Subject: Seminar Notice - K. Chaput Thur. May 17
From: "Stacey, Lisa A" <[email-masked]>
To: "[email-masked]'" <[email-masked]>, "[email-masked]'" <[email-masked]>, "[email-masked]'" <[email-masked]>
Date: Fri, 11 May 2012 14:26:00 -0400

MATERIALS SCIENCE AND ENGINEERING
SEMINAR

Effect of Biomodal Grain Distribution on Severely Plastically Deformed Copper

by

Kevin Chaput
Purdue MSE Prelim 1
Advisor:  Professor K. Trumble

ABSTRACT

In recent years there has been a demand for research in the area of ultra-fine grained (UFG) materials.  The superior strength of these materials is due to the Hall-Petch strengthening provided by ultra-fine grains has led to a drive to further understand this process and the other properties of this unique processing method.  One of the most important material property trade-offs is strength vs. ductility.  With the relatively high strength of UFG materials the poor ductility is expected since the mechanisms that cause high strength usually lead to poor ductility.  For these materials to ever be used commercially a higher ductility in these materials must be achieved.

            While there have been a few proposed mechanisms to achieve this property the most promising path has been in the creation of a multi-scale grain distribution. The bi-modal and multi-modal grain distribution can be produced through either secondary recrystallization or particle consolidation.  The resulting microstructure will be a mixture of typical coarse grains and UFG grains.  The basic idea behind this process is that the fine grains will act as effective strengthening mechanism while the larger grains allow for increased area for the dislocations to interact and strain harden the material which due to Considere's criterion prolongs, the onset of necking.  The effectiveness of this mechanism and the resulting properties will be the primary area that will be under investigation.

            There is some conflict in the properties of the multi-scale microstructures that vary between bi-modal and multimodal as well as between investigators.  While the general consensus is that this procedure increases the ductility it is important to notice the resulting effect has on the strength since that is the primary strength of this property.  While most investigators believe that the material's ratio of strength to ductility is typical for alloy or metal it is made of, some experimenters, Wang et. al., have published some results that show an increased ratio which is an exciting possibility for these materials.

            To do a thorough investigation into the engineering possibilities that can come from this a complete understanding into what aspect of the ductility is important.  While for production and processing of metals the traditional definition of ductility is important this definition for structural applications will not suffice.  The amount of plastic deformation before fracture is important for processes like extrusion and deep drawing but for structural applications the onset of necking displays the highest strength that can be sustained before failure of the part so this will be far more important and this will be taken into consideration when ductility values are reported.

Date:       Thursday, May 17, 2012

Time:      9:00 AM
Place:      ARMS Rm. 1021

Lisa Stacey
Secretary/Development Assistant
Purdue University
School of Materials Engineering
765/494-4100