PHASE DIAGRAMS. IE-114 Materials Science and General Chemistry Lecture-10

Ebat: px

Şu sayfadan göstermeyi başlat:

Download "PHASE DIAGRAMS. IE-114 Materials Science and General Chemistry Lecture-10"

Emine Aksu
6 yıl önce
İzleme sayısı:

1 PHASE DIAGRAMS IE-114 Materials Science and General Chemistry Lecture-10

2 Importance of Phase Diagrams There is a strong correlation between microstructure and mechanical properties. Phase diagrams provides information about: - The development of microstructure during heating or cooling can be understood from the phase diagrams. - Melting, casting, crystallization, etc.

Question: What is the solubility limit at 20 o C? Answer: 65wt% sugar.

3 Phase-Diagram of Water-Sugar System Solubility Limit At some specific temperatures, there is a maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution; this is called solubility limit. Question: What is the solubility limit at 20 o C? Answer: 65wt% sugar. If C o < 65wt% syrup If C o > 65wt% syrup + sugar. Solubility limit increases with T: T = 20 o C, solubility limit = 65 wt% sugar. T = 100 o C, solubility limit = 80 wt% sugar.

substitutional or interstitial positions in the solvent lattice (,, etc,.

4 Component: Components are pure metals/or compounds of which alloy is composed. e.g. Brass (Cu-Zn) ; components are Cu and Zn, Fe and C in carbon steel, H 2 O and NaCl in salted water Solid Solution: A solid solution consists of solute atoms, which occupy either substitutional or interstitial positions in the solvent lattice (,, etc,..) Phase: Homogenous portion of a system that has uniform physical and chemical characteristics Aluminum-Copper Alloy Every pure material is considered to be a phase; so also is every solid, liquid and gaseous solution For example if a substance can exist in two or more polymorphic forms (BCC and FCC) each of these structures is a separate phase because their physical properties are different.

5 Homogeneous system: A single phase system Mixture or heterogeneous system: System of two or more phases. Most of the metallic alloys,ceramics, polymeric and composite systems are heterogeneous. Phase Equilibria: A system is said to be at equilibrium when the free energy, which is the internal energy and randomness of the atoms, is at minimum under some specified combination of temperature, pressure and composition.

6 Equilibrium Phase Diagrams Phase diagram is also called equilibrium or constitutional diagram. These diagrams defines the relationship between the temperature and compositions or quantities of phases at equilibrium. External pressure could also be another parameter affecting the phase distribution but it remains constant at 1 atm in most of the applications. - Isomorphous Binary Phase Diagrams - Eutectic Binary Phase Diagrams

Example: Cu-Ni There are 2 phases : - L (liquid) - α-solid solution There are 3 phase fields :

7 1) Isomorphous Binary Systems: Binary systems are composed of two components and they are isomorphous since there is a complete solubility of liquids and solids. Example: Cu-Ni There are 2 phases : - L (liquid) - α-solid solution There are 3 phase fields : liquid, L+α, α Liquidus line:the line separating L and α+l phases. Solidus line: The line separating α+l and α phases is called. Cu wt.% Ni Ni

Number and types of phases If we know T and C o, then we know the number and types of phases present.

8 From the phase diagrams we can learn the followings: -Number and types of phases that are present at different temperatures for a fixed composition -Composition of the phases -Fractions of the phases 1) Number and types of phases If we know T and C o, then we know the number and types of phases present. Examples: 1) Cu-35Ni Alloy at 1250 o C (Co = 35 wt.%ni) 2 phases: α+l 2)Cu-60Ni Alloy at 1100 o C (Co = 60 wt.%ni) 1 phase: α

9 2) Composition of phases: If we know T and C o, then we know the composition of each phase. For Cu-35Ni Alloy (C o =35wt%Ni) at T A : -Phases: 1(only Liquid) -Composition of the alloy: C L = C o (=35 wt%ni, 65 wt%cu) at T B : -Phases: 2 (Liquid +α) -Composition of the alloy: C L = C liquidus (32wt%Ni, 68 wt% Cu) C α = C solidus (43wt%Ni, 57wt%Cu) at T D : -Phases: 1 (only α) -Composition of the alloy: C α =C o (35 wt%ni, 65 wt%cu)

$3) Weight fractions (or percentage) of$ the amount of each phase (given in wt%).

