Casting Alloys, Wrought Alloys, and Solders PDF

casting alloys, wrought alloys and solders 1) Alloys may be : 2) casting alloys for cast restorations (casting) 3) ceramic bonding alloys 4) Wrought alloys 5) solders Introduction Gold was used for thousands of years :easy to melt ,purity and manipulation Gold foil weld...

casting alloys, wrought alloys and solders 1) Alloys may be : 2) casting alloys for cast restorations (casting) 3) ceramic bonding alloys 4) Wrought alloys 5) solders Introduction Gold was used for thousands of years :easy to melt ,purity and manipulation Gold foil weld in a cavity FUNDAMENTAL CONCEPTS ABOUT METALS AND ALLOYS Noble Metals, Base Metals, and Nonmetals Fundamental concepts about metals and alloys Noble metals base metals Titanium Ti Gold Au Nickel Ni Palladium Pd Copper Cu Platinum Pt Silver Ag Zinc Zn Base but not bad Silver Gold Excellent corrosion ressistance good malleability ,yellow color and low melting point Pure for direct gold or alloy for casting. carat = 24 X %Gold /100 Palladium High melting point white and harder than gold Corrosion properties like gold Whitens the color of gold 90% gold + 10% palladium = white alloy Platinum High melting point ,harder than Paladium It is not used much since it doesn’t mix with gold. non Noble elements Copper :reddish and hardens the alloy Silver for hardening Zinc low melting and oxidation prevention in trace amounts Nickel ,cobalt ,titanium Iron for porcelain bond Titanium for implant Indium :small grain formation Grains and crystal structure in alloys (light microscope level) Grains are metallic crystals Grain refiners Base metals have large grains  At atomic level (lattice) random ordered Heating to organize lattice position Heat treatment structure hardening Nobel metals Base metals Improves properties Deteriorates properties Important Physical and Mechanical Properties of casting alloys  Melting Range 1400 Base metal alloys LIQUID TEMPERATURE (C) 1100 Melting Completion (Liquidus) Noble alloys LIQUID + SOLID High Noble metals 950 Melting Onset (Solidus) SOLID 25 50 75 100 Melting range is important for: Casting temperature should be higher than liquidus point and determines investments Solidus for soldering Solidus for porcelain firing  Density: g/cm3 Base metals gold Titanium-Based alloys 18g/cm3 4.5g/cm3 Easier casting Difficult to cast More expensive cheap4.5g/cm3 Difficult to cast cheap  Yield strength Mpa, Offset 750 Mpa 0.2% offset Dental alloys yield strength range 260 to 1150 Mpa x x Yield Strength (or Hardness) STRESS Modulus (Stiffness, Slope of Line) STRAIN  Hardness Base metals gold soft(125kg/mm2) hard(380kg/mm2)  Categorizing Casting Alloys Nobel and non Nobel: the sum of Au,Pt,Pd Ex.60%Au,10%Pd,5 % Pt,25%Cu = 75% nobility Gold based or nickel based Ex 75%Au= gold based,60% Nickel=Nickel based white or yellow(not a predictor for composition) Categorizing Casting Alloys  Common Casting Alloys High noble noble Base metals 60% noble 25 % noble High density(13 Moderate density(10 Minor amounts of noble g/cm3) g/cm3) Nickel ,cobalt & titanium Easy to cast Au1064 Strength & hardness Very complex Pt 1772 & Pd1554 ^ higher Difficult to cast liquidus Good corrosion Low density Excellent corrosion Used for all metal or PFM Cheap Used for all metal restorations High strength Cannot be used for Corrosion problems ceramic–alloy Used for crowns bridges melting range is too low removable implants … CERAMIC-BONDING CASTING ALLOYS  Consideration for ceramic bonding alloys PFM,Substructure Thickness of different layers Chemical bond via oxide layer Appropriate melting range 850-1350 C Coefficient of Thermal expansion for the alloy should be about 0.5×10−6/°C greater than ceramic Problems encountered with ceramic bonding alloys Color of oxide :yellow for high noble but dark for base metals Greening (silver) Debonding of ceramic :problem in oxide layer or coefficient of thermal expansion Wrought alloys Wrought alloys: Fibrous sructure Stainless steel Titanium Nickel titanium (Nitinol) Cobalt Chromium Nickel (Elgiloy) PGP (pt,Au,Pd) for clasps. Excessive heat may degrade the fibrous structure  Solders Solders are special alloys used to join other alloys. The alloys to be joined are generally called substrate alloys. Used to: 1) 1- Join an orthodontic wire to a band 2) 2- Join a clasp wire to a partial denture framework 3) 3- Join two units of a fixed partial denture together 4) 4- Add a proximal contact to a crown or repair an occlusal defect in a casting Liquidus of solder is lower than solidus of restorations Laser ,torch or oven Biocompatibility of alloys