In a high-energy ball milling process, the powder particles put in the mill are subjected to a high energetic collision. The process is also referred to as mechanical alloying or nanotechnology. This process has been found to produce a fine and uniform dispersion of oxide particles in nickel-based superalloys. This, however, may not have been possible with the use of conventional metallurgical methods.Microstructurally, the mechanical alloying process can be divided into four stages:
(a) initial stage
(b) intermediate stage
(c) final stage
(d) completion stage.
(a) Initial Stage: The powder particles are smoothened at this early stage by the compressive forces as a result of the collision of the balls. Micro-forging results in changes in the shapes of the particles, or cluster of particles being impacted time and again using the milling balls with high kinetic energy. Such deformation, however, shows no net change in the mass of the powders.
(b) Intermediate stage: The middle level of the mechanical alloying process features massive changes as compared with that experienced in the initial stage of the ball milling. Cold welding is now significant. The special blend of the constituents of the powder reduces the diffusion distance to the micrometre range. Although a few dissolution may occur, the chemical composition of the alloyed powder is still no longer homogeneous.
(c) Final Stage: At the last stage of the mechanical alloying process, sizeable refinement and decreased particle size are evident. The microstructure of the particles also appears to be extra homogenous in microscopic scale than the ones at the first and intermediate degrees. Actual alloys might also have already been formed.
(d) Completion stage: The particles of the powder at this end stage of the mechanical alloying process possess a high degree of deformed metastable structure. The lamellae, at this juncture, are no longer resolvable by way of optical microscopy. Beyond this stage, any further mechanical alloying will not be able to improve the dispersoid distribution physically. Alloys with similar composition to the starting constituents are consequently formed.
There are different apparatus that can be used in the mechanical alloying process namely the planetary mill, attritor or the horizontal ball mill. The ball mill manufacturers have built all these techniques to operate on the same technique.
Planetary ball mill is a more commonly used system for the mechanical alloying process; this is because only a small amount of powder particles is required. Consequently, it is suitable particularly in the laboratory for research purposes.
Nanotechnology plays a very crucial role in many key technologies of the new millennium. The chemical and physical properties of aluminium (Al) especially its nanoparticles are suitable enough to make them applicable to various applications.
Such applications include alloy powder metallurgy parts for automobiles and aircraft, corrosion, heat shielding coatings of aircraft, resistant, conductive and heat reflecting paints, conductive and decorative plastics, soldering and termite welding, pyrotechnics and military applications.
Nanoparticles, compared to the bulk metals, show unique properties and as such lots of research works have been written on synthesis and applications of metal nanoparticles.