Microstructure-Property Relationships in Wear Resistant Alumina/SiC "Nanocomposites"

Abstract

Alumina/SiC “nanocomposites” consist of a dispersion of SiC “nanoparticles” in an alumina matrix with conventional grain size. The nanocomposites are much more resistant to severe wear than pure alumina and this paper explores the mechanisms responsible by examining microstructure-property relationships. Results correlating (i) microstructure, (ii) wear rate in a simple abrasive wear test and (iii) quantitative analysis of the appearance of the worn surfaces, are presented. The results show that the reduction in wear rate caused by the SiC is a consequence of the reduction in surface pullout by brittle fracture only. For small volume fractions ( 5vol%), the main effect of the SiC additions is to reduce the dimensions (diameter, depth) of the individual pullouts. This is suggested to be a consequence of the change in fracture mode from intergranular in alumina to transgranular in the nanocomposites. For greater additions of SiC nanoparticles (10vol%), the brittle fracture responsible for the cracking is also suppressed, and it is proposed that this is a consequence of the blocking of the formation of the long twins or dislocation pileups that are thought to be responsible for crack initiation by intragranular SiC particles (i.e. a form of slip homogenisation).