Volume 41 (2023): Issue 1 (March 2023)

Titanium carbonitride coatings are widely used to improve the wear resistance of surfaces. The results of tribological investigations of TiC, TiN, and TiCN coatings deposited on an AISI 304 steel substrate by the magnetron sputtering method were presented. The research aimed to describe the wear processes of the coatings during friction in an emergency situation, i.e. with a lack of lubrication and concentration of pressure in a small contact area. Tribological tests were performed on a ball-on-disk tribotester in reciprocating motion under technically dry friction conditions. The Hertz pressure in the contact area was ph = 2500-2700 MPa. Additionally, scratch tests and microscopic observations of the surfaces of the samples were performed after tribological tests to describe the wear process of the coatings. The results showed cracking, and coatings detachment from the substrate occur during friction. Deformation wear was observed as bulges in the material at the edge of the friction path. The deformation occurred primarily in the substrate material despite friction occurring on the surface of the coating. The best coating in terms of tribological properties was the TiN coating, which showed the highest resistance to wear in an emergency situation and the friction coefficient in the final stage of the test (above 90 cycles of movement) was only slightly higher than the values recorded for the other coatings. The TiN coating had high hardness, showed good adhesion to the substrate, and was not cracked, protecting it from damage.

Failure starts with creation of a crack, then the propagation of the crack and eventually the fracture of the material. Furthermore, material selection, geometry, processing and residual stresses are critical factors that may contribute to uncertainty and prospective failure mechanisms in engineering. These issues may also arise in computational analysis, a problematic model, for instance, a three-dimensional surface fracture that may necessitate numerous degrees of freedom during analysis. However, considering the multiple incidents of material failure, detailed analysis and efforts to prevent premature material failure for safety and engineering integrity can be carried out. Thus, the objective of this study is to model crack growth in a surface-cracked structure. Aluminium alloy 7075-T6 was the material of interest in this study. The S-version finite element method (SFEM) was used to study fracture propagation. The numerical approach developed in this research was the probabilistic SFEM. Instead of mesh rebuilding, a typical finite element approach, the SFEM uses global–local element overlay method to create a fatigue crack growth model, which was then used for crack research. Empirical computation and previous experimental data were used to evaluate the stress intensity factor (SIF), surface crack growth and fatigue life. The SIF was determined using a virtual crack closure method (VCCM). In addition, the probabilistic approach is also a critical method to generate random parameters, such as Monte Carlo and bootstrap methods. The SIF, fatigue life and surface crack growth were validated and deemed to be within the acceptable range.

This work reports on the optical, structural, and morphological properties of silver oxide thin films obtained by postoxidation of silver deposited previously by the thermal evaporation technique. The samples were deposited on glass substrates using the oblique angle deposition technique for different angles of incidence γ (γ=0°, 20°, 40°, 60°, 75°, and 85°). γ is defined as the angle between the particle flux and the normal to the substrate. The resulting thin films were annealed in the free air at two temperatures (300°C and 400°C). X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible-NIR spectrophotometer were performed to study the crystal structure, as well as the morphological and optical properties (transmittance and reflectance), of the Ag_xO samples. X-ray diffraction analysis revealed the presence of the Ag_xO phase for the silver films deposited at a high angle of incidence and for the annealing temperature 300°C. In contrast, the diffractograms of the silver films annealed at 400°C show an amorphous behavior. Optical results indicated that the direct band gap energy increases pursuant to increasing the angle of incidence γ. The absorption coefficients of Ag_xO thin films were found to be in the range of 10³–10⁵ cm⁻¹. Additionally, we determined the birefringence for the layers annealed at 400°C and found that the highest value of birefringence is obtained corresponding to the angle of incidence 60°. Morphological analysis indicated that the porosity increases with the angle of incidence and highlights the amorphous nature of the films, which is attributed to the columnar structure.

