CHAPTER9. Phase Diagrams Equilibrium Microstructural Development

Transcription

1 CHAPTER9 Phase Diagrams Equilibrium Microstructural Development The microstructure of a slowly cooled eutectic soft solder ( 38 wt%pb wt % Sn) consists of a lamellar structure of tin-rich solid solution (white) and lead-rich solid solution (dark), 375X. (From ASM Handbook, Vol. 3: Alloy Phase Diagrams, ASM International, Materials Park, Ohio, 1992.)

2 Figure 9-1 Single-phase microstructure of commercially pure molybdenum, 200. Although there are many grains in this microstructure, each grain has the same, uniform composition. (From Metals Handbook, 8th ed., Vol. 7: Atlas of Microstructures, American Society for Metals, Metals Park, Ohio, 1972.)

3 Figure 9-2 Two-phase microstructure of pearlite found in a steel with 0.8 wt % C, 500. This carbon content is an average of the carbon content in each of the alternating layers of ferrite (with <0.02 wt % C) and cementite (a compound, Fe 3 C, which contains 6.7 wt % C). The narrower layers are the cementite phase. (From Metals Handbook, 9th ed., Vol. 9: Metallography and Microstructures, American Society for Metals, Metals Park, Ohio, 1985.)

4 Gas T( C) 100 Steam Liquid Water 1 atm (a) Solid Pressure (log scale) Figure 9-3 (a) Schematic representation of the one-component phase diagram for H 2 O. (b) A projection of the phase diagram information at 1 atm generates a temperature scale labeled with the familiar transformation temperatures for H 2 O (melting at 0 C and boiling at 100 C). 0 (b) Ice

5 Gas Liquid T( C) Liquid atm Pressure (log scale) (a) Figure 9-4 (a) Schematic representation of the one-component phase diagram for pure iron. (b) A projection of the phase diagram information at 1 atm generates a temperature scale labeled with important transformation temperatures for iron. This projection will become one end of important binary diagrams such as Figure (b)

6 L Liquidus Melting point of B Temperature Melting point of A Solidus L + SS SS A B wt % B wt % A Composition (wt %) Figure 9-5 Binary phase diagram showing complete solid solution. The liquidphase field is labeled L and the solid solution is designated SS. Note the two-phase region labeled L + SS.

7 Composition of L at T 1 State point L System temperature T 1 L + SS Composition of SS at T 1 SS A X 1 B System composition Figure 9-6 The compositions of the phases in a two-phase region of the phase diagram are determined by a tie line (the horizontal line connecting the phase compositions at the system temperature).

8 F = C P + 1 F = = 2 F = = 0 F = = 1 F = = 2 A Composition Figure 9-7 Application of Gibbs phase rule (Equation 9.2) to various points in the phase diagram of Figure 9 5. B

9 L system All liquid (L system ) T 1 L 1 Crystallites of SS 1 in matrix of L 1 SS 1 Polycrystalline solid (SS system ) SS system A B System composition Composition Figure 9-8 Various microstructures characteristic of different regions in the complete solid-solution phase diagram.

10 C Atomic percentage nickel L Cu Weight percentage nickel Ni Figure 9-9 Cu Ni phase diagram. (After Metals Handbook, 8th ed., Vol. 8: Metallography, Structures, and Phase Diagrams, American Society for Metals, Metals Park, Ohio, 1973, and Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.)

11 C L 2400 L + SS 2200 SS 2000 NiO Mole % MgO 80 MgO Figure 9-10 NiO MgO phase diagram. (After Phase Diagrams for Ceramists, Vol. 1, American Ceramic Society, Columbus, Ohio, 1964.)

12 Eutectic temperature A + L L Liquidus Solidus L + B A + B A Eutectic Composition B Composition Figure 9-11 Binary eutectic phase diagram showing no solid solution. This general appearance can be contrasted to the opposite case of complete solid solution illustrated in Figure 9 5.

13 All liquid (L eutectic ) Crystallites of A in matrix of L 1 L 1 L 2 Crystallites of B in matrix of L 2 L eutectic Eutectic microstructure fine, alternating layers of A and B A Composition Figure 9-12 Various microstructures characteristic of different regions in a binary eutectic phase diagram with no solid solution. B

14 C 1500 Atomic percentage, silicon L A Weight percentage, silicon Figure 9-13 Al Si phase diagram. (After Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.) Si

15 L Temperature A Composition Figure 9-14 Binary eutectic phase diagram with limited solid solution. The only difference from Figure 9 11 is the presence of solid-solution regions α and β. B

16 All liquid (L eutectic ) L eutectic L 1 L 2 A Composition Figure 9-15 Various microstructures characteristic of different regions in the binary eutectic phase diagram with limited solid solution. This illustration is essentially equivalent to Figure 9 12 except that the solid phases are now solid solutions (α and β) rather than pure components (A and B). B

17 C Atomic percentage tin L Pb Sn Weight percentage tin Figure 9-16 Pb Sn phase diagram. (After Metals Handbook, 8th ed., Vol. 8: Metallography, Structures, and Phase Diagrams, American Society for Metals, Metals Park, Ohio, 1973, and Binary Alloy Phase Diagrams, Vol. 2, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.)

