合金铸造基础(有色金属铸造).ppt

BSE METAL CASATING ALLOYS
Base metal alloys contain no gold,
silver, platinum or palladium. The
two monly used base
metal alloys in dentistry are:
1. The nickel-chromium (Ni/Cr) alloys which monly used for crown and bridge casting.
The cobalt-chromium (Co/Cr) alloys which monly used for partial denture framework castings.
3. Titanium and titanium alloys.
Cobalt-Chromium Alloys (stellites)
Composition: These alloys
generally contain
35-65% cobalt.
20-35% chromiun.
0-30% nickel.
Trace quantities of other elements such as molybdenum, silicon, beryllium, boron and carbon.
Cobalt and nickel are hard, strong metals. The main purpose of the chromium is to further harden the alloy by solution hardening and also to impart corrosion resistance by the passivating effect
The minor elements are generally added
to improve casting and handling
characteristics and modify mechanical
properties.
Carbon affects the hardness, strength and
ductility of the alloys.
The exact concentration of carbon is one
of the major factors controlling alloy properties.
Nickel-Chromium Alloys
Composition:
70-80% nickel.
10-25% chromium.
Small quantities of other elements as described for the Co/Cr alloys.
Manipulation of base metal casting alloys
The fusion temperatures of the Ni/Cr and Co/Cr alloys vary position but are generally in the range 1200-1500ºC.
Investment moulds for base metal alloys must be capable of maintaining their integrity at the high casting temperatures used.
The density values of base metal alloys are approximately half those of the casting gold alloys.
The greatest expense involved in producing a Co/Cr dental casting is in the time required for trimming and polishing.
Base metal alloys, and particularly the Co/Cr type, are very hard and consequently difficult to polish.
Properties
The Co/Cr and Ni/Cr alloys are very hard materials.
Co/Cr and Ni/Cr alloys have very good
corrosion resistance by virtue of the
passivating effect.
Co/Cr al