer from the inner layers of the product depends on many parameters, including a moisture diffusion coefficient. The study aim is to create a methodology for determining the moisture diffusion coefficient within vacuum drying of fruits, by taking into account cracks, channels and capillaries formed in the dry layer of the product through the resistance coefficient to evaporation. The work essence consists in the determining of the moisture diffusion coefficient as a driving force, a difference between water activity and air humidity, by considering the resistance coefficient to evaporation, characterizing the effect of hydrodynamic resistance of the dried dry layer of the product. This approach was used to determine the moisture diffusion coefficient during vacuum drying of the Baiterek apple sort and the Zhazdyk pear sort of Kazakhstani selection. It was established that in the first period of drying the moisture diffusion coefficient decreases on average from 24,4∙10‒7 m2/s to 13,2∙10‒7 m2/s. The critical humidity for pear is 37.4 %, and for apple 35.1 %. As result of the formation of dry layer on the surface and subsequent layers, the moisture diffusion coefficient gradually decreases. In the second drying period, the moisture diffusion coefficient decreases from 5,42∙10-8 m2/s to 2,12∙10‒8 m2/s. The work practical significance is related with the application of the obtained results in the determination of the optimal drying regime with maximum preservation of the product original quality. The proposed methodology can be used in the practice to study the moisture diffusion coefficient within vacuum drying of fruits, by considering the product properties and the hygroscopic parameters of the drying matter

Effect of plasma spray FeCrAly coating on microstructural and mechanical properties of Ni61Cr22Mo9Fe5 - ER2209 nickel based alloy fabricated using wire arc additive manufacturing process

In this current research, the Ni61Cr22Mo9Fe5 (NiCr) - ER2209 (FeCr) wire was proposed to produce a nickel based alloy materials utilising the wire arc additive manufacturing (WAAM) process. Wire arc additive manufacturing (WAAM) and wire arc additive manufacturing coated (WAAM-C) samples of two different types were created. In order to improve the WAAM sample's mechanical strength and corrosion resistance, the outer surface layer was coated using the plasma spray FeCrAlY composite coating technique. The deposition of powder was kept as constant as 200 µm during plasma spray coating process. Microstructure analyses showed that the composite bonding sample had NiFe2O4, Single phase nickel ferrite (SPNF), Ni-Co ferrite, α-phase, and Spinel ferrite structures. The metallic functional phase (MFP) of Ni61Cr22Mo9Fe5 - ER2209 wire was shaped utilizing additive manufacturing process, whilst homogeneous structure and NiCr structure were established collateral bonding in the base materials. Texture results of WAAM-C sample showed As1 < 111 > , As2 < 200 >, As3 < 211 > and As4 < 222 > cub structure at the outer surface. The hardness values of outer surface layers of WAAM-C have been continuously increased by 4 % compared to the WAAM sample. The hardness values of WAAM-C and WAAM were seen as 180 HV and 166 HV, respectively. The WAAM-C showed the elongation of 3 % and yield strength of 600 MPa. Further, the fracture morphology revealed that both the samples did not show dimples, void, crack and hole. WAAM-C materials achieved higher corrosion resistance and good surface finish. Further, potential dynamic investigations were conducted on both WAAM and WAAM-C samples.

Mechanistic Origin for High Structural Stability of Single Crystalline Nickel‐Rich Cathode Materials Via Al and Sm Co‐Doping

AbstractNickel‐rich layered oxides have attracted many attentions for their superior specific capacity and low cost, but they are subjected to fast structural degradation during cycling. Herein, the Al and Sm co‐doped LiNi0.83Co0.07Mn0.10O2 (SC‐NCM‐AS) single‐crystal is demonstrated to overcome their cycling instability issue, and its mechanistic origin for improved structural stability is investigated. It is found that soluble Al ions are homogenously incorporated in the LiNi0.83Co0.07Mn0.10O2 (SC‐NCM) lattice, while Sm ions tends to aggregate in the SC‐NCM outer surface layer. The Li/Ni cation disordering is greatly suppressed through the pillaring effect of stronger AlO bond in SC‐NCM single crystals. Sm‐concentrated outer surface layer can effectively prevent the dissolution of transition metals from SC‐NCM‐AS and inhibit undesirable side reactions induced by the organic electrolyte. This synergistic effect facilitates to suppress the formation of LiOH/Li2CO3 and oxygen vacancies, resulting in released the internal strain, decreased in‐plane transition metals migration and gliding, and eventually preventing formation of nanocracks in SC‐NCM‐AS single crystals upon cycling at high cut‐off voltage. Consequently, Al and Sm co‐doped SC‐NCM exhibits a high specific capacity of 222.4 mAh g−1 and remarkable cycling performance with a capacity retention of 91.1% for 100 cycles.