18 L Eutectic temperature Eutectoid temperature A B Eutectoid composition Eutectic composition Composition Figure 9-17 This eutectoid phase diagram contains both a eutectic reaction (Equation 9.3) and its solid-state analog, a eutectoid reaction (Equation 9.4).

19 A B Composition Figure 9-18 Representative microstructures for the eutectoid diagram of Figure 9 17.

20 C Atomic percentage carbon L C L + Fe 3 C 6.69 Fe 3 C (cementite) 0 Fe Weight percentage carbon Figure 9-19 Fe Fe 3 C phase diagram. Note that the composition axis is given in weight percent carbon even though Fe 3 C, and not carbon, is a component. (After Metals Handbook, 8th ed., Vol. 8: Metallography, Structures, and Phase Diagrams, American Society for Metals, Metals Park, Ohio, 1973, and Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.)

21 C Atomic percentage carbon L + C C (graphite) Fe Weight percentage carbon Figure 9-20 Fe C phase diagram. The left side of this diagram is nearly identical to that for the Fe Fe 3 C diagram (Figure 9 19). In this case, however, the intermediate compound Fe 3 C does not exist. (After Metals Handbook, 8th ed., Vol. 8: Metallography, Structures, and Phase Diagrams, American Society for Metals, Metals Park, Ohio, 1973, and Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.)

22 Composition of liquid formed upon melting of AB L L + B A + L L + AB AB + B A + AB A AB B Composition Figure 9-21 Peritectic phase diagram showing a peritectic reaction (Equation 9.5). For simplicity, no solid solution is shown.

23 Crystallites of B in matrix of L 1 L Polycrystalline solid (compound AB) A AB Composition B Figure 9-22 Representative microstructures for the peritectic diagram of Figure 9 21.

24 C L 2054 L + Al 2 O SiO 2 (cristobalite) + L L + mullite(ss) Al 2 O 3 + mullite(ss) SiO SiO 2 (cristobalite) + mullite(ss) Al 2 O 3 mullite(ss) Mole % Al 2 O 3 Figure 9-23 Al 2 O 3 SiO 2 phase diagram. Mullite is an intermediate compound with ideal stoichiometry 3Al 2 O 3 2SiO 2. (After F. J. Klug, S. Prochazka, and R. H. Doremus, J. Am. Ceram. Soc. 70, 750 (1987).)

25 Figure 9-24 (a) Binary phase diagram with a congruently melting intermediate compound, AB. This diagram is equivalent to two simple binary eutectic diagrams (the A AB and AB B systems). (b) For analysis of microstructure for an overall composition in the AB B system, only that binary eutectic diagram need be considered. Temperature L A + L AB + L B + L L + AB A + AB AB + B A AB Composition (a) B L Temperature A + L L + AB AB + L B + L A + AB AB + B A AB Composition (b) B

26 L A A 2 B AB AB 2 AB 4 B Composition (a) Temperature L A A 2 B AB AB 2 AB 4 B Composition

27 C 3000 L Periclase (SS) + L L + spinel (SS) L + Al 2 O 3 Periclase (SS) Spinel (SS) 1500 Periclase (SS) + spinel (SS) Spinal (SS) + Al 2 O MgO Al 2 O 3 Mole % Al 2 O 3 Figure 9-26 MgO Al 2 O 3 phase diagram. Spinel is an intermediate compound with ideal stoichiometry MgO Al 2 O 3. (After Phase Diagrams for Ceramists, Vol. 1, American Ceramic Society, Columbus, Ohio, 1964.)

28 Atomic percentage, copper C L η Al Cu Weight percentage, copper Figure 9-27 Al Cu phase diagram. (After Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.)

29 C Atomic percentage, magnesium L δ Al Weight percentage, magnesium Figure 9-28 Al Mg phase diagram. (After Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.) Mg

30 ºC Atomic percentage, zinc º Atomic percentage Cu L L º Zn º Weight percentage Cu º º º º 558º º º % at 100º 50 0 Cu Zn Weight percentage, zinc Figure 9-29 Cu Zn phase diagram. (After Metals Handbook, 8th ed., Vol. 8: Metallography, Structures, and Phase Diagrams, American Society for Metals, Metals Park, Ohio, 1973, and Binary Alloy Phase Diagrams, Vol. 1, T. B. Massalski, ed., American Society for Metals, Metals Park, Ohio, 1986.)

