The main difference between ductility and malleability is that ductility is the ability of a metal to undergo tensile stress, while malleability is the ability of a metal to undergo compressive stress.
Ductility and malleability are properties related to the deformation of metals. These two remarkable properties are due to the unique metallic bonding found only in metals.
Key Areas Covered
1. What is Ductility
– Definition, Characteristics
2. What is Malleability
– Definition, Characteristics
3. Difference Between Ductility and Malleability
– Comparison of Key Differences
4. FAQ: Ductility and Malleability
– Frequently Asked Questions
Key Terms
Ductility, Malleability
What is Ductility
When a force is applied at the two ends of a material to pull each other away, stress is applied to the material. This is called the tensile stress. Plastic deformation occurs due to tensile stress. Tensile stress is applied along a single axis, and the material can be rolled into a wire. Most metals show great ability to withstand this tensile stress. Copper, as an example, shows high ductile properties, whereas Bismuth shows comparatively low ductility and tends to rupture easily due to tensile stress.
Moreover, ductility depends on the grain size of the material. The lower the grain size, the harder the motion of dislocations due to greater resistance; therefore, ductility decreases. With larger grain sizes, vice versa occurs.
Ductility owes to the ability of metal atoms to slip over each other and deform under stress. This is also proportional to temperature. When metals are heated, their ductility increases. However, lead shows an exception by becoming more brittle when it is heated.
Figure 1: Ductile material can be rolled into wires
The process of stretching metal is called twining. Chains and necklaces are produced by twining valuable metals such as gold and silver.
Ductility is understood by the tensile stress of a material. The higher the tensile stress, the higher the ductility and the easier the material to be stretched.
Ductility is measured by a bend test. This is done by bending the specimen to a predetermined angle or until it fractures. Ductile materials are used to produce tubes, wires, and various other vehicle parts.
Furthermore, alloys are highly ductile as the compositions are not pure. Materials such as carbon are less ductile. However, by increasing the composition of carbon, steel can be made more ductile.
What is Malleability
Malleability correlates to the ability of plastic deformation of a material under a compressive test. Compressive stress results in shortening the dimensions of a material, making its volume smaller. Moreover, metals are highly malleable as the sea of electrons surrounding the positive metal ions can adjust themselves to withstand their small volume.
Figure 2: Ductile materials can be rolled into sheets
A malleable material can be rolled into thin sheets, pressed or hammered without breaking it. Different materials show different malleability owing to their arrangement of the crystal structure. NaCl has an ionic lattice structure which requires positive and negative ions to be located in specific places. Therefore, when pressure is applied, the ions are unable to dislocate, and the structure is broken. Therefore, NaCl is not a malleable material. Cu, in contrast, can adjust its crystal structure when pressure is applied. Hence, it is highly malleable.
Some examples of highly malleable materials include gold, silver, iron, copper, aluminum, tin and lithium. Antimony and bismuth are much harder as their atoms don’t line up when pressure is applied. Therefore, the material is harder and brittle.
The increase in temperature increases the malleability as well. Even impurities affect malleability. They make the dislocations hard to move. Moreover, malleability is useful for making various objects by changing the shape of metals.
Difference Between Ductility and Malleability
Definition
Ductility refers to the ability of a material to stretch under tensile stress, whereas malleability refers to the ability to deform and change shape under compressive stress.
Shape
Ductile materials can be rolled into wires, while malleable materials can be rolled into sheets.
Measurement
While ductility is measured by a bend test, malleability is measured by the ability to withstand pressure.
Factors that Affect Malleability and Ductility
Ductility is affected by the grain size, but malleability is affected by the crystal structure.
FAQ: Ductility and Malleability
Which metal has more ductility and malleability?
- Metals such as gold, silver, and platinum are highly ductile and malleable, allowing them to be easily shaped and stretched for various applications.
Which metal is ductile but not malleable?
- Zinc is an example of a metal that is ductile but not highly malleable.
How are malleability and ductility different in metals and nonmetals?
- In metals, malleability refers to their ability to be shaped into thin sheets, while ductility refers to their ability to be stretched into thin wires. Nonmetals, on the other hand, are generally not malleable or ductile and tend to break when subjected to mechanical stress.
Conclusion
Ductility refers to the ability of a material to stretch under tensile stress, while malleability is the ability to deform and change shape under compressive stress. Thus, this is the main difference between ductility and malleability. Both these properties generally increase with increasing temperature.
Reference:
1. “Malleability .” Infoplease. N.p., n.d. Web. 15 Feb. 2017.
2. “Malleability in metals.” Physics Stack Exchange. N.p., n.d. Web. 15 Feb. 2017.
3. Truitt, Benjamin.”Compressive Stress: Definition, Formula & Maximum.” Study.com. N.p., n.d. Web. 15 Feb. 2017.
4. Bell, Terence. “Malleability Explained | Compressive Stress and Metals.” The Balance. N.p., n.d. Web. 15 Feb. 2017.
Image Courtesy:
1. “Enamelled litz copper wire” By Alisdojo – Own work (CC0) via Commons Wikimedia
2. “Mg sheets and ingots“By CSIRO (CC BY 3.0) via Commons Wikimedia
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