Synthesis of Al4C3 from aluminium-carbon powders after mechanical alloying and post treatments

Ill SYNTHESIS OF AI4C3FROM ALUMINUM-CARBON POWDERS AFTER MECHANICAL ALLOYING AND POST TREATMENTS (Ph.D. Thesis) Bülent BOSTAN GAZI UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY June 2003 ABSTRACT In this work, mixture of pure aluminium and carbon powders were mechanically alloyed via a horizontal attritor. Powders were processed in a water cooled system under a protective atmosphere of argon which was purified by passing through copper scrap at 475 °C. The ratio of balls to powders was 20:1 where Al powders were mixed with 2 % graphite and milled in the horizontal attritor running at a speed of 600 rev. /min for 1 and 2 hours. Later, samples of alloyed powders were cold pressed under 600 and 1200 MPa pressure conditions and then sintered at 550 °C for 2-64 hours again under purified argon gas. To study the effect of MA and its duration on several parameters, the size and distribution of powders were quantified and XRD analyses were conducted to verify any occurrence of AI4C3 precipitates during the MA process. The same alloyed powders were sequentially cold formed by 50 % before and after the process of sintering to clarify the effect of deformation on AI4C3 formation. The sintered samples were examined by optical, scanning (SEM) and transmission electron microscopy (TEM) techniques. Particularly, for TEM studies, carbon replicas and thin foils were used. Also, hardness values and resistivities of samples were analysed. Through these investigations, the duration of MA and the pressure of cold pressing were found to be effective on sintering. Results of XRD and TEM analyses revealed that, particular, afterIV sintering the rate of AI4C3 formation increased considerably. It was found that AI4C3 particles were 10-60 nm in size and resistivities of all samples were with in the order of 10"6 ohm. Science Code Key Words Page Numbers Adviser 626.19.01 Al, C, MA, Sintering, AI4C3, Synthesis 121 Doç. Dr. A.Tamer ÖZDEMİR