Date | Time
24/01/2018 | 2 h 00 min - 5 h 00 min
In the Quest for High-Strength, High-Ductility Material
Due to the push for weight saving designs, designers have been looking to use materials with high-strength and high-ductility. High-strength materials can be made by using, among the several other methods, Severe Plastic Deformation (SPD) process or by making Metal Matrix Composites (MMC). However, there are several limitations of these processes, especially their loss in ductility. A loss in ductility means a loss in toughness, which makes designing and maintenance that much more difficult. The ductility can be improved to some extent by use of heat treatments (in SPD) and use of nano-particles as reinforcements (in MMcs). We have attempted to use Friction Stir Processing (FSP) to overcome the disadvantages of both SPD and MMCs. FSP is a process in which a non-consumable rotating tool is plunged into a material and is moved forward. This induces a large strain in the deforming zone at temperatures high enough to give fine grained recrystallized structure. FSP, is also amenable to mixing of materials. However, when trying to mix, for example, ceramic particles into the matrix significant wear of the tool is observed (especially when processing of aluminum and its alloys using steel tools). The wear of the tool is less severe when using nano-particles for mixing. However, nano-particles are expensive and difficult to handle. An FSP process that has all the advantages and that overcomes the disadvantages while making MMCs would be ideal. In the process developed, a soft material that becomes hardened by later heat treatment is dispersed using FSP. The particles being soft gets fractured during FSP and become nano-sized. These nano-sized particles either get converted to harder particles during the process or are converted to harder particles by heat treatment. By optimizing the materials used and controlling the process parameters materials with more than 3 times the strength of the parent material and without significant loss in ductility are created (toughness increases). The talk covers the process and properties of such materials developed for plain copper and aluminum. In copper hardness of more than 5 times, with yield strength increase by 2.5 times without loss in ductility were developed. In aluminum yield strength of more than 4 times without significant loss in ductility have been developed. The basic mechanism postulated for this increase in strength and toughness is Orwan strengthening mechanisms and pinning of grain boundaries.