Single solid phase binary alloy -1
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Single solid phase binary alloy -1 Phase rule predicts that solid lines on one component systems become areas on a binary. Results in region where solid and liquid are in equilibrium, instead of a line.
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Single solid phase binary alloy -1. Phase rule predicts that solid lines on one component systems become areas on a binary. Results in region where solid and liquid are in equilibrium, instead of a line. Single solid phase binary alloy - 2. - PowerPoint PPT Presentation
Transcript of Single solid phase binary alloy -1
Single solid phase binary alloy -1
Phase rule predicts that solid lines on one component systems become areas on a binary.
Results in region where solid and liquid are in equilibrium, instead of a line.
Single solid phase binary alloy - 2
As cool from the melt and cross the liquidus line, crystals begin to form and then grow as cooling proceeds.
The composition of the crystal follows the solidus line, ideally, and the composition of all crystals adjusts continuously, not just simply the crystal being formed at a particular temperature.
Single solid phase binary alloy - 3
In reality the diffusion rate of atoms inside a crystal is very slow.
The composition of the crystals is unable to change at the rate indicated by the diagram.
The composition of each crystal varies from the center outwards - known as coring
BINARY ALLOY WITH EUTECTIC
Solubility limits
and are the solid solutions
Solubility limits are given by triple points
Eutectic is given by central triple point
FIRST EXAMPLE
Line that crosses into solid solution phase
Cross liquidus - crystals begin to form
Cross into single phase region - crystals fill material
Cross into two phase region - crystals from inside crystals
Precipitation hardening
SECOND EXAMPLE
Eutectic Alloy
Alloy has the eutectic composition
Converts directly from liquid to two solid phases
THIRD EXAMPLE
Complex Phases Cross liquidus
crystals begin
Grow as T drops
Cross eutectic line
Remaining liquid converts into + forming eutectic grains
Final state consists of grains and eutectic grains
Cu - Ag System
Same general shape as Pb-Sn
Melting points different
Solubility limits different
Eutectic different
General features of behavior are the same
COMPOUND FORMATIONForms Mg2Pb
Treat as two phase diagrams fused together
One is phase diagram of Mg with Mg2Pb
Other is phase diagram of Pb with Mg2Pb
Vertical line means Mg2Pb does not form solid solutions
IRON CARBON DIAGRAM
Phase diagram of Fe and Fe3C
Would be a simple eutectic if not for fcc - bcc change
Left hand axis shows changes in Fe crystal structure
At high T bcc - fcc transition
At lower T fcc - bcc transition
Generates two additional horizontal lines
Higher one is called peritectic
Lower one is called eutectoid
THE EUTECTOID REGION
HYPO-EUTECTOID
STEEL
Carbon content less than eutectoid composition
Soft steel used for plates and pressing operations
HYPER – EUTECTOID STEEL
Carbon content more than eutectoid composition
Used for machine tools, knives, etc
TIME-TEMPERATURE-TRANSFORMATION DIAGRAM
FOR EUTECTOID STEEL
MARTENSITE – not on phase diagram
Bct crystal structure
“stretched” bcc
Hardest of the phases
Hardness increases with carbon content
HARDNESS OF PEARLITE DEPENDS ON MICROSTRUCTURE
HEAT TREATMENTS
(a) Conventional
(b) Martempering
(c) austempering
