UDC 669.245

CHEMISTRY

R. B. GOLUBTSOVA

SELECTIVE ISOLATION OF THE METALLIC COMPOUNDS Ni$_3$Al AND Ni$_3$Ti FROM MULTICOMPONENT NICKEL ALLOYS

(Presented by Academician I. I. Chernyaev, February 18, 1965)

The properties of many heat-resistant nickel alloys are associated with the formation in them of an intermetallic phase based on the metallic compound Ni$_3$Al ($\gamma'$-phase), which is a phase of variable composition. The following elements dissolve in it to varying degrees: titanium, chromium, tungsten, molybdenum, silicon, manganese, vanadium, etc. The lattice parameter of the $\gamma'$-phase isolated from Ni—Cr—Ti—Al alloys can vary primarily depending on the content of aluminum, titanium, and chromium in the phase, within the limits from 3.56 (the parameter of the pure Ni$_3$Al phase) to 3.59 Å. It has been established that titanium has a great influence on the properties of the Ni$_3$Al phase; it can replace $^3/_5$ of the aluminum atoms in the phase ($^1$), and therefore the Ni$_3$Al phase may be represented in the form Ni$_3$(Al$_x$, Ti$_{1-x}$). In various nickel alloys containing aluminum and titanium, the following phases may be present: Ni$_3$Ti, Ni$_3$Al, and Ni$_3$(Al$_x$, Ti$_{1-x}$) ($^{1,2}$). The structure of the last two phases is close to that of the solid $\gamma$-nickel solution and is isomorphous with it. The parameters of their crystal lattices differ very little, which makes detection of these phases by the X-ray method difficult.

The literature describes methods for the electrolytic isolation of the intermetallic phases Ni$_3$Ti and Ni$_3$Al from complex alloys ($^{3-8}$).

The present investigation was carried out on a two-phase ternary alloy,* containing 75 wt.% Ni$_3$Ti and 25 wt.% Ni$_3$Al (the composition of this alloy according to chemical analysis (in wt.%): Ni 80.63, Ti 16.10, Al 3.32), and on a multicomponent nickel alloy having a three-phase structure and the following composition (in wt.%): Ni$_3$Ti 52.5, Ni$_3$Al 17.5, $\gamma^4$ 30 ($\gamma^4$—nickel solid solution, containing: Cr 10, W 6, Mo 3%). The composition of this alloy according to chemical analysis (in wt.%): Ti 11.6, Al 2.21, Cr 2.74, W 1.77, Mo 0.90, Ni balance.

Electrolytic selective isolation of the intermetallic phases Ni$_3$Ti and Ni$_3$Al when they are present together in an alloy is very difficult, because the values of their electrode potentials ($^9$) in different electrolytes are close. The literature describes aqueous electrolytes for anodic isolation of the Ni$_3$Al phase from chromium-nickel alloys ($^{3,10}$). However, in the indicated electrolytes the anodic precipitate of the alloys investigated by us is not separated. This circumstance evidently indicates the special anodic behavior of an alloy containing two metallic compounds: Ni$_3$Ti and Ni$_3$Al.

To select electrolytes for the selective separation of phases, we studied the electrochemical behavior of the alloys investigated in various electrolytes by recording anodic polarization curves (Figs. 1 and 2) by the compensation circuit, relative to a standard calomel electrode, using a high-resistance P-300 potentiometer. Potential—time curves were also recorded (Fig. 3).

* The alloys were prepared and provided for the investigation by L. I. Pryakhina ($^{11}$).

Table 1

Microchemical analysis of anodic precipitates isolated from a binary alloy
(75 wt. % Ni₃Ti and 25 wt. % Ni₃Al) at a current density of 0.1 A/cm².
Duration of the experiment: 3 hours

* Analysis performed by K. P. Myasnikova.

Table 2

Microchemical analysis of an anodic precipitate isolated from a multicomponent alloy.
Electrolyte: 50 ml HNO₃ (1.40), 20 ml HClO₄ (57%), 1000 ml CH₃OH,
at a current density of 0.1 A/cm².
Duration of the experiment: 3 hours

X-ray analysis data* for anodic powders. 2 phases: Ni₃Ti with a hexagonal lattice, $c=8,19$, $a=5,07$, $c/a=1,615$, and a Ni₃Al phase with a face-centered cubic lattice, $a=3,595$ kX.

