This article describes the kinetics of phase transformations of undercooled austenite of 38CrSiMo4-2-3 alloy steel. The tested steel is called a model alloy, whose chemical composition represents a group of steels for heat improvement. In the research part, microstructural analysis was used, dilatometric method was used and hardness was measured. For the analysis of phase transformations under continuous cooling, steel samples were austenitized at 880°C, annealed for 20 min, and then cooled at various speeds in the range of 20°C/s÷0.1°C/s. On the developed CCT diagram of 38CrSiMo4-2-3 steel, the onset of ferrite and perlite evolution was observed in the cooling range of 1°C/s and 0.1°C/s. In turn, the "nose" of bainitic transformation occurs for a cooling curve of 10°C/s. The temperature at the beginning of the martensitic transformation Ms was 350°C. The steel was characterized by rather "low" hardenability, because to obtain the martensite itself in its microstructure, the use of cooling at a rate greater than 20°C/s was required.
Celem badań było wyznaczenie podstawowych właściwości dynamicznych niskowęglowej stali typu TRIP w warunkach dynamicznego zrywania. Na podstawie uzyskanych wyników podjęto również próbę oceny wpływu wybranych parametrów obróbki cieplnej na uzyskane właściwości mechaniczne.
The results of the research of mechanical properties, obtained under dynamic loads by impact tensile tests, are presented and discussed in this paper. Based on the obtained results the sensitivity of the investigated 13MnSi6–5 TRIP steel to the loading rate was found. This sensitivity manifested itself by higher values of the strength and plasticity than values obtained in the static tests. A high tendency of the investigated steel to the increase of the deformation resistance in the initial stage of its dynamic loading was also stated. A distinct effect of the heat treatment on the basic mechanical properties, determined under conditions of the dynamic loading, was also shown in the hereby paper.
In the paper, the effect of vibro-compaction in processing of sintered SiCp - aluminium matrix composite was presented. The composite with 15% vol. of SiCp, obtained with three stages: vibro-compaction with use of different amplitude (0.75 mm, 1.125 mm and 1.5 mm), cold pressing and pressure less sintering. The obtained composites were characterized by porosity measurements, microhardness, quantitative metallography analysis and dry sliding tests. It was proved that the application of chosen compaction method, for powder mixture consisting of powders with different density (Al and SiC), allows to obtain graded structure composite. An increase of SiC particles volume fraction as well as microhardness increase was observed towards the bottom of the sample. The most beneficial effect, in SiCp distribution and microhardness values, was noted for the sample were the amplitude of vibro-compaction was 1.5 mm. Moreover, the tribological examinations showed differences in friction coefficients and mass losses for opposite surfaces of composite samples, due to different SiCp volume fraction across the sample. The vibro-compacted material revealed lower porosity, higher mean value of friction coefficient and lower mass loss comparing to the reference composite.
The paper presents an analytical, numerical and experimental analysis of the state of stress in a plate with stress concentrator in the form of circular hole subjected to uniaxial tension. This type of the plate have found wide spread applications in the field of aerospace, marine and automobile engineering. The maximum difference in the values of reduced stresses calculated analytically in relation to the results obtained experimentally was δσa red = -19.74%. However, the maximum difference in the values of reduced stress calculated numerically using the finite element method (FEM) with the ANSYS program in relation to the results obtained experimentally δσn red = -31.86%, The study showed that the analytically calculated and numerically determined stresses are lower than the stresses obtained experimentally, which results in less operational safety of the structural element. However, the numerical method in the form of the finite element method becomes, in the case of a very complicated element shape, the only method for determining the magnitude and distribution of stresses near the notch in the designed element.
