Metals and Alloys Flashcards
What effect does rapid cooling have on metals and alloys?
Forms more nuclei per unit volume and decreases the grain size
What does ductility and malleability mean?
The ability of atomic centers to slide against each other into new positions within the same crystal lattice
How does finer grain size affect metals and alloys?
Can raise the yield strength, increase the ductility, and raise the ultimate strength
Why would a material fracture?
B/c a crack opens up on a grain boundary
When is a fracture more likely to occur in metals and alloys?
In large grain metals when the planes can not be slipped into the adjacent grains
Changes of what properties with grain size are related to plastic deformation and fracture?
Yield strength, ductility, and ultimate strength
What is the mechanism of plastic deformation called?
Dislocation motion
What are dislocations?
Flaws in the crystal that allows atomic centers to slide past each other one plane at a time instead of forcing all planes to be overcome simultaneously
What is cold working (wrought)?
Causing plastic deformations by hammering, drawing, cold forging, cold rolling or bending.
What does cold working produce?
Many dislocations that can not slip easily thru each other as the lattice becomes more distorted
What happens to grains in cold working?
They are broken down and entangled in each other.
What kind of metal has a melting range? Melting point?
Metal alloy.
Pure metal has a melting point
The areas between a liquid and a solid alloy on graph is referred to as what?
Melting range
What are the three things that you can get from an alloy that is heated and cooled down?
Soluble - solid solution
Not soluble - eutectic
Sometimes the elements react to form an intermetallic compoung
When metals are mixed together in a molten state and cooled - what does the result depend on?
The solubility of the metals in each other
What are solid solutions?
Metals such as Au and Cu - are soluble in each other at any combination
What happens to solid solutions when cooled?
The form a solid with random distribution of Au and Cu atoms in the F-C cubic array
What is an ordered solution?
At a certain % of Au they form an ordered solution - Au and Cu occupy specific positions in the F-C cubic
What do ordered solutions impart?
Impart higher hardness and strength to alloys
What are eutectic alloys?
Occurs when 2 metals are soluble as liquids but nearly insoluble as solids
What does a pure eutectic have?
A melting point (not a range) that is lower than either of the pure components
For a material to be classified as a noble alloy, what is the lower limit of % by weight of noble metal content?
25% by weight of noble metal
What is a carat?
Refers only to the gold content of the alloy. Represents 1/24 of the the whole. 24 carat (k) = pure gold
What is fineness?
Refers only to the gold content of the alloy. Represents the # of parts of gold in each 1000 parts of the alloy.
What is the fineness of 24k gold? 18k gold?
100% gold = 1000 fineness
75% gold = 750 fineness
How does adding 10% of Cu to Au affect the tensile strength? How does it affect the BHN (Brinell Hardness Number)?
Increases it from 105 to 395.
Increases BHN from 28 to 85
How does an ordered solution affect hardness, elongation, and yield strength?
Increases hardness and yield strength but lowers elongation
What is the composition of high noble metal?
Noble metal at least 60% and gold content at least 40%
What is the composition of NOBLE metal?
Noble metal at least 25% and no gold stipulation
What is the composition of predominantly base metal?
Noble metal less than 25%
What do fine grain produce?
Greater tensile strength and greater elongation. As well as, uniformity from casting to casting
