Wear Behavior Of SiC Particle Reinfoeced Magnesium Matrix Composites

Dry sliding wear behaviors of Si C particle reinforced AZ91 matrix composites fabricated by stir casting were investigated. In the as-cast composites, Si C particles exhibited typical necklace-type particle distribution. This paper investigated the effect of this typical particle distribution on wear behavior of Si C particle reinforced AZ91 matrix composites. First, this paper studied the effects of the friction condition(like sliding distance, applied loads, sliding speed) and the factors of material(particles size and particle) on the wear mechanism of as-cast composites. Then, hotextruding process has been adopted with composites to change the necklace-type particle distribution, and studied the wear behaviors of as-extrued composites.The studies showed that Si C particles exhibited typical necklace-type particle distribution in the as-cast composites. This distribution caused the weak interface bonding between Si C and matrix in particle-segregated zones. And this kind of particle distribution promoted the wear mechanism of delamination.The as-cast composites shown two stages for grinding-in and stable worn. As the sliding distance increased, the wear mechanism of composites changed. During dry sliding with higher applied loads, Si C particles were easy to debond from matrix. Thus, the presence of Si C particles promoted the wear rates at higher loads, although Si C particles lowered the wear rates at lower load of 10 N. At low sliding speed, the Si C particle prevented the contact of matrix and steel disc, then this enhanced the wear resistance of composites. But higher sliding speed could result worn surface getting soft. Thus, the effect of Si C particle disappeared. In addition, the necklace-type particle distribution became more evident with the decrease of particle sizes or the increase of volume fractions. Larger particles had better interface bonding, so they can delay the transition of the wear mechanism from oxidation to delamination and offer higher load-bearing capacity. Thus, the composites reinforced by the larger Si C particles exhibited higher wear resistance. Similarly, the Si C particles were more easily extracted from matrix in the composites with a higher volume fraction during the dry sliding. Thus, the wear rates of the composites increased with the increase of particle volume fractions. We also found three wear mechanisms in the wear tests of composites,such as oxidation,abrasion and delamination.In the as-extruded composites, the particle distribution was homogeneous instead of typical necklace-type particle distribution. This homogeneous distribution improved the interface bonding between Si C and matrix. This distribution lightened the extent of delamination but promoted the adhesion. The as-extruded composites shown three stages which were low wear rate, constant wear rate for a long distance and decrease of wear rate. As the sliding distance increased, the wear mechanism of composites also changed. During dry sliding with higher applied loads, Si C particles were difficult to debond from matrix. Meanwhile, the homogeneous distribution also caused adhesion. The Si C particle could put off the plastic deformation of matrix. At low sliding speed, the Si C particle prevented the contact of matrix and steel disc, then this enhanced the wear resistance of composites. But higher sliding speed could result worn surface getting soft. Thus, the effect of Si C particle disappeared. The necklace particle distribution had higher resistance for adhesion which compared with the homogeneous distribution. As the increase of particle size or decrease of particle volume fractions, the particle distribution was more homogeneous. Thus, the large particle or high volume fractions caused adhesion easyly. At last the wear resistance of as-extruded composites was influenced by wear mechanisms of delamination and adhesion.