The content of the article assumes the description and comparison of three selected criteria of cracks: MPS, S-Criterion and T-Criterion. The analyses carried out were a simulation of the steel cracking process in a dimensionless tensor space, using the components of a stress tensor. The research concerned the analysis of the slot propagation direction in relation to the adopted angle, taking into account the criterion used. Depending on the criterion used, the analysis assumed taking into account various types of gap loads (KI, KII, KIII), which were responsible for the tearing, longitudinal shear and transverse shear successively. Initial stresses have been properly taken into account and transferred to the Cartesian system depending on the type of deformation used. During the analysis, study will be the angle of displacement fractures α, in considered range to π/2. It was noted that the S-criterion for Flat State of Deformation (FSD), had a straight run, with lift of the angle θ was 6.22, including the tolerance of 0.01. The angle of inclination α, was considered taking into account the angles of 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40° and 45° for each of the analysed criteria. The methods involves the use a dedicated computer program created in the C++ environment. The computational module of the computer program in the form of matrix equations algorithm, analysed the distribution of tensors of occurring stress. The result values are summarized in tabular form and then presented in the form of a graph. The results are purely theoretical, and therefore a dedicated program, because of its severity may contain errors.
Piaskowanie jest procesem technologicznym stosowanym w celu oczyszczenia powierzchni elementów mechanicznych ze związków organicznych i nieorganicznych. Ma więc bezpośredni wpływ na strukturę geometryczną powierzchni przedmiotu obrabianego i jego właściwości funkcjonalne po procesach obróbki cieplno-chemicznej. Celem pracy była charakterystyka wpływu warunków procesu piaskowania na kształtowanie się warstwy nawęglonej wytworzonej w procesie nawęglania próżniowego. Wykonano proces nawęglania z bezpośrednim hartowaniem do temperatury pokojowej. Zakres prezentowanych badań obejmował analizę wpływu procesu piaskowania ze zmienną wartością ciśnienia na chropowatość powierzchni przed i po nawęglaniu oraz ocenę profilu stężenia węgla i twardości w funkcji odległości od powierzchni podłoża stali na przekroju warstwy nawęglonej.
W pracy zaprezentowano analizę statystyczną wykonaną na podstawie ponad 500 wyników prób zmęczeniowych dostępnych w literaturze naukowej, dla których pokazano wpływ obróbki cieplnej stali austenitycznej na trwałość niskocyklową stali austenitycznej. Przeprowadzono analizę regresji dla zgromadzonych danych oraz analizę wariancji dla różnych grup parametrów obróbki cieplnej. Przeprowadzona analiza statystyczna pozwala na wyselekcjonowanie istotnych parametrów wpływających na trwałość materiału, pozwalając jednocześnie odrzucić parametry nieistotne, co w efekcie pozwala na poprawne opisanie zjawiska. W pracy ograniczono użyte dane do odpowiadających typowym parametrom pracy elementów odprowadzających spaliny w turbinach gazowych.
The paper presents a statistical analysis based on more than 500 fatigue tests available in the scientific literature, for which the influence of thermal treatment of austenitic steel on the low-cycle life of gas turbine exhaust elements is shown. The confidence range of regression parameters for test data is shown and an analysis of variance for different groups of parameters was carried out. Conducted statistical analysis allows to select important parameters affecting the life of the material, while allowing to reject non-essential parameters, which in effect allows correct description of the phenomenon. The collected data from fatigue tests was limited to those whose parameters correspond to the typical work conditions of gas turbine exhaust elements. The tested material is austenitic steel type AISI240 TP304 in various states of heat treatment: aging, tempering and in an as-fabricated condition. The tests were carried out in isothermal conditions with a fast-changing cycle or a cycle with tensile load hold during stretching.
