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Copper’s enhanced hardness under extreme strain

May 29, 2024
Technology

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Context (TH): Researchers from MIT and Northwestern University found that pure copper, when heated and subjected to extreme strain, behaves like a harder material.
The new study shows the change in material strength response above 1 million /s strain rate.

Strain: Deformation of material under stress.
Strain rate: Rate at which strain changes, measured per second.

Experimental Method & Findings

In their study, the researchers accelerated aluminium oxide microparticles using lasers and shot them at a copper substrate at around 860 km/hr.
Findings: When the temperature of the copper object was increased while the strain rate was 10 million /s, copper behaved like a harder material at impact spots. At strain rates lower than 1 million /s, the copper became softer.
- Comparison with Steel: At 10 million/s strain rate and 177º C, copper strength is over 300 megapascal (MPa). Comparable to the conventional strength of 304 stainless steel at the same 177º C.
- The researchers also reported similar effects with pure titanium and gold.

Basics: Metals become softer when heated and strained at certain rates (0.000001/s and 10,000/s).
SAE 304 steel is the most common form of stainless steel today.

Applications

Potential new strategies for designing devices for extreme conditions.
Relevant for high-speed manufacturing and aerospace engineering.

Copper

It is a good conductor of electricity and is ductile [able to be drawn out into a thin wire].
Alloys of Copper
- Iron + chromium + nickel with carbon +silicon + manganese = Stainless Steel.
- Copper + Nickel == Morel Metal.
- Copper + Aluminium == Duralumin.
- Copper + Zinc == Brass.
- Copper + Tin == Bronze.
Copper ore is found in ancient as well as in younger rock formations.
Mining for copper is costly because most of the copper ores contain a small percentage of the metal.
India has low-grade copper ore (less than 1% metal content, international average 2.5%).
The major part of supply comes from the USA, Canada, Zimbabwe, Japan and Mexico.

Stone Age to Metal Age: Evolution of Metals

End of Stone Age: Copper smelting and alloying. Introduced metalworking, better agricultural tools, culture, trade, governments, and new weapons.
Iron Age: Iron replaced copper and tin.
- Steel is made by adding carbon to iron. Iron’s unique property is that it dissolves carbon. Repeated heating and cooling with carbon produces steel, a hard iron-carbon alloy.
- Impact of Steel: Harder than copper, tin, or iron.

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