31 Tetragonal ZrO2SS + Cubic ZrO2SS C 4 CaO (wt %) Tetragonal ZrO2SS Cubic ZrO 2 SS Cubic ZrO 2 SS + ZrCaO Monoclinic ZrO 2 SS + Cubic ZrO 2 SS 0 ZrO CaO (mol %) Figure 9-30 CaO ZrO 2 phase diagram. The dashed lines represent tentative results. (After Phase Diagrams for Ceramists, Vol. 1, American Ceramic Society, Columbus, Ohio, 1964.)

32 L A A 2 B AB AB 2 AB 4 B Composition

33 L L + SS T 1 SS A Composition (wt % B) B m L + m SS = m total 0.30m L m SS = 0.50m total m L = 0.60m total m SS = 0.40m total Figure 9-31 A more quantitative treatment of the tie line introduced in Figure 9 6 allows the amount of each phase (L and SS) to be calculated by means of a mass balance (Equations 9.6 and 9.7).

34 (a) Fulcrum (b) Figure 9-32 The lever rule is a mechanical analogy to the mass balance calculation. The (a) tie line in the two-phase region is analogous to (b) a lever balanced on a fulcrum.

35 L system 100% liquid (L system ) L 1 T 1 T 2 T 3 L 3 L 2 SS 3 SS 2 SS 1 10% SS 1 in matrix of L 1 40% SS 2 in matrix of L 2 SS system 90% SS 3 in matrix of L 3 A Composition B 100% Solid (SS system ) Figure 9-33 Microstructural development during the slow cooling of a 50% A 50% B composition in a phase diagram with complete solid solution. At each temperature, the amounts of the phases in the microstructure correspond to a lever rule calculation. The microstructure at T 2 corresponds to the calculation in Figure 9 31.

36 L eutectic 100% liquid (L eutectic ) T 1 T 2 A Composition B *The only differences from the T 1 microstructure are the phase compositions and the relative amounts of each phase. For example, the amount of b will be proportional to Figure 9-34 Microstructural development during the slow cooling of a eutectic composition.

37 L system 100% liquid (L system = 80% B) L 2 L 1 T 2 (= T eutectic + 1 ) T 3 (= T eutectic 1 ) A Composition (wt % B) Figure 9-35 Microstructural development during the slow cooling of a hypereutectic composition. 100 B

38 100% liquid (L system = 40% B) L system L 1 T 2 (= T eutectic + 1 ) T 3 (= T eutectic 1 ) A Composition (wt % B) Figure 9-36 Microstructural development during the slow cooling of a hypoeutectic composition. 100 B

39 L system 100% liquid (L system = 10% B) L A Composition (wt % B) (a) 100 B 100% liquid (L system = 20% B)uid (L system = 20% L system Temperature L A Composition (wt % B) (b) 100 B

40 100% liquid (3% C) L Weight percentage carbon 6.7 Figure 9-38 Microstructural development for white cast iron (of composition 3.0 wt % C) shown with the aid of the Fe Fe 3 C phase diagram. The resulting (low-temperature) sketch can be compared with a micrograph in Figure 11 1a.

41 Weight percentage carbon Figure 9-39 Microstructural development for eutectoid steel (of composition 0.77 wt % C). The resulting (low-temperature) sketch can be compared with the micrograph in Figure 9 2.

42 Proeutectoid cementite + pearlite Weight percentage carbon Figure 9-40 Microstructural development for a slowly cooled hypereutectoid steel (of composition 1.13 wt % C).

43 Proeutectoid ferrite + pearlite Weight percentage carbon Figure 9-41 Microstructural development for a slowly cooled hypoeutectoid steel (of composition 0.50 wt % C). 6.7

44 100% liquid (3% C) L 1 C flakes (from eutectic and eutectoid reactions) in matrix of ferrite Weight percentage carbon Figure 9-42 Microstructural development for gray cast iron (of composition 3.0 wt % C) shown on the Fe C phase diagram. The resulting low-temperature sketch can be compared with the micrograph in Figure 11 1b. A dramatic difference is that, in the actual microstructure, a substantial amount of metastable pearlite was formed at the eutectoid temperature. It is also interesting to compare this sketch with that for white cast iron in Figure The small amount of silicon added to promote graphite precipitation is not shown in this two-component diagram.

45 The phase diagram for this alloy system is T A B