Properties of Metal Alloys

Self-Diffusion

• Self-diffusion is the process of atoms of one metal diffusing to the same metal
• Factors that influence diffusion are the diffusing species and temperature

Metal Alloys

• Alloys are composed of two or more chemical elements, at least one of which is a metal
• Most metals used in engineering applications are some form of alloy

Alloying

• Alloying consists of two basic forms: solid solution and inter-metallic compounds

The Iron-Carbon System

• Ferrite: a solid solution of body-centered cubic iron with a maximum solid solubility of 0.022% carbon at 727°C (1341°F)
• Ferrite is relatively soft and ductile, and is magnetic from room temperature to 768°C
• Austenite: has a solid solubility of up to 2.11% carbon at 1148°C
• Cementite: 100% iron carbide (Fe3C) with a carbon content of 6.67%, a hard and brittle inter-metallic compound

Heat Treatment of Ferrous Alloys (Microstructure)

• Pearlite
• Spheroidite
• Bainite
• Martensite
• Retained austenite
• Tempered martensite

Hardenability of Ferrous Alloys

• Hardenability is the capability of an alloy to be hardened by heat treatment
• It is a measure of the depth of hardness that can be obtained by heating and subsequent quenching
• The fluid used for quenching the heated alloy also affects hardenability

Heat Treatment of Non-Ferrous Alloys and Stainless Steel

• Solution treatment: heating the alloy to within the solid-solution phase and then cooling rapidly
• Precipitation hardening:
  • Aging: a time and temperature dependent process, also known as age hardening
  • Maraging: a precipitation-hardening treatment for a special group of high strength iron-base alloys, derived from martensite age hardening

Annealing

• Annealing is the restoration of a cold-worked or heat-treated metal or alloy to its original properties
• It increases ductility, reduces hardness and strength, or modifies the microstructure
• Annealing also relieves residual stresses in a manufactured part for improved machinability and dimensional stability

The Annealing Process

• Heating the workpiece to a specific range of temperature
• Holding it at that temperature for a period of time
• Cooling it slowly

Classifications of Annealing

• Process annealing: restoring ductility, part or all of which may have been exhausted by work hardening during cold working
• Stress-relief annealing: reducing or eliminating residual stresses

Self-Diffusion

• Self-diffusion is the process of atoms of one metal diffusing to the same metal
• Factors that influence diffusion are the diffusing species and temperature

Metal Alloys

• Alloys are composed of two or more chemical elements, at least one of which is a metal
• Most metals used in engineering applications are some form of alloy

Alloying

• Alloying consists of two basic forms: solid solution and inter-metallic compounds

The Iron-Carbon System

• Ferrite: a solid solution of body-centered cubic iron with a maximum solid solubility of 0.022% carbon at 727°C (1341°F)
• Ferrite is relatively soft and ductile, and is magnetic from room temperature to 768°C
• Austenite: has a solid solubility of up to 2.11% carbon at 1148°C
• Cementite: 100% iron carbide (Fe3C) with a carbon content of 6.67%, a hard and brittle inter-metallic compound

Heat Treatment of Ferrous Alloys (Microstructure)

• Pearlite
• Spheroidite
• Bainite
• Martensite
• Retained austenite
• Tempered martensite

Hardenability of Ferrous Alloys

• Hardenability is the capability of an alloy to be hardened by heat treatment
• It is a measure of the depth of hardness that can be obtained by heating and subsequent quenching
• The fluid used for quenching the heated alloy also affects hardenability

Heat Treatment of Non-Ferrous Alloys and Stainless Steel

• Solution treatment: heating the alloy to within the solid-solution phase and then cooling rapidly
• Precipitation hardening:
  • Aging: a time and temperature dependent process, also known as age hardening
  • Maraging: a precipitation-hardening treatment for a special group of high strength iron-base alloys, derived from martensite age hardening

Annealing

• Annealing is the restoration of a cold-worked or heat-treated metal or alloy to its original properties
• It increases ductility, reduces hardness and strength, or modifies the microstructure
• Annealing also relieves residual stresses in a manufactured part for improved machinability and dimensional stability

The Annealing Process

• Heating the workpiece to a specific range of temperature
• Holding it at that temperature for a period of time
• Cooling it slowly

Classifications of Annealing

• Process annealing: restoring ductility, part or all of which may have been exhausted by work hardening during cold working
• Stress-relief annealing: reducing or eliminating residual stresses