Papers by Keyword: Microhardness

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Authors: Lin Zong, Zheng Jun Liu
Abstract: The in-situ ceramic phases reinforced Fe-based surface coating had been produced by prepared high-carbon ferrochromium, ferrovanadium and graphite power on 20g steel through plasma transferred arc weld-surfacing process(PTA). The microstructure and properties were investigated by means of optical microscopy(op), scanning electron microscopy(SEM), X-ray diffraction(XRD) and microhardness meter. The results showed that the substrate and the coating formed good metallurgical bonding.The microstructure of coating consists of primary M7C3 carbide and eutectic structures[M+γ′+M7C3+VC]. The primary hexagonal (Fe,Cr,V)7C3 with larger size evenly distributed in coating and the fine VC particles were globular shape. The microhardness appeared reasonable distribution from substrate to the top ,which ensured that the materials had good abrasive wear resistance.
Authors: Shao Kang Guan, Zhen Wei Ren, Jun Heng Gao, Yu Feng Sun, Shi Jie Zhu, Li Guo Wang
Abstract: In this paper the in vitro degradation of ultrafine grained (UFG) Mg-Zn-Ca alloy produced by HPT was investigated by electrochemical measurements and immersion tests in SBF. It was found that UFG Mg alloy had better degradation properties and also higher microhardness value than as-cast Mg alloy. The corrosion current density of UFG Mg alloy decreased by about two orders of magnitude, compared with that of as-cast alloy. Through electrochemical impedance spectroscopy (EIS) test,UFG Mg alloy showed a higher charge transfer resistance value. In immersion test, UFG Mg alloy in SBF exhibited more uniform corrosion and lower degradation rate (0.0763 mm/yr) than as-cast alloy. The degradation properties were related with the microstructure evolution, namely the grain refinement and redistribution of second phase. Keywords: Mg-Zn-Ca alloy; High-pressure torsion (HPT); Degradation behavior; Simulated body fluid (SBF); Microhardness
Authors: M. Borrell, R.I. Grynszpan, N. Ji
Authors: Wen Liang Chen, Chun Ping Huang, Li Ming Ke
Abstract: Carbon nanotubes(CNTs) reinforced copper matrix composites were successfully produced by Friction Stir Processing (FSP). The effect of applying multiple FSP passes on the forming of composites was studied, the microstructure, microhardness and conductivity of the good forming composite were analyzed. The experimental results showed that CNTs uniformly distributed and good forming composite can be obtained by three FSP passes. Compared to the parent material, the grain size of the composite has significantly refined, and the microhardness of the composite has also greatly improved, but the conductivity of the composite has a small decrease.
Authors: How Ji Chen, Chien Kuo Lin, Wen Po Tsai, Te Hung Liu
Abstract: If concrete is observed at the microscopic level, it can be seen to contain many interfacial transition zones (ITZ), resulting in the weakening of its mechanical properties; as the physical properties of lightweight aggregates (LWA), such as their high absorption, are clearly different from those of normal weight aggregates (NWA), they may lead to variations in the ITZ of lightweight aggregates concrete (LWAC), making its mechanical behavior different from that of normal concrete.This study takes three types of LWA with different rates of absorption as its subjects in order to examine the effects of LWA absorbency on ITZ. The main variables tested include water/binder (W/B) ratio, amount of fly ash substituted for cement, and the saturation states of the four types of LWA, with three different types of microscopic tests used to observe the microstructure of ITZ in concrete, and analyze and compare their differences with ITZ in concrete made with NWA. The results of the study indicate that in LWAC, ITZ with weaker tensile strength did not appear around highly absorbent LWA; only the sample group with a W/B ratio of 0.29 did not show apparent absorption due to the higher viscosity of the mortar, resulting in a slight downward trend in tensile strength, but it was still superior to the tensile strength of ITZ in typical NWA.Observation using scanning electron microscopy (SEM) found that inner pores and cracks of ITZ in LWAC were all smaller than in NWC; X-ray diffraction (XRD) tests indicated that the amount of CH crystals in ITZ was greater than LWAC; and microhardness testing found that microhardness values were higher closer to the surface of the LWA, with some even exceeding that of concrete. The increase in the tensile strength of ITZ in LWAC subsequent to the addition of pozzolanic materials was limited; their improvement of the weakness planes formed by ITZ in NWA concrete, however, was more apparent. An LWA has higher water absorbency capacity when in an absolutely-dry condition, which can markedly increase the strength of ITZ; conversely, if an LWA is in saturated surface dry (SSD) condition, its ITZ behave like those of concrete.
Authors: Armansyah Ginting, Mohammed Nouari, Nadhir Lebaal
Abstract: In this paper, the surface integrity is studied when machining the aeronautical titanium alloys. Surface roughness, lay, defects, microhardness and microstructure alterations are studied. The result of surface roughness judges that the CVD-coated carbide fails to produce better Ra value than the uncoated. Lay is characterized by cutting speed and feed speed directions. Feed mark, tearing surface, chip layer formation as built up layer (BUL), and deposited microchip are the defects. Microhardness is altered down to 350 microns beneath the machined surface. The first 50 microns is the soft sub-surface caused by thermal softening in ageing process. Microstructure alteration is observed in this sub-surface. Down to 200 microns is the hard sub-surface caused by the cyclic internal work hardening and then it is gradually decreasing to the bulk material hardness. It is concluded that dry machining titanium alloy is possible using uncoated carbide with cutting condition limited to finish or semi-finish for minimizing surface integrity alteration.
Authors: Wei Feng He, Yu Qin Li, Xiang Fan Nie, Rui Jun Liu, Qi Peng Li
Abstract: In this paper, the microstructure and hardness of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy with and without laser shock peening (LSP) were examined and compared. The titanium alloy samples were laser shock peened with different layers at the same power density. The microscopic structure after LSP are tested and analyzed by SEM and TEM. The results indicated that LSP changed the microstructure evidently. After 3 layers laser shock peening, there are nanocrystallization in the LSP zone. The shock wave provided high strain rate deformation and generated high-density dislocations in the material. Multiple severe plastic deformation caused by 3 to 5 LSP layers helped to rearrange the resultant dislocation, to form dislocation networks, leading to the formation of nanocrystallites. On the other hand, the microhardness across the polished surfaces of the titanium materials with and without LSP was measured. It is obvious that the laser shock peening improved the microhardness of the Ti-5Al-2Sn-2Zr-4Mo-4Cr for about 16% at the surface, and the affected depth is about 300 microns from the surface.
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