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1

Evaluation of the retained austenite mechanical stability in the mediumcarbon TRIP steel

Kokosza A.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

323--330

EN

Purpose: The aim of this study was to evaluate the inclination to mechanical destabilization of retained austenite in the microstructure of the TRIP steel containing 0.4% C, 1.5% Mn and 1.2% Si. Design/methodology/approach: The new, simple method for evaluating the mechanical stability of retained austenite was proposed, which is based on the bending test and the measurement of volume fraction of retained austenite by X-ray quantitative phase analysis. The relationship between stress and local strain as well as local volume fraction of this phase in selected locations on the surface of the bending sample were revealed. Findings: The applied heat treatment, modified with respect to the classic one, allowed remain approximately 25 vol.% of the retained austenite in the microstructure of the investigated TRIP steel. It was pointed that retained austenite has high mechanical stability if stress is low. Under influence of the higher stress a partial destabilization this phase occurred. It was found that in the examined steel such mechanical destabilization of retained austenite has two - or three-stage nature. Research limitations/implications: Results of this study indicate a significant stability of retained austenite in the investigated TRIP steel. It is advisable to check how will change the stability of this phase when the stress or strain will be higher than those that occurred in this research. Practical implications: The new method of the evaluation of the retained austenite mechanical stability provides the possibility of an easy and effective estimation of this phase tendency to mechanical destabilisation and to martensite transformation in the steel. In addition, this method allows analysing the influence of the stress as well as the strain on changes in this phase volume fraction, which occur during three-point bending. Originality/value: The proposed method may be used for evaluation of susceptibility of retained austenite on transformation under load. Moreover, developed relationships between volume fraction of retained austenite-stress as well as volume fraction of retained austenite-strain, can be used for interpretation and analyze of mechanical properties changes of heat-treated steels.

2

Strength tests of sandwich composite materials connected by means of screw joints

Żółkiewski S.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 49, nr 2

577--584

EN

Purpose: of this thesis is to present the exemplary results of strength tests of sandwich composite materials consisted of the laminate plate and the metal sheet plate. Design/methodology/approach: The strength tests were carried out in the laboratory stand by means of the electric resistance wire strain gauge. The laboratory stand was specially designed for the purpose of testing composite materials. Findings: The results are presented in the form of graphs. In graphs the maximal and minimal strains in the time function are presented. Research limitations/implications: The tests were carried out for different configurations of the samples. The specimens were prepared as the samples with the external steel plate or with the steel plate arranged among the laminate layers. Practical implications: The experimental tests are still necessary in analysis of the composite materials. The real parameters of the samples should be determined in an experimental way. However, the numerical computer simulation of the composite materials is possible e.g. in Unigraphics software, but modelled in the computer environment composites have very often some errors and results of simulation is not proper. Originality/value: The sandwich composite materials were tested in the laboratory stand by means of extensometers. The results could be used in designing of mechanical parts and mechanisms made of the laminate connection in the steel plate by means of screws. The fundamental mechanical properties of such a type materials were derived.

3

Application of artificial neural networks in properties modelling of PVD and CVD coatings

Dobrzański L.A., Staszuk M., Honysz R., Honysz R.

Archives of Computational Materials Science and Surface Engineering

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2010

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Vol. 2, nr 3

141-148

EN

Purpose: The aim of this paper is to describe the application of artificial neural networks in development of a model, which describes the influence of PVD and CVD coatings properties on the cutting edge durability from sintered carbides covered with these layers. Design/methodology/approach: The input data used for the artificial neural networks were PVD and CVD coatings microhardness, thickness, grain size and their adhesion to the substrate. On the network's output is the durability of the PVD and CVD coatings coated on sintered carbide blades determined in technological cutting trials of grey cast iron. Findings: Research results shows, that the greatest influence on the durability of coated sintered carbide blades is adhesion to the substrate. Smaller influence on blades durability has the size of grains. Other properties have a minor influence on the cutting tool. Practical implications: The presented results indicates, that the coating material selection and design of PVD and CVD coatings deposition process should be implemented with taking into consideration in the first place the best coating's adhesion to the substrate. Originality/value: The application of artificial neural networks for influence determination of PVD and CVD coatings microhardness, grain size, thickness and adhesion to the substrate on the durability of the sintered carbide blades covered with investigated coatings.