* Analysis performed by K. P. Myasnikova.

Table 3

Microchemical analysis of an anodic precipitate isolated from a multicomponent alloy.
Electrolyte: 35 g citric acid, 5 g ammonium sulfate, 15 ml HNO₃ (1.40),
1000 ml CH₃OH, at a current density of 0.1 A/cm².
Duration of the experiment: 3 hours

* Analysis performed by K. P. Myasnikova.
Note. The numbers above the line are weight percent; those below the line are atomic percent.

During anodic dissolution of a two-phase alloy (75 wt.% $\mathrm{Ni}_3\mathrm{Ti}$ and 25 wt.% $\mathrm{Ni}_3\mathrm{Al}$) in electrolyte No. 1, two phases—$\mathrm{Ni}_3\mathrm{Ti}$ and $\mathrm{Ni}_3\mathrm{Al}$—are released simultaneously in the anodic residue, whereas in electrolyte No. 3 one phase is released—$\mathrm{Ni}_2\mathrm{Al}$, in which part of the aluminum atoms is replaced by titanium atoms and, consequently, its composition should be: $\mathrm{Ni}_3(\mathrm{Al}, \mathrm{Ti})$. A study of the effect of current density showed that the optimum current density is $0.1\ \mathrm{A/cm^2}$. The results of microchemical analysis of the anodic residues of the alloy are presented in Table 1.

Fig. 1. Curves of anodic polarization: A—of a two-phase ternary alloy (charge composition: 75 wt.% $\mathrm{Ni}_3\mathrm{Ti}$, 25 wt.% $\mathrm{Ni}_3\mathrm{Al}$), B—of a multicomponent alloy (charge composition: 52 wt.% $\mathrm{Ni}_3\mathrm{Ti}$, 17.5 wt.% $\mathrm{Ni}_3\mathrm{Al}$, 30 wt.% $\gamma^4$). Electrolytes:
1—20 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{CH_3OH}$;
2—20 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{C_2H_5OH}$;
3—35 g citric acid, 5 g $(\mathrm{NH}_4)_2\mathrm{SO}_4$, 15 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{CH_3OH}$;
6—50 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{CH_3OH}$;
7—50 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{C_2H_5OH}$;
10—20 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{H_2O}$.

Fig. 2. Potential–time curves of the alloy ($\mathrm{Ni}_3\mathrm{Ti}$—$\mathrm{Ni}_3\mathrm{Al}$—solid solution). Electrolytes:
2—20 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{C_2H_5OH}$;
3—35 g citric acid, 5 g $(\mathrm{NH}_4)_2\mathrm{SO}_4$, 15 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{CH_3OH}$;
6—50 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{CH_3OH}$;
7—50 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{C_2H_5OH}$;
10—20 ml $\mathrm{HClO}_4$ (57%), 50 ml $\mathrm{HNO}_3$ (1.40), 1000 ml $\mathrm{CH_3OH}$.

The results of microchemical analysis of the anodic residues of the multicomponent alloy having a three-phase structure indicate that, when it is dissolved in electrolyte No. 1, two phases are released in the anodic powder: $\mathrm{Ni}_3\mathrm{Ti}$ and $\mathrm{Ni}_3\mathrm{Al}$ (Table 2). Table 3 presents the results of microchemical analysis of the anodic residue selectively isolated in electrolyte No. 3 and consisting of the intermetallic $\gamma'$-phase based on the compound $\mathrm{Ni}_3\mathrm{Al}$, in which part of the aluminum atoms is replaced by other elements. The composition of this phase is as follows: $(\mathrm{Ni}, \mathrm{Cr})_3(\mathrm{Al}, \mathrm{Ti}, \mathrm{W}, \mathrm{Mo})$, where $\mathrm{Ni}, \mathrm{Cr}/\mathrm{Al}, \mathrm{Ti}, \mathrm{W}, \mathrm{Mo} = 4.50$.

Thus, selective isolation of the two metallic compounds $\mathrm{Ni}_3\mathrm{Ti}$ and $\mathrm{Ni}_3\mathrm{Al}$ can be carried out in the selected electrolytes.

Institute of Metallurgy
named after A. A. Baikov

Received
3 II 1965

REFERENCES CITED

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