10 3) Weight fractions (or percentage) of phases: If we know T and C o, then we know the amount of each phase (given in wt%). W L S R S x x wt % W R R S x100 = 27wt%

11 Microstructural development during cooling a Cu-Ni alloy Binary System (2 components) Isomorphous i.e., complete solubility of one component in another; phase field extends from 0 to 100wt% Ni.

12 Binary Eutectic Sistemlerde, verilen herhangi bir sıcaklık ve kompozisyonda oluşacak mikroyapıların kompozisyonlarını ve miktarlarını hesaplayabiliyor olmalısınız. Eutectic reaction: Liquid (71.9%) heating (8%Ag) + (91.2% Ag) Cooling Melting point of pure Cu Eutectic composition: 71.9wt%Ag, 28,1wt%Cu Eutectic temperature: 779 o C There are three phases : Liquid, SOLIDUS LIQUIDUS and Binary Eutectic Systems Melting point of pure Ag Max. Solubility of Ag in Cu 8 wt% Ag at C SOLVUS max. solubility of Cu in Ag (8.8 wt%) Cu Ag Eutectic line. This line shows the minimum temperature for the liquid phase existence.

13 For a 40wt%Sn-60wt%Pb alloy at 150 o C, find: 1) the phases present 2) the compositions of the phases

For a 40wt%Sn-60wt%Pb alloy at 150 o C, find: --the phases

89wt%Cu C = 99wt%Sn, 1wt%Cu --the relative amounts of each

herhangi bir sıcaklık ve kompozisyonda oluşacak

14 For a 40wt%Sn-60wt%Pb alloy at 150 o C, find: --the phases present: + --the compositions of the phases: C = 11wt%Sn, 89wt%Cu C = 99wt%Sn, 1wt%Cu --the relative amounts of each phase: x100 x100 Bu tip bir faz diyagramı üzerinde, verilen herhangi bir sıcaklık ve kompozisyonda oluşacak mikroyapıların kompozisyonlarını ve miktarlarını hesaplayabiliyor olmalısınız.

15 Microstructural Development During Cooling of Pb-Sn Alloys Sınav öncesinde bu iki şekli çizebiliyor, oluşan mikroyapıların çeşit ve miktarlarını karşılaştırıp yorum yapabiliyor olmanız lazım.

16 18.3wt%Sn < C o < 61.9wt%Sn Room temperature microstructure: crystals and a eutectic microstructure Bu tip bir faz diyagramı üzerinde, verilen herhangi bir sıcaklık ve kompozisyonda oluşacak mikroyapıların kompozisyonlarını ve miktarlarını hesaplayabiliyor olmalısınız.

17 Cooling of an Alloy Having Eutectic Composition The alloy having eutectic composition is called eutectic alloy alternating layers of and crystals.

18 Hypoeutectic and Hypereutectic Alloy

19 Intermetallic Compounds For some alloy systems, discrete intermediate compounds rather than solid solutions may be observed in phase diagrams. For example; Mg-Pb system. These are called intermetallic compounds. The compound Mg 2 Pb is shown as a vertical line on the diagram rather than a phase region since it exists precisely at the composition defined.

20 Eutectoid and Peritectic Reactions Consider Cu-Zn system. Eutectoid reaction: C and 74 wt% Zn-26 wt% Cu cooling heating γ + Peritectic reaction: C and 78.6 wt% Zn-21.4 wt% Cu + L cooling heating

Congruent and Incongruent Phase Transformation Phase transformations can be classified according to whether or not there is any change in composition.

21 Congruent and Incongruent Phase Transformation Phase transformations can be classified according to whether or not there is any change in composition. Phase transformations in which there is no changes in composition are called as congruent transformations. The opposite is incongruent transformation. Allotropic transformations are congruent as well as melting pure metals. Eutectic, eutectoid or melting alloy systems are incongruent transformations.

