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Principles of Oxide Dispersion Strengthening
Published in Anshuman Patra, Oxide Dispersion Strengthened Refractory Alloys, 2022
The strengthening during oxide dispersion is associated with the Zener Pinning effect. During the interaction of a spherical particle with the grain boundary an attractive force (the pinning force) is operative, which acts against the boundary dragging on the force. During the boundary-particle interaction, the grain boundary area decreases and furthermore, the grain boundary area increases to remove the particle, which is made possible by increasing the energy of the system. The force related to the pinning, considering the particle incoherency is [35]: F=2πrγcosθsinθ
Solute drag effect on austenite grain growth in hypoeutectoid steel
Published in Philosophical Magazine Letters, 2020
Vipin Kumar Devra, Joydeep Maity
Zener pinning and solute drag are two different phenomena. Zener pinning is caused by carbide or nitride precipitates. However, solute drag results from dissolved solute atoms which are present either as segregations at grain boundaries (higher-energy sites) or in a concentrated form (such as clusters); however, they do not precipitate out as carbides or nitrides. It is worth mentioning that, in ferrous system, the majority of the research work carried out so far has concentrated on grain-boundary pinning by second-phase precipitate, in particular during grain growth of austenite in low-carbon alloy steels containing carbide- and nitride-forming alloying elements [9–11]. In alloy steels, Zener pinning is often exploited for grain refinement with a two-step heat treatment process. The alloying elements, being dissolved at a high temperature in an initial step, precipitate out in the form of alloy carbides or nitrides in a following step, which involves isothermal holding at a lower temperature. This process pins down grain growth. However, work on the solute drag effect for ferrous system is sparse, particularly in the case of plain carbon steel. An initial attempt by the present corresponding author [12] to explain the solute drag effect in plain carbon steels on the basis of Beck’s relationship was successful for higher solute (carbon) content in hypereutectoid steel, where a substantial solute drag effect was indicated by a significant lowering of the time exponent. However, this approach failed to show a solute drag effect for a relatively low solute content.
Microstructure and mechanical properties of copper surface composite layers reinforced by nano and microscale SiC particles via friction stir processing
Published in Advanced Composite Materials, 2019
Ali Shamsipur, Sanaz Asadkarami
Meanwhile, the use of metal-matrix composites is an established method for improving the surface properties of copper metal. Copper metal-matrix composites (CMMCs) are surface composites containing ceramic particles concentrated at the surface. CMMCs are used when there is a need to improve wear resistance without changing the properties of the metal’s inner matrix. The presence of hard and brittle ceramic particles is well known to reduce the ductility and toughness of CMMCs, while the inner matrix maintains its properties [6,7]. Many reinforcing particles with various sizes have been used in the preparation of copper surface composites. In this context, it has been reported that the use of graphite particles can create excellent wear resistance due to the excellent lubrication properties of graphite. By increasing the size of the graphite particles to several microns, the wear resistance increases [8,9]. Furthermore, the use of SiC [10,11] and specially nanoscale SiC particles significantly reduces the wear rates [3]. It is considered that the pinning effect by the nano-sized SiC particles retarded the grain growth of the matrix. Zener pinning considers the effect of small second-phase particles on grain boundaries. Ultrafine grains are achieved by nearly uniform dispersion of nano-sized SiC reinforcements in the fabricated composite layer [12–14].
An examination of microstructure, mechanical and dry wear properties of stir cast brass/Al2O3 composites
Published in Canadian Metallurgical Quarterly, 2021
Hassan Abdoos, Shayan Memar, Mohammad Reza Riahi
The microstructures of brass-based composites containing different reinforcement values are shown in Figure 6. As can be seen, the coarse equiaxed grains in the unreinforced specimen become finer needle-like Widmanstätten structure in the composites. Widmanstätten structure can be formed in the duplex brass alloys [32]. Furthermore, according to Figure 6, increasing the amount of reinforcement reduces the grain size. The reinforcement at the grain boundaries can create Zener pinning effect and restrict the grain growth. For stir-casted Al-based composites, Shayan et al. [26] reported that reinforcement can refine the cast structure owing to the enhanced heterogeneous nucleation.