Phase transformations in alloys of the Ni–Cr system

Ustinovshikov, Y.

doi:10.1016/j.jallcom.2012.05.120

Cited by 22 publications

(27 citation statements)

References 8 publications

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“…in the form of conventional clusters ( Figure 47, clusters are visible due to absorption contrast ). A similar structure of clusters of chromium atoms was observed in the electron microscopic image of the Ni 68 Cr 32 binary alloy after quenching the alloy from 1200 and 1000°C [43].As is known from reference books, the optimum combination of corrosion resistance and ductility of most Hastelloytype alloys is observed after a heat treatment at 1150 -1175°C (cooling in water or air). As it follows from reference75, it is at Chemical Bond in Metallic Alloys: Electron Microscopic Study …”

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confidence: 76%

“…However, it was noticed that with a decrease in the temperature of heat treatment the number of clusters reduces and their contours become still more blurred [43]. At the same time, the Ni 2 Cr phase in this alloy was not found at all.…”

Section: Alloys Of the Ni-cr Systemmentioning

confidence: 87%

“…Figure 11: The same alloy. Water-quenching from 700°C, electron diffraction pattern (inset), dark-field micrograph using a (-100) super lattice spot from inset [11,43]. According to the conventional phase diagram of Ni-Cr, at compositions close to the Ni 40 Cr 60 alloy, a eutectic is formed in the Ni-Cr system [11].…”

Section: Alloys Of the Ni-cr Systemmentioning

confidence: 99%

“…In this case, we can assume that the phase transition 'ordering-phase separation' occurs in such a system not only with a change of the temperature but also with a change in the composition of alloys. In this case, the research should be continued by the procedure proposed for the Ni-Cr system, which has been discussed above (3.3) [43,44]. From the above discussion, it follows that introduction of such a concept as the phase transition 'ordering-phase separation' into common use changes our previous understanding of the driving forces of the process of new phase formation.…”

confidence: 99%

“…A comparison of the data obtained in the study of alloys of this system leads to the conclusion that in this system, at all temperatures, there is a tendency to phase separation, i.e. the atoms of Mo and Cr tend to diffuse not to each other to form a chemical compound, but on the contrary, from each other and, therefore, they, in principle, cannot participate in the formation of any chemical compounds, as it is supposed in references [73,74,75].As was shown in reference, in the part of the diagram of Ni-Cr, where concentration of nickel atoms prevails (for instance, the Ni 68 Cr 32 alloy), heat treatment at any temperature leads to formation of clusters of chromium atoms (after quenching from the liquid state, as well) [43]. Therefore, the tendency to phase separation takes place in the diffusion couple Ni/Cr at any heating temperature of the alloy studied.…”

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confidence: 91%

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Chemical Bond in Metallic Alloys: Electron Microscopic Study

Ustinovshikov¹

2017

NSTOA

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Aplastic anemia in systemic lupus erythematosus: A better prognosis acquired aplastic anemia Copyright: © 2016 Pannu and VarmaThe first experimental study to verify the existence of the high-temperature phase separation in alloys of the ironchromium system was undertaken by the example of the Fe-45% Cr alloy [15]. Using the method of TEM, it was found that the microstructure of this alloy after quenching from 1150 -1200°С was similar to that which had been obtained in Reference [14]. However, they interpreted such precipitations as chromium nitrides, i.e., as a kind of an "added" phase formed by the chemical reaction of chromium atoms (from the alloy) with atoms of nitrogen (from the air) during a high temperature heat treatment for quenching. A second study was conducted using the Fe 51 Cr 49 alloy, with the help of Mossbauer spectroscopy [16]. It is obvious that the choice of the method of research in Reference was poor, since it was hardly possible to judge a local phase separation of the alloy by the change of the partial gamma-resonance peaks corresponding to pure iron. Therefore, they did not manage to find the structure of phase separation [16]. Figure 2 shows the iron-rich part of an iron-chromium phase diagram, built on the results of electron microscopic studies of the microstructure of alloys of iron with 20, 30, 40 and 50 wt. % of chromium [17]. From the diagram, it can be seen that in the Fe-Cr system, there occur two phase transitions, in the result of which, for example, the microstructure that has formed as a consequence of the tendency to ordering is dissolving and a microstructure of phase separation is forming in its place (and vice versa). This occurs within the temperature ranges of 1100 -850°C and 600 -550°C (Figure 2) On the basis of these data, it could be concluded that at the level of microstructures, such a phase transition is bound to pass through the stage of the existence of the solid solution in the alloy. The authors have given this phase transition the name "orderingphase separation" [17]. Since the discovery of this transition, 17 binary systems have so far been studied and in 16 of them the transition has been experimentally found. The transition occurs at a temperature, specific for each system, at which the sign of the chemical interaction between atoms of A and B is reversed. It is obvious that the transformation of the microstructure formed as a result of the tendency to ordering into the microstructure formed as a result of the tendency to phase separation, and vice versa, is a consequence of the phase transition ordering -phase separation. The transition itself, that is, the process of changing the sign of the chemical interaction between dissimilar atoms, occurs at the level of changes in the electronic structure of the alloy.Before considering the physical essence of this transition, we would like to decide on the issue of the use of such terms as "ordering energy", "mixing energy", "enthalpy of mixing" and so on. Each of the above terms refers to basically the same no...

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supporting

confidence: 76%

Section: Alloys Of the Ni-cr Systemmentioning

confidence: 87%

Section: Alloys Of the Ni-cr Systemmentioning

confidence: 99%

mentioning

confidence: 91%

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Chemical Bond in Metallic Alloys: Electron Microscopic Study

Ustinovshikov¹

2017

NSTOA

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Heredity of medium-range order structure from melts to the microstructure of Ni–Cr–W superalloy

Gao

Wang

et al. 2015

Appl. Phys. A

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The structure factor S(Q), intensities and pair distribution function g(r) of liquid Ni-Cr-W superalloy at different temperatures have been measured by a hightemperature X-ray diffractometer. Coordination N min , correlation radius r c , the nearest atomic distance r 1 , solidification microstructure and compression performance have been studied. The results show that a pre-peak exists on the structure factor curve at the liquidus temperature, and a fine structure of equiaxed, globular and non-dendritic primary grains can be achieved by casting the alloy at liquidus temperature. Liquid structure feature of Ni-Cr-W superalloy is found to depend on temperature. During the solidification, some structural information carried by the medium-range order (MRO) structure is inherited from the melt to the microstructure, which is beneficial for grain refinement. The maximum yield strength measured from typical microstructure of the equiaxed and non-dendritic grains at 1400°C is 543 MPa. The results show that refinement and non-dendritic grain is beneficial to the improvement of the yield strength.

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