Despite its predominantly empirical nature, metallographic etching remains an important sample preparation method that enables microstructural characterization. The poor repeatability is due to the ignorance of etching mechanisms and the human factor, which is mainly associated with the conventional approach. This approach is most commonly practiced by manual immersion of the sample in the etchant. The solution should be gently stirred so that reaction products do not settle on the surface and uneven etching does not occur. Often, stirring is provided by the sample itself or by a magnetic bar. In terms of spatial orientation, etching with the polished surface facing upwards allows the surface to be observed during the process. Some authors recommend etching with the polished surface downwards to minimize the deposition of reaction products. In some cases, a vertical orientation of the sample is recommended to reduce pitting. In this paper, the effect of the etchant stirring method on the surface quality of a metallographic structural steel specimen will be presented. In addition to different etchant stirring methods, different spatial orientations of the sample will also be investigated. To ensure better repeatability and accurate etching time, the samples will be etched using our automated apparatus. The resulting surface of the samples will be analyzed using light optical microscopy (LOM) and confocal laser scanning microscopy (CLSM). The development of more reproducible etching methods is essential to obtain accurate microstructure information without artifacts and for advanced quantitative image analysis using deep learning.
This paper concerns influence of grit blasting parameters (grid blast media size and blasting pressure) on blasted surface contamination by entrapped grid blast particles and roughness of a blasted mild steel surface and a subsequent influence of specific surface specifications on a thermal spray coating adhesion strength. Review of sources concerning this issues showed some ambivalent results from different papers, thus a decision to make specific research effort has been made, with this paper presenting some partial results regarding one blasting material and one coating material. Main goal of an experiment presented in this paper is to optimize grid size of alumina oxide blasting medium and blasting pressure in order to reduce surface contamination by grid residues trapped on the surface. Those residues are known to cause reduction in adherent forces between coating and blasted substrate, functioning as major stress concentrators especially under high mechanical and/or temperature loads. Mutual relations between grid size and blasting pressure as input parameters, and surface contamination, surface roughness and adhesion of an atmospheric plasma sprayed ceramic coating is evaluated.
The work presents the influence of selected parameters of the EDM machining process on the parameters of the geometric structure of the surface. The EDM treatment was performed on the Alnico alloys. The tests were carried out on the PB 93L EDM machine. In order to assess the influence of the current intensity, pause time and discharge time, a planned experiment was used: 3-factor, 3-level experiment planned according to Box Bekhen's plan. Thanks to the use of proprietary processing with the use of additional rotational movement of the tool and the workpiece, it is possible to increase the effectiveness of the surface shaping processes. The measurements of the geometrical structure of the surface were made on the Talysurf CCI Lite optical profilometer. The analysis also included surface determination using scanning electron microscopy (SEM) and examination of its surface morphology by means of optical microscopy (OP). The processing of the results was performed using the Statistica software. ACKNOWLEDGEMENTS: The research reported herein was supported by a grant from the National Center for Research and Development. Program: Lider XI, grant title: "Improvements in the technology of machining the surfaces of spherical rings of magneto mirrors through the use of electro-erosion machining (EDM)", contract number: LIDER / 59/0246 / L-11/19 / NCBR / 2020.
Steels 32CrMoV12-10 and 31CrMoV9 are used not only for components in the automotive industry, but also for firearms parts in the weapons industry. For these parts, high strength and surface layer hardness is required while maintaining the toughness of the core, which is achieved by nitriding.
The aim of the work was to determine which of the steels exhibits better physical, mechanical and chemical properties after nitriding in a gaseous atmosphere. The structure of the nitride layer was compared on metallographic samples after nitriding. Hardness measurements, fracture toughness determination, Charpy impact test and corrosion resistance evaluation were also carried out. After the tests, it can be concluded that the 31CrMoV9 steel shows better physical and chemical property results than the 32CrMoV12-10 steel.
Additive manufacturing (AM) technology is increasingly expanding into different types of industries. Still many of potential applications are restricted due to the limited choice of materials used in AM. A suitable solution could be a combination of AM and thermal spraying of functional parts of the surface to achieve superior surface properties. This work aims to study a possibility to prepare surface by AM technology to direct application of coating by thermal spraying without any additional surface preparation. To verify this possibility, the parameters of the 3D printing technology were adjusted to achieve suitable surface structures for the following thermal spraying. Several variants of modifications with a different surface properties were selected. The samples were printed from maraging steel using the DMLS technology. The coatings chosen for testing were WC-CoCr and Stellite 6 sprayed by HVOF and further NiAl and Al2O3 TiO2 sprayed by APS. The adhesion of the coating was tested by an adhesion test performed under the ASTM C633 79 standard. The bonding of the coating on the surface was studied by metallographic analysis. The achieved results indicates that the adhesion of HVOF sprayed WC-CoCr coating on 3D printed surface is excellent for most surface modifications. The Stellite 6 exhibit good adhesion on several surface modifications. The APS sprayed coating shows significantly lower adhesion, the NiAl and Al2O3 TiO2 coatings can be successfully sprayed only on selected surface modifications.
