Papers by Keyword: Hardness

Abstract: The influence of chemical composition, hardness and microstructure on resistance to abrasive wear of four kinds surfacing materials was studied. According to the results, coarse and massive carbides are not benefit for abrasion resistance, by decreasing continuity of matrix. Tiny and fine dispersed carbides combined with high toughness matrix, despite the relatively low hardness, ensure excellent abrasion resistance. Besides, material with single phase of martensite shows low hardness and low abrasion resistance.

Abstract: Hard anodized layers were produced by two different manufacturers on the same type of aluminium alloy on a vacuum pump part of complex shape. The sulphuric acid/water solution was used to produce alumina layers, which were subsequently sealed in demineralized water. A comparative analysis based on metallographic methodology, with the aim to control the stability of alumina formation process and to identify its defects, was performed by means of light and scanning electron microscopy, surface profilometry and microhardness measurements. To determine the thickness of alumina layers, the image analysis was also used.

Abstract: Surface coatings protection is one of the most important processes ensuring efficient and economic use of basic materials, mostly of lower-quality. At interface of clad and basic material intermetallic phases are formed, representing quite different matrix with dissimilar properties unlike the welded materials. One type of surface coating is explosive bonding which belongs to group of pressure welding. The work is focused on some mechanical properties, micro-and nanohardness controlled by AFM and interface shape line, in homogeneities in vicinity of the wave joint both in basic material and in vicinity of the Ti and Cr/Ni stainless steel matrix weld line. Investigated weld was both in as-received state and after heat treatment carried out at 600°C/90 minutes/air. Phases has been identified X-ray diffraction performed BW-5 beamline applying synchrotron radiation, and Tiα, Fe-fcc and Fe-bcc were detected at interface area, whereas intermetallic phases were not revealed.

Abstract: Compacts for the synthesis of composite zones in castings were obtained by cold pressing powders of the TiC reactants under a pressure of 250, 300, 500 and 600 MPa. The all compacts made under different pressures were placed in a mould cavity and poured with liquid unalloyed low-carbon steel. From the resulting casting, four composite zone A, B, C, D, produced in this casting by in situ method. In all composite zones, TiC and ferrite (αFe) were obtained. Additionally, in zones A, B and C the presence of graphite (C_gr) was also stated. The surface friction (S_f) of C_gr decreases in composite zones A ÷ D, while both the S_f of TiC and hardness VH30 increase in these zones with increasing compaction pressure of the reactants. Too low compaction pressure applied to the TiC reactants impedes the effective propagation of the reaction of synthesis.

Abstract: The stainless steel group AISI 310 is very often used for application in high-temperature conditions. This study investigated the effect of long-term annealing on microstructure and hardness of AISI 310S (24.3% Cr-19.3% Ni 1.8% Mn 0.21% Mo 0.67% Si, wt.%) heat-resistant steel. Microstructural changes and hardness distribution were analyzed after isothermal annealing at 800 °C in long-term exposure (from 1 to 1740 hours). Microstructure and fracture surface mode were analyzed using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). It was found that after annealing the sigma phase particles were precipitated at grain boundaries and within austenite grains. The chromium content in the sigma phase increased with the prolongation of annealing time. The morphology of sigma phase was changed from fine precipitates at lower annealing times to coarser particles at higher annealing times. Also, presence of sigma phase was confirmed by transmission electron microscopy (TEM). At annealing temperature of 800 °C the hardness began to increase after 16 hours. With longer times of annealing the fracture surfaces were changed. This change is associated with a change of content and the morphology of sigma phase.

Abstract: In this paper the influence of Electron Beam Welding (EBW) on the microstructure, mechanical and magnetic properties of Non-Oriented Electrical steels was presented and evaluated. Single pass welds free of defects were produced at welding speeds and pulsed currents following a predesigned protocol. The samples microstructure and the macrohardness tests were concluded with the magnetic measurements (Barkhausen Noise) in order to correlate the structural and mechanical properties with the magnetizing behavior of Non-Oriented Electrical Steel.

Abstract: Commercial hot extrusion is a billet-by-billet cyclic process, with high thermal and mechanical stresses generated in the die set. The die is a costly piece of equipment, and its long service life is essential for profitable operation. Extrusion dies primarily fail by fracture, wear, and plastic deformation. To avoid early failure, it is essential to have an optimum combination of toughness and hardness in the die. This combination can be achieved through a judicious mix of heat treatment and surface hardening. Experiments were conducted to determine mechanical properties of H13 steel after various heat treatment sequences. Heat treatment strategy is described in detail, and effect of different tempering temperatures on fracture toughness and hardness of the tool steel is reported. Changes in mechanical properties are also related to the variation in microstructure. For use in commercial hot extrusion dies, optimum tempering temperature for H13 steel was found to be near 525-600oC, for the best combination of toughness and hardness.

Abstract: Addition of nanoparticles currently in polymer blends has brought tremendous transformation in polymer engineering field. Incorporation of TiO₂ nanofillers is believed to enhance the physical and mechanical properties of PVC/ENR blends due to its excellent characteristics including non-toxicity, long term stability and UV light discoloration resistance. The main objective of this research work is to introduce titanium dioxide (TiO₂) nanofillers in a range of 0 - 6 phr into polyvinyl chloride (PVC) and epoxidized natural rubber (ENR) blends. Modification on mechanical properties of PVC/ENR blends has successfully been carried via irradiation crosslinking technique. The addition of TiO₂ nanofillers has improved the tensile strength and hardness of the nanocomposites. Nevertheless, at higher loading of 6 phr, the results obviously showed an insignificant difference of performances for both tensile strength and shore hardness properties. Upon radiation of 50 kGy, the increase in Ts of the PVC/ENR blends with addition of 4 phr TiO₂ was found to be optimum before the Ts value drops with higher exposure to irradiation dose rate. Gel fraction of irradiated PVC/ENR/TiO₂ nanocomposites indicates the nanocomposites are crosslinked upon electron beam irradiation. Degree of crosslink was also increased with the addition of 4 phr and 6 phr TiO₂.

Abstract: Every material is structured in its unique way and has its own recognizable microstructure. There are a number of approaches in establishing the relationship between mechanical properties and microstructure of a material, but none of them is universal and correlation free, probably because of luck of attention to the sub-grain structure. The possibility of calculating the hardness number using only geometric sizes of microstructural formations is discussed in this paper, where the grain is meant to be a container of the two most frequently occurred shapes in the microstructures globula and lamellae.

Abstract: The contribution deals with prediction of tensile properties based on measurement of microhardness. First of all, the database of stress strain, s-e vs. hardness data was created. Tensile strength, yield strength, ductility and parameters of Ludwig-Hollomon equation σ = σ₀+kεⁿ ; k, n were correlated with hardness. Various hardness values found in literature were recalculated to Brinell hardness. In tensile testing measured s-e curves were compared with that obtained from the correlation. The investigated materials were API 5 L grade steels X70 after different deformation exposition. The results give good agreement between compared data. The most difference between estimated and measured curve is in area of yield strength, because of Lüders deformation on investigated steel.