Papers by Keyword: Hardness

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Authors: Xiang Peng Xiao, Bai Qing Xiong, Qiang Song Wang, Guo Liang Xie, Li Jun Peng
Abstract: The microstructural features and heat treatment response of Cu-2.1Ni-0.5Si-0.2Zr-0.05Cr (wt.%) alloy have been investigated. The alloy was aged at 400°C、450°C and 500°C after a cold deformation of 70% reduction. The variation in hardness and electrical conductivity of the alloy was measured as a function of aging time. The results indicated the highest peak hardness value of approximately 205HV for the alloy aged at 400°C for 4h after the solution treatment and cold deformation. The alloy has two main phases, one is Ni2Si phase, and the other is Cr2Zr phase. The strengthening mechanisms of the alloy include spinodal decomposition strengthening, ordering strengthening and precipitation strengthening.
Authors: Zhi Qiang Wang, Yun Bo Zhong, Kang Deng, Zhong Ming Ren
Abstract: A direct current was imposed during the ageing treatment of cold worked Cu-Cr-Zr alloys. The effect of increasing current density and ageing time on the electrical conductivity and microhardness has been investigated. The electrical conductivity was found to increase by about 22% IACS to a maximum value of 90% IACS. Furthermore, the microhardness increased by 21 HV up to 176 HV. A number of Cr precipitates and Cr-rich clusters were observed after the ageing treatment with direct current. The direct current was found to significantly enhance the efficiency of precipitation which is most probably due to the electron wind force and the electromigration-induced mass transport.
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: Shao Chen Zhang, Zhi Bin Wang, Yun Fan Dong, Kang Wang, Qi Wang, Jin Feng Leng
Abstract: The effect of aging treatment on the aging hardening of 0% Yb and 0.4% Yb modified A356.2 alloy was investigated by hardness measurements and optical microscope. In this work, A356.2 was first subjected to 535°C for 5h and then subjected to 150°C, 180°C for 2h-12h hours. Results show that during aging process, there was a hardness peak along the increasing of aging temperature and time. With increasing aging progress, the morphology of Si phases became shorter and spherical. After optimum time, Si phases was coarse and the dendritic grain was broken. The peak-aged of unmodified alloys was 150°C for 10h and 180°C for 6h,and corresponding hardness values were 62.35HB and 77.10HB, respectively. With Yb addition, the hardness reached 87.58HB and 98.28HB on peak aging of 150°C/8h and 180°C/ 6h, respectively. The greatest degree of hardness was increased by 40.46% and 27.47%, combined with no Yb addition. XRD shows the interplanar crystal spacing of A356.2 with 0.4% Yb addition, which was larger than fresh A356.2 alloy. When adding 0.4%Yb under 180°C for 6h aging progress, the ultimate tensile strength was 284 MPa 12.7% increasing compared with former work.
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.
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