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ADAMSON UNIVERSITY

COLLEGE OF ENGINEERING

DEPARTMENT OF ELECTRONICS ENGINEERING

FUNDAMENTALS OF MATERIALS SCIENCE & ENGINEERING

Topic Phase Diagrams for Metallic Systems

Course Code ECE409

Section/Schedule 59052/MWF/10-11am

Group No. 9

Submitted by Delos Santos, Jesi V. & Cabatac, Mark Tristan Angelo M.

Submitted to Engr. Rosalie De Ocampo

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INTRODUCTION

Alloy Phase Diagrams are useful to metallurgists, materials engineers, and materials

scientists in four major areas: (1) development of new alloys for specific applications, (2)

fabrication of alloys into useful configurations, (3) design and control of heat treatment

procedures for specific alloys (to produce the required mechanical, physical, and chemical

properties), and (4) solving problems from the performance of specific alloys in commercial

applications, that improves product predictability. Explicitly seen, using the phase diagrams

allows research, development, and production to be done more efficiently and cost

effectively.In addition, data from phase diagrams is essential in the design and development of

alloys. More so, it is reasonably accessible for binary systems.

Definitions and Basic Concepts

Component: Pure metal or compound (e.g., Cu, Zn in Cu-Zn alloy, sugar, water)

Solvent: Host or major component in solution

Solute: Dissolved, minor component in solution

System: Set of possible alloys from same component (e.g., iron-carbon system.)

Solubility Limit: Maximum solute concentration that can be dissolved at a given

temperature

Phase: Part with homogeneous physical and chemical characteristics

Phase Diagrams: Show the relationships between the various phases that appear within

the system under equilibrium conditions to be able to record and

visualize the results of studying the effects of state variables on a system

Binary Diagrams: Are composed of two components [(e.g, two metals - Cu and Ni), or a

metal and a compound (Fe and Fe3C), or two compounds (Al2O3 and

Si2O3)]. Usually they show variations in temperature and composition

only. Additionally, they consist only one liquid phase.

Isomorphous Sys.: Show one complete liquid and solid solubility

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DISCUSSION

Phase diagram, also known as equilibrium or constitutional diagram, depicts the

existence of different phases of a system under equilibrium.

Equilibrium phase diagrams represent the relationships between temperature and thecompositions and the quantities of phases at equilibrium. In general practice, it is sufficient to

consider only solid and liquid phases, thus pressure is assumed to be constant (1 atm.) in most

applications.

A phase diagram is a collection of solubility limit curves. The phase fields in equilibrium

diagrams depend on the particular systems being depicted. Set of solubility curves that

represents locus of temperatures above which all compositions are liquid are called liquidus,

while solidus represents set of solubility curves that denotes the locus of temperatures below

which all compositions are solid. Every phase diagram for two or more components must show

a liquidus and a solidus, and an intervening freezing range, except for pure system, as melting

of a phase occurs over a range of temperature.

There are certain locations on the phase diagram where the liquidus and solidus meet,

whether the components are metals or nonmetals. For a pure component, a contact point lies

at the edge of the diagram. The liquidus and solidus also meet at the other invariant positions

on the diagram.

For almost all alloy systems, at a specific temperature, a maximum of solute atoms can

dissolve in solvent phase to form a solid solution, which is known as solubility limit. Generally,

solubility limit changes with temperature. If solute available is more than the solubility limit, it

may lead to formation of either a solid solution or compound. Phase equilibrium is the set of

conditions where more than one phase may exist. It can be reflected by constancy with time in

the phase characteristics of a system. In most metallurgical and materials systems, phase

equilibrium involves just solid phases. However, the state of equilibrium is never completely

achieved due to very slow rate of approach of equilibrium in solid systems, that leads to non-

equilibrium or meta-stable state, which may persist indefinitely and has more practical

significance than equilibrium phases. An equilibrium state of solid system can be reflected in

terms of characteristics of the microstructure, phases present and their compositions, relative

phase amounts and their spatial arrangement or distribution.

Phase diagrams are classified based on the number of components in the system. Single

component systems have unary diagrams, two-component systems have binary diagrams, and

three-component systems have ternary diagrams, and so on. Having more than two

components in the system makes the diagrams to be complicated and difficult to represent.