Deposition of polytetrafluoroethylene coatings by means of the innovative PED technique
In the study, polytetrafluoroethylene coatings were deposited on a silicic substrate in the process of Pulsed Electron Beam Deposition (PED). Depositing polymer coatings using PED is a relatively unknown technique. Due to the limited knowledge on the use of this technique in the deposition of polymer coatings, the conducted studies had exploratory character. The deposition of polytetrafluoroethylene coatings was carried out at 24°C with various pressures in the range of 0.133÷1.467 Pa and various voltage values: 10, 12, 15 and 17 kV, with the number of shots: 1,211 and 5,000. The deposition of coatings took place in the presence of argon and nitrogen. It was observed that the increase of the coatings’ thickness directly affects the increase of roughness, regardless of the deposition parameters. Infrared spectroscopy FTIR revealed the presence of typical PTFE functional groups. A light microscope was used to evaluate the surface of the coatings after an adherence test. The evaluation of the adhesion of the coatings and a preliminary assessment of their mechanical properties were performed using a nanohardness tester. The influence of the deposition parameters on their mechanical properties was evidenced, however, a simple interpretation of the results was hard to gain, due to the random nature of the performed works.
The effect of y phase content on the martensitic transformation and mechanical properties of Co-Ni-Al alloys was investigated. For nine Co-Ni-Al alloys with different chemical composition corresponding to the e/a ratio from 7.9 to 7.55, a quantitative microstructure investigations as well as tensile tests have been performed. The alloys were induction melted, casted, homogenized, plastically deformed by hot rolling with thickness reduction of 90% and finally again annealed and water quenched (solution treated). Quantitative image analyse of microstructure after homogenization allowed to determine the γ content from 14 to 39% for alloys containing from 25 to 30 at. % Al respectively, while further hot rolling and solution treatment caused reduction of γ phase content from 6 to 23%. Linear relationships between Ms temperature and e/a ratio was found for alloys with the e/a ratio from 7.9 to 7.72, in which the amount of γ phase increases slightly from 21 to 23%, and for composition where e/a decreases from 7.69 to 7.55 and γ phase content rises up from 6 to 12%. Tensile tests revealed that alloys with the highest γ phase content (about 20%) have the best mechanical properties; strength at the level of 1000 MPa combined with plasticity at the level of 18%.
The article presents information from area of the practical surface engineering related with selection of materials and coatings’ deposition technology for power plant industry with special attention to possibility of modification of the final coatings and their adaptation to operating in complex and aggressive environments. The different types of corrosion and erosion resistant coatings and technology of their deposition such as high velocity thermal spraying and electrical deposition of coatings were described. Furthermore, the characterization of technological and materials problems concomitant application of those processes to deposition of high-quality coatings with complex chemical and phases composition are shown. Advantages and disadvantages of the utilized technology as well as fundamental steps in the deposition of coatings were also presented in the paper. Finally, the application of different types of sprayed coatings in power plant industry were described. The presented reflections are the result of many years of work and experience of the authors in the field of spraying processes and applications of protective coatings for the energy and machine industry. The following review article shows the problem of coatings’ selection, deposition and operating from point of view of coatings contractor rather than researcher.
The specimens sintered from Distaloy AB iron powder have been examined to evaluate evolution of morphological characteristics under complex deformation conditions. The sintering procedure, in particular, the pressure and the temperature have been adjusted in order to obtain about a 15% porosity level. All examinations were performed on the specimen in as-sintered state, as well as after plastic deformation (compression with cyclic torsion). The volume fraction and pores shape have been described quantitatively before and after deformation. On the basis of statistical analysis, it was found that compression with cyclic torsion with amplitude 3° and frequency 0.5 Hz better reduce porosity than deformation with amplitude 6° and frequency 1 Hz. All shape factors that were used to describe pores geometry, except convexity, differ significantly after plastic deformation in comparison to values before deformation. The Principal Component Analysis of the pores shape factors showed, that it is possible to reduce the characterization of the pores to two principal components. Alternatively, it is sufficient to fully characterize pores shape with three shape factors: circularity, Malinowska’s factor and not correlated with them aspect ratio.
