15
Precious metal alloys
Figure 15.1 Face-centered tetragonal superlattice of AuCu.
Box 15.1 Requirements of casting alloys
Castability
Solderability
Accuracy of fit
Mechanical strength
Corrosion resistance
Box 15.2 Noble metals
Gold
Platinum
Palladium
Iridium
Rhodium
Osmium
Ruthenium
Table 15.1 Effect of hardening on gold alloys
| As-cast | Hardened | |
|---|---|---|
| Proportional limit (MPa) | 359 | 587 |
| Tensile strength (MPa) | 483 | 794 |
| Elastic modulus (GPa) | 97 | 100 |
| Elongation (%) | 15 | 5 |
| Hardness (BHN) | 130 | 220 |
Table 15.2 Dental gold casting alloys
Table 15.3 Average properties of dental casting alloys
Table 15.4 Average properties of low-gold casting alloys
Table 15.5 Casting conditions for low-gold alloys
Table 15.6 Heat treatments for gold alloys
| Hardening | Softening |
|---|---|
| Heat at 450° for 2 minutes Slow cool to 250° over 30 minutes Water quench to room temperature or Heat at 350° for 10–15 minutes Water quench to room temperature |
Heat to 700° Water quench to room temperature |
Table 15.7 Casting defects
| Problem | Possible cause |
|---|
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