Kinetics of Mechanical Alloying, Mechanical Properties of Micro and Nanostructural Al-C Systems

Abstract

A method of mechanical alloying process is described. Carbon transformation to Al 4 C 3 is characterized within the different heat treatment schedules and nine commercial carbon powders are tested. The micromecha nism of carbon incorporation into the metallic powder, and its compacting are described. The influence of dis persed carbides on mechanical properties is evaluated together with the influence of deformation on microstruc ture and properties. It was proved that the transformation efficiency of carbon to Al 4 C 3 by heat treatment of alumin ium with the porous furnace black and electrographite is higher than that of the hard cracked graphite. Microstruc ture changes consisted of the fracture processes and welding of the particles with incorporation of C phase and forming of final granules. The dispersed phase Al 4 C 3 parti cle size was measured on thin foil structures, and it was constant and as small as 30 nm. The particle size was influenced neither by the carbon type nor by the heat treatment technology applied. Subgrain size measured in the range of 100 grains in thin foils depended on the carbon type, as well. It ranged from 0.3 to 0.7 mm. Using a DSI (depth sensing indentation technique), the Martens hardness, indentation modulus E and deformation work W for Al matrix and Al 4 C 3 particles have been measured. The temperature dependence of ductility, and reduction of area in the temperature range of 623-723 K and strain rate of 10 −1 s −1 , indicated a considerable increase of these properties. In a case when the volume fraction of Al 4 C 3 changes from lower to higher, the grain rotation mecha nism dominates instead of the grain boundary sliding. The comparison of the tensile test results and changes in fracture for the AlAl 4 C 3 system at two temperatures and two strain rates is summarized. The dependence of the minimum deflection rate on the applied force as well as the dependence of the time to fracture on the applied force for two temperature levels (623 and 723 K) by small punch testing are depicted. The composite was tested in two dif ferent states: a) as received by mechanical alloying with hot extrusion (HE) as the final operation and b) ECAPed (mean grain size of 100-200 nm). The dependence of the minimum deflection rate on the applied force as well as the dependence of the time to fracture on the applied force for two temperature levels are evaluated. The anisotropy of the creep properties and fracture using small punch tests for the AlAl 4 C 3 system produced by ECAP were analysed.

Synthesis of Nono-Crystalline Aluminum Carbide Using Thermal Treatment of Mechanically Activated Al and Graphite Mixture

“…Mechanical alloying is considered as a solid-state synthesis method that is more simple and economic than other synthesis methods such as melting. This method is based on the repeated collisions between starting materials and balls, the deformation and decomposition of powder particles and welding of power particles during mechanical alloying processes [1]. In fact through the milling treatment, substances react to each other and change to the desired production depending on experimental conditions such as the milling time, the rotation speed and ball-powder ratio.…”