Papers by Keyword: Hardness

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Authors: Zhong Kui Zhao, Tie Tao Zhou, Pei Ying Liu, Chang Qi Chen
Abstract: 1.1%Li was added to 7075 alloys to obtain the Li-containing Al-Zn-Mg-Cu alloys. The microstructure and hardness of the alloys are investigated by transmission electron microscopy (TEM) and Vickers hardness. The hardness of the single-aged alloys is low. When the alloys were double-aged or multi-aged, the hardness is comparable to that of Al-Zn-Mg-Cu alloys at peak ageing. Two peaks were present in the hardness curves of the multi-aged Li-containing Al-Zn-Mg-Cu alloys. With the last-step temperature increases, two-peak phenomenon becomes prominent. The density and size of precipitates are influenced remarkedly by the ageing processes. Coarse grain boundary precipitates and PFZ (precipitate free zone)can be observed when the Li-containing Al-Zn-Mg-Cu alloys were multi-aged, and the higher the last-step ageing temperature, the wider the PFZ is.
Authors: A.Z. Nur Hidayah, J.B. Shamsul, K.R. Ahmad, A.A. Sinar, Ahmad Mujahid Ahmad Zaidi
Abstract: Powder metallurgy metal matrix composites based on AZ91 alloy matrix reinforced with 0.3, 0.6 and 0.9 weight percent of multiwall carbon nanotube (MWCNT) were investigated from the point of view of their response to artificial ageing as compared to the unreinforced AZ91 matrix alloy. Mg-Zn-Al (AZ91) and its composite were prepared by milling the raw materials and followed by sintering at 450°C for 2 hours. The sintered samples were solution treated at 415°C for 2 hours and followed by artificial ageing at 175°C. The ageing behavior was monitored by following the phase analysis and hardness of the samples examined. Microstructure of the sintered composites indicated that MWCNT was embedded in the AZ91 matrix alloy. All composites indicated lower hardness than matrix, however AZ91reinforced with 0.6 and 0.9 weight percent of CNT showed accelerated ageing. X-ray diffraction pattern indicated the present of β-phase (Mg17Al12) that responsible for the hardening behavior.
Authors: Mehtap Deniz Unlu, Onur Meydanoglu, Huseyin Cimenoglu
Abstract: Air oxidation behavior of a Ti6Al7Nb alloy was examined over the temperature range of 873 –1173 K for different time intervals ranging in between 12 and 72 h. The rate of oxidation evaluated according to the weight gain measurements, fitted parabolic kinetics by yielding oxidation activation energy of 226 kJ/mol. Rutile and anatase modifications of TiO2 formed on the surface as the result of air oxidation. Oxidation temperatures higher than 923 K encouraged rutile formation rather than anatase. As temperature of oxidation was increased, the thickness of the oxide layer increased. Thicker oxide layer provided higher surface hardness and better protection against a corrosive media (5 M HCl solution) was provided.
Authors: Lan Jiang, Yu Juan Shi, Jian Ding, Chun Bing, Gao Feng Fu
Abstract: Aluminium matrix composites reinforced by Al2O3 particles has been produced by adding NH4AlO(OH)HCO3 into molten ADC12 Al-Si alloy, where the γ-Al2O3 reinforcement particles are formed by decomposing reaction of NH4AlO(OH)HCO3 during stirring. The results show that the Al2O3 particles are distributed more uniformly in the matrix than that by direct adding of Al2O3 particles. Hardness and wear properties have also been examined and the results show that the hardness of the composites increases with increasing volume fraction of the reinforced particles. Wear rate of the composites decreases with increasing volume fraction of the reinforced particles and increases with the applied load. The mechanical properties of the composites prepared by adding of NH4AlO(OH)HCO3 are superior and more wearable than that prepared by direct adding of Al2O3 particles. Wearing mechanism of the surfaces of the unreinforced alloy and composites is dominantly abrasive.
