Papers by Keyword: Hardness

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Authors: Chih I Hsu, Kung Hsu Hou, Ming Der Ger
Abstract: In this study, hardness and wear resistance of electroless Ni–P and Ni–P/Al2O3 composite coating have been investigated. These composite coatings are applied on iron substrate by electroless deposition process and then they were heat treated at 400°C for 1h. Surface and cross-section morphology of composite deposits have been investigated by scanning electron microscopy (SEM) and microstructural changes were evaluated by X-ray diffraction (XRD) analysis. The results showed that the Al2O3 particles co-deposited in Ni–P matrix led to an increase in the hardness and improve wear resistance, especially when the heat treated at 400°C will have the maximum hardness and wear resistance.
Authors: Mariano Casas Luna, Edgar Benjamin Montúfar Jimenéz, Miroslava Horynová, Pavel Gejdoš, Lenka Klakurková, Sebastián Díaz de la Torre, Jozef Kaiser, Ladislav Čelko
Abstract: The fabrication of a composite material based on magnesium (Mg) and tricalcium phosphate is reported in this work. Rods of β-tricalcium phosphate (β-TCP) were processed and consolidated together with pure Mg powder through spark plasma sintering (SPS). The microstructure at the interface, the chemical composition and transformation of the components and the microhardness were analysed. The microstructure of the composite shows two zones with well-defined and continuous interface between them: a ceramic zone composed by β-TCP filled with Mg and the metallic zone constituted by Mg and Mg rich eutectic. Vickers hardness shows the excellent mechanical interaction between the two zones.
Authors: Hajo Dieringa, Sanjeev Das, Dmitry Eskin, Zhong Yun Fan, Lydia Katsarou, Manfred Horstmann, Gerrit Kurz, Chamini Mendis, Norbert Hort, Karl Ulrich Kainer
Abstract: Intensive melt shearing is a process that can be used for mixing ceramic particles into magnesium melt. It applies shear stress to the melt and can de-agglomerate nanoparticle additions to magnesium melts without the use of electromagnetic fields or ultrasound. A wrought magnesium alloy AM30 was selected for processing with intensive melt shearing and subsequent twin-roll casting. AM30 with additions of CaO and SiC were also processed by this route and the hardness and microstructure were investigated. Sheets were rolled and their tensile strength was determined. The work was done as part of the European Union research project ExoMet. Its target includes the production of high-performance magnesium-based materials by exploring novel grain refinement and nanoparticle addition in conjunction with melt treatment by means of external fields.
Authors: Jiří Habr, Jiří Bobek, Petr Lenfeld, Luboš Bĕhálek, Martin Seidl
Abstract: This paper deals with optimization of mechanical properties mainly hardness and stiffness of flexible part of two component injection molded part regarding production systems. Optimization is performed on two material combinations: Thermoplastic - thermoplastic elastomere and thermoplastic - silicone. Polymers used for two component part are suitable for medical applications.
Authors: Clemens Müller, Tilman Bohn, Enrico Bruder, Peter Groche
Abstract: Linear flow splitting is a new continuous cold forming process where the edge of a sheet metal is formed into two flanges by splitting and supporting rolls. Thus the production of bifurcated profiles from sheet metal without lamination of material becomes feasible. The production of such structures takes place incrementally in a modified roll forming machine. Experimental investigateons on a HSLA steel show, that even at a surface increase of the sheet edge of about 1800% no cracks were nucleated in the profiles. EBSD measurements in the splitting centre reveal that similar to other SPD processes UFG microstructures develop in the processing zone. Thus a steady state is reached in the processing zone where increasing strain has no more (or little) influence on the materials properties i.e. its deformability, as it is typical for SPD-processes. The formation of UFG microstructures is considered to be a mandatory condition for the linear flow splitting process, as it improves the formability of the material to the extremely high level required for this process. The mechanical properties of profiles produced by linear flow splitting are characterised by large gradients, depending on the local deformation and the resulting microstructure. Very high hardness is measured at the former processing zone, i.e. the splitting centre and the flange surface, where severe plastic deformation takes place and UFG microstructures are present. In direction to lower deformation i.e. with increasing distance to the splitting ground or flange surface the hardness decreases close to the level of the undeformed material. In the present paper the linear flow splitting process is introduced and the microstructural development in the process zone is discussed on the base of EBSD measurements on profiles of the steel ZStE 500. The repartition of mechanical properties in a bifurcated profile is demonstrated by detailed hardness measurements.
