There are 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. This includes producing stock materials, designing components used in devices, machines, and structures, and solving component failures and production quality problems.
The concepts apply to all materials, not just metals, but this article will focus on metals.
The first fundamental principle is
The properties of a material depends on its composition and microstructure.
For metals, composition refers to the elements in a metal. This includes the main element, alloying elements, and impurity elements. For metals, microstructure refers to the grain size, phases present and their relative amounts, dislocation density, and other microscopic structures. Microstructure has a huge effect on metal properties. So, although we need microscopes to see these microscopic structures, it’s important to recognize their presence and effects.
Learn more: Metal Conversations podcast episode on the two fundamental metallurgy principles
The second fundamental principle is
The microscopic structures present in a material depend on its composition and how the material was processed.
For metals, processing includes mechanical treatments, thermal treatments, casting, and others. Mechanical treatments include cold rolling, drawing, extruding, and forging. Thermal treatments include heat treating. There are also thermomechanical treatments such as hot rolling and hot forging.
The implication of this principle is that a material with a certain composition can be processed in different ways, resulting in different microstructures, which results in different properties. An example is carbon steel that contains about 0.4% carbon. The three images show the microstructures for the steel after the following treatments: hot-rolling, spheroidize anneal, and quench and temper.
The hot-rolled steel consists of grains of ferrite and regions of pearlite (parallel plates of cementite with ferrite between the plates). The spheroidize annealed steel consists of cementite particles distributed throughout ferrite grains. The quench and tempered steel consists of martensite. The yield and tensile strengths shown beneath each image illustrate the effects of the different heat treatments and resulting microstructure.
Applying these two principles is critical for producing metals and fabricating components and joints that have the desired properties, and doing so at low-cost. The principles are also applied to determining the root cause of component failures and production quality problems.
The tricky part is understanding the microstructures of different alloys, the effects of composition and processing on the microstructures, and the relationship between alloy composition, microstructure, and properties for specific types of alloys – carbon steel, stainless steel, wrought aluminum, cast iron, …
Finally, as mentioned earlier, the two fundamental principles of materials science apply to all materials - metals, ceramics, polymers and new materials being developed. However, the specific composition and microscopic structure details are different for the different classes of materials and the processing used is different for the different materials.