The key difference between ductility and malleability is that ductility of solid material is the ability to undergo tensile stress without fracture or damage whereas the malleability of a material is the ability to undergo compressive stress without fracture or damage.
Ductility and malleability are two properties that are of great importance in selecting materials for building and manufacturing products. These properties describe the plasticity of solid materials. In metals, ductility and malleability are very high due to their ability to sustain large amounts of plastic deformations within the crystal structure. For example, platinum is the most ductile material, and gold is the most malleable material.
CONTENTS
1. Overview and Key Difference
2. What is Ductility
3. What is Malleability
4. Side by Side Comparison – Ductility vs Malleability in Tabular Form
5. Summary
What is Ductility?
Ductility is the ability of a solid material to undergo tensile stress without damage. We can measure this property of a solid material, and it describes the extent to which the solid material can undergo plastic deformation without fracture. It is often depicted by the ability of the solid to stretch into a wire when pulled at the ends.
Figure 01: Tensile Test for Cast Iron
This is a mechanical property, and we can quantify it by the fracture strain, which is the strain at which the material fractures when we apply increasing tensile stresses along a single axis. The reduction of the area from the initial point to the fracture during the test is also a measure for this property. Ductility is a property that we especially look for in metals. Metals have very high ductility. Therefore, we can easily manipulate metals compared to other solid materials.
What is Malleability?
Malleability is the ability of solid materials to undergo compressive stress without damage. Metals are highly malleable compared to non-metal materials. Therefore, we can shape metals using forming methods such as forging, rolling, extrusion and indenting. Since gold is highly malleable we can forge it into very thin foils, sometimes only a few atoms thick.
Figure 02: We can obtain Gold Sheets due to its Malleability
We can measure the malleability of a substance by determining how much pressure (compressive stress) it can withstand without breaking. But, this property is different from one substance to another depending on the crystal structure of the substance. During the compression, atoms roll over one another into new positions. But, they tend not to break the metallic bond between them. Most of the times this position change is permanent.
What is the Difference Between Ductility and Malleability?
Ductility of a solid material is the ability to undergo tensile stress without fracture or damage. Simply the ability to draw a material into a wire by pulling at the ends. Whereas, malleability of a material is the ability to undergo compressive stress without fracture or damage. Simply, it is the ability to be hammered or pushed into thin sheets without breaking. Therefore, this is the key difference between ductility and malleability.
However, in most cases, ductility and malleability are coexisting. For example, silver and gold are highly malleable and ductile. But in some cases ductility is high while malleability is low or vice versa. For example, Lead and cast iron are highly malleable though they have a lower ductility.
The below infographic tabulates the difference between ductility and malleability in more detail.
Summary – Ductility vs Malleability
Ductility and malleability are two aspects of the plastic deformation process of solid materials. Since metals have a crystal structure and free electrons to allow large amounts of dislocations, they are both highly malleable and ductile. The key difference between ductility and malleability is that the ductility of solid material is the ability to undergo tensile stress without fracture or damage whereas the malleability of a material is the ability to undergo compressive stress without fracture or damage.
Reference:
1. Bell, Terence. “An Explanation of Malleability and the Treatment of Metals.” The Balance. Available here
2. “Ductility.” Wikipedia, Wikimedia Foundation, 17 Oct. 2018. Available here
Image Courtesy:
1.”Cast iron tensile test”By Sigmund – Own work, (CC BY-SA 3.0) via Commons Wikimedia
2.”Kanazawa Gold Factory”By Eckhard Pecher – Own work, (CC BY 2.5) via Commons Wikimedia