The Importance of Material Selection in Engineering - Part One - Basic Metallurgy


Metallurgy is at the very core of Engineering

The principle of creating metal alloys - the process of melting metallic elements together to combine specific strengths of each to produce a new, superior, metallic alloy - dates back to the Bronze Age of 3300-300BC.


By this stage in human history, humankind was of a sufficient level of development to create pottery kilns capable of producing temperatures in excess of 1000 degrees Celcius (1832 degrees Fahrenheit) which were found to be sufficient to melt Copper and thereby combine it with the much lower melting point Tin (232 degrees Celcius, 450 degrees Fahrenheit), creating a new metallic alloy, Bronze.


This ginormous step forward towards the advent of the Iron Age, and the Industrial Revolution which later followed, leads us right up to the present day where we are still looking to discover new metal alloys, composites, and hybridised materials to extol the virtues of individual materials by combining them into one singular super material.


The greatest question behind this is "Why?" "What was wrong with Copper on its own that it needed the help of Tin, nearly 4000 years after it has first been discovered to be used on its own, to make it into an alloy worth talking about?"


The answer is simple: whilst Copper was easy to work without needing to be heated, it was quite soft and brittle as an element. The addition of Tin married to this established metal created Bronze which was harder, stronger, and easier to form by heating than Copper alone.


To truly understand how this works, we have to look at a simple piece of chemistry. The structure of pure Copper is face cubic centred (FCC), offering a ductile and easily cold worked material. Conversely, this also makes Copper brittle. Tin, on the other hand, has a body centred tetragonal (BCT) structure, featuring a rectangular prismic cube-based crystalline organisation (Martensitic) which are known for possessing the ability to be heat treated. Combining these two elements allowed Bronze Age man to create an alloy which was work hardenable, whilst still being malleable and corrosion resistant.


From this point on, Copper went from merely being a material used to create jewellery and andornments to becoming, upon alloying into Bronze, a metal used for arrow heads, hammers, spear tips and countless other applications. This experimentation with alloys evolved until we reached the next metal age: The Iron Age.

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