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Phase Rule

The Phase Rule, introduced by J. Willard Gibbs in 1876, relates the physical stateof a

mixture to the number of constituents in the system and to its conditions. Gibbs was also the

first one who each homogeneous region in a system by the term "phase." When pressure and

temperature are the state variables, the rule can be written as follows:

P + F=C + 2

where f is the number of independent variables(called degrees of freedom), c is the

number ofcomponents, and p is the number of stable phasesin the system.

Binary Eutectic Systems

Binary Eutectic Systems obtain phases present, concentration of phases and theirfraction (%).

Solvus line is the limit of solubility, Eutectic or invariant point. Liquid and two solid

phases exist in equilibrium at the eutectic composition and at the eutectic temperature.

*Note: the melting point of the eutectic alloy is lower than that of the components. At most two

phases can be in equilibrium within a phase field. Two-phase regions separate single-phase

regions.

Some sets of invariant reactions that may occur in binary systems are:

1.Eutectic Reaction

a liquid transforms into two solid phases

1a. Eutectoid Reactionthe solid state-analog of eutectic reaction wherein one

solid phase with eutectoid composition turns into two different solid phases

2. Peritectic Reactiona solid phase reacts with a liquid phase to produce a new solid

phase

2a.Perictoid Reactiontwo solid phases react to form a new solid phase

*Note: peritectic and peritectoid reactions do not give rise to micro-constituents as the eutectic

and eutectoid reactions do

3. Monotectic Reactiona liquid phase transforms into a solid phase and a liquid phase

of different composition (wherein two liquids are immiscible e.g,. oil and water).

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The IronIron Carbide (FeFe3C) Phase Diagram

Iron-carbon system is useful in many aspects such as (1) steels constitute greatest

amount of metallic materials used by man and (2) solid state transformations that occur in

steels are varied and interesting.

This is one of the most important alloys for structural applications. The diagram FeC is

simplified at low carbon concentrations by assuming it is the FeFe3C diagram. Concentrations

are usually given in weight percent. The possible phases are:

a-ferrite (BCC) Fe-C solution

g-austenite (FCC) Fe-C solution

d-ferrite (BCC) Fe-C solution

liquid Fe-C solution

Fe3C (iron carbide) or cementite. An intermetallic compound.

The maximum solubility of C in a- ferrite is 0.022 wt%. D-ferrite is only stable at high

temperatures. Austenite has a maximum C concentration of 2.14 wt %. It is not stable below

the eutectic temperature (727 C) unless cooled rapidly. Cementite is metastable, decomposing

into a-Fe and C when heated for several years between 650 and 770 C.

*Note: Ferrite is soft and ductile; Cementite is hard and brittle. Thus, combining these two

phases in solution, an alloy can be obtained with intermediate properties.

STATEMENT OF THE PROBLEM

The equilibrium state that can be obtained in combining two elements.

Invariant reactions that may occur in binary systems and the phases of matter produced

in each reaction.

METHODOLOGY

Data for this report were gathered from 9 September to 15 September 2014. The topic

of Phase Diagram for Metallic Systems was researched online and by the in-depth study of theBook Materials Science and Engineering, and then a series of reading was conducted to collect

data for the given topic. Analysis of the data revealed the interesting part of the topic and the

compilation was made. This report is supported by a PowerPoint presentation and a video for

visual purposes.

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CONCLUSION

In conclusion, the phase diagram is essential to understanding the materials, its

structure, composition, and specially the phase changes. On metals, it is very important to

familiarize the phase diagram so that we can determine the amount of heat and pressure to

make a metal or alloys to change its phase. A phase diagram will tell you what phase or state a

binary alloy will be in at any given temperature or composition. One thing to remember is that

phases do not necessarily mean gas, liquid, solid, vapor. in the case of the Fe-C example, it can

be seen that iron and carbon can have several different solid states at the same temperature

depending on the composition. Also, phase diagrams literally shows how much heat and

pressure a metal or alloy can withstand before changing its phase since metals are used as

strongholds materials. This is commonly studied for enhancing the durability of metallic

materials.