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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 ... – PowerPoint PPT presentation

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Date added: 25 September 2019
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Title: Single solid phase binary alloy -1


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.
2
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.
3
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
4
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
5
FIRST EXAMPLE Line that crosses into solid
solution phase
Cross liquidus - a crystals begin to form Cross
into single phase region - a crystals fill
material Cross into two phase region - b crystals
from inside a crystals Precipitation hardening
6
SECOND EXAMPLE Eutectic Alloy
Alloy has the eutectic composition Converts
directly from liquid to two solid phases
7
THIRD EXAMPLE Complex Phases
Cross liquidus a crystals begin Grow as T
drops Cross eutectic line Remaining liquid
converts into a b forming eutectic grains Final
state consists of a grains and eutectic grains
8
Cu - Ag System
Same general shape as Pb-Sn Melting points
different Solubility limits different Eutectic
different General features of behavior are the
same
9
COMPOUND FORMATION
Forms 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
10
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
11
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12
THE EUTECTOID REGION
13
HYPO-EUTECTOID STEEL Carbon content less than
eutectoid composition Soft steel used for plates
and pressing operations
14
HYPER EUTECTOID STEEL Carbon content more than
eutectoid composition Used for machine tools,
knives, etc
15
TIME-TEMPERATURE-TRANSFORMATION DIAGRAM FOR
EUTECTOID STEEL
16
MARTENSITE not on phase diagram
Bct crystal structure stretched bcc
Hardest of the phases Hardness increases with
carbon content
17
HARDNESS OF PEARLITE DEPENDS ON MICROSTRUCTURE
18
  • HEAT TREATMENTS
  • Conventional
  • Martempering
  • austempering
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