Milling dynamics: Part. III. integration of local and global modeling of mechanical alloying devices

In previous articles, we have attempted to describe the global dynamics of an attritor and a SPEX mill, two devices commonly used for mechanical alloying (MA). In this, the last of this series, we compare and contrast these devices with respect to a number of features. These include alloying kinetics and the properties, scale, and structure of processed powder. In addition, we illustrate how a local description of MA is useful in examining the interaction between material properties and process parameters, the latter of which is often imposed by the characteristics of the device used to achieve MA

Modeling of particle size evolution during mechanical milling

The process of mechanical alloying (MA) involves the repeated deformation, welding, and fracture of powder materials during grinding in high-energy mills. During MA, the size and size distribution of the particles change as a result of the particles’ different fracture and welding rates. The evolution of particle volume distributions during such a combined “fission-fusion” process can be described via a differential-integral equation. While analytical solutions are known for systems in which only fusion takes place, there is apparently no such solution for the fission-fusion problem. In this article, we describe a discretized form of the fission-fusion equation and apply it to modeling of particle size distributions during milling of elemental powders using previously determined fracture and welding rates appropriate to the global system of particles. Predicted particle size distributions mimic well those determined experimentally

Milling dynamics: Part I. Attritor dynamics: Results of a cinematographic study

The motions of grinding media and powder in an attritor canister were studied by means of filming the agitated charge and frame-by-frame scrutiny of the footage. In conjunction with auxiliary experiments, this permitted semiquantitative analysis of the milling action. In particular, the mill can be divided into several regions characterized by different balances between direct impacts and rolling/sliding of the grinding media. Simple calculations suggest that impacts are more capable of effecting mechanical alloying (MA) than are rolling or sliding events in an attritor. Powder circulation within an operating mill was also investigated. Based on the results and the accompanying analysis, concepts for improved attritor design are presented. © 1993 The Minerals, Metals and Materials Society, and ASM International