Examination of the Effect of Cooling Rate after Extrusion to Formability of 6061 Automotive Profiles

As part of the present project, an inquiry is being conducted into the impact of the cooling rate subsequent to extrusion on both the mechanical characteristics and microstructure of 6061 alloy extruded profiles tailored for application in the automotive industry. Water quenching, air cooling, and step-cooling (combination of air cooling and water quenching) were performed after a solution heat treatment for simulating different cooling processes on the exit of the extrusion press. Microstructure examination was performed after artificial aging for every cooling method accompanied by three-point bending and tensile testing for investigation of differences in formability characteristics in each one of the three cases. Electron fractography, texture, and grain boundary misorientation analysis consisted the main analytical techniques, allowing the correlation between grains orientation resulting from the extrusion process with cracking initiation behavior in mechanical testing and for the determination of the regions which were more prone to cracking. From the examination, the positive role of rapid cooling for improved formability was highlighted. Through the grain boundary misorientation analysis and the formation of Taylor factor maps, it was shown that crack initiation preferably took place at subsurface regions even though “roughening” of the bent surface was obvious and expected to lead to crack initiation in the more ductile samples. Considerable amounts of LAGBs (Low Angle Grain Boundaries) (14.7%) and SGBs (Subgrain Boundaries) (4.5%) were detected in the sample which was subjected to step cooling accompanied by an outer and inner surface layers (surface zone) of 200–250 μm thicknesses exhibiting different orientations. The results of this project will be used for optimization of the automotive extruded profiles production process, ensuring improved mechanical performance and resistance to premature fracture.

Acetic acid‐assisted mild dealloying of fine CuPd nanoalloys achieving compressive strain toward high‐efficiency oxygen reduction and ethanol oxidation electrocatalysis

AbstractDealloying by which the transition metal is partially or completely leached from an alloy precursor is an effective way to optimize the fundamental effects for further enhancing the electrocatalysis of a catalyst. Herein, to address the deficiencies associated with the commonly used dealloying methods, for example, electrochemical and sulfuric acid/nitric acid treatment, we report an acetic acid‐assisted mild strategy to dealloy Cu atoms from the outer surface layers of CuPd alloy nanoparticles to achieve high‐efficiency electrocatalysis for oxygen reduction and ethanol oxidation in an alkaline electrolyte. The leaching of Cu atoms by acetic acid exerts an additional compressive strain effect on the surface layers and exposes more active Pd atoms, which is beneficial for boosting the catalytic performance of a dealloyed catalyst for the oxygen reduction reaction (ORR) and the ethanol oxidation reaction (EOR). In particular, for ORR, the CuPd nanoparticles with a Pd/Cu molar ratio of 2:1 after acetic dealloying show a half‐wave potential of 0.912 V (vs. RHE) and a mass activity of 0.213 A mgPd−1 at 0.9 V, respectively, while for EOR, the same dealloyed sample has a mass activity and a specific activity of 8.4 A mg−1 and 8.23 mA cm−2, respectively, much better than their dealloyed counterparts at other temperatures and commercial Pd/C as well as a Pt/C catalyst.

Super-assembled mesoporous thin films with asymmetric nanofluidic channels for sensitive and reversible electrical sensing

Bioinspired artificial nanochannels have emerged as promising candidates for developing smart nanofluidic sensors due to their highly controllable size and surface functionality. However, little attention has been paid to the role of the outer surface of the nanochannels in enhancing the detection sensitivity. Herein, an asymmetric nanochannel-based responsive detection platform with ultrathin tannic acid modified mesoporous silica (TA-MS) layer and alumina oxide (AAO) thin film is prepared through super-assembly strategy. The functional TA-MS outer surface layer provides abundant phenolic groups on the nanochannels for ions and molecules transport, which paves the way for the development of heterochannels for label-free, reversible and highly sensitive dopamine (DA) detection based off of cation displacement effect. Notably, by engineering optimal thickness of the TA-MS, the sensing performance can be further improved. After optimization, the linear response ranges for DA detection are 0.001–1 μM, 1–10 μM and 10–200 μM with the detection limit of 0.1 nM. The prepared sensor exhibits stable reversibility after several detection cycles. In addition, this method was successfully applied for DA detection in fetal bovine serum sample. Theoretical calculations further prove the detection mechanism. This work opens a new horizon of using mesoporous materials to construct nanofluidic sensors for ultrasensitive small molecule detection and recognition.