Nowadays in case of long-term implants, the most common postoperative complications are bacterial infections, which in consequence may provoke loosening of the implants in the primary phase of stabilization. Bacterial infections are currently the most frequent cause of revision surgery of the implants such as hip joint endoprosthesis, knee joint endoprosthesis and dental implants. In order to provide the local and long-term antibacterial cover in the tissues surrounding the implant, research is performed on materials that are carriers of drugs, which release active substances only in the case of the pH change in the system during inflammation. In consequence, biomaterials ensure antibacterial protection for a long time, not only in short post-operative period. An example of such materials are biopolymers. Biopolymers sensitive to change in pH value of the environment of live tissue that surround the implants can be used as an independent implants or as the coatings on the implants. In this case in the polymer`s matrix is dispersed often used drugs such as doxorubicin, gentamicin, vancomycin and cefuroxime. Drugs are released from this biomaterial according to three main mechanisms: diffusion, swelling and material degradation. This review paper presents the mechanism of bacterial interaction with implant surface and biofilm formation, and mechanism of drugs release from the biological active substance. Therefore, the natural and synthetic polymer materials sensitive to the lower value of pH such as chitosan, Eudragit E 100, Poly (L-histidine) and Poly (4-vinyl pyridine) are described.
Marek Opiela Thermomechanical treatment of Ti and Ti-V microalloyed steel forgings
The research results of the effect of thermomechanical treatment conditions on the microstructure and mechanical properties of the Ti and Ti-V microalloyed steels were presented. The steel forged parts studied were intended to be used in the automotive industry. The method of thermomechanical treatment and forging conditions were developed based on the analysis of precipitation kinetics of MX interstitial phases in a solid solution and the austenitizing temperature effects on the prior austenite grain size. To reveal the microstructure, the light microscopy and transmission electron microscopy techniques were used. Very high mechanical properties of the forgings along with guaranteed toughness were obtained as a result of the optimal use of grain refinement and precipitation strengthening by dispersive particles of carbides, carbonitrides and nitrides of microadditions introduced into steel. Depending on the variant of thermomechanical treatment used to the forgings, the following range of the mechanical properties, after tempering at 600°C, were obtained: YS0.2 from 696 to 850 MPa, UTS from 770 to 932 MPa, KV from 186 to 215 J, and the HBW hardness of 220÷250.
Józef Lelątko, Zdzisław Lekston, Michał Tarnowski, Dariusz Chrobak, Bożena Łosiewicz, Tomasz Goryczka, Tadeusz Wierzchoń Characterization of low-temperature nitrided NiTi shape memory alloy
The paper presents the results obtained from studies on the influence of the low temperature glow discharge nitriding process on the structure, kinetics of martensitic transformation, one-way shape memory effect, superelasticity effect, mechanical properties, and corrosion resistance of the NiTi alloy. The changes observed in a structure after nitriding process do not affect negatively the shape memory effect. Moreover, applied surface modification increased hardness and frictional coefficient of the NiTi.
Oxidation of zirconium alloys is a process that takes place during the operation of nuclear reactors and is essential for assessing the durability of fuel claddings. The present study was aimed to determine the oxidation kinetics of the Zircaloy-4 alloy using GDOES (glow discharge optical emission spectroscopy) at temperature 673 K corresponding to the conditions of use of fuel pellets. The tests were performed on non-oxidized samples as well as after their oxidation for 0.5, 2, 15 and 48 h. Oxygen layer growth was also investigated by thermogravimetric analysis after oxidation for 0.5 h. The naturally generated oxide at room temperature, designated as non-oxidized, had a thickness of 23±2 nm. After 2 h oxidation, an oxide possessing a thickness of 42±4 nm with about 155 nm of oxygen traces was observed. Oxidation for 15 h resulted in formation of an oxide with a thickness of 130±10 nm with a transition distance to the pure alloy of 240 nm. Finally, a layer with a thickness of 235±10 nm appeared after oxidation for 48 h, while the distance after which the measurement included only a pure alloy without the oxygen traces, was about 310 nm. The results show that oxidation can be described by the exponential kinetic equation, that has the parabolic form after 15 or 48 h of oxidation, which well fits the previous results. However, at shorter oxidation times the kinetic equation has the quasi-parabolic form (n < 2). The reason for changing the form of the equation can be attributed to the effect of defective crystalline structure on oxygen diffusion in the oxide layer as the porosity, crevices and cracks.
