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1、1,The Science and Engineering of Materials, 4th ed Donald R. Askeland Pradeep P. Phul,Chapter 10 Dispersion Strengthening and Eutectic Phase Diagrams,2,Objectives of Chapter 10,Discuss the fundamentals of dispersion strengthening to determine the microstructure. Examine the types of reactions that p
2、roduce multiple-phase alloys. Examine in some detail the methods to achieve dispersion strengthening by controlling the solidification process.,3,Chapter Outline,10.1 Principles and Examples of Dispersion Strengthening 10.2 Intermetallic Compounds 10.3 Phase Diagrams Containing Three- Phase Reaction
3、s 10.4 The Eutectic Phase Diagram 10.5 Strength of Eutectic Alloys 10.6 Eutectics and Materials Processing 10.7 Nonequilibrium Freezing in the Eutectic System 10.8 Ternary Phase Diagrams,4,Dispersion strengthening - Increasing the strength of a material by forming more than one phase. Matrix - The c
4、ontinuous solid phase in a complex microstructure. Precipitate - A solid phase that forms from the original matrix phase when the solubility limit is exceeded. Eutectic - A three-phase invariant reaction in which one liquid phase solidifies to produce two solid phases.,Section 10.1 Principles and Ex
5、amples of Dispersion Strengthening,5,Figure 10.1 Considerations for effective dispersion strengthening: (a) The precipitate phase should be hard and discontinuous.,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,6,Figure 10.1 Consi
6、derations for effective dispersion strengthening: (b) The dispersed phase particles should be small and numerous.,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,7,Figure 10.1 Considerations for effective dispersion strengthening:
7、(c) The dispersed phase particles should be round rather than needlelike.,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,8,Figure 10.1 Considerations for effective dispersion strengthening: (d) Larger amounts of dispersed phase in
8、crease strengthening.,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,9,Intermetallic compound - A compound formed of two or more metals that has its own unique composition, structure, and properties. Stoichiometric intermetallic c
9、ompound - A phase formed by the combination of two components into a compound having a structure and properties different from either component. Nonstoichiometric intermetallic compound - A phase formed by the combination of two components into a compound having a structure and properties different
10、from either component. Ordered crystal structure - Solid solutions in which the different atoms occupy specific, rather than random, sites in the crystal structure.,Section 10.2 Intermetallic Compounds,10,11,Figure 10.2 (a) The aluminum-antimony phase diagram includes a stoichiometric intermetallic
11、compound .,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,12,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,Figure 10.3 The strength and ductility of the interm
12、etallic compound Ti3Al compared with that of a conventional nickel superalloy. The Ti3Al maintains sits strength to higher temperatures longer than does the nickel superalloy.,13,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,Figu
13、re 10.4 (a) In an ordered structure, the substituting atoms occupy specific lattice points,(b) while in normal structure, the constituent atoms are randomly located at different lattice points.,14,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein u
14、nder license.,Figure 10.5 The unit cells of two intermetallic compounds: (a) TiAl has an ordered tetragonal structure, and (b) Ni3Al has an ordered cubic structure.,15,Design a material suitable for the parts of an aerospace vehicle that reach high temperatures during re-entry from Earth orbit. Exam
15、ple 10.1 SOLUTION The material must withstand the high temperatures (1600oC - 1700oC) generated as the vehicle enters Earths atmosphere. Some ductility is needed to provide damage tolerance to the vehicle. Finally, the material should have a low density. TiAl and Ni3Al have good high-temperature pro
16、perties and oxidation resistance and, at high temperatures, have at least some ductility. Thus, carbon or aramid fiber-matrix composites (based on KevlarTM), coated properly to protect oxidation, also will be very good choices for outer space applications.,Example 10.1 Materials Selection for an Aerospace Vehicle,16,Peritectic - A three-phase reaction in which a solid and a liquid combine to produce a second solid on cooling. Monotectic - A three-phase rea
