Allen Hunter

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Allen Hunter
Research: Copper Strengthened Steel Alloys
Education: Application Engineer DualBeam FIBs, FEI Co. 2013-present
Research Fellow, University of Michigan
Ph.D. Materials Science, Northwestern University, 2012
B.S. Materials Science and Engineering, Michigan Technological University, May 2007
Minor: Metal Casting Enterprise, Michigan Technological University, May 2007
Publications: Publications by Hunter in our database

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The main strengthening addition of conventional steels is carbon, which forms various carbide phases that strengthen the alloy. However, an increase in carbide volume fraction is accompanied by a decrease in elongation and toughness due to the brittle nature of the carbides. Thus, a tradeoff exists between high strength and high toughness in carbon steels. Additionally, steel plate is typically joined by welding. The rapid cooling rate associated with the weld and heat affected zones tend to form martensite in high carbon steels. This phase is much more brittle than the steel substrate and will lead to brittle failure along weld lines unless expensive post-weld heat treatments are performed.

A way around these issues is to replace the strengthening mechanism. Copper has a low solubility in iron and forms nano-scale precipitates that effectively strengthen the alloy. The carbon level in the steel can be practically eliminated with suitable amounts of copper and other alloying elements resulting is a combination of high strength and toughness. Additionally, the steels are easily weldable due to the minimum carbon concentration.

A copper bearing steel alloy, designated as NuCu140 was developed at Northwestern to exploit the properties of the copper precipitates. This steel has a low carbon content (0.05 wt%) and is alloyed with Cu, Ni, Mn, and Al for strengthening. The alloy can be cast as ingots using conventional methods and hot rolled to plate thickness or forged to shape. Solution treatment at 900 celsius followed by aging at 550 celsius causes supersaturated copper precipitates to form with sizes less than 5 nm, depending on aging times.

In addition to the NuCu alloys, our group is also focusing on development of Ni containing steels and modifications of HSLA-100 steels. The end goal of our research is high toughness/high strength materials.