Material science - Research Paper Example

Grain Boundary Sliding in Material Science Grain Boundary Sliding in Material Science Material science is an engineering discipline that covers various types of materials and their application in manufacturing. Materials fall in different categories including metals, plastics/polymers, semiconductor materials, ceramics and composite materials. One of the most important phenomena that influence various properties of materials is grain boundary sliding (GBS). There is a general consensus that grain boundaries can result to weakening of polycrystalline solids at high temperatures and that GBS can happen at individual grain boundary surfaces (Poirier 194).

GBS has also been found to be a major means of deformation for polycrystalline materials leading to the belief that GBS controls superplasticity properties. GBS refers to the displacement occurring when two grains subjected to external stress slide over one another in which the movement occurs at or in closer proximity to the common interface between the grains (Langdon 598). The occurrence of grain boundary sliding has been demonstrated by several scholars over the years. Grain boundary sliding has increasingly become an area of interest among material scientists.

Two different forms of GBS have been suggested. The first form of GBS suggested by Rachinger in 1952 involves the displacement of nearby grains in which the grain’s original shape and size is retained despite being evidently displaced over each other (Mayo and Nix 2). This phenomenon has been demonstrated as a form of deformation in polycrystalline materials under creep situations where the number of grains within the measured length increases in the same direction as the external tensile stress (Rachinger 81).

Rachinger GBS exists under two different situations namely; conventional creep where the size of the grain d exceeds that of the equilibrium sub-grain as well as in superplasticity where the grain size is smaller than the equilibrium size of the sub-grain (Langdon 598). Both GBS GBS also exists in form of Lifschitz sliding which represents the offsets in the boundaries that occur due to stress and does not increase the number of measured grains (Langdon 598). The main difference between the two GBS forms is that while Lifschitz is an accommodation process by itself, Rachinger sliding entails accommodation through intragranular grip (Nieh, Sherby and Wadsworth 40).

The two GBS types have been unified through rate equations which are consistent with empirical observations (Vastava and Langdon 2339).Grain boundary sliding also plays a significant role in superplasticity. Superplasticity represents the ability of certain materials to pull out under high strain without breaking (Mikhail et al. 74). Studies have established that shape and size is also retained in superplastic alloys even under conditions of extreme strain. Superplasticity occurs under two conditions which include; small and constant size of grain and high temperature (Kawasaki and Terence 86).

Rachinger GBS plays a significant role in superplasticity as it allows the grains to slide over one another without elongation along the axis of tension. Lifshitz sliding is a characteristic feature in diffusion creeps and that its contribution to the general strain varies according to the specific strains and the elongation of the grains resulting from vacancy flow. In conclusion, the contribution of GBS to the total strain in deformation of polycrystalline materials can be measured using a procedural approach.

These methods have been utilized in measuring Rachinger GBS in ceramic materials, metals and physical materials as well as in measuring Lifshitz grain boundary sliding in diffusion creep. The importance of GBS under conditions of extremely small grain size has been recently demonstrated through computer generated models (Chandra and Dang 657). Despite the current developments in material science, there is need for further research to establish the exact role of grain boundary sliding in ultra-fine and nanostructures.

Works CitedChandra, N. & Dang P. “Atomistic simulation of grain boundary sliding and migration”. J. Mat. Sci. 34 (1999): 655-666. Kawasaki, Megumi & Terence Langdon. “Grain boundary sliding in a superplastic Zinc-Aluminum alloy processed using severe plastic deformation”. Materials Transactions, 49, 1(2008):84-89.Langdon, Terence. “Grain boundary sliding revisited: developments in sliding over four decades”. J. Mat Sci. 41 (2006): 597-609.Mayo, Mariella and William Nix. “A model for superplasticity not controlled by grain boundary sliding”.

Stanford University, 2001. Mikhail et al. Plastic Deformation in Nanocrystalline Materials. New York: Springer, 2004. Print. Nieh T, Sherby O. & Wadsworth J. Superplasticity in Metals and Ceramics. Cambridge: Cambridge University Press, 2005. Print. Rachinger, W. Journal institute of Metals 33 (1952): 81. Vastava, R. & Langdon, T. Metallic Transactions, 5(1974): 2339. Poirier, Jean-Paul. Creep of Crystals: High-temperature Deformation Processes in Metals, Ceramics, and Minerals. Cambridge: Cambridge University Press, 1985. Print.