High-strength graphites for carbon piston applications Original Research Article

Recent studies have shown that carbon pistons are highly thermal-resistant in comparison to pistons made of aluminium alloys and can contribute to lower hydrocarbon (HC) emissions. A graphite piston material has to meet requirements which will be discussed in this paper. The near-net-shape manufacturing process is regarded as a cost-effective approach to producing carbon pistons. This process will be discussed in connection with results of our own material studies. The results include studies on forming, sintering and evaluation of mesophase carbon materials. 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 > 20 were found. The thermal conductivity was determined to be ca 105 W mK−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 reproduced near-net-shape inner contour.