What are the temperature-related properties of materials?

Temperature-related properties of materials are the properties that change or show any variation with temperature variations. Various properties of materials include physical properties, mechanical properties, chemical properties, electrical properties, magnetic properties, etc. The chemical, electrical, and magnetic properties of materials are important, but the physical and mechanical properties are more important. Based on their composition and chemical bonding, materials are classified as metals, ceramics, polymers, and composites.

Physical properties of materials

Physical properties are density, shape, viscosity, conductivity, size, homogeneity, thermal diffusivity, and heat capacity. Materials exist as solids, liquids, and gases. The density is the most important physical property of materials among all three states, but it is not affected by the temperature effect. The heat capacity is affected by temperature on a very narrow scale. The physical properties of materials dependent on the temperature effect are freezing point, boiling point, size, and shape of materials. The freezing point is the temperature at which the liquid material solidifies during the cooling process. The supercool liquid is obtained by keeping the material below its freezing point when the liquid material solidifies earlier than the freezing point, and hence, the freezing point decreases. When the supercool liquid is kept above its freezing point, the freezing point increases. The boiling point is the temperature at which the liquid vaporizes. During high temperatures, the boiling point of the material decreases, and during low temperatures, the boiling point of the material increases. The size and shape of the materials, especially metals deform with temperature variations. With the increase in temperature, metals tend to expand and with the decrease in temperature, metals tend to contract.

Mechanical properties of materials

The mechanical properties of materials include strength, hardness, toughness, elasticity, plasticity, ductility, brittleness, creep, and so on. The strength, hardness, plasticity, brittleness, and all other mechanical properties of a material are not much affected by high temperatures or low temperatures. The mechanical properties such as ductility, creep, and elasticity, are highly affected by high temperatures and low temperatures.

Ductility

Ductility is a property of the metals, by which they can be drawn into thin wires. It is influenced by grain size and temperature. In crystalline materials, ductility decreases with a decrease in grain size, whereas in nanomaterials, ductility increases with a decrease in grain size. The grain sizes are also responsible for causing dislocations in materials due to shear stress as shear stress is dependent on grain size. The changes in ductility with varying temperature is different for different materials.

Annealing

Annealing is giving heat treatment to the metals to change their physical and chemical properties. It turns the material more ductile and decreases the hardness to make them more workable. The annealing process is done on steel and iron. The various specialized cycles of annealing include normalization in which uniform fine-grained structure is given to metals, intermediate annealing in which ductility is restored in the metals, full anneal in which the material is heated slightly to form a full austenite structure and then cooled. Another method known as tempering can be done on metals to decrease the hardness of metals and increase the toughness, that is the resistance to fracture of metals.

Creep

Creep is defined as the ability of a material to deform slowly under high stresses below the yield strength of the material. Creep occurs when stress occurs in the metals when the metals are near their melting point. Hence, for different types of metals, the temperature for creeps differ, depending upon the yield strength of materials. Concrete is another important material that is affected by creep. The creep in concrete occurs due to the presence of calcium silicate hydrates in the concrete. The creep in concrete is not dependent on the stress at yield strength but occurs at all stresses at any temperature.

Elasticity

Elasticity is the ability of a material to regain its shape after being stretched due to loading. The elastic materials obey Hooke's law while undergoing elastic deformation. According to Hooke's law, the stress is directly proportional to the strain up to the elastic limit. The resistance of the material to elastic deformation is measured using the elastic modulus. The elastic modulus varies with the temperature effect. Due to variations in elastic modulus, with an increase in temperature, the materials get elongated and due to a decrease in temperature, the materials get contracted. The materials also get affected due to the effect of tensile stress along with the thermal effect until the yield stress of the material is exceeded. With the increase in tensile stress along with thermal stress, the material gets elongated until the yield stress is reached. The material also undergoes plastic deformation along with elastic deformation and thermal deformation before getting fractured due to exceeding loads above tensile strength.

Effect of temperature on strength of a material

The strength of the material is influenced by the temperature. With increasing temperature, the elasticity of material varies, and the material becomes ductile, and with decreasing temperature, the material becomes brittle. Hence, the variation in strength is observed. Also, after the removal of thermal loads, the residual stresses tend to vary the strength of the material. The temperature changes also cause dislocation into the atoms of material as a result, the high strength is not achieved. It is necessary to analyze the temperature effects and effects of residual stresses on materials properly to achieve high strength.

Context and Applications

The topic temperature-related material is taught in the following courses:

• Bachelors of Technology (Civil/Mechanical/Metallurgical)
• Masters of Technology (Metallurgical/Process Metallurgy)

Practice problems

1.  Which of the following is not a physical property of a material?

1. Density
2. Shape
3. Elasticity
4. Viscosity

Answer- c

Explanation- Elasticity is not a physical property of a material.

2. What change occurs in a metal due to an increase in temperature?

1. The metal elongates
2. The metal contracts
3. No change occurs
4. Metal freezes

Answer- a

Explanation- The metal elongates with an increase in temperature.

3.  Which of the following is defined as the ability of metals to be drawn into thin wires?

1. Ductility
2. Elasticity
3. Viscosity
4. Tensile strength

Answer- a

Explanation– Ductility is defined as the ability of metals to be drawn into thin wires.

4. What is the ability of a material to deform slowly under high stresses below the yield strength of the material?

1. Elasticity
2. Ductility
3. Creep
4. Tensile strength

Answer- c

Explanation- Creep is the ability of a material to deform slowly under high stresses below the yield strength of the material.

5. According to Hooke's law, stress is directly proportional to strain up to which limit?

1. Ductile limit
2. Flexural limit
3. Thermal limit
4. Elastic limit

Answer- d

Explanation- According to Hooke's law, stress is directly proportional to strain up to the Elastic limit.