Considering the serious wear of disk cutters in tunnel project and the low prediction accuracy of existing methods, a new method for wear prediction of disk cutters from an energy perspective was proposed. Based on contact mechanics, the rock breaking process of cutters was analyzed, and the combined action of sliding and rolling friction was considered. Furthermore, the wear prediction model of disk cutters was established, which realized the predicted wear of disk cutters under different geological conditions throughout the construction line. In addition, considering the influence of penetration on the wear prediction model, the predicted wear values under different penetrations were obtained, and their average values were taken as the predicted wear values of disk cutters considering penetration. Finally, the predicted wear values were compared with the actual wear value of disk cutters. The results showed that the average relative error between the predicted wear value of disk cutters considering sliding and rolling friction and the actual wear data was 12.8%. The average relative error between the predicted value of wear considering only sliding friction and the actual value of disk cutters is 18.3%. The average relative error between the predicted value of disk cutter wear considering penetration and the actual wear data was 12.2%, which proved the feasibility and accuracy of the prediction model. Meanwhile, it is more accurate than the model only considering sliding friction. The research results provided a scientific theoretical basis for the design of a tool change scheme in tunnel construction.

With the continuous expansion of the urban scale, the development of engineering construction has been accelerated. In this process, excavated engineered soils produced in the construction process are facing the problem of difficult treatment. In this work, the influence of the composition ratio of different curing agents on the strength of fluidized solidified soil was studied. It was found that when the proportion of fly ash and quicklime in the curing agent was 1:1, and the percentage of the curing agent in the soil was 15%, the 28 days unconfined compressive strength of fluidized solidified soil reached the maximum value. When the composition and content of the curing agent and the slump of the fluidized solidified soil remained unchanged, the strength and water stability of the fluidized solidified soil increased with the increase of the sand ratio of the excavated engineered soil. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) showed that with the increase of sand in the soil ratio, more needle-like ettringite crystals were produced in the fluidized solidified soil, which were more compact, had fewer voids, and had higher overall compactness. The carbon emissions of the prepared fluidized solidified soil and the common backfill materials were calculated, and it proved that the carbon emissions of the fluidized solidified soil were the lowest. Therefore, this work offers a new method for resource utilization of excavated soil and provides a carbon emission reference for green low-carbon building materials. Finally, it was recommended to choose engineered excavation soil with high sand content to obtain higher performance from fluidized solidified soil.

This study reports on the exfoliation of bulk hexagonal boron nitride (hBN) by high-energy ball milling and the development of Al-hBN (alumninum-hexagonal boron nitride) nanocomposites by the powder metallurgy (PM) route via the incorporation of the exfoliated hBN in the Al matrix as a nanoreinforcement. The effect of ball milling on the morphology, crystallite size, lattice strain, and thermal stability of hBN powder have also been reported in this paper. Commercially available bulk hBN was ball milled for up to 30 hours in a high-energy planetary ball mill in order to exfoliate the hBN. Although no new phases were formed during milling, which was confirmed by the XRD (x-ray powder diffraction) spectra, ball milling resulted in the attachment of functional groups like hydroxyl (OH) and amino (NH₂) groups on the surface of the hBN, which was confirmed by FTIR (Fourier Transform Infrared Spectroscopy) analysis. HRTEM (high resolution transmission electron microscopy) analysis confirmed the synthesis of hBN having few atomic layers of hBN stacked together after 20 hours of milling. After 20 hours of milling, the hBN particle size was reduced from ~1 μm to ~400 nm, while the crystallite size of the 20-hour-milled hBN powder was found to be ~18 nm. Milling resulted in a flake-like structure in the hBN. Although milling involved both exfoliation as well as reagglomeration of the hBN particles, a significant decrease in the diameter of the hBN particles and their thickness was observed after a long period of milling. The average thickness of the 20-hour-milled hBN flakes was found to be ~32.61 nm. HRTEM analysis showed that the hexagonal structure of the milled hBN powder was maintained. Al-based nanocomposites reinforced with 1%, 2%, 3%, and 5% by weight hBN were fabricated by PM route. The Al-hBN powder mixtures were cold-compacted and sintered at 550°C for 2 hours in argon (Ar) atmosphere. The maximum relative density of ~94.11% was observed in the case of Al-3 wt.% hBN nanocomposite. Al-3 wt.% hBN nanocomposite also showed a significant improvement in hardness and wear resistance compared to the pure Al sample that was developed in a similar fashion. The maximum compressive strength of ~999 MPa was observed in the case of Al-3 wt.% hBN nanocomposite and was approximately twice that of the pure Al sample developed in a similar fashion.

