Papers by Keyword: Hardness

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Authors: Shu Mei Wang, Kenji Matsuda, Tokimasa Kawabata, Susumu Ikeno
Abstract: The transition metals such as chromium and manganese are usually added to 6000 series Al-Mg-Si alloys to control recrystallization and grain size and thus the properties of alloys. In Cr/Mn-addition alloys, Cr or Mn will expense Si to form the dispersoids as AlMnSi or AlCrSi and tend to decrease its aging effect. The aim of this work is to investigate the effect of transition metals (TMs) addition on the hardness and the microstructural features of Al-Mg-Si alloys. Al-Mg-Si alloys, which can be remarked as the quasi-binary alloys of Al-Mg2Si, are prepared with Cr or Mn addition by laboratory casting. Some other transition metals, such as Co and Ni, are also added to Al-Mg-Si alloys. The grain size of four alloys decreases with TMs addition, which consequently increases the as-quenched hardness of the alloys comparing with that of the Al-Mg2Si alloy without TMs addition. The difference between Cr/Mn-addition alloy and Co/Ni-addition alloy is that the dispersoids are formed in Co/Ni-addition alloy without expensing Si. Therefore, there is little effect on the aging effect of Si in Co/Ni-addition alloy. Keywords: transition metals, hardness, microstructural, Al-Mg2Si, dispersoids.
Authors: Tatsuaki Sakamoto, Kiyomichi Nakai, Munehiro Maeda, Sengo Kobayashi
Abstract: Microstructure evolutions and hardness variation during aging in metastable β titanium alloy TIMETAL®LCB have been examined. In as-quenched specimen after solution treatment, athermal ω phase formed. Isothermal ω phase formed during aging at 623 K, and α phase formed after precipitation of isothermal ω phase during aging at 673 and 773 K. Alpha phase nucleated at isothermal ω phase, and had the orientation relationship with β and ω, (111)β//(0001)ω//(1120 )α and [10 1 ]β//[1120 ]ω//[0001]α . During aging at 873 K, α phase formed without isothermal ω phase. Hardness increased with increasing aging time and decreasing aging temperature, partly because number density of isothermal ω or α precipitates increased with increasing aging time and decreasing aging temperature.
Authors: M.J. Adinoyi, Necar Merah, Zuhair M. Gasem, N. Al-Aqeeli
Abstract: Epoxy-clay nanocomposites have recently gained considerable attention due to their interesting physical, thermal and mechanical properties. These properties, however, depend on a number of parameters such as the clay type, clay modifying agent, polymer matrix and the adopted mixing process. In the current work, epoxy-clay nanocomposites were prepared from Araldite GY6010 CRS and Nanomer I.30E nanoclay using different sonication (mixing) periods (5 to 60 minutes) and different concentrations of clay (2 to 5%wt). The effect of sonication time and clay loading on the tensile and hardness properties of the resulting nanocomposites were investigated. The results showed that the ultimate strength and fracture strain of the nanocomposites were below that of the neat epoxy, but the elastic modulus was generally enhanced by the addition of the nano-clay content. Increasing the sonication time enhanced the tensile strength on the expense of reducing the modulus of elasticity. Hardness of the nanocomposites did not show significant change with either the addition of clay or processing under different sonication times.
Authors: Viktor Malau, Latif Arifudin
Abstract: Vickers microindentation hardness test has been applied for a long time to determine the mechanical properties of a small volume of samples. The procedure of this hardness test consists of using a constant load on a rigid indenter and measuring the dimensions of the indenter residual impression (indentation imprint) on the surface of the sample tested after loading and unloading. The objective of this research is to characterize the mechanical properties and material constants of HQ (High Quality) 705 alloy steel mainly its VHN (Vickers Hardness Number) and tensile strength before and after quenching and tempering heat treatments. The characterization is based on Vickers microhardness dependence load curves.Quenching treatment was performed in a furnace by heating the samples at austenite temperature of 850 o C with holding time of two hours and then the samples were rapidly cooled in oil bath. Tempering processes were conducted by heating again the quenching samples to temperatures of 150, 200, 250, 300, 350, 400, 450, 500, 550 and 600 o C with holding time of two hours for each sample. Finally, all samples were slowly cooled in atmospheric temperature. The mechanical properties of samples were characterized by using Vickers microhardness dependence load curves.The results show that VHN (Vickers Hardness Number) depends on indentation load and VHN increases with increment of load for indentation load lower than 5 N. VHN is almost constant for indentation load greater than 5 N. The raw material (without heat treatment) has the VHN and tensile strength of 3413 MPa and 1050.61 MPa respectively and the quenched samples have the VHN and tensile strength of 5407 and 1861 MPa respectively. The Vickers hardness and tensile strength decrease with the increment of tempering temperatures. The higher tempering temperature produces lower hardness and tensile strength. The raw material tensile strength of 1058.8 MPa obtained by tensile test is comparable to its tensile strength of 1050.61 MPa obtained by Vickers indentation. This result indicates that Vickers microindentation is valid to use for evaluating the tensile strength of HQ 705 alloy steel.
