Five Key Metallurgy Concepts - Industrial Metallurgists

Five Key Metallurgy Concepts

<a href=''>Five Key Metallurgy Concepts</a>

In a recent blog post I explained about the two fundamental principles that are the foundation of materials science. Understanding and applying these principles are critical for applying materials science to engineering decisions and problems.

One of the principles is that a material’s properties depend on its composition and microstructure. Microstructure refers to microscopic structures.

There are five key metallurgy concepts that must be understood to apply metallurgy to

The rest of this article discusses the five concepts. These concepts apply to all metals.


Metals are crystalline, which means the atoms in a metal are arranged in a periodic manner. The specific arrangement of atoms differs from metal to metal and even within a metal. The arrangement of atoms affects a metal’s properties.

Disruptions in the periodicity of the atoms within a metal result in many grains through a piece of metal. Thus, all commercially available metals are polycrystalline, i.e. comprised of many grains. Within each grain, the atoms are arranged in a periodic manner. Grain size and shape affect metal properties.

Understanding crystallinity is important for understanding the differences between phases, grains, and defects in the crystallinity enable alloying, heat treating, and metal mechanical properties.


Phases are physically distinct materials within metals. Phases have distinct properties, are comprised of the elements present in an alloy, and can be either a mixture or a compound,. Metals can be comprised of one phase or multiple phases. The properties of a metal depend on the phases present, their relative amounts, and their shape and size, all of which depend on a metal’s composition and how it was processed.

Understanding the phases that can be present in an alloy and what can be done to influence the phases present is important for understanding how to use composition and processing to modify the phases present to modify the properties of the metal.

Examples of phase in metals are ferrite and cementite in steel and aluminum and aluminum-copper precipitates in certain aluminum alloys.

Ferrite and cementite in steel
Aluminum grains with Al-Cu precipitates

Phase transformation

Phase transformations involve changes to the phases present in a metal. The result is changes to metal properties. Through alloy composition and heat treating we can control the phases present in a metal as well as their relative amounts, shape, and size, all of which influence metal properties.

Steel quenching and tempering and aluminum aging are examples of heat treatments that involve phase transformations, which result in increased metal strength.


Diffusion involves the motion of atoms through a metal. Diffusion enables microstructure changes to occur during heat treatment, resulting in changes to metal properties. The microstructure changes that occur by diffusion include changes to grain structure and phase transformations. Understanding diffusion is important for understanding the changes that occur during heat treatment.


Dislocations are defects in the arrangement of atoms in metals. An example of one type of dislocation is shown. It consists of an extra plane of atoms above the dashed line. On the right is an electron microscope image of dislocations in a metal. Dislocations are present in all metals. There are about 10 million dislocations per square centimeter in as-cast metals and up to a trillion dislocations per square centimeter in heavily cold-worked metals.

Dislocations move through a metal when the stress applied to the metal is large enough. Metal strength and other mechanical properties depend on dislocation motion. These properties can be modified through alloy composition, cold working, grain size, and phase microstructure. By understanding how dislocations move through a metal and the things that affect dislocation motion, metals can be engineered to modify metal strength and other mechanical properties.

Applying these concepts

As with anything technical, the fundamental concepts are not complicated. However, it gets complicated when applying the concepts to different situations. In the case of metals, things get complicated for different alloys, the phases present, response to thermal and mechanical treatments, and of course properties.

Still, without an understanding of the five concepts discussed, and the two fundamental principles, it’s difficult to understand the metallurgy of different alloys and it’s difficult to apply metallurgy to make better, lower-cost products and quickly solve metal problems.

Interested in learning more? Watch the recording of the 5 Key Metallurgy Concepts webinar or take our Principles of Metallurgy online course. All of our metallurgy training references these concepts.

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