Electrical resistivity recovery in cold-worked 60 per cent silver-40 per cent palladium alloy

ACTA

900

METALLURGICA,

References 1. P. M. KELLY und J. NUTTINU, J. Inst.Met. 87, 385 (1958-

59). 2. W. PITSCE und A. SCHRADER, Arch ~,~~~h~~e~u~, 29, 485 (1958). 3. E. C. BAIN, Truns Amer. In&. Min. (Metall.) Engng. 70, 25 (1924). 5. W. C. LESLIE, R.iV.Frs~~~und N. SEN,Acta Met. 7, 632 (1959). 5. K. W. ANDREWS, persijnliche Mitt&lung. 6. G. KUR~JQMOV und G.SACRS, 2. Ph‘ys.64,325 (1930). * Received

January 30, 1962.

Electrical resistivity recovery in cold-worked 60 per cent silver-40 per cent palladium alloy * investigations(1~2) on the effect of plastic deformation on resistivity in the two systems silverpalladium and gold-palladium indicate that both the magnitude and the sign of the change in resistivity due to deformation depend on the amount of strain and on the composition of the alloy. For alloys that show a decrease in resistivity with plastic deformation, Aarts and Houston-Macmillan(l) suggested that distortion of Brillouin zones in certain directions increases the number of electrons available for carrying current, thus ove~iding the usual increase in resistivity due to lattice defects. If this hypothesis is true, the electrical resistivities of such alloys should show a further decrease in resistivity at temperatures at which the point defects are annealed out. This effect was indeed found in an isochronal recovery study of plastically deformed (elongated at room temperature by 8 per cent) 60 per cent silver40 per cent palladium. The specimen was held at each temperature for a period of Recent

I

I

VOL.

10,

1962

30 min and all measurements were made at liquid nitrogen temperature. As shown in Fig. l? noticeable decreases in resistivity are observed between 80-120°C and again between 240-3OO’C. Sosin and Brinkman(3) have found that point defects anneal out in t’he same temperature ranges. Besides possible Brillouin zone effects, Logic et aZ.@) suggested that local static strains contribute a negative term to the resistivity at point,s where the density of states curve is concave downwards. A third tentative explanation is that the decrease in resisbivity due to cold working is the result of the possible existence of a miscibility gap in silver-palladium alloys. W. M. Reck oratory ojpEngineering Materials

K. KRISHNA

RAO

California. Institute of Technology Pasadena, California

References 1. W. H. AARTS and A. S.HOU~TON-M.~~~IL~~N,A~~~

52.5 (1957). 2. H. J. LOWE, J. JACKSON, I. C. ANDERSON NABARRO, ActaMet. 9, TO7 (1961). 3. A. SOSIN and T. 8. BRINKMAN. Act/rMet.

Xel. 5,

and F. R. N.

7, 478 (1959).

* Received February 16, 1962. Solute segregation

to stacking

faults*

As pointed out by Suzuki(l), a stacking fault in an alloy should have a composition differing from that of the matrix at equilibrium. The differences in composition between the fault and matrix is of considerable interest; previous treatments of this problem lead to an approximate result using ideal and regular solution treatments.‘lJ) The recent stacking fault energy measurements of Howie and Swarm@) on Cu and Ag alloys permit of a,more precise solut,iomto this problem. The stacking fault energy S per mole of fault is the difference between the molar free energies of the fault phase (Gf) and matrix (G) : S = G’ -

G.

(I)

Using the relation G = ZQG, + x$&,, where x1 and x2 are the atom fractions of components 1 and 2, resp., in the alloy then: s = xJ,f

TEMPERATURE

*C

FIG. 1. Isochronal recovery of resiativity in 60% Ag, 40% Pd alloy following an 8 per cent elongation at room temperature. Ap does not represent absolute change.

+ x&f

-

x,0

-

x.$7.

(2)

The 0’s are the chemical potentials of the two components in the two phases evaluated at the composition of the alloy. On substituting GI = RT In aI + GIO,etc., we obtain: S = RT(x, In a{ - gI In a, + x2 In u2f -

5Ina,)

+

x1&0

+

x@20

(3)