ABSTRACT
The process of mechanical alloying (MA) starts with mixing of the powders in the desired proportion and loading of the powdermix into themill along with the grinding medium (generally steel balls). Sometimes a process control agent (PCA) is added to prevent orminimize excessive cold welding of powder particles among themselves and/ or to the milling container and the grinding medium. This mix (with or without the PCA) is then milled for the required length of time until a steady state is reached. At this stage alloying occurs and the composition of every powder particle is the same as the proportion of the elements in the starting powder mix. However, alloying is not required to occur during mechanical milling (MM) (since one starts with prealloyed powders or materials with uniform composition throughout), but only particle/grain refinement and/or some phase transformations should take place. The milled powder is then consolidated into a bulk shape and subsequently heat treated to obtain the desired microstructure and properties. Figure 4.1 shows a schematic of the different steps involved in preparing a component starting from the constituent powders by the process of MA. Thus, the important components of the MA process are the raw materials, the mill, and the process variables. We next discuss the different parameters involved in the proper selection of raw materials and describe the different types of mills available for conducting MA/MM investigations. A brief description of the selection process of the grinding media is also presented. The role of process variables during MA in achieving the desired constitution in the final product is discussed separately in Chapter 5.
