alloys

• • an alloy is a mixture of two or more elements
  • at least one elemets is a metal
• • pure metals are too soft for use
  • so, they are mixed with other metals to make them harder
  • so an alloy is formed
• • pure iron is very soft
  • tungsten is added to iron to make steel
  • mild steel is made of carbon and iron, and is easy to bend and pull into wires
  • tool steel is made of tungsten and iron, and is hard and heated very high
  • stainless steel is chromium and iron, as is hard and does not rust easily
• • when a metal is solid, atoms arranged in layers
  • when force is applied, layers may slide
  • greater force needed, harder the metal
  • pure metals need small force to make layers slide
  • so, they are soft
• • alloys have atoms of different sizes
  • the different atom sizes of element distort layers of atoms in pure metal
  • so, greater force needed for layers to slide over each other
  • so, alloys are harder than pure metals