HIGH-STRENGTH GRAPHITES FOR CARBON PISTON APPLICATIONS

Recent studies have shown that carbon pistons are highly thermal-resis tant in comparison to pistons made of aluminium alloys and can contrib ute to lower hydrocarbon (HC) emissions. A graphite piston material ha s to meet requirements which will be discussed in this paper. The near -net-shape manufacturing process is regarded as a cost-effective appro ach to producing carbon pistons. This process will be discussed in con nection with results of our own material studies. The results include studies on forming, sintering and evaluation of mesophase carbon mater ials. The mechanical and physical properties of a crucible acting as a piston showed properties comparable to those of a commercial graphite block. Flexural strength of up to 116 MPa and a Weibull modulus m > 2 0 were found. The thermal conductivity was determined to be ca 105 W m K(-1) with an open porosity of 10 vol%. The properties of the powder, the densification and the controlled release of volatile matter during the temperature treatment appear to be the key factors to achieve the high performance of the graphite. Further results are reported on the successful cold isostatic pressed piston blank with a completely repr oduced near-net-shape inner contour. (C) 1998 Elsevier Science Ltd. Al l rights reserved.