Grzegorz Moskal, Agnieszka Tomaszewska, Damian Migas, Dawid Niemiec Cyclic oxidation resistance of Co-9Al-9W new cobalt-based superalloy
Cobalt-based superalloys are class of new heat-resistant materials for components of turbine engines. The γ/γʹ phase microstructure similar to nickel-based analogue, provide excellent creep resistance as well as resistance to corrosion and oxidation. Superior high temperature resistance drives intensive development of Co-based superalloys. The aim of paper is assessment of high temperature oxidation behaviour of Co–9Al–9W alloy in as-cast state. The cyclic oxidation performance of Co–9Al–9W alloy was studied at temperature 800°C and 900°C. The cyclic oxidation test was carried out under laboratory air atmosphere with time of exposure 25 hours and multiplicity of it. The scale morphology after cyclic oxidation test was investigated. The evaluation of scale concerned macrostructure, microstructure, chemical and phase composition of surface. Surface of tested alloys after oxidation was characterized using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and light microscopy (LM). Obtained data revealed that Co-9Al-9W alloy showed acceptable resistance to cyclic test at temperature 800°C. The oxide scale at this variant showed mainly Co oxides as an dominant phase. At higher temperature - 900°C the strong effect of spallation of scale was observed as results of CoWO4 complex oxide formation.
Marcin Godzierz, Anita Olszówka-Myalska, Patryk Wrześniowski Wear resistance of composites with Mg-Zn-RE-Zr alloy matrix and open-celled carbon foam
In this article, a magnesium matrix composite, reinforced with open-celled carbon foam and fabricated by pressure infiltration method, was examined. The main problem analysed was the usefulness of two commercial magnesium alloys RZ5 and ZRE1 as matrices in terms of composite tribological properties. Results of composite microstructure examinations by LM and SEM with EDS, porosity and hardness measurements were presented, and wear resistance in a dry friction conditions was characterized by a pin-on-disc method. The friction coefficient, the mass loss of sample and cast iron countersample, and wear trace depth were measured, as well as the mechanism of wear was examined by SEM observations of the wear traces. Obtained results show good infiltration of open-celled carbon foam and microstructural effects at an interface similar to the particulate and fibrous composites of C–Mg systems. Differences in wear resistance, dependent on applied matrix alloy, were revealed, and the ZRE1 magnesium alloy was indicated as more favourable, due to a composite lower friction coefficient, less mass lost, and wear trace depth. The wear of open-celled carbon foam was regular and without cracks in the reinforcement, fragmentation, or pulling out.
Mateusz Konieczny, Henryk Achtelik, Grzegorz Gasiak Research of maximum stresses zones in circular perforated plates made of S235JR steel loaded with concentrated force
The paper proposes a numerical approach to determining the internal forces in a circular perforated plate loaded with concentrated force Pi applied in the geometric centre of the plate. The finite element method program Femap was used for numerical calculations. The test plate with diameter D = 300 mm has holes in ten circles. The plate made of S235JR steel has holes with diameter d1 = 3.5 mm on the first inner circle, and holes on the tenth outside circle have a diameter d10 = 20.5 mm. The plate of the above geometry was simply supported and loaded with different values of concentrated force. By means of numerical calculations using the finite element method, the coordinates of concentration zones of reduced stress in the perforated plate were determined. These zones were located on the plate bridges between perforation holes. The most hazardous place in the analysed perforated plate is associated with the 8 zone with the hole radius d3 = 5.0 mm at the circle radius R3 = 33.0 mm, where the highest stress concentration occurs. In this zone, the reduced stress is σred max = 217.20 MPa (point with the coordinates x, y, z [mm], i.e. P2[5.2; 30.6; 4.5]). The results of numerical calculations were verified with experimental results. The differences between the results of numerical calculations of the state of stress and those obtained experimentally did not exceed 10%.