Authors: S.K. Shaha, A.S.W. Kurny, Mahbub Hasan, S. Dyuti
Abstract: Al based MMCs have attracted a lot of attention particularly for their desirable combination of high stiffness and low specific gravity. In the present study, Al-4.5Cu-3.8Fe in-situ composites were manufactured by using solidification process. During solidification Al-Fe intermetallic was formed in a matrix of Al-Cu alloy. The composite was hot rolled at different degree using a two high rolling mill. Subsequently the composites were characterized by SEM, XRD, hardness measurement and wear testing. Wear testing was conducted on a pin-on-disk machine by applying 10 KN load. After the wear tests, the worn surfaces of the composite specimens were examined under an optical microscope. According to experimental results, as cast in-situ composites exhibited the highest wear rate. The hardness increased and wear rate decreased with the extent of rolling. The presence of reinforcing Al3Fe phase and fragmentation of those particles during hot rolling are suggested to contribute to the better wear resistance of the composites. The extent of abrasive wear was largest in the case of as cast composites, as evidenced by deep grooves on the worn surface and highest weight loss.
Authors: Natalia Lvova, K. Kravchuk, I. Shirokov
Abstract: The automatic scratch geometrical parameters analysis algorithms based on the images obtained by scanning probe microscopy have been developed. We provide a description of the technique to determine the contact area and the scratch volume with and without account of the pile-ups. The developed algorithms are applied to measure the dynamic hardness by sclerometry on the submicron and nanometer scale.
Authors: Hong Jie Zeng, Lai Qi Zhang, Jun Pin Lin, Shao Jie Zhang, Guo Liang Chen
Abstract: High Nb containing TiAl based alloys exhibit excellent corrosion resistance to molten zinc. They are expected to serve as the potential coating materials of corrosion resistance to molten zinc. Four TiAl-Nb alloys of good oxidation resistance and their powders were prepared by arc-melting and ball milling, respectively. The Microstructure, Hardness, Coefficient of thermal expansion, and grain size distribution of four as-cast TiAl-Nb alloys and their powders were investigated. In addition, EPMA analysis was employed to further examine the existential state of element Y in as-cast TiAl-Nb alloys. It was found that element Y existed in the form of YAl2 phase in the grain boundaries and triple junctions. Higher content of Al in TiAl-Nb alloy results in bigger Coefficient of thermal expansion. Lamellar microstructures and fine grains exert a positive influence on hardness. Powders prepared by ball milling displayed angular and irregular morphology.
Authors: Yang Tao Xu, Tian Dong Xia, Wen Jun Zhao, Xiao Jun Wang
Abstract: Co-Al-W supperalloy used pure element powder, according to the ratio of different atomic percentage composition to make ingredients. It is mixed by planetary ball mill, pressed into blocks after the melting shape. Vacuum arc melting process was prepared by melting, after grinding, polishing, and after a volume of 5% perchloric acid and 95% of the electrolytic etcheing solution prepared in ethanol corrosion observed after analysis of the microstructure and phase composition by XRD analysis .It can be found that Co-Al-W superalloys were mainly composed of cobalt-rich matrix of austenite precipitation of γ phase and coherent with matrix of the L12 structure of γ′-Co3(Al,W) phase. In addition, Nb have effect on grain refinement and refine grain. Rockwell hardness test and analysis, It can be found that Nb can clearly improve the Co-Al-W superalloy hardness.
Authors: Jaroslav Sedláček, Dušan Galusek, P. Švančárek, A. Brown, R. Brydson
Authors: D. Sujan, C.W. Yeo, Muhammad Ekhlasur Rahman, M. Mohan Reddy, Md Abdul Maleque, Mohammad Yeakub Ali
Abstract: Stir casting method is used in the production of SiC reinforced-aluminium metal matrix composite (AMMC) to enhance the properties of base metal. Different weight fraction of Silicon carbide, SiC (5 wt%, 10 wt% and 15 wt %) particulate-reinforced AMMCs are fabricated and characterizations of physical and mechanical properties of the materials are performed based on the experimental. The microstructure of the fabricated composite material are studied and analyzed. The results indicate that the mechanical properties of the composite, including yield strength, tensile strength and hardness are enhanced by the increment of the weight fraction of reinforcing phase. Nevertheless, the elongation and fracture toughness of the composite decreased as the reinforcing phase increased. This is mainly due to the brittleness of the SiC particles which act as micro void initiator.
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