22 Iron Carbon System This is the most important system in manufacturing since primary structural materials are essentially Fe-C alloys, such as, steel and cast iron. MT1, MT2 ve Final sınav öncesi sayfa arasını yeniden gözden geçirmenizi tavsiye ederim. STEEL IS an ALLOY OF;

23 Iron-Iron Carbide Equilibrium Phase Diagram MT1, MT2 ve Final sınav öncesi sayfa arasını yeniden gözden geçirmenizi tavsiye ederim. Phases and phase mixtures present in iron alloys; Ferrite (α) Cementite (Fe 3 C) Pearlite (ferrite + cementite) Austenite (γ) -ferrite Ledeburite (austenite + cementite)

24 Definition and Properties of Phases 1) Ferrite : -iron, Solid Solution, max. Carbon solubility 0.022%wt. at 727 o C BCC structure, SOFT 2) Cementite : Iron carbide(fe 3 C), contains 6.67% wt. C Orthorhombic structure, HARD and BRITTLE MT1, MT2 ve Final sınav öncesi sayfa arasını yeniden gözden geçirmenizi tavsiye ederim. 3) Pearlite : Phase mixture (ferrite+cementite), Lamellar structure, contains ~0.8% wt. C Produced from austenite decomposition 4) Austenite : -iron, Solid solution, stable at higher temperatures (>727 o C) Max. Carbon solubility is 2.14%wt. at 1147 o C, FCC structure HIGH TOUGHNESS 5) Ledeburite: Eutectic phase mixture(austenite+fe 3 C), seen in cast irons Contains 4.3 %wt. Carbon, forms at 1147 o C 6) -ferrite : Solid solution, max. carbon solubility is 0.1%wt. At 1493 o C

25 Invariant reactions in Fe-Fe 3 C Phase diagram 1) At 1493 o C, 0.18 %wt C (PERITECTIC REACTION) Liquid(l, 0.5%C)+ -ferrite(,0.1%c) cooling heating Austenite(, 0.18%C) 2) At 1147 o C, 4.30 %wt C (EUTECTIC REACTION) Liquid(l, 4.30 %C) cooling heating Austenite(, 2.14 %C) + Cementite(Fe 3 C,6.67%C) LEDEBURITE 3) At 727 o C, 0.77 %wt C (EUTECTOID REACTION) Austenite(, 0.77 %C) cooling heating Ferrite(, %C) + Cementite(Fe 3 C,6.67%C) PEARLITE MT1, MT2 ve Final sınav öncesi sayfa arasını yeniden gözden geçirmenizi tavsiye ederim.

26 Hypoeutectoid Steel Eutectoid Steel Hypereutectoid Steel STEELS CAST IRONS

27 Eutectoid Steel

28 Hypoeutectoid Steel

29 Hypereutectoid Steel

30 Effect of Carbon on Mechanical Properties MT1, MT2 ve Final sınav öncesi sayfa arasını yeniden gözden geçirmenizi tavsiye ederim.

31 EXAMPLE1: For an annealed (cooled in equilibrium conditions after austenitization) hypoeutectoid steel; 1) Determine the composition of the steel (C wt.%) if quantitative metallographic analyses revealed 22% secondary ferrite (assume solubility of carbon in ferrite is nil) 2) Calculate the weight fraction ratio of secondary ferrite and cementite present in pearlite. 3) Determine the total amount of carbon dissolved in secondary ferrite at room temperature for the corresponding steel if the total weight of the steel part in kgs is equal to 80.(Room temperature solubility of carbon in ferrite is 0.008%) EXAMPLE2: The mass fraction of eutectoid cementite in iron carbon alloy is On the basis of this information, is it possible to determine the composition of the alloy? If so, what is its composition? MT1, MT2 ve Final sınav öncesi sayfa arasını yeniden gözden geçirmenizi tavsiye ederim.

Benzer belgeler

BMM 205 Malzeme Biliminin Temelleri

BMM 205 Malzeme Biliminin Temelleri Faz Diyagramları Dr. Ersin Emre Ören Biyomedikal Mühendisliği Bölümü Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü TOBB Ekonomi ve Teknoloji Üniversitesi Ankara