THE CHROMIUM AND COBALT DISTRIBUTION IN THE DIFFUSION LAYER OF STEEL X35CrNi2-3 DURING THERMОDIFFUSION SATURATION

For parts of machines and equipment operating under the influence of aggressive media, abrasive, high temperatures, the creation of a hard, wear-resistant surface is an urgent task. Cobalt is used as a binder to create hard alloy materials that work under these conditions. It was of interest to evaluate the possibility of using cobalt as an additive in complex thermal diffusion chromium plating of structural steel. The article describes the features of thermal diffusion saturation of steel X35CrNi2-3 with chromium and cobalt at a temperature of 1000°C. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using the JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied using the optical metallographic microscope Axio Observer D1.m. The X-ray phase analysis was carried out with the Rigaku Ultima IV diffractometer. The hardness measurement was carried out with the FM-800 microhardness tester at a load of 50 g. Data were obtained on the distribution of chromium and cobalt in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists mainly of a substitutional solid solution based on Cr‒Fe‒Co with bcc lattice and chromium carbides. The average diffusion coefficients of chromium in the α-phase of chromium were determined to be DCr = 3,22·10‒15 м2/с; in the γ-phase of iron DCr = 9,41·10‒15 м2/с. The diffusion coefficient of cobalt in the γ-phase of iron DCo = 7,89·10‒15 м2/с. The depth of the outer coating on the sample was about 15–20 µm, the depth of the diffusion layer of chromium in the base metal was about 70 µm, and that of cobalt was about 40 µm. The maximum hardness of the outer surface layer was 1740 HV, the diffusion layer in the base metal was 900–560 HV, and the base metal was about 510 HV.

Anti-mold and hydrophobicity of cutinized bamboo prepared via different annealing processes

To improve the hydrophobicity and anti-mold properties of bamboo, cutinized bamboo was prepared by impregnating a mixture of food-grade carnauba wax and paraffin at annealing temperatures of 78 °C, 80 °C, and 83 °C. The thermal properties and microstructures of the wax films were analyzed to understand the mechanism of wax interface phase. The contact angle, water absorption rate, dimensional stability, and microstructure of the cutinized bamboo were investigated. The results showed that phase separation occurred in the mixed wax and that the microstructure of the mixed wax films was reconstructed after annealing treatment. The thickness of the cutinized coating varied with the annealing temperature. The initial contact angle on the outer layer surface of cutinized bamboo reached 110.73°, and the surface energy was reduced by 53.6% at an annealing temperature of 83 °C. The water absorption and dimensional stability of the cutinized bamboo improved significantly. In addition, bamboo toothbrush handles modified at annealing temperature of 80 °C demonstrated good anti-mold. The annealing process of wax treatment is expected to benefit bamboo product protection. • Cutinized bamboo was prepared with mixed wax and annealed under different temperature. • The microstructure of mixed wax coating was reconstructed with phase separation after annealing. • The hydrophobicity of cutinized bamboo increased with annealing temperature. • Better hydrophobicity and anti-mildew were obtained after annealing treatment.

Dielectric Responses of (Zn0.33Nb0.67)xTi1−xO2 Ceramics Prepared by Chemical Combustion Process: DFT and Experimental Approaches

The (Zn, Nb)-codoped TiO2 (called ZNTO) nanopowder was successfully synthesized by a simple combustion process and then the ceramic from it was sintered with a highly dense microstructure. The doped atoms were consistently distributed, and the existence of oxygen vacancies was verified by a Raman spectrum. It was found that the ZNTO ceramic was a result of thermally activated giant dielectric relaxation, and the outer surface layer had a slight effect on the dielectric properties. The theoretical calculation by using the density functional theory (DFT) revealed that the Zn atoms are energy preferable to place close to the oxygen vacancy (Vo) position to create a triangle shape (called the ZnVoTi defect). This defect cluster was also opposite to the diamond shape (called the 2Nb2Ti defect). However, these two types of defects were not correlated together. Therefore, it theoretically confirms that the electron-pinned defect-dipoles (EPDD) cannot be created in the ZNTO structure. Instead, the giant dielectric property of the (Zn0.33Nb0.67)xTi1−xO2 ceramics could be caused by the interfacial polarization combined with electron hopping between the Zn2+/Zn3+ and Ti3+/Ti4+ ions, rather than due to the EPDD effect. Additionally, it was also proved that the surface barrier-layer capacitor (SBLC) had a slight influence on the giant dielectric properties of the ZNTO ceramics. The annealing process can cause improved dielectric properties, which are properties with a huge advantage to practical applications and devices.

Effect of Microstructural Evolution on Mechanical Properties and Fracture Modes of AlSi10Mg Blocks Fabricated by Selective Laser Melting after Stress Relief Annealing

AlSi10Mg parts fabricated by selective laser melting (SLM) are frequently reported to have heterogeneous microstructures. How this affects the mechanical properties of SLM parts still requires further study. Herein, AlSi10Mg blocks with simple cuboid shape are printed and annealed at 300 °C. Their microstructure changes significantly from edge to center and from top to bottom. Low‐temperature annealing is not sufficient to eliminate structural heterogeneity. Before annealing, the Si‐rich phase is fine and mainly exists in the form of a eutectic network. The as‐printed blocks have high tensile strength, and the fracture surface exhibits a mix of transcellular pits and pores. After annealing, the network structure is completely broken or disappeared in most locations in the blocks. The Si‐rich phase is significantly coarsened and even segregated locally along the melt pool boundaries. Yield strength is reduced by 25%–47%, but elongation values are doubled. Tensile samples are fractured by an along‐the‐pool boundary fracture mode along the boundary. Micropores formed during the printing process are aggregated in the about 200 μm thick outer surface layer of the block. They also have a significant effect on the local elongation both before and after annealing.