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1.
《Materials Science & Technology》2013,29(8):976-982
AbstractThe friction and wear behaviour of a nanophased AISI grade M2 tool steel was studied under dry sliding conditions and compared with that of a conventional AISI M2 steel. The nanocrystalline steel was produced by mechanosynthesis followed by cold and hot isostatic pressing. Slider-on-cylinder tests were performed against a ceramic coated countermaterial under loads of 10, 20, and 30 N and sliding speeds of 0.3 and 1.2 m s-1 up to 10 km sliding distance. The nanocrystalline material underwent mild wear with low coefficient of friction under all testing conditions. The commercial M2 steel displayed distance dependent transitions from a regime of mild wear with low coefficient of friction, to a regime of severe wear with high coefficient of friction. The first tribological regime was due to the formation of a layer of iron oxides on the worn surfaces. In this regime, the wear resistance of both steels is mainly dominated by the mechanical properties of the carbides which have high load carrying capability. The second tribological regime, observed in the commercial steel, was due to the formation of cracks both on the mechanically mixed layer and at a depth beneath this layer, which also led to the detachment of carbides from the matrix. This abrasive ‘third body’ produced high wear damage of the commercial steel under high applied loads. 相似文献
2.
《Materials Science & Technology》2013,29(9):1088-1094
AbstractThe authors present a study on the hot formability of 7020 aluminium alloy. Isothermal hot compression tests of solid cylindrical specimens were performed in the temperature range of 300–550°C and the strain rate range of 0·001–10 s–1. Stress–strain curves obtained from the experiment data are fitted using the Sellars–Tegart constitutive equation to obtain the constitutive parameters. Using the dynamic material model, the authors develop a processing map based on the flow stress data. The map shows that the parameters suitable for hot working are a temperature range of 450–550°C and a strain rate range of 0·001–0·1 s–1. This parameter range is where the efficiency of power dissipation is above 27% and where dynamic recrystallisation occurs. Unstable regions to be avoided in hot forming are deduced from an instability condition. The processing map is validated by comparing the microstructures of deformed compression specimens. 相似文献
3.
Aluminium alloy of Al–4.5Zn–1.5Mg system, belonging to age hardenable, high strength category is being used for the fabrication of various components. The Al alloy component was part of a conduit line for filling the liquid chemical to its storage tank. The component consisted of an extruded tube, TIG welded to a bulb, which was fabricated from Al alloy forgings. A crack was observed on the conduit tube at the region where tube was welded to the bulb. Detailed investigations were carried out on the cracked component, which revealed insufficient working of the ingot during forging, resulting in remnant cast structure along with a heavy network of low melting point compound throughout the material. The cracks, which were initiated under the stresses induced during thermal treatment, machining and assembly, were found propagating through the eutectic network.
This paper highlights the investigations carried out on the failed components. 相似文献
4.
《Materials Science & Technology》2013,29(2):263-268
AbstractSeveral homogenisation treatments were applied to direct chill (DC) cast ingots of aluminium alloy 6063, in order to analyse the resulting microstructures developed from these diverse conditions and their effects on the hot ductility of this alloy. Imaging was performed using scanning electron microscopy (SEM) and a focused ion beam (FIB) instrument. These techniques identified variations in distribution and morphology of second phase particles (AlFeSi and Mg2Si). FIB results for the various AlFeSi particles correctly identify their shapes in three dimensions (3D). The particles were identified by energy dispersive spectroscopy (EDS) in the SEM, and by X-ray diffraction (XRD) for bulk samples. Hot tensile testing (HTT) was conducted between 470 and 600°C to asses the hot ductility for each condition. The inferior ductility of as cast samples was due to the poor bond strength of the β AlFeSi phase at the grain boundaries. Homogenised samples, which contain α AlFeSi, exhibited improved ductility. Samples that were water quenched following homogenisation were absent of Mg2Si precipitates, when these elements remained in solid solution. These exhibited the highest ductility. 相似文献