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The friction stir process (FSP) can be used to prepare carbon nanotubes (CNTs) forming reinforced Al matrix composites. The effect of CNTs content on the wear behaviour and hardness of aluminium based composites was studied. Adding CNTs effectively strengthens the matrix, and significantly improves the hardness of the composites. Composite wear test results showed that the addition of CNTs could enhance the wear resistance of the matrix. With increasing CNTs content, the wear resistance of the matrix markedly improved. The wear curve of the materials is a smooth curve.

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The microstructures and tensile properties of electrodeposited nanocrystalline Ni (nc-Ni) with a broad grain size distribution after annealing at 150, 200 and 300°C for 500 s were investigated. The as deposited broad grain size distribution nc-Ni sample exhibited a moderate strength σUTS of ∼1107 MPa but a markedly enhanced ductility ϵTEF of ∼10, compared with electrodeposited nc-Ni with a narrow grain size distribution. Annealing below 200°C increased the strength but caused a considerably reduction in tensile elongation. This behaviour is attributed to the grain boundary relaxation and the increased order of grain boundaries after annealing, which can make the grain boundary activities, such as the grain boundary sliding and grain rotations, more difficult. Further annealing at 300°C decreased both the yield strength and tensile elongation significantly due to significant grain growth.

Abstract. In the present study defect-free nanocrystalline (nc) Ni-Co alloys with the Co content ranging from 2⋅4-59⋅3% (wt.%) were prepared by pulse electrodeposition. X-ray diffraction analysis shows that only a single face-centred cubic solid solution is formed for each alloy and that the grain size reduces monotonically with increasing Co content, which is consistent with transmission electron microscopy (TEM) observations. In the nc Ni-Co alloys, both the ultimate tensile strength and the elongation to failure increase as the Co content increases. The TEM observations reveal that stress-induced grain growth during tensile deformation is significantly suppressed for the nc Ni-Co alloys rich in Co in sharp contrast to those poor in Co. We believe that sufficient solutes could effectively pin grain boundaries making grain boundary motions (e.g. grain boundary migration and/or grain rotation) during deformation more difficult. Thus, stress-induced grain growth is greatly suppressed. At the same time, shear banding plasticity instability is correspondingly delayed leading to the enhanced ductility.