The article presents the results of a complex comparative analysis of the abrasive wear resistance of tools made of X153CrMoV12 steel after different heat treatment variants. These investigations aimed to select the most durable material for application in tools forming a mass band in the production of ceramic roof tiles. The tests included the determination of resistance to abrasive wear in ball-on-disc tests, hardness measurements, and microstructure analysis, including the assessment of changes occurring in the subsurface area, as well as impact tests (at a working temperature for the tools of 50°C). The comprehensive test results showed that the best effects of increasing the resistance to abrasive wear can be obtained through a heat treatment that consists of hardening at 1020°C and then tempering at 200°C for about 2 hours. The next stage of research will be to compare the results obtained with another popular material for tools for the production of roof tiles - Hardox steel, which is characterized by high resistance to abrasive wear.

This paper studies the material aspects of roller cone bits with milled teeth. The research concerns the properties of commercial product overlays provided by the company Glinik Drilling Tools. The analyzed coatings were produced according to the company’s procedures using two surfacing methods: gas welding and plasma transferred arc (PTA) welding. Metallographic observations and chemical composition analyses were carried out. The evaluation criteria in the context of the surfacing application were mechanical properties: hardness, impact strength, and abrasion resistance. The overlays produced by gas welding were characterized by lower hardness, impact strength, and abrasion resistance. The study showed that it differed from the deposit made by the PTA method in the matrix material and in the average size of the tungsten carbides. The dissolution of primary carbides and formation of secondary carbides such as Fe3C and Ni17W3 were found to occur in both surfacing types. This contributes to the increased brittleness of the matrix and reduced wear resistance of the materials.

The effects of heat treatment and cooling rate on the microstructure and properties of T92 welded joints were studied. Under the same tempering holding time, the diffusion ability in the deposited metal increased as the tempering temperature increased. The phase-change temperature was lower than the A_C1 points. In the 5-20s range of t_8/5, the deposited metal toughness decreased as the cooling rate increased. When the t_8/5 was equal to 70s, the toughness increased and the hardness decreased. The higher heat input induced coarse grain tendency. The lower welding heat input should be used in conjunction with the reasonable post-weld heat treatment.

This paper investigates the effect of high temperatures on the compressive strength, flexural strength, and splitting tensile strength of ultra-high-performance concrete (UHPC), and ultra-high-performance, fiber-reinforced concrete (UHPFRC). The experimental variables in this study were fiber type, fiber content, and high-temperature exposure levels. Three different types of fibers were evaluated, including steel fibers, polypropylene (PP), and polyvinyl alcohol (PVA) fibers. Six concrete mixes were prepared with and without different combinations of fibers. One mix was made with no fibers. Others were made with either steel fibers alone; a hybrid of steel fibers and PVA; and a hybrid system of steel, PP, and PVA fibers. These mixes were tested under a range of temperatures and compared for strength. The UHPC and UHPFRC were exposed to high temperatures at 100°C, 300°C, 400°C, and 500°C for 3 hours. The results showed that UHPFRC did not exhibit any significant degradation when exposed to 100°C. However, reductions of approximately 18% to 25%, 12% to 22%, and 14% to 25% in the compressive strength, splitting tensile strength, and flexural strength were observed when the UHPFRC was exposed to 400°C. UHPFRC made of steel fibers showed higher mechanical properties after exposure to 400°C compared to UHPFRC made of PP and PVA fibers. The results also demonstrate the use of PVA and/or PP fibers, along with steel fiber, to withstand the effects of highly elevated temperature and prevent spalling of UHPC after exposure to elevated temperature. The observed spalling was a direct result of the melting and evaporation of PVA and/or PP fibers when exposed to high temperature, an effect that was confirmed using scanning electron microscopy.

This study investigated the mechanical performance of short aramid fiber on polypropylene, polyethylene, polyamide 6, and polyamide 12. Extrusion, press molding, and CNC cutting methods were used in the production of composite samples. Tensile, three-point bending, drop weight and hardness tests of the composites were carried out. As the fiber volume fractions increased, the mechanical properties of the composites improved, but the most efficient fiber fractions for each matrix changed. To analyze the performance of the fibers in the matrix on the composites, scanning electron microscope (SEM) images of the fractured surfaces as a result of tensile and drop weight tests were examined. As the fiber volume fractions increased, the fiber deformation increased, and as a result, the mechanical performance of the composites was adversely affected. Analysis of variance (ANOVA) and F test were performed using signal/noise values to analyze in detail the effect of experimental parameters on output values. Finally, the results of a regression equation model were compared with the experimental readings. It was found to be in good agreement with the model and the results of the experiment.

