The effects of sliding speed and microstructure on the dry wear properties of metal-matrix composites


Sahin Y., Murphy S.

WEAR, cilt.214, sa.1, ss.98-106, 1998 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

The effects of sliding speed and microstructure on the dry wear and friction properties of unreinforced 2014 aluminium alloy matrix and its unidirectional boron fibre-reinforced composites were investigated. Tests were conducted on the composites with fibres oriented normal and parallel to the sliding direction, rubbing against a rotating steel disc at speeds of 0.6, 1.0 and 1.6 m s(-1) under different loads. Wear surfaces and subsurface sections of the wear samples of the matrix and composites were examined by scanning electron microscopy after wear testing. The metal-matrix composites showed excellent wear resistance compared with the unreinforced matrix, but the orientation of the fibres with respect to the sliding direction was found to affect the wear rates. The normal orientation (N) displayed a better wear resistance than the parallel orientation (P) when the tests were conducted at speeds of 0.6 and 1.0 m s(-1), but there was little difference at the highest speed of 1.6 m s(-1). The presence of fibres reduced the amount of surface damage and subsurface plastic deformation for both sliding directions The fibres in the surfaces of the N-oriented samples were chipped at the ends during wear tests, and the detached fragments of fibre became embedded into the soft aluminium alloy matrix, giving a low wear rate, especially at low sliding speed. At higher speeds more rapid wear occurred, but the onset of oxidative wear at the highest speed of 1.6 m s(-1) gave a very low wear rate. In the P-oriented samples, at low speed. many segments of fibres were pulled out from the wear surfaces owing to friction against the disc, and surface ploughing occurred, giving a high wear rate which mostly peaked at 1.0 m s(-1). At the highest speed, fibre fragmentation replaced pull-out and the small fibre fragments remained embedded in the surface, which with the development of surface oxides, reduced the weal rate to its minimum value. In general the friction coefficient of the matrix and composites decreased with increased sliding speed, but many tests showed a peak at a speed of 1.0 m s(-1). The matrix had a lower friction coefficient than the composites. and at the lower load the friction coefficient increased with fibre content for both fibre orientations, but at the higher load behaviour was erratic owing to the opposing effects of fibre fracture and matrix oxidation. For the P-orientation the friction coefficients of the composites were lower than those of the N-orientation, and most peaked at the intermediate speed. (C) 1998 Elsevier Science S.A.