Graphite Dendrites in Cast Iron and Their Fundamental Role in the Control of Morphology to Obtain Aero-Eutectic Graphite

This work analyzes the growth of graphite in the eutectic system of gray cast iron, focusing on laminar type A and undercooled type D morphology, and a modified morphology, such as vermicular or compact graphite. The objective of the study is to find an optimal graphite structure, from which a new class of lightweight materials results that has been called aero-eutectic graphite (AEG). The method to obtain AEG consists of dissolving the gray iron ferrous matrix by means of a chemical attack. From experiences of unidirectional solidification, it has been found that laminar graphite grows in a non-faceted way, coupled to austenite, while in vermicular the growth is through foliated dendrites. This characteristic allows vermicular graphite to have a higher specific intrinsic surface area. According to the Brunauer-Emmett-Teller (BET) analysis, the surface of the vermicular was 106.27 m2 g−1, while those corresponding to type A and D were 83.390 m2 g−1 and 89.670 m2 g−1, respectively. AEG with graphite type D was used as a cathode in Li-O2 batteries with satisfactory results, reaching more than 70 charge and discharge cycles, and 150 cycles at this time and still cycling, using Ru(bpy)3(ClO4)2 as redox mediator.

An Experimental Research On Friction And Wear Behaviour Of Compact Graphite Iron At Elevated Temperatures

Compact Graphite iron (CGI) is mainly used in automobile engine cylinder blocks and disc brakes. CGI has interconnected by vermicular shape graphite. Melting of steel and treatment of CGI is useful for getting sound castings. In automobiles the components manufactured by CGI are exposed to friction including wear, abrasion, thermal stresses and fatigue. Friction and wear characteristics at elevated temperatures are studied in the present study. Friction tests on CGI are conducted with pin on disc wear testing machine between CGI and hard steel disc. The deviations in frictional forces and wear behaviour are observed from the experimental results. The results shows that the wear rate and frictional forces of CGI at 400°C and 500°C temperatures was strongly influenced by the variation in induced temperatures. Scanning Electron Microscopy (SEM) is used to examine CGI pins surfaces. Temperature variations during experiments are influenced the CGI coefficient of friction.

Investigation of Grey Cast Iron Microstructure Influence on its Heat Resistance

Grey cast iron is one of the most common engineering materials used to make castings which work in thermal cycling. Under thermal cycling conditions, heat resistance is an important operational property of grey cast iron, which depends to the greatest extent on its structure – size and shape of the graphite inclusions, as well as the metal matrix composition. In this paper, the heat resistance of unalloyed grey cast iron with lamellar and compact graphite distributed in perlitic and perlitic-ferritic metal matrices was determined. The tests were carried out at temperatures of 500 – 800 °C. The results of the studies showed an insignificant difference of perlitic and perlitic-ferritic grey cast iron with lamellar graphite heat resistance. The heat resistance of perlitic ferritic grey cast iron with compact graphite is 16 – 48 % higher than the heat resistance of perlitic ferritic grey cast iron with lamellar graphite. Thus, when the shape of the graphite inclusions changed from lamellar to compact, a significant increase in the heat resistance of unalloyed grey cast iron occurred.