Today, there are many diagnostic methods and advanced measurement techniques enabling the correct diagnosis and assessment of the type and degree of wear of cogwheels (gears, pumps, etc.). The ...present study presents an analysis of the surface defects of a cogwheel of an oil pump prototype (3PW-BPF-24). The test object operated for a certain number of hours under controlled operating and environmental parameters. The damage to the surface layer was caused by fatigue phenomena and previous thermo-chemical treatment. On the basis of the significant percentage share (~30%) of residual austenite in the volume of the diffusion layer, a hypothetical conclusion was drawn about the suboptimal parameters of the thermo-chemical treatment process (in relation to the chemical composition of the analyzed pinion). A large number of research studies indicate that the significant presence of residual austenite causes a decrease in tooth surface hardness, the initiation of brittle cracks, a sharp decrease in fatigue strength, an increase in brittleness and a tendency to develop surface layer cracks during operation. High-resolution 3D scans of randomly selected pitting defects were used in the detailed study of the present work. It was indicated that the analysis of the morphology of surface defects allowed some degree of verification of the quality of the heat/chemical treatment. The martensitic transformation of residual austenite under controlled (optimum) repeated heat treatment conditions could significantly improve the durability of the pinion (cogwheel). In the case analyzed, the preferred treatment was the low-temperature treatment. The paper concludes with detailed conclusions based on the microscopic and macroscopic investigations carried out.
Hadfield steel, under unit pressure conditions, strengthens itself by forming a high density dislocation structure, which results in increased resistance to dynamic impact wear. However, under ...abrasion conditions, the homogeneous microstructure of the cast steel is insufficient to achieve the expected service life. The aim of the research is to conduct a comparative analysis of the material in its as-delivered state and after two-stage heat treatment (isothermal annealing followed by re-austenitisation). It was found that after isothermal annealing of X120Mn12 grade steel at a temperature of 510 °C, a microstructure with a complex morphology consisting of colonies of fine-grained pearlite, (Fe,Mn)
C carbides distributed along the grain boundaries of the former austenite and needle-like (Fe,Mn)
C carbides was obtained in the austenite matrix. The subsequent thermal treatment of the steel with the use of supersaturating annealing at 900 °C resulted in a heterogeneous microstructure consisting of evenly distributed globular carbide precipitations in a matrix of considerably finer austenite grains in comparison with the as-delivered original state. As a result of the final microstructural changes achieved, a 16.4% increase in abrasion resistance was obtained compared to the delivered condition.
This work concerns two stages of research into plasma nitriding (change of nitriding steel and modification of nitriding parameters). In the first stage, pins obtained from currently used steel were ...compared with pins made of an alternative material available on the market, using the same nitriding process parameters. As a result of the metallographic tests carried out, in the first case, the presence of a thin, porous, and heterogeneous nitrided layer or its absence was found, with the core in its raw state and not thermally improved. In the second case, the presence of a nitrided layer of small thickness with noticeable porosity on the surface of the sample was found, but with a core after heat treatment (incorrect process parameters). Therefore, modification of the parameters of the nitriding process was proposed, in terms of a mixture of gases, currents, time, and temperature of the nitriding process. As a result, a satisfactory effective thickness of the nitrided layer was obtained, consisting of a white near-surface zone with ε and ε + γ′-type nitrides with a thickness of 8.7 to 10.2 µm, and a dark zone of internal nitriding with γ′ nitrides. The nitrides layer was continuous, compact, and well adhered to the steel surface. In the core of the samples, the presence of a fine-needle tempering sorbite structure with a small amount of fine bainite, which is correct for the steel after heat treatment and nitriding, was found. The most favorable parameters of the ion nitriding process were gas flow rate (1.5 L/min N; 0.4 L/min H; 0.3 L/min Ar); currents (BIAS—410 V 4.0 A, SCREEN—320 V 4.0 A); time (26 h and 35 min); and temperature (550 °C).
Abstract Objectives The paper presents preliminary results on the assessment of algorithms used in image processing of the grain damage degree. The purpose of the work is developing a tool allowing ...to analyse sample cross-sections of rye germs. Methods The analysis of the grain cross-sections was carried out on the basis of a series their photos taken at equal time intervals at a set depth. The cross-sections will be used to create additional virtual cross-sections allowing to analyse the whole sample volume. The ultimate plan is to generate two cross-sections perpendicular to each other. Based on volumetric data read from the sample section, a three-dimensional model of an object will be generated. Results The analysis of model surface will allowed us to detect possible grain damage. The developed method of preparing the research material and the proprietary application allowed for the identification of internal defects in the biological material (cereal grains). Conclusions The presented methodology may be used in the agri-food industry in the future. However, much research remains to be done. These works should primarily aim at significantly reducing the time-consuming nature of individual stages, as well as improving the quality of the reconstructed image.
