Local Structure and Short-Range Order in a NiCoCr Solid Solution Alloy

Multielement solid solution alloys are intrinsically disordered on the atomic scale, and many of their advanced properties originate from the local structural characteristics. The local structure of a NiCoCr solid solution alloy is measured with x-ray or neutron total scattering and extended x-ray absorption fine structure (EXAFS) techniques. The atomic pair distribution function analysis does not exhibit an observable structural distortion. However, an EXAFS analysis suggests that the Cr atoms are favorably bonded with Ni and Co in the solid solution alloys. This short-range order (SRO) may make an important contribution to the low values of the electrical and thermal conductivities of the Cr-alloyed solid solutions. In addition, an EXAFS analysis of Ni ion irradiated samples reveals that the degree of SRO in NiCoCr alloys is enhanced after irradiation.

Figure 1

(a) XRD pattern of polycrystalline NiCoCr fitted with the fcc structure model. (b) Structure factor $S(Q)$ of NiCoCr measured with a time-of-flight neutron.

Figure 2

(a) Comparison of the x-ray (red line) and neutron (blue line) pair distribution function of NiCoCr solid solution alloy in the 30 Å range. (b) Rietveld refinement of the neutron PDF profile in the 20 Å range ($R_w=0.086$).

Figure 3

Magnitude of EXAFS functions measured in the $K$ edge of Ni, Co, and Cr and the slight difference in the position of the first peak indicates that the bond length of Ni, Co, and Cr with its surrounding atoms may be different. The Fourier transform of all the $k^2$-weighted EXAFS functions were conducted in the same $k$ range: $3.0–11.0{\AA }^{-1}$.

Figure 4

(a) Profile of Ni ion irradiation induced damage in NiCoCr predicted using the Kinchon-Pease damage calculation in the SRIM code. (b) Lattice constant and Debye-Waller factor of NiCoCr alloys with different doses of Ni ion irradiation. (c) EXAFS spectrum of single crystal samples irradiated with different doses of Ni ions ($k^2$-weighted with $k$ range: $3.0–11.0{\AA }^{-1}$).