Friction and wear behavior of C4 Al2O3/Al composites under dry sliding conditions

The wear resistance of MMCs can be improved by increasing the volume fraction of the reinforcing ceramic phase (HRC) by as much as 70%. Among the various types of HRC composites, a new Al2O3-Al co-continuous ceramic/metal composite (referred to as C-4 composite) has been recently produced at The Ohio State University. A new method of preparation, based on a displacement reaction between a silica precursor (whose frame is faithfully reproduced in the composite product) and molten aluminum, allows the production of a MMC where both the Al2O3 and Al phases are continuous and interpenetrating. The aim of the present work was to investigate the tribological behavior of C-4 Al2O3/Al composites under dry sliding conditions using a computer-controlled slider-on-cylinder tribometer. The tests were carried out at applied loads in the range 5-30 N and sliding speeds in the range 0.3-1.8 m/s, for sliding distances up to 10 km. Wear scars and debris were characterized by means of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), with an EDS analyzer and Xray diffraction (XRD) analysis. Under the adopted testing conditions, the C4 composites underwent only mild wear, mainly as a consequence of the high load-bearing capacity of the ceramic phase which enhances wear resistance. The high wear resistance is also related to the nature of the third-body, mainly constituted by Fe2O3, which is produced by the abrasive action carried out by the hard ceramic phase on the counterfacing steel. Under the adopted testing conditions, the transition from mild to severe wear, observed at a critical load in conventional MMCs, was never observed in the C4 materials. Both the continuity between aluminum and alumina, and the increase in interfacial bonding, played an important role in influencing the wear behavior of the C-4 composites. These aspects led to an improvement of wear resistance of the C-4 composites over conventional MMCs, under the same experimental conditions, and probably shifted the transition from mild to severe wear regimes to higher critical loads. (C) 1998 Elsevier Science S.A All rights reserved.