Friction-stir processing (FSP) is a property enhancement technique which, not only removes the defects of initial casting process, but also improves the microstructure of the metals and metal matrix composites (MMCs). The process is based on frictional heating which results in a considerable dynamic plastic deformation within the metals. FSP can be specifically applied to develop fine-grained microstructures throughout the thickness of metal surface, to impart super plasticity and ensure homogeneous distribution of reinforced particles, if any. This chapter is a dedicated effort to consolidate the latest developments contributed by different researchers in last few years. The work covers various components and parameters, selected and used, for FSP to obtain specific desired results. Also, it includes past researches to exhibit various changes in mechanical properties with a keen focus on morphological study (by scanning electron microscopy) of these MMCs. In the last, a brief discussion on application and future scope of FSP processed MMC materials, is presented.
TopIntroduction
Friction stir processing (FSP) is a technique applied to fabricate or modify the microstructural features of surface composites (Mishra RS et al.2003). It is serving as a common metallurgical tool for refinement of grains and homogeneous alloying of reinforcing elements, which establishes and governs the desired properties in the base metal, via dynamic recrystallization. Friction Stir Processing works on the principle of friction stir welding, which was developed by “The Welding Institute” in UK (Thomas WM et al. 1991). After inception, its successful adaption and wider acceptability through its applications to many areas, it is further modified to Friction Stir Processing (FSP) (Mishra RS et al. 2000, Ma ZY 2002), which has also attracted attention. It is considered to be a ‘‘green’’ technique, due to its efficient energy utilization, environment friendliness, versatility of use and without emission of harmful gases and noise. Also, FSP technique does not alter the shape and size of the processed materials. Presently it is viewed as a promising technology for property enhancement of the metals and composites, homogeneous reinforcements. A complete manufacturing technology is connected to these on large scale, because of its wide acceptability and growing recognition. It is used for enhancing the strength of the metals, along with ductility and corrosion resistance. It also contributes in enhancement of resistance to fatigue and formability, in addition to other properties. The resulted fine grain structures impart super plasticity to the materials. Figure 1 demonstrates the various micro structural features and friction stir process attributes. [Mishra RS et al.2014].
Figure 1. Evolution of microstructural features
TopFriction Stir Processing Concept
To fabricate surface composites (SC), many techniques have been reported so far, but FSP has been identified as one of the most promising techniques. FSP is developed my R S Mishra (Mishra RS et al 1999), which works on the same principle, as that of friction stir welding (FSW). Conventional liquid phase processing techniques suffers from the limitation like, formation of intermediate detrimental phase and porosities due to elevated temperature and various processing conditions, and requires critical control of process parameters to get control on the solidified structure (Mishra RS et al 2001).
The main advantages of Friction Stir processing over other methods i.e. it has one step process for depth control of processing thickness in the material and only pin length is governing the feature. It can be easily repeatable and ensures meticulous grain refinement of the area processed, along with homogenization. Friction stir processing is free from any fumes, smoke, noise and solvents for degreasing and cleaning, which makes it an environmental friendly technique of metal processing. Figure 2 shows the process of friction stirring of a metal surface.
Figure 2. Schematic illustration of FSP