Severe plastic deformation (SPD) is a perspective method for preparation of ultrafine-grained materials. A coarse-grained aluminium with different purity and its alloys was processed by equal-channel angular pressing (ECAP) to evaluate the effect of severe plastic deformation on the thermal stability of resulting ultrafine-grained microstructure after ECAP and on creep behaviour of the SPD processed sample. These materials were subjected to ECAP up to 8 passes by route BC at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The microstructural investigations were performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with an electron back-scatter diffraction (EBSD) unit. Creep tests in tension were conducted at temperature of 473 K on a both states of materials. It was found that creep behaviour of aluminium and its alloys is influences by resulted grain size, its stability during creep test, material purity, precipitate strengthening and fraction of high-angle grain boundaries development during ECAP process. While creep resistance of aluminium is improved already after 1 ECAP pass, ECAP process leads to degradation of creep life in case of Al alloys.
Paper describes the combination of gas cementation with local laser hardening of hot work tool steel AISI H13 to achieve higher surface wear resistance of forging dies. The experimental material was 100×100×100 mm cubes. The gas cementation parameters were chosen with concerning the higher alloying of the material. The process temperature was chosen to be 980 °C. The cooling rate after the cementation process corresponded to the cooling rate in the open air. Since the main objective of the work is maximum abrasion resistance of the surface, laser surface hardening was included after cementation. This was done to increase the subsurface hardness, which is important for the use of forging dies while maintaining sufficient toughness of the core.
This article introduces new options for high-temperature permanent ink marking of machine parts. As experimental materials, ferrous metals (EN X5CrNi18-10, EN X40CrMoV5-1, EN 16MnCr5-1), aluminium alloys (EN AW 2017, EN AW 6063) and titanium (Ti6Al4V) have been printed. The paper presents the temperature-dependence curve of Ceramic phosphors. Generally, the most commonly used pigments are based on ZrSiO4, ZrO2 and SiC (each has a different refractive index). In our case, TiO2-based powder was also used. The respective pigments were subjected to several technological processes. These included nitriding, carburizing and vacuum heat treatment. The printing or its effect was evaluated by LM, SEM and microhardness measurements. The new method of marking machine parts appears to be suitable for non-destructive marking of parts for applications requiring resistance to high temperatures.
The article is aimed on evaluation of Ni and NiCr Cold Spray layers as a potential method for repairing components in energy industry by replacing or refilling flawed material. For the purpose of testing, various cold spray layers were prepared. Spraying with nozzle for inner tube application from two NiCr powders of different particle sizes and with nozzle types for inner and outer tube applications from Ni powder of one particle size was applied. The evaluation is aimed on mechanical properties and metallographic analysis of cold spray layers as received and after defined heat treatments, comparing small and large testing specimens. It summarizes tensile properties at room temperature and microstructure of used powders and final cold spray layers. Ultimate tensile strength, hardness and plastic elongation are evaluated from the mechanical point of view. Metallographic analysis is focused on ovality and size of particles in powders and of splats in final cold sprays. Porosity of sprayed layers is evaluated on tested specimens and the influence due to specimen dimensions is discussed.
The production of sheet safety parts for car bodies is currently carried out using press hardening technology. This technology enables the creation of complex-shaped profiles even from high-strength steels without a significant spring-back effect. In combination with modern high-strength steels, which have retained austenite in their structure, it is possible to achieve high ultimate strength and ductility values. As a result, these parts are used in bodywork areas with high energy absorption requirements during impact. To achieve the required mechanical properties, suitable processing parameters must be selected. High-strength steel with 0.2%C, 3%Mn and 2%Al was used for the experiment. Press-hardening was carried out in a tool fixed in a hydraulic press and can be heated up to temperatures around 450 °C. Different tool temperatures of room temperature and 425 °C were tested and different holding times in the tool from 1 s to 600 s. After hardening in a tool at RT, the ultimate strength of about 1400 MPa with a ductility of 18 % was obtained. But quenching and holding in the preheated tool caused the ductility to increase to 28% with a drop in ultimate strength to 1050 MPa.