The correct manufacture of products using FDM printers is not an easy task, taking into account the value and repeatability of material properties. The properties of elements manufactured in this way depend on many factors, both technological and material. Poly(lactic acid) PLA is one of the most willingly used materials in additive techniques. It is sold in a very wide range of colours. This work was intended to answer the question of how the type of pigment affects the mechanical and thermal properties of products obtained from PLA. The correlation between the material properties and the structure of the material as well as the macroscopic structure of the product has also been investigated. The paper analyses the mechanical and thermal properties of products made of PLA filaments in 12 basic colours obtained from one supplier. Bending, impact strength, HDT and Vicat softening point tests were carried out. The percentage content of residues after calcination the samples was determined. Additional analysis (DSC) was performed to interpret the obtained tests results. They indicate that the mechanical properties differ significantly between different types of PLA with differences of up to 45%. Vicat softening point tests indicate differences of 5°C between the extreme values of these parameters. The DSC interpretive study did not clearly show the reasons for these differences in the properties of the filaments.

The aim of this study is to explore the structural and optoelectronic properties of Cu-Cr-O thin films when processed by the magnetron sputtering method using a single equimolar CuCr alloy target. These films were then post-annealed in a controlled Ar atmosphere at 500°C to 800°C for 2 h. The as-deposited Cu-Cr-O thin film consisted of an amorphous phase and exhibited extremely poor optoelectronic properties. After annealing was conducted at 500°C, monoclinic CuO and spinel CuCr₂O₄ phases were simultaneously formed in the film. Upon increasing the annealing temperature to 600°C, the CuCr₂O₄ phase reacted completely with the CuO phase and transformed into the delafossite CuCrO₂ phase, possessing optimal optoelectronic performance. It has an electrical resistivity of 41 Ω-cm and a light transmittance of 49.5%, making it suitable for p-type transparent conducting electrodes. A further increase in annealing temperature resulted in larger grains and greater surface roughness and void density, which, in turn, degraded the optoelectronic performance.

A double-jet electrospinning method was adopted to fabricate In₂O₃/Co₃O₄ nanofibers (NFs). The sensitivity of In₂O₃/Co₃O₄ NFs and In₂O₃ NFs were compared and analyzed, and the morphology, structure, chemical composition, and gas-sensing properties of the samples were comprehensively characterized. The results show that the introduction of Co₃O₄ can improve the response of In₂O₃/Co₃O₄ to acetone, to 29.52 (In₂O₃/Co₃O₄) and 12.34 (In₂O₃) to 200 ppm acetone at 2000°C, respectively. In addition, the doping of Co₃O₄ was found to reduce the optimum working temperature of pure In₂O₃ from 275°C to 200°C. The composite of Co₃O₄ and In₂O₃ not only enhances the sensing performance, but also leads to a conversion of p-n conductivity type. The phenomenon of the p-n transition is relevant to operating temperature and proportion of In₂O₃ and Co₃O₄. While the enhanced acetone sensing properties of In₂O₃/Co₃O₄ NFs may be attributed to the p-n heterojunction between n-type In₂O₃ and p-type Co₃O₄ crystalline grains, which promotes the electron migration. The synergistic effects between In₂O₃ and Co₃O₄ and the large specific surface area of NFs additionally contribute to the improvements of acetone sensing performance.

The quality of the powder layers in the 3D printing process is extremely important and directly corresponds to the quality of the structures made with this technology. Therefore, it is essential to control it. It can be made in-line with a vision system combined with image processing algorithms, which can significantly improve control of the process and help with the adjustment of powder spreading systems, especially in case of difficult-to-feed powders like magnetic ones – e.g., Fe-based metallic glass powder – Fe_56.04Co_13.45Nb_5.5B₂₅. In this work, two algorithms – machine learning – Support Vector Machines (SVM), deep learning – Convolutional Neural Networks (CNN) – were evaluated for their ability to detect and classify the enumerated anomalies based on powder layer images. The SVM algorithm makes it possible to efficiently and quickly analyze the powder-spreading process. CNN, however, appears to be a more promising choice for the developed application, as they alleviate the need for complex image operations.