4

Mechanical and structural aspects of high temperature deformation in Ni alloy

Nowotnik A.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 26, nr 2

143-146

EN

Purpose: Experimental results on hot deformation and dynamic structural processes of nickel based alloy were reviewed. The attention was given to the analysis of dynamic structural processes which operate during hot deformation of the material. Design/methodology/approach: Hot compression tests were performed on solution treated precipitations hardenable nickel based superalloy of Inconel 718 within a temperature range of 720-1150*C at constant true strain rates of 10 -4, 4x10 -4 s -1. The flow stress curves and microstructure of deformed nickel based superalloy were presented. Findings: During hot compression of solution treated material, highly localized flow was observed at relatively low deformation temperatures 720-850*C. The particle distribution and their morphology were not found to be affected by localized flow within the investigated strain range. At low strain rate the shear banding and intergranular cracks and cavities growth were found to be responsible for the observed flow stress decrease at 720, 800 and 850oC and might result in a sample fracture at larger strains. Research limitations/implications: In spite of intense strain hardening due to deformation and phase transformation overlapping, light optical microstructure observation of deformed samples did not reveal significant effects of heterogeneous distribution of the phase components. Therefore, in order to complete and confirm obtained results it is recommended to perform further analysis of the alloy by using transmission electron microscopy technique (TEM). Practical implications: An interaction between dynamic precipitation and flow localization may become an important feature of high temperature performance and may also allow producing specific structures of materials. Originality/value: The contribution of flow localization to the strain hardening or flow softening and the flow stress-strain behavior during hot deformation of precipitation hardenable alloys is still a subject of extensive researches. The interaction between the flow localization and dynamic precipitation process was a subject of a very limited research works only.

5

Identification of dynamically precipitated phases in hot-working Inconel 718 alloy

Nowotnik A., Sieniawski J., Mrówka-Nowotnik G.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

275-280

EN

Purpose: The main purpose of this paper was to analyze how localized flow/structural inhomogeneties that may develop during hot deformation can affect a precipitated phases and to determine what kind of particles are present in the microstructure of hot-worked Inconel 718 superalloy. Design/methodology/approach: Compression tests were carried out on precipitations hardenable nickel based superalloy of Inconel 718 at constant true strain rates of 10 -4 and 4x10 -4 s -1 at temperature of 720 and 850° C. The dynamic behaviour were explained through observation of the microstructure using standard optical, scanning and transmission electron microscopy. Precipitated phases were identified using EDS technique and based on selected area diffraction pattern. Findings: Microstructural observations of deformed at high temperatures, previously solution treated Inconel superalloy revealed non uniform deformation effects. Distribution of molybdenum- and niobium-rich carbides affected by localized flow was found. Microstructural examination of the alloy also shown shear banding penetrating through the whole grains. Practical implications: The experiments on hot deformation of age hardenable Inconel 718 superalloy and the analysis of dynamic precipitation process have a practical aspect. This interaction could become an important feature of high temperature performance and may also influence the production of specific structures of this material. Originality/value: Even though the number of research has focused on the hot deformation behaviour of Inconel 718, there is still scarcity of data referring to the analysis of dynamic structural processes which operate during hot deformation of this precipitation hardenable alloy: in particular dynamic precipitation and dynamic particles coarsening.

6

Mechanical and tribological properties of TiC-based composites for ED machining

Figiel P., Zimowski S., Klimczyk P., Dziwisz T., Jaworska L.

Archives of Materials Science and Engineering

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2008

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Vol. 33, nr 2

83-88

EN

Purpose: The goal of this work is comparative study of TiC-(Mo, Ni) composites with different TiC-phase content to obtain material with an optimal mechanical and tribological properties, which can be easy shaped by Electro Discharge Machining (EDM). Design/methodology/approach: Three variants of TiC-(Mo, Ni) composites with the different hardening phase to the bonding phase ratio were sintered in vacuum. The influence of the initial TiC hard phase content in the sintered composites on their mechanical and tribological properties as well as ED machinability were investigated. The density, Young modulus, hardness, fracture toughness were measured. Tribological tests were carried out conducted using "pin-on-disc" and "ball-on-disc" methods. Wire Electro Discharge Machining (WEDM) performance preliminary test were realised also. Findings: The microstructure of sintered TiC-(Mo, Ni) materials is characterized by a ring structure of carbides. Mechanical properties and wear resistance are better for samples with higher TiC content. All variants of investigated materials are characterized by good WED machinability. Research limitations/implications: Obtained materials are characterized by good mechanical, tribological and working properties but homogeneity of microstructure should be improved. Farther works will be continued also for limitation of the metallic phase content up to 5 vol. %. Practical implications: After additional technological evaluation tests, obtained materials could be used for the different parts of machines and wear components (e.g. nozzles, plungers) shaped by EDM. Originality/value: New type of TiC-metal bonded composite with high content of hard phase which could be shaped by EDM.

