Fe-Ni-C System

The extension of the austenite field in the C-Fe-Ni system below 900°C has been calculated [1977Uhr, 1978Uhr] and was reported in Fig. 5. The line with an arrow indicates the composition of the austenite (yFCjNi) in simultaneous equilibrium with (Fe,Ni)3C and ferrite (aFe). Slight modifications have been done according to the binary edges. 

The isopleflis at 1 mass% Ni and 0.3 mass% C have been experimentally determined in flic iron rich comer of the C-Fe-Ni system [1970Zem], The polyfliermal section proposed at 0.3 mass% by [1970Zem] does not fit well wifli the binary C-Fe and has been rejected. The accepted isopleth at 1 mass% Ni from [1970Zem] shown in Fig. 15 matches well wifli flic Fe-Ni binary system. The solubility of C in (aFe,Ni) (1 mass% Ni) presents a maximum of 0.022 mass% at 800°C... 

Table 3. Invariant Equilibria in the C-Fe-Ni System Under a Pressure of 6 GPa ...

Gab] Gabriel, A., Gustafson, P., Ansara, L, A Thermodynamic Evaluation of the C-Fe-Ni System , Calphad, 11(2), 203-218 (1987) (Assessment, Phase Diagram, Thermodyn., Phase Relations, 41)... 

We now describe briefly martensitic transformations in three contrasting systems which illustrate some of the main features of this type of transformation and the range of behavior that is found [15]. The first is the In-Tl system, where the lattice deformation is relatively slight and the shape change is small. The second is the Fe-Ni system, where the lattice deformation and shape change are considerably larger. The third is the Fe-Ni-C system, where the martensitic phase that forms is metastable and undergoes a precipitation transformation if heated. 

The crystallography of the f.c.c.— b.c.t. martensitic transformation in the Fe-Ni-C system (with 22 wt. %Ni and 0.8 wt. %C) has been described in Section 24.2. In this system, the high-temperature f.c.c. solid-solution parent phase transforms upon cooling to a b.c.t. martensite rather than a b.c.c. martensite as in the Fe-Ni system. Furthermore, this transformation is achieved only if the f.c.c. parent phase is rapidly quenched. The difference in behavior is due to the presence of the carbon in the Fe-Ni-C alloy. In the Fe-Ni alloy, the b.c.c. martensite that forms as the temperature is lowered is the equilibrium state of the system. However, in the Fe-Ni-C alloy, the equilibrium state of the system in the low-temperature range is a two-phase mixture of a b.c.c. Fe-Ni-C solid solution and a C-rich carbide phase.5 This difference in behavior is due to a much lower solubility of C in the low-temperature b.c.c. Fe-Ni-C phase than in the high-temperature f.c.c. Fe-Ni-C phase. If the high-temperature... 

Hil] Hillert, M., Qiu, C., A Reassessment of the Cr-Fe-Ni System , Met. Trans. A, 21(6), 1673-1680 (1990) (Assessment, Calculation, Phase Diagram, Phase Relations, 40) [1990Yam] Yamada, A., Umeda, T., Kimura, Y, Calculation of Liquidus and Solidus Surfaces of the Iron Rich Comer of the Fe-Cr-Ni System , J. Iron Steel Inst. Jpn., 76(12), 2137-2143 (1990) (Calculation, Phase Diagram, Phase Relations, 25)... 

Gab] Gabriel, A., Pastor, H., Deo, D.M., Basu, S., AlUbert, C.H., New Experimental Data in the C-Fe-W, C-Co-W, C-Ni-W, C-Fe-Ni-W and C-Co-Ni-W Cemented Carbide Systems and their Application to Sintering Conditions , Int J. Refract Met Hard Mater., 5(4), 215-221 (1986) (Phase Diagram, Phase Relations, Experimental, Magn. Prop., Meehan. Prop., 46)... 

Art, 1964Pil] developed the model of Zener and Carr to prediet the Curie temperatures in the ternary alloys, based on the binary data. For the Co-Fe-Ni system the predicted values eorrespond to the experimental ones within 30°C. 

As the amount of iron increases in the powders (above 50 at.%), the number of different crystals detected on the agglomerate surfaces also increases. In the powders electrodeposited from the solutions with Ni/Fe = 1/3, a very small amount of agglomerates is covered with spherical crystals, while most of them are characterized with the presence of several different shapes of crystals. These crystals are presented in Fig. 8.24a-f. It is quite difficult to explain the reasons for their appearance, since so many different phases do not exist in the Fe-Ni system and the only reasonable explanations could be that these crystals represent some superstructures formed under massive hydrogen evolution. Their shapes could be defined as follows (a) Christmas tree-like crystals, (b) triangle-like crystals growing layer by layer, (c) propeller-like crystals, (d) plate-like crystals, (e) tetrahedral crystals, and (f) traversed polyhedron. 

The Co system is more reactive as well as much more selective than the Ni and Rh catalyst systems (Table XVII). The best systems allow almost 100% conversion with almost 100% yield of c -l,4-hexadiene. The best of the Ni and Rh systems known so far are still far from such amazing selectivity. The tremendous difference between the Ni system and the Co or Fe system must be linked to the difference in the nature of the coordination structures of the complexes, i.e., hexacoordinated (octahedral complexes) in the case of Co and Fe and tetra- or penta-coordinated (square planar or square pyramidal) complexes in the case of Ni. The larger number of coordination sites allows the Co and Fe complex to utilize chelating phosphines which are more effective than monodentate phosphines for controlling the selectivity discussed here. These same ligands are poison for the Ni (and Rh) catalyst system, as shown earlier. 

CoO and NiO all take the NaCl-type structure and the difference in nonstoichiometry relates to the relative stability of the formal di- and trivalent oxidation states. The stability of the trivalent state and the degree of non-stoichiometry decreases from Fe3+ to Ni2+. Hence the non-stoichiometric nature of Fcj yO is made possible by the relatively high stability of Fe3+ that is reflected in the fact that Fe2C>3 is a stable compound in the Fe-0 system, whereas M2O3 is not in the Ni-O system. This relative stability of the different oxidation states is also reflected in Figure 7.11(c). 

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