Gold, CoCr alloys

Question 1

What are the components of gold alloys and their functions?

Answer 1

1. Gold: Imparts corrosion resistance, increases hardness (heat treatment with copper), increases ductility
2. Copper: Increases hardness (with gold), increases ductility, decreases tarnish resistance, decreases melting temperature
3. Silver: Counteracts orange colour of copper, increases strength and hardness, decreases melting temperature
4. Platinum: Increases melting temperature, increases hardness, increases tarnish and corrosion resistance
5. Palladium: Increases melting temperature, increases hardness together with zinc
6. Zinc: Oxide scavenger, improves castability, increases hardness together with Pd
7. Indium: Oxide scavenger, improves castability

Question 2

What are the components of CoCr and their functions?

Answer 2

1. Chromium: Increases tarnish resistance, solid solution hardener, decreases castability if >30%
2. Cobalt: Increases strength, hardness and MOE
3. Nickel: Increases ductility, decreases strength, hardness and MOE and fusion temperature
4. Carbon: Imparts strength, hardness and ductility but in excess (>0.4%) results in brittleness
5. Manganese: Deoxidiser, decreases brittleness, increases ductility
6. Silicone: Deoxidiser, decreases brittleness, increases ductility
7. Boron: Deoxidiser, increases hardness, decreases ductility
8. Beryllium: Decreases fusion temperature, increases hardness and improves castability
9. Molybdenum: Solid solution hardener
10. Aluminium: Solid solution hardener
11. Iron: Solid solution hardener
12. Copper: Solid solution hardener

Question 3

What are the general trends of these properties of gold alloys:

1. Gold content
2. Hardness
3. Proportional limit
4. MOE
5. Elongation (Ductility)
6. Ultimate tensile strength
7. Melting ranges

Answer 3

1. Gold content: Decreases from type 1 to 4
2. Hardness: Increases from type 1 to 4 (hardness increases with decreasing gold content)
3. Proportional limit: Increases from type 1 to 4
4. MOE: Increases from type 1 to 4
5. Elongation (Ductility): Decreases from type 1 to 4
6. Ultimate tensile strength: Increases from type 1 to 4
7. Melting ranges: Decreases from type 1 to 4