Various ion sputtering parameters were applied prior to the deposition of S phase coatings in order to determine their effect on the efficiency of cleaning an austenitic steel surface. For this purpose, two types of atmospheres were used (100% Ar and 5% Ar + 95% H2) at two different pressures (1.33 Pa and 2.67 Pa). In addition, substrates with two different initial states — without polishing and with polishing — were investigated. The thickness of the diffusion layer, obtained in the austenitic substrate after depositing an S-phase coating by magnetron sputtering, was used as a measure of the surface cleaning effectiveness (passive oxide layer removal). The research showed that all the considered parameters had a significant effect on the effectiveness of the cleaning treatment. It was found that the initial state of the substrate has an influence on the thickness of the diffusion layers, with thicker layers obtained on nonpolished substrates. The total gas pressure affects the substrate cleaning effectiveness in different ways depending on the gas composition used. It is possible that a physical sputtering mechanism occurs in the case of argon and a chemical reduction mechanism in the case of hydrogen. In addition, it was found that the degree of surface cleaning determines the texture of the S phase coatings.
The main aim of current research is to improve wear resistance of tool steels. Chemical heat treatment is a well-known method to do this. Nitriding is a well known method of improving surface hardness and wear resistance. Due to high hardness, low thickness, these coatings often crack and spall out of the substrate. We supposed that varying hardness and composition of the coating will facilitate wear resistance and will help to avoid coating cracking. In this order we propose to use selective laser treatment of cutting edge by laser beam after chemical heat treatment. This locally changes the structure of steel, thus changing the thickness and hardness of coating. A following chemical heat treatment was done - single- (nitriding with laser pre-treatment) and bilayer (nitriding + metallization with laser post-treatment) coatings. Laser post-treatment provides local hardening of steel substrate, with no influence on diffusion layer chemistry. In a work we considered the structure, phase and chemical composition, microhardness of surface areas of steel P6M5 (substitute of PN SW7M, EN HS6-5-2) after chemical heat treatment: nitriding with further titanizing or chromizing and laser post-treatment. For this we used laser installation LATUS-31, radioelectron microscope REMMA 101A. The content of chemical elements was determined by EDS (heavy elements) and WDS (light elements) methods using REMMA 101A built-in facilities. Dry wear test was performed in sliding conditions using block-on-ring test layout. It is proved that combined coatings have better wear resistance versus coatings formed by common nitriding. Laser treatment of substrate prior to chemical heat treatment has a superior effect on the properties of diffusion coatings, increasing their wear resistance in order of two (compared with untreated coatings) Results of analysis indicate that nitrochromized coating on laser post-treated tool steel P6M5 has the best wear resistance under dry sliding friction.
The specimens of C-Mn-Si-steel wire rod 5.5 mm in diameter with 0.005% B and without B addition from Moldova Steel Works have been studied. The specimens characterized by multi-phase ferrite-martensite (bainite)-pearlite) microstructure. The studies of static strain aging (SSA) and dynamic strain aging (DSA) of wire rod specimens made of C-Mn-Si steel with B and without B revealed decrease of strengthening properties and increase of ductility for specimens with B. These results could be explained by "de-nitrogenous" and "de-carbonaceous" mechanisms, when boron atoms from alfa-Fe sub-interstitial solid solution during wire rod production and its strain aging thermal treatment at temperature 150÷450°C generate boron-nitrogenous and boron-carbonaceous- nitrogenous precipitations. By realizing these mechanisms nitrogen and carbon atoms are partly excluded from the dislocation pinning's process. This, in fact, explains to inhibit the development of strain aging (SSA and DSA) in C-Mn-Si steel with boron microaddition.