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Understanding the Cu-Zn brass alloys using a short-range-order cluster model: significance of specific compositions of industrial alloys.

Hong HL, Wang Q, Dong C, Liaw PK - Sci Rep (2014)

Bottom Line: Two types of formulas are pointed out, [Zn-Cu12]Zn(1~6) and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications.In these formulas, the bracketed parts represent the 1(st)-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms.Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied.

View Article: PubMed Central - PubMed

Affiliation: 1] Key Laboratory of Materials Modification (Dalian University of Technology), Ministry of Education, Dalian 116024, China [2] Mechanical Engineering Department, Sanming University, Sanming 365004, China.

ABSTRACT
Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn(1~6) and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1(st)-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys.

No MeSH data available.


Structure of a Cu3Zn ordered state.The 1st and 2nd nearest-neighbor configurations of a possible low-temperature ordered Cu3Zn state with the AuCu3-structure type, where the twelve 1st neighbors are occupied by Cu and the six 2nd neighbors by Zn.
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f1: Structure of a Cu3Zn ordered state.The 1st and 2nd nearest-neighbor configurations of a possible low-temperature ordered Cu3Zn state with the AuCu3-structure type, where the twelve 1st neighbors are occupied by Cu and the six 2nd neighbors by Zn.

Mentions: It has been long suspected that behind the many “anomalous” behaviors at specific Zn concentrations lies a short-range-order mechanism in α-brasses (see for instance1011 and the references quoted therein), involving internal friction, stress relaxation, yielding, work-hardening, activation energy of creep, activity coefficient, specific heat, cold-working, electrical resistance, etc. The first direct evidence of short-range ordering was provided by a neutron-diffuse-scattering experiment in combination with a Monte Carlo simulation on an α-brass single crystal containing 31.1 atomic percent (at.%) Zn12. The Warren-Cowley short-range-order parameter for the nearest-neighbor position (1,1,0), α1 = −0.1373, is negative, signifying that the dissimilar Cu-Zn nearest order is favored. The α parameter for the second-nearest neighbor position (2,0,0) is positive, α2 = 0.1490, suggesting that the second neighbors are preferentially occupied by the Zn atoms. In accordance with this picture, the short-range order would reach eventually an ordered Cu3Zn state with the AuCu3-structure type. Figure 1 presents the 1st-neighbor cuboctahedral polyhedron [Zn-Cu12] and the 2nd-neighbor octahedron consisting of six Zn atoms, identified in Cu3Zn. A calculation of ground-state properties based on a Green's function technique13 confirmed that the mixing energies between Cu and Zn are always negative, ΔHCu-Zn < −6 KJ/mol, and, coincidently, the 1st-neighbor Warren-Cowley short-range-order parameter, α1, is always negative over the complete concentration range.


Understanding the Cu-Zn brass alloys using a short-range-order cluster model: significance of specific compositions of industrial alloys.

Hong HL, Wang Q, Dong C, Liaw PK - Sci Rep (2014)

Structure of a Cu3Zn ordered state.The 1st and 2nd nearest-neighbor configurations of a possible low-temperature ordered Cu3Zn state with the AuCu3-structure type, where the twelve 1st neighbors are occupied by Cu and the six 2nd neighbors by Zn.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4233332&req=5

f1: Structure of a Cu3Zn ordered state.The 1st and 2nd nearest-neighbor configurations of a possible low-temperature ordered Cu3Zn state with the AuCu3-structure type, where the twelve 1st neighbors are occupied by Cu and the six 2nd neighbors by Zn.
Mentions: It has been long suspected that behind the many “anomalous” behaviors at specific Zn concentrations lies a short-range-order mechanism in α-brasses (see for instance1011 and the references quoted therein), involving internal friction, stress relaxation, yielding, work-hardening, activation energy of creep, activity coefficient, specific heat, cold-working, electrical resistance, etc. The first direct evidence of short-range ordering was provided by a neutron-diffuse-scattering experiment in combination with a Monte Carlo simulation on an α-brass single crystal containing 31.1 atomic percent (at.%) Zn12. The Warren-Cowley short-range-order parameter for the nearest-neighbor position (1,1,0), α1 = −0.1373, is negative, signifying that the dissimilar Cu-Zn nearest order is favored. The α parameter for the second-nearest neighbor position (2,0,0) is positive, α2 = 0.1490, suggesting that the second neighbors are preferentially occupied by the Zn atoms. In accordance with this picture, the short-range order would reach eventually an ordered Cu3Zn state with the AuCu3-structure type. Figure 1 presents the 1st-neighbor cuboctahedral polyhedron [Zn-Cu12] and the 2nd-neighbor octahedron consisting of six Zn atoms, identified in Cu3Zn. A calculation of ground-state properties based on a Green's function technique13 confirmed that the mixing energies between Cu and Zn are always negative, ΔHCu-Zn < −6 KJ/mol, and, coincidently, the 1st-neighbor Warren-Cowley short-range-order parameter, α1, is always negative over the complete concentration range.

Bottom Line: Two types of formulas are pointed out, [Zn-Cu12]Zn(1~6) and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications.In these formulas, the bracketed parts represent the 1(st)-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms.Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied.

View Article: PubMed Central - PubMed

Affiliation: 1] Key Laboratory of Materials Modification (Dalian University of Technology), Ministry of Education, Dalian 116024, China [2] Mechanical Engineering Department, Sanming University, Sanming 365004, China.

ABSTRACT
Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn(1~6) and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1(st)-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys.

No MeSH data available.