Authors: Hui Gon Chun, Yun Kon Joo, Jae Hong Yoon, Tong Yul Cho, Wei Fang, Shi Hong Zhang
Abstract: For the Improvement of wear and corrosion resistances of Inconel718 (In718) surface, high velocity oxygen fuel (HVOF) thermal spray coating of micron-sized WC-Cr-C-Ni powder was coated onto Inconel718 surface and laser heat-treatment of the coating was carried out. Porous coating of porosity 2.2±0.4% was prepared by HVOF coating, and it was improved by laser heat-treatment, reducing the porosity to 0.35±0.08%. Micro-hardness of laser heat-treated coating increased more than four times compared to the surface of In718. Friction coefficient decreased by HVOF coating and laser heat-treatment. Wear resistance improved, decreasing the wear depth by the coating and laser heating. The interface between coating and In718 was compacted, and elements diffused from both coating and inconel718 substrate to interface, forming metal rich buffer zone (interface) and enhancing the adhesion of coating. Corrosion resistance improved by coating in sea water 3.5% NaCl solution and in 1M HCl acid, but it worsened in 1M NaOH base. For the improvement of wear and corrosion resistances of Inconel718, HVOF WC-metal power coating and laser heat-treatment are recommended.
Authors: Ján Balko, Martin Fides, Richard Sedlák, Pavol Hvizdoš, Sergej Hloch, Ján Kľoc, Peter Monka
Abstract: Several bone cements were prepared in two ways of mixing (manual and vacuum bowl). Wear behavior, friction coefficient were studied by ball on disc method. Nano-hardness and Young`s modulus was studied by instrumented indentation. Obtained results were summarized by taking into account their way preparation, antibiotics content and testing conditions. There was found no significant time dependence of saline acting on Young`s modulus and nano-hardness values. Friction coefficient in saline was less than half in compare to dry sliding conditions
Authors: Yuan Bo Wang, Teng Fei Su, Ming Liang Yin, Xue Han, Xin Ying Li, Ce Liang, Jian An
Abstract: Wear behavior of AZ51 magnesium alloy was studied using a pin-on-disc type wear apparatus at 20-360 N and 0.785 m/s. Wear mechanisms were determined using scanning electron microscope (SEM), including abrasion, oxidation, delamination, thermal softening and surface melting. Microstructural evolution, plastic deformation and microhardness in the subsurfaces were examined with optical microscope and hardness tester before and after mild to severe wear transition. The subsurface microstructure experienced deformation, dynamic recrystallization (DRX) and surface melting successively with increasing load. These changes in subsurface microstructure result in strain hardening and thermally-activated softening in the near-surface layers. The thermal softening originating from DRX and surface melting in subsurface is responsible for the mild to severe wear transition.
Authors: Radim Ctvrtlik, Jan Tomastik
Abstract: Human teeth are exposed to various chemical and mechanical factors. From mechanical point of view it includes attrition, abrasion or their combination. Teeth and dental restorative materials are subjected to normal and shear loads. Therefore the contact-based stresses during mastication and teeth wear are of considerable importance. In order to study wear behavior of enamel, dentine and two dental restorative composite materials scratch test at various contact conditions was employed. Hardness and elastic modulus were measured using nanoindentation with spherical and pyramidal indenters. Residual wear tracks were observed using laser scanning confocal microscopy.
Authors: S. Dyuti, S. Mridha, S.K. Shaha
Abstract: The formation of hard surface layer on steel provides a protective coating against wear, thermal loads and corrosion. In the present work a hard composite layer is formed on steel surfaces by preplacement of titanium powder and melted under nitrogen environment. Surface melting was conducted using TIG torch with different energy inputs. The microstructure and the morphology of the melt tracks were investigated using SEM and X-ray diffraction. The in-situ melting of titanium powder in nitrogen atmosphere produced dendritic microstructure of titanium nitride. The melt layer contained dispersed TiN, Ti2N dendrites highly populated at the surface compared to the deeper melt and gave a maximum surface hardness of around 1927 Hv. The wear property of the melt track was investigated using pin-on-disk tribometer at room temperature. The modified surface layer gave a low friction value of 0.12 and wear rate of 0.007895 ×10-4 compared to 1.648 × 10-4 mm3/N/m for the uncoated steel surface.
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