The subject of the paper is the results of the material analysis of the cracked axle of the tram. Fractographic analysis of the fracture surface was performed, the microstructure of the damaged part was observed, hardness profiles were measured and local chemical composition was determined by the EDX method. The failure occurred through a fatigue mechanism. The crack was initiated from surface defects of the welded material on the surface of the axle. The cause of the accident was the interplay of several negative factors: poor welding repair technology, unsuitable consumables, high levels of residual stresses and mechanical damage during assembly.
Powder metallurgy is a very useful fabrication way also for magnetic compacted powder materials as a group of soft magnetic materials with expanding application range for electromotors, transformers, sensors, and other types of electrical equipment, operating at DC or frequencies up to ~50/60 Hz where high magnetic performance is required. Despite the fact that many technological steps in the production of very successful materials produced by powder metallurgy methods are well known and proven, there is still the possibility to include a new element in the production cycle of powder compacted materials, which will bring benefits in terms of improved properties of the final product. One of these approaches is the method of mechanical smoothing the surfaces of powder particles before compaction and sintering, which brings the possibility of preparing powder particles with higher purity surfaces and surfaces without sharp edges. The paper quantifies the positive effect of smoothing the surfaces of NiFeMo powder particles on a threefold increase in maximum permeability, as one of the most important parameters for characterizing the functional properties of soft magnetic materials.
This work was financed by Slovak Research and Development Agency under the contract APVV-20-0072; and by Scientific Grant Agency of Ministry of Education of Slovak Republic and Slovak Academy of Science - projects VEGA 1/0225/20 and 1/0143/20.
NiTi alloy with shape memory effect that exhibits excellent mechanical and chemical properties presents an attractive material for various types of biomedical application. The Young’s modulus of low temperature phase version of NiTi alloy is very low and closer than any other metallic materials to the elastic properties of the human bone. So, it is of high interest to find an appropriate combination of superelastic properties and mechanical strength that could be applied in various traumatology or orthopedic plates and nails. In this work the influence of the heat treatment and strain rate on the superelastic properties of NiTi alloy was studied in the tensile testing. NiTi thin sheets with a thickness of 2.0 mm and with a content of 56.31 Ni and 43.69 Ti (in wt. %) were tested in the different heat-treated conditions. The flat specimens were tensile tested at two different strain rates in the stage as-received, after aging at 450 °C and after solution treatment at 850 °C followed by aging at 450 °C. The microstructure and phase analyses of the NiTi specimens in three heat-treated conditions were examined using of an optical and scanning electronic microscopies and related to the superelastic behavior.
Directed energy deposition (DED) technology enables the manufacturing of materials in combinations that would be highly problematic using conventional technologies. These materials with the tailored properties of bimetallic material structures have potential applications in the energy, automotive and petrochemical industries. The combination of materials such as austenitic stainless steel 316L in combination with nickel superalloy Inconel 718 may satisfy requirements for corrosion and oxidation resistance, while maintaining suitable strength even at increased temperatures, at reasonable costs. The experimental programme of the present study aimed at optimizing the laser power of the DED process with respect to the quality of the interfaces of functionally graded materials in terms of microstructure evolution, interface quality and mechanical properties. One of the main objectives of the research was the analysis of two types of interfaces and the reduction of crack generation and propagation on the interface transition from Inconel 718 to 316L depending on the applied laser power. The presence of solidification cracking together with ductility dip cracking played the most significant role in terms of the quality of this type of interface and significantly affected the values of the mechanical properties.
Electrical discharge machining (EDM) is a nontraditional machining process which removes metal by a series of discrete electrical discharges. These discharges cause high temperatures which is enough to melt or vaporize the metal. The paper presents the results of experimental tests carried out with EDM drilling with a spherical copper electrode (99.9% Cu) in an AlNiCo alloy. The surface roughness was investigated using various process parameters and the spherical radius were measured. The measurement of the roundness profile of the inner surfaces of the rings was carried out on the Talyrond 365 measuring system using the radius measurement method with a rotating table. Additionally, the hollow element was scanned on a computed tomography. The radius of curvature was measured using VG Studio 3.5.2 software. The obtained results from the contact measurements and from the tomographic measurements of the hollow detail were compared and verified with the dimensions of the electrode used.