7

Multiaspect analyzes of blow moulding process

Szczepański K., Kwiatkowski D., Koszkul J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

157--160

EN

Purpose: The main purpose of the performed investigations was a multi-aspect analyzes of the blow moulding process in a mould which takes two-stage nature of the process and the occurrence of uncontrolled phenomena which influence the shape, size and quality of the products into consideration. Design/methodology/approach: The value for the Barus number for different dimensions of the nozzle gap and the distribution of the temperature field during blow moulding process have been determined; the product thickness profile has been defined; phenomena which occur during blowing stage have been registered. The investigations have been performed by means of the blow moulding machine of UFP-05 type by IPTS – Metalchem Toruń using the designed and prepared blow mould with the sight-glass made of polycarbonate. Findings: The performed investigations enabled the insight study of uncontrolled phenomena which occur during each individual stage of the process and they showed the dependencies between these phenomena and the process parameters. Moreover, the detailed analyses enabled to determine the influence of these parameters on the physical features and dimensions of the finished goods. Research limitations/implications: The continuation of the investigations with use of extended blow mould design equipped in polycarbonate sight-glass which enabled the determination of the influence of the structure and mould cavity dimensions on the finished product wall thickness seems to be justified. It would be also useful to design the station for the precise non-touch measurements of Barus effect which enabled, except the measurements of the external diameter, the measurements of the finished product wall thickness. Originality/value: The complex analysis of the blow moulding process was possible thanks to innovative and original approach to the experimental tests which enables e.g. the optical registration of the phenomena which occur during blow moulding process.

8

Influence of magnetic field and inoculation on columnar structure transformation

Szajnar J., Wróbel T.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

209--212

EN

Purpose: The main aim of investigations was the reduction of grain size and unification of structure for clean metal casting by introduction of small amount of inoculant, with rotate and impulse reverse magnetic field. Design/methodology/approach: Experimental plan was planed on the basis of statistical factor design on two levels for three variables: pulse frequency, current intensity and inoculant quantity. The output parameters: area of equiaxed crystals zone, average area of equiaxed crystal, average area of columnar crystal and most important equiaxed crystals zone content were calculated by computer program Multi Scan Base (program to processing and image analysis) after macroscopic metallographic research. Findings: The results of investigations and their analysis show relationship between area of equiaxial zone and pouring parameters: induction of magnetic field, pulse frequency of magnetic field and quantity of inoculant sort AlTi5B. Research limitations/implications: Towards lack of resolute relations between casting parameters and structure was selected statistical analysis to determine these relations using stepwise regression. In order to obtain accurate results, authors of this paper are going to extend the resarch range and use Zr and V to inoculation. Practical implications: The work presents refinement of structure methods which are particularly important in continuous and semi-continuous casting where products are used for plastic forming. Large columnar crystals zone result in forces extrusion rate reduction and during the ingot rolling delamination of external layers can occur. Thus, in some cases ingot skinning is needed, which rises the production costs. Originality/value: The value of this paper resides in coupling of two fineness of structure methods. The first method is internal factor – inoculation with Ti+B and the second method is external factor – influence of electromagnetic field on crystallization process.

9

Degradation of the cast steel parts working in power plant pipelines

Renowicz D., Hernas A., Cieśla M., Mutwil K.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

219--222

EN

Purpose: Purpose of this paper is to identify the influence of loading history and the processes of material degradation on the initiation of cracking and on durability under creep and fatigue conditions. Design/methodology/approach: The aim of the research was to identify the properties of the material of the fittings cut out of a start-up pipeline connecting two OP-140 boilers with turbines, as well as to identify the reasons of failure of these parts after 100000 hours of operation. Results of the investigations were the basis of predicting the lifetime of machine parts and components of devices subjected to complex mechanical and thermal influence. Numerical simulation of work conditions was also performed. Problem of life assessment of the pipelines is currently the object of interest of many research centers. Findings: Due to extreme conditions of the start-up pipeline operation, its T-connections are subject to quick wear, and their properties determine the operational reliability and safety of the whole pipeline. For the reason it is necessary to verify the criteria of pipelines’ durability evaluation applied so far, based on the parameters characteristic of the creep process exclusively. Research limitations/implications: In the case discussed, i.e. a T-connection being a start-up pipeline part, the present criteria should be expanded with critical values describing fatigue/corrosion processes. Practical implications: The paper introduces the results of investigations of the 0.2C-1.2Cr-0.6Mo-0.3V cast steel used for parts of live steam pipelines working in power plants. Such parts include, e.g. T-connections. Originality/value: The paper show the possibilities of numerical models application.