Studies of stress corrosion in X12Cr13 and X20Cr13 steels used for rotor blades of steam turbines have been conducted for determining the average rate of corrosion cracking development da / dt. ...Specimens were exposed to the salt mist environment of 1,2 ppm NaCl concentration in temperature of 60° C. The research environment represents the initial condensate of humidity from 3÷4%. Average rate of corrosion cracking development for specimens of the X12Cr13 is by 0,005 µm/h higher from specimens of the X20Cr13 steel. Course of the corrosion cracking initiation depends to a high degree on metal structure, and probably the close value of cracking propagation rate depends on the similar structure of those steels – high-tempered martensite with carbides at grain boundaries.
This work presents the results of research on a Co49Ni21Ga30 magnetic shape memory single crystal. Based on a literature review, it was identified that analyses of phase transformations have been ...limited to specific heating and cooling rates, which could lead to an incomplete description of the resulting phenomena. Differential scanning calorimetry (DSC) performed with different heating/cooling rates enabled the precise determination of enthalpy values, which deviate from literature values. Weak and previously unnoticed thermal phenomena at temperatures below 190 K were also observed. Their presence was confirmed by low‐temperature in situ transmission electron microscopy (TEM). Through DSC measurements and TEM observations, a model of the discovered phenomenon was proposed, which may have an impact on a better understanding of the physics of magnetic shape memory materials.
A Co49Ni21Ga30 magnetic shape memory single crystal was studied using in situ imaging and low‐temperature calorimetry. Both methods confirmed the occurrence of local reconstruction of the crystal lattice at temperatures below 190 K.
This article presents the results of brake disc tests aimed at identifying the causes of its failure. The first part of the article presents an analysis of the damageability of selected vehicle ...components, which showed that among the reported failures, the most failure was the braking system.
The assessment of the brake disc worn "properly" as a result of operation and the deformed brake disc after a very short period of operation, which was the subject of further analysis. The next part of the article presents issues related to the modeling of thermal loads, and then, trying to assess and search for the cause of abnormal wear of the brake system element, the use of the Finite Element Method for the analysis and assessment of brake disc wear was proposed. In the final part of the article, conclusions and directions for further work were formulated.
An innovative method of manufacturing of Ti-Al-C MAX/Al-Si MMC composite materials was developed using squeeze casting infiltration of open-porous MAX phase preforms. Self-propagating ...High-temperature Synthesis (SHS) in microwave-assisted mode was applied for the creation of preforms in the Ti-Al-C system, that were subsequently infiltrated with Al-Si alloy to create dense composite materials. Microstructure and phase composition, structural defects and potential impacts between constituents of manufactured composites were characterized by the means of SEM and TEM microscopies and XRD analysis. No undesired reaction at the interface was observed, but TiC inclusions were identified in the material. Among the mechanical properties, the instrumental Young's modulus and Vickers hardness were established. The hardness and the elastic modulus of the matrix were enhanced 4 to 5 times. Wear behaviour was tested with a “pin-on-flat” method with the reciprocating motion for different load values (0.1, 0.2 and 0.5 MPa) for tool steel counterpart. Wear resistance of the composite material (WR = 1.6–2.3 × 10−4 mm3/Nm) was twofold higher than for the sole matrix (WR = 3.5–4.8 × 10−4 mm3/Nm). The developed manufacturing method allows the effective fabrication of pore-free MAX phase based MMC composite materials, with significantly higher wear resistance than the widely applied Al-Si alloys.
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•Open-porous MAX phase preforms were synthesized by Microwave Assisted Self-propagating High-temperature Synthesis•Manufactured preforms were infiltrated by Al-Si alloy with the use of Squeeze Casting method to create pore-free composites•Obtained materials were characterized by the means of SEM, TEM and XRD analyses•Mechanical properties were tested and discussed in relation to the microstructures
The paper presents results of microstructural observations and phase analysis of electron-beam-welded fusion zones in superalloy Inconel 713C using transmission electron microscopy. In the fusion ...zone, a 90% fraction of fine-grained
γ′ precipitates was found, with sizes up to 30 nm. No dislocations were observed in the precipitates or at the
γ–
γ′ interface. Primary, undissolved inclusions of
γ′ were found in the heat-affected zone (HAZ). In the HAZ, a very high concentration of dislocations was found at the
γ–
γ′ boundaries, as well as inside the
γ′ particles and in the
γ solid solution. The increased dislocation density indicates loss of coherence of that phase and the creation of a semi-coherent boundary, and is related to dissolution of the particles and intensified diffusion through the interphase
γ–
γ′ boundary. The lattice misfit coefficient Δ
a/
a between the
γ′ particles and
γ solution in the HAZ indicates negative values from −
0.20% to −
0.06%. The presence of semi-coherent boundaries and the negative lattice misfit coefficient leads to dislocation locking and can result in cracking in the HAZ.
