Materials Science and Engineering A242 (1998) 304 – 307 Letter Subsurface damage of ceramic paticulate reinforced Al – Li alloy composite induced by scratching at an elevated temperature Zhenfang Zhang, Liangchi Zhang, Yiu-Wing Mai * Centre for Adanced Materials Technology (CAMT), Department of Mechanical and Mechatronic Engineering J07, Uniersity of Sydney, Sydney, NSW 2006, Australia Received 31 May 1996; received in revised form 18 August 1997 Abstract The wear resistance mechanisms of a silicon carbide (SiC) paticulate reinforced Al – Li alloy composite at 250°C by a pyramidal indenter have been studied. It is found that the subsurface damages that control the wear resistance are: generation of dislocations and cracks in the SiC particles, interface debonding between matrix and reinforcements and plastic deformation of the matrix. © 1998 Elsevier Science S.A. Keywords: Alloy; Al – Li alloy; Composite; Ceramic particulate Wear resistance of particle reinforced metal matrix composites depends on the matrix property, particle strength and particle – matrix interface characteristics. Significant modifications of the material underneath the sliding contact area may take place due to the local stress intensity and heat produced. It has been found that particle fracture, interface voiding and matrix de- formation would occur under repeated sliding [1 – 3], which favour delamination wear [4]. However, detailed evidence of subsurface damage in the case of single-pass sliding, which otherwise would offer insight into the formation mechanisms of sliding wear, is lacking. The present work aims to investigate such subsurface dam- age by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite material used was an Al – Li alloy reinforced with 10% (by weight) SiC particles with an average diameter of 13 m. The composite was prepared by hot isostatic pressing (HIPping) method using Al – Li pow- der smaller than 105 m. Its nominal chemical compo- sition by weight (%) is Li: 2.5, Cu: 2.0, Mg: 1.0, Zr: 0.15 and Al: balance. The material tested was solution treated at 530°C for 0.5 h and artificially aged at 190°C for 6 h. Within this temperature range, the coefficient of thermal expansion (CTE) of the SiC particle is 4.63 ×10 -6 K -1 [5] and that of the Al–Li matrix is 23.5 ×10 -6 K -1 [6]. The effect of differential thermal expansion on the microstructure of the composite will be discussed later in this communication. Adding lithium to aluminium not only lowers the density but also increases the elastic modulus and the strength [7]. Also, copper and magnesium improve the strength of Al – Li alloys through solid solution and precipitate strengthening and minimise the formation of precipi- tate-free zones near the grain boundaries. Zirconium, which forms the cubic Al 3 Zr coherent dispersoid, sup- presses recrystallization and stabilizes subgrain struc- tures [8]. The sliding wear experiments were carried out on a reciprocating scratch machine with a pyramidal inden- ter having an apex angle of 136° at a temperature of 250°C. The indenter was oriented with one of the pyramidal surfaces as the leading plane to simulate the wear process. Rectangular samples were polished down to 1 m with diamond paste and etched by a Graff/Sar- gent reagent. A normal load of 10 N and an average linear velocity of 6 mm s -1 were used over a wear track * Corresponding author. Tel.: +61 2 93512290; fax: +61 2 93513760; e-mail: mai@mech.eng.usyd.edu.au 0921-5093/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0921-5093(97)00731-4