ACKNOWLEDGEMENTS: The research reported herein was supported by a grant from the National Centre for Research and Development. Program: Lider XI, grant title: "Improvements in the technology of machining the surfaces of spherical rings of magneto mirrors through the use of electro-erosion machining (EDM)", contract number: LIDER/59/0246/L-11/19/NCBR/2020.
The development, research and production of new materials are of particular importance in different interactions. Nowadays, great importance is placed on magnetic materials due to their interesting properties and rich use, are of particular importance for technical practice and have caused the revolution in material research, electrical engineering, environmental engineering and others.
The shape, in which these alloys are usually prepared is in many cases not suitable shape for industry applications. One of the ways to prepare 3-D material suitable for industrial applications is the compaction of powder, which can be produced by the mechanical milling or alloying of ribbon, powders mixture, or others pre-cursor. Another aim is to use these powders to prepare composite materials. The advantage of this process technology is that the powder can be produced in large quantities and the processing parameters can be easily controlled.
This work was realized within the frame of project “FUCO” financed by Slovak Research and Development Agency under the contract APVV-20-0072 and by Scientific Grant Agency of Ministry of Education of Slovak Republic and Slovak Academy of Sciences projects VEGA 1/0143/20 and 1/0301/20.
Requirements for mechanical properties of steels are constantly increasing, and the combination of quenching and tempering is the method generally chosen for achieving high strength in medium carbon steels. The SiCr (54SiCr6 and 42SiCr) steels belong to spring steels with high strength and at the same time reach sufficient values of elongation and reduction of area. Further improve of mechanical properties requires to include a thermomechanical treatment or to modify chemical compositions of steels. This contribution is focused on the effect of silicon and copper alloying elements on mechanical properties of the SiCr steel.
The DRECE method is a progressive method for forming sheet metal strips using the principle of severe plastic deformation (SPD). The DRECE method is characterized by extruding the sheet metal strip with a forming device which creates a forming angle of 108 ° in the deformation zone. During the practical verification of the DRECE method, it was found that the materials formed by the method show a significant increase in mechanical properties after the first pass through the forming equipment while maintaining sufficient ductility of the materials. With each subsequent pass of the material through the forming device, the mechanical properties increase. For the subsequent industrial use of the DRECE method, the key technological parameter of the forming equipment is the feed speed of the sheet metal strip. At present, the forming device makes it possible to regulate the feed speed of the sheet metal strip in the range of 10 - 100 mm / s. The device allows continuous sensing and recording of torque, extrusion force and feed rate of the sheet metal strip during the forming process. These facts are very important for the subsequent use of the method in industrial practice.
In this study, the analysis of microstructural and mechanical properties of tool hardenable martensitic steel processed by selective laser technology and subsequent heat treatment was carried out. A design of experiment was performed before the start of the experiment to determine appropriate combinations of heat treatment parameters, which suggested 17 variations of heat treatment regimes. The experimental samples in this work can be divided into three series. The first series was left in the post-printing state and then precipitation hardened. The second series of samples was annealed at 820 °C for 1 h followed by precipitation hardening and the last series was annealed at 940 °C for 2 h again followed by hardening. Microstructural analysis of the starting powder and the processed samples was performed by scanning electron microscopy and electron backscattered diffraction. Mechanical properties were determined by tensile testing and hardness measurement. The last part of the experiment was to evaluate the effect of heat treatment parameters on the mechanical properties using the design of experiment, showing that the optimal model to explain the largest number of data is different for yield strength, ultimate yield strength and ductility. Each of these models is affected by different heat treatment parameters.
The aim of the study was to design the heat treatment of incomplete austempering followed by martensitic quenching and tempering of Ovako 677L steel, allowing to produce a submicron multiphase microstructure based on bainite and martensite (approx. 60-70%) with stable austenite (30-40%) and fine dispersion carbides. This type of treatment should guarantee high hardness and strength of the material, while improving the impact toughness. In order to optimize the heat treatment parameters, a series of dilatometric tests, hardness measurements, phase composition tests and microscopic observations of heat-treated laboratory samples were carried out. It has been shown that, depending on the parameters of the heat treatment, it is possible to produce a multi-phase microstructure with a hardness in the range of 420-540 HV2 and austenite content of up to 30% and impact toughness above 7J. ACKNOWLEDGEMENTS: The research was supported by Warsaw University of Technology and the National Center for Research and Development under the project no. TECHMATSTRATEG-III/0028/2019-00. Development of innovative hybrid surface layers composed of anti-wear coatings dedicated to gears for conveyor drive assemblies working in difficult operating conditions.