4Metals&Alloys Flashcards
Rapid cooling forms more nuclei per unit volume and _______ the grain size.
decreases
What type of grained alloys are desirable in dentistry?
Fine Grained Alloys!!
What are the two properties that describe a metal’s ability of atomic centers to slide against each other into new positions within the same crystal lattice?
Ductility and Malleability
What does the Finer Grain Size do to Yield Strength? Ductility? and the Ultimate Strength? What are the changes in these properties RELATED TO??
INCREASES Yield Strength….INCREASES ductility….Increases the Ultimate Strength…..THESE changes are RELATED to PLASTIC DEFORMATION and FRACTURE (think about the graph!)
On the other hand, a material will fracture because a crack opens up on a grain boundary. This is more likely to occur in _____ _____ metals when the planes can not be slipped into the adjacent grains.
LARGE GRAIN
What is the name for the mechanism of plastic deformation?
Dislocation Motion
What is another name for COLD working a metal?
Wrought
What is the term for causing plastic deformation by hammering, drawing, cold forging, cold rolling or bending that produces many dislocations that can not slip easily
through each other as the lattice becomes more distorted and grains are broken down and entangled in each other.
Cold Working/Wrought
What is the area on a phase diagram underneath the liquid, but above the solid?
The Melting RANGE
What is the result of cooling a soluble group of metals?
A solid solution
What is the result of cooling a NON soluble group of metals?
A EUTECTIC solution
What is the 3rd outcome of mixing metals if it is not solid or eutectic?
an intermetallic compound
What was our example of 2 metals that are soluble and thus form a solid solution?
Au and Cu
IN MIXING Cu and Au: At a certain % of Au they form an ______ ______ – Au and Cu occupy specific positions in the F-C cubic. _______ _______ impart higher hardness and strength to alloys.
Ordered Solution
_______ _______ impart higher hardness and strength to alloys.
Ordered Solutions
What happens when 2 metals are soluble as liquids, but NEARLY INSOLUBLE as solids?
A Eutectic Alloy!
What about the phase diagram is very unique to a Eutectic Alloy?
It has a define MELTING POINT
What is an everyday example of a eutectic alloy in dentistry?
AMALGAM!
What is the ADA limit for amount of noble metals for an alloy to be considered a noble alloy? What would it be considered if it fell below that minimum?
25% or more of noble metals to be a noble alloy…Lower is considered a Base Metal
ASIDE: what is a carat (k)?
1/24th of the whole (24k=pure gold)
What does adding 10% Cu do to the tensile strength and the BHN of Au?
Adding 10% Cu TRIPLES both tensile strength and BHN!
What does an ordered solution do for the Hardness, Elongation, and Yield strength of an alloy?
Ordered solution increases hardness, decreases elongation, and increases yield strength
What are the two stipulations for High Noble metals?
Noble Metal of >60% and At least 40% Gold Content!!
What is the requirement for Noble metal?
Noble metals >25% (NO gold stipulation)
