Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Summary of Material Science Chapter 1: Science of Materials Chapter 2: Properties of Materials Chapter 3: Material Testing Chapter 4: Alloys of Materials Chapter 5: Plain Carbon Steels Chapter 6: Heat Treatment Chapter 7: Cast Iron Chapter 8: Plastics/Polymers Chapter 9: Composite Materials Chapter 10: Ceramics Chapter 11: Semiconductors & Diodes Chapter 12: Biomaterials Chapter 13: Electrochemistry

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering HEAT TREATMENT DRAW Temperature Time Critical Temperature, e.g. Austenite steel, 727 o C Annealing Normalising (Post Rolling/forming) Stress Relieving Hardening (Quenching) Cooled in Furnace Cooled out of Furnace Softest form casting

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering QUENCHING MEDIA Oil, water and air The rate at which any quenching medium conducts heat from a heated component depends on the heat transfer conditions. Water can conduct heat from a heated component approximately twice as fast as oil. More rapid quenching use iced brine (water and salt solution) It is important to remember that rapid cooling can lead to cracking and distortion.

Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering CASE HARDNENING 1.The pack method The component is placed in a box surrounded by a carbon rich material and placed in a furnace at 920 o C. To carburise to a depth of 1 mm the component will need to be left in the furnace for up to 12 hours. After cooling, the component is immersed in a bath of molten salt at 780 °C. The component remains immersed for a half an hour and it is then quenched in water.

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering CASE HARDNENING 2.Salt bath carburising The molten salt contains a mixture of sodium cyanide, sodium carbonate and sodium chloride. The component is placed in the salt bath at 900 °C for one hour. This gives a thin carbon case and not too much grain growth. The component is then quenched in water to harden the surface. 3.Gas carburising Gas carburising is carried out in a special furnace. The carburising agent is a carbon- rich gas circulating in the furnace chamber. This is a faster method of carburising than the pack method and greater control over the process is possible.

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering CASE HARDNENING Nitriding Heating in ammonia gas produces nitrides on surface. 500 °C, <100 hours depending on the case depth required. A nitride is an ultra hard particle Carbonitriding Carbonitriding is carried out in gas atmosphere in a special furnace. Three Steps: 1.Pre-heating: gas atmosphere (propane (C 3 H 8 ), butane (C 4 H 10 ), ammonia (NH 3 )) 2.Quenching 3.Heat treating: low temperature tempering ( ˚C) Case depth of 0.01 mm. Lower temperature than carburizing, higher than nitriding.

HARDNENING Induction & Flame Hardening

HARDNENING Induction Heat & Quench

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering QUENCHING

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering AGE HARDNENING Following quenching from high temperature, an aluminium alloy is often allowed to stand at room temperature. Over a period of a few days the material increased in hardness. This phenomenon is known as age hardening. Ferrous and non-ferrous metals can be age hardened. Duralumin, an aluminium alloy containing about 4% copper, can be age hardened. It is used in the space industry because of its lightweight and high strength.