CHAPTER 2
BACKGROUND
This chapter will provide the background necessary to
understand the crystallography and precipitate types that
will be described in detail in Chapter 5. It additionally
provides some seminal ideas on nucleation mechanisms for
the ordered nonequilibrium coherent phases that will be
shown to precipitate in the otherwise disordered gamma
matrix. All the known equilibrium phases are also
described and the relevant phase diagrams presented.
Interpretation of the diffraction patterns of the NixMo
coherent phases is explained last.
2.1Phase Diagrams
2.1.1 Binary Phase Diagrams
2.1.1.1 Ni-Mo
The binary Ni-Mo equilibrium phase diagram is shown
in Figure 2.1 (Hansen, 1958). This diagram has been
recently confirmed by Heijnegen and Rieck (1973). Three
equilibrium intermetallic phases can occur: N4M0, a Dla
superlattice, N3M0, an orthorhombic phase, and NiMo, an
orthorhombic phase. Only NiMo is ever at equilibrium with
the liquid.
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