Authors: Sergiy A. Firstov, Tamara G. Rogul, Victor F. Gorban, Engel P. Pechkovsky
Abstract: The influence of passing from a microcrystalline to a nanocrystalline structure on the mechanical properties of chromium deposited by magnetron sputtering is studied. The possibility of additional strengthening nanomaterials due to enrichment of grain boundaries by “useful” additives elements is established. A wide spectrum of materials in different structural states was investigated by the method of micromechanical tests. The notions of the “theoretical” hardness (largest hardness for the material) and “limit tool” hardness, connected with tool limitations in indentation, are introduced.
Authors: Hirotaka Kato, Kazufumi Yasunaga
Abstract: Sliding friction is one of the most powerful processes for microstructural evolution in the sub-surface, including grain refinement and recrystallization of deformed structure. Pin-on-disc sliding tests were carried out for 0.45 mass % carbon steels, and TEM microstructure and hardness of the specimens were investigated. Particularly effects of friction conditions on the microstructure at the surfaces and wear properties of the friction induced microstructure were studied. It was found that ultra-fine equi-axed grains in the 30 - 50 nm size range were produced in the case of a high friction speed of 5.0 m/s in an air atmosphere. Moreover, nano-crystalline microstructure can be produced in a vacuum atmosphere even if the friction speed was low. The friction induced nano-crystalline surface layers, which exhibited significant high hardness, showed good wear resistance.
Authors: Xin Zhao, Xiao Ling Yang
Abstract: Steel plates with lath martensite microstructure were rolled up to 68% reduction at 673 K and then annealed at 473-973 K. The microstructure evolution was studied by using an optical microscope and a transmission electron microscopy. And the properties were investigated by using tensile tests and hardness tests. Results show that ultrafine grains + nano-carbides are obtained in the steel plates. The specimen annealed at 823 K has a good combination of strength and ductility. The tensile strength and total elongation are 1028 MPa and 7.2%, respectively. And the hardness is 338 Hv.
Authors: Alokesh Pramanik, Animesh Basak
Abstract: Electroless-nickel (EN) and very few other materials are suitable for ultra-precision machining. This material exhibits excellent properties such as hardness, corrosion resistance which are essential for molding die. This paper discusses the properties of EN and links with the ultra-precision machinability of this material. It is found that chip formation processes changes with the cutting condition. Phosphorus content and heat treatments significantly affect the machinability of EN in terms of tool wear, machining force and surface finish.
Authors: Yuki Ito, Yosuke Harai, Tadayoshi Fujioka, Kaveh Edalati, Z. Horita
Abstract: This study introduces a process of high-pressure torsion (HPT) using ring samples and compares with the results of conventional disk HPT. Both types of HPT were conducted at room temperature on pure Al and pure Cu. The microhardness was measured along the diameters of the disks and rings. Microstructures were examined using transmission electron microscopy. When hardness values were plotted against equivalent strain, all data points fell on a single line for each material. There was a hardness maximum for pure Al but no such a maximum was present in pure Cu. In pure Al, many dislocations were visible within grains up to the equivalent strain corresponding to the hardness maximum but beyond this strain, grains with low dislocation density appear. All materials exhibited steady state where the hardness remains constant with respect to imposed equivalent strain. This study concludes that use of ring samples is effective as an alternative to the disk samples.
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