Papers by Keyword: Hardness

Abstract: Radiation processing of polymers is a well-established and economical commercial method of precisely modifying the properties of polymers, especially physical properties. The physical properties of modified polyamide 11 samples by beta rays were measured at the ambient and elevated temperature. The tested samples showed significant changes of physical properties between ambient (23°C) and elevated (80°C) temperature. From this point of view, new applications could also be seen in areas where more expensive materials are used, especially for application in automotive industry.

Abstract: Fluidised bed technology is commonly applied in the pharmaceutical, agricultural and food production technology. The aim of this work is to identify the optimum process parameters in order to gain the best hardness and density values for the urea granules from the fluidised bed granulation. The layout of the experiments are based on Central Composite Design of Response Surface Method. The analyzed data shown that the optimize value for each of these parameter are 0.10MPa, 32.11Hz, 50% w/w, 42.25⁰C for spray pressure, fan speed, urea solution concentration and inlet air temperature with 1.71 kgf/granule hardness and 1.85 g/cm³ density were predicted. Experimentally, using the predicted optimize input parameter, the hardness and density observed were 0.20 kgf/granule and 1.30 g/cm³ respectively.

Abstract: Rail welded joints are integral part of continuous welded rail. However, they often do not have sufficient reliability during the operation. The article is devoted to the assessment of temperature influence effect on the mechanical properties and structure of weld metal and welded rails. The temperature distribution across the rail section in welded zone during the cooling process of aluminothermic rail welding is obtained using simulation by LVMFlow. The results of the study of hardness and structure of metal rail aluminotermitic welded joints are given. It is shown that the hardness of rail welded joints increases from 24 HRC to 38 HRC in the fusion zone of the weld metal and rail metal. It is due to the harmful effects of overheating of the metal during the welding process. The hardness is confirmed by microstructural analysis. Microstructural analysis showed the differences in the grains sizes of metal welded zone and heat affected zone. The structure of welded metal is acicular dendritic. Owing to a difference between structures of the welded joint zones the probability of occurrence of cracks on the boundary of fusion weld and metal is increased.

Abstract: In the laboratory conditions were manufactured flux cored wire system Fe-C-Si-Mn-Mo-Ni-V-Co samples, studied the influence of tungsten and chromium appending in surfacing wire charge. Conducted metallographic researches of surfaced metal: microstructure evaluate, grain size, nonmetallic oxides inclusions impurity. Defined hardness and wearout speed of the deposited layers. Conducted evaluation of the chemical composition influence on surfaced metal wearout and hardness.

Abstract: In the article is shown the comparative analysis between structures of surfaced by the flux coded wire metal systems Fe-C-Si-Mn-Cr-Ni-Mo-V and Fe-C-Si-Mn-Ni-Mo-W-V. These powder wires are supposed to be used in recovering details and equipment components and machines, that works in conditions of intensive abrasive – shock wear. Manufacturing and surfacing of flux cored wires samples were made in laboratory conditions. Defined chemical composition of the surfaced metal. Deposited metal samples hardness and wear resistance were researched. In the course of deposited meta surface metallographic analysis were made following metallographic researches: defined nature and level of nonmetallic oxides impurity, type and morphology of the microstructure, grain size of surfaced samples. Estimation of the chemical composition components influence on the hardness and wear resistance were obtained.

Abstract: The problems related to welding of the high strength steel, aimed for manufacturing of welded structures operating in the prominent wear conditions, is considered in this paper. The paper presents an analysis of possibilities and prescribing the technology for welding the high strength steel HARDOX 450. The methodology for estimate the weldability of this steel was established in the theoretical part of the paper, as well as calculations of the welding parameters, while the hardness was investigated in details and the macro and micro structures of the individual welded joint zones were estimated in the experimental part. Obtained experimental results could be usefully applied for selecting and establishing the optimal welding technology for structures made of this steel. The technology thus established and the GMAW welding regime can enable successful execution of the welded joints and reduce the possibility for appearance of flaws and cracks to a minimum.

Abstract: The present work aims at determining the effects of Nickel addition on the phase’s distribution in sintered part. It aims equally at identifying the effect of such addition on the microstructure and the mechanical properties. The addition to mixtures of alloying elements in their primitive form can lead to the formation of a heterogeneous microstructure in the sintered parts produced by the powder metallurgy (PM) process. It has been proved that the addition of nickel to an iron powder mixture forms nickel-rich areas (NRA) in the sintered parts. This is basically related to the low diffusion rate of nickel in iron at conventional sintering temperatures.

Abstract: Thermal-sprayed alumina–titania coatings (Al₂O₃:Ti wt ratio = 60:40) were prepared by a new multi-chamber gas-dynamic accelerator. The coatings were examined by using scanning electron microscopy, X-ray phase analysis and Vickers hardness tester at a test load 0.2 kg. The coating was well-adhered with corrosion-resistant steel substrate. The results show that the microstructure of the alumina–titania coatings consists of areas with different degrees of melting: the lamella built up from the fully melted particles of the powder, and partially melted areas. The developed coating is highly dense (porosity is less than 0.7%). Research results show that hardness of alumina–titania coatings (Al₂O₃:Ti wt ratio = 60:40) can achieve up to 655 HV_0.2 and the specific wear rate of alumina-titania coatings is 52.40∙10^-5 mm³ (m∙N)^-1.

Abstract: Mechanical alloying (MA) is a high-energy ball milling process results in the obtaining of simple and stable microstructures having increased homogeneity compared to other non-equilibrium synthesis methods. The aim of this paper was to develop a high entropy alloy with an improved hardness value suitable for coating turbine blades working in geothermal steam. CoCrFeNiMo high entropy alloy was processed in solid state, using mechanical alloying. After 40h milling time in a planetary ball mill the alloyed sample was consolidated using spark plasma sintering process. The samples obtained were investigated with the aid of optical and electron microscope, X ray diffraction and the hardness value was determined. The results obtained revealed that the powder was completely alloyed after 40 hour milling and the mixture between BCC and FCC phases resulted in 34% improved hardness value in comparison with a stainless steel usually used for turbine blades working in geothermal environment.

Abstract: Traditional alloys is based on a single element called matrix and to improve some mechanical properties (strength, ductility, strength) are added and other metallic elements in the system. High entropy alloys have become a field of increasingly explored in the world of materials. Excellent mechanical properties obtained of the high entropy alloys recommend them to be from year to year as investigated. In the last decade more than 500 high entropy alloys journal and conference papers have been published [1]. High entropy alloys are alloys who have in their composition 5 to 13 metal elements and the concentration of each component is between 5% and 35%. These elements in the composition of high entropy alloys are divided into elements of minority and majority elements. They are called minority elements because their molar fraction is less than 5%. High entropy alloys have mixing entropy higher than traditional alloys, ΔScons≥1.61R (R = 8.314 J / (mol • K)) [1]. High entropy alloy have been obtained in the laboratory of Science and Materials Engineering faculty from Iasi using a medium frequency induction furnace with 8000 Hz. Because they have excellent mechanical properties high entropy alloys can be used in various fields with high wear and corrosion degree or electronic, magnetic applications [1]. In this work we selected pure metallic elements like: Fe, Ni, Cr, Mn and Al. The quantity of alloy developed varied between 0.5 and 1.5 kg. Metal load necessary for the preparation of metal alloys were formed technical grade, industrial accessible prices and satisfying. Friction and wear rezistance were studies by using a reciprocating sliding test machine , in a pin on disk configuration, using aluminum as counter face.In this paper it investigated the wear resistance of high entropy alloys obtained, microstructure and their mechanical properties.