Papers by Keyword: Cu-Based Alloys

Abstract: In this chapter, we present computational kinetics of diffusion-controlled phase transformations in Cu-based alloys, which becomes possible only most recently due to the establishment of the first atomic mobility database (MOBCU) for copper alloys. This database consists of 29 elements including most common ones for industrial copper alloys. It contains descriptions for both the liquid and Fcc_A1 phases. The database was developed through a hybrid CALPHAD approach based on experiments, first-principles calculations, and empirical rules. We demonstrate that by coupling the created mobility database with the existing compatible thermodynamic database (TCCU), all kinds of diffusivities in both solid and liquid solution phases in Cu-based alloys can be readily calculated. Furthermore, we have applied the combination of MOBCU and TCCU to simulate diffusion-controlled phenomena, such as solidification, nucleation, growth, and coarsening of precipitates by using the kinetic modules (DICTRA and TC-PRISMA) in the Thermo-Calc software package. Many examples of simulations for different alloys are shown and compared with experimental observations. The remarkable agreements between calculation and experimental results suggest that the atomic mobilities for Cu-based alloys have been satisfactorily described. This newly developed mobility database is expected to be continuously improved and extended in future and will provide fundamental kinetic data for computer-aided design of copper base alloys.

Abstract: Cu-Hf-Al alloys are considered to be relatively new ones among Cu-based bulk amorphous alloys. Cu-Hf-Al alloys have high strength in amorphous state and this property makes many applications feasible for the industry. During the production of amorphous alloys the most important purpose is to produce them in the biggest diameter to make them suitable for a wide range of applications. The circumstances of the production process have a great influence on the developing structure. In the present work solidification of Cu-Hf-Al alloys were investigated. The alloys were cast into different shapes with different Al contents with special regard to the appearance of the amorphous/crystalline structure. The appearance and the structure of crystalline phases were determined by X-ray diffraction and X-ray, DSC and metallographic measurements were used to investigate the developing structure.

Abstract: The influence of Sn addition on the amorphization of CuTiZrNi alloys processed by mechanical alloying of a mixture of pure elemental powder was studied. The thermal stability and crystallization behaviour of the amorphous mechanically alloyed powders was determined and compared with rapidly quenched ribbons with the same nominal chemical compositions. X-ray diffraction and differential scanning calorimetry were employed as the experimental techniques for samples characterization. Both applied samples preparation techniques resulted in the formation of fully amorphous Cu47Ti34Zr11Ni8 and Cu37Sn10Ti34Zr11Ni8 alloys. However, significant differences in thermal stability and crystallization behaviour have been found, depending not only on the alloy composition, but on the fabrication method as well. The observed influence of Sn addition was more evident for the ribbons, resulting in the change of the number of crystallization effects, their temperatures and activation energy of crystallization. For mechanically alloyed powders these changes were not so dramatic.

Abstract: Recently one of the most significant research-field in the development of amorphous alloys is the research of the Cu-based amorphous alloys. The Zr-based alloys developed earlier can be replaced by the newly developed Cu-based alloys as the high price of the Zr-based alloys limits their utilization in spite of their favourable properties. Production of Cu-based alloys having the same or more favourite properties than Zr-based alloys is cheaper and this fact can promote their increasing utilization. Cu-Zr-Ti and Cu-Hf-Ti alloy systems – they are Cu-based alloys – have excellent mechanical properties. In this paper investigations of crystallization of amorphous Cu44,25Zr36Ag14,75Ti5 powder produced by ball milling (these processes have not been investigated yet according to the reference data) are described. In the course of investigation of the crystallization process, samples were heated to a temperature of investigation by means of a DSC equipment and the developed state was frozen by chilling. The investigation of the developed structure and to identify the phases formed during heat treatment, X-ray diffraction method was used.

Abstract: Selective laser sintering (SLS) of a multi-component Cu-based alloy, which consisted of a mixture of Cu, CuSn, and CuP powder, was successfully processed. The XRD, SEM, and EDX analysis shows that the bonding mechanism of this process is liquid phase sintering with partial melting of the powder occurred. The CuSn powder with lower melting point acts as the binder, while the Cu powder with higher melting point acts as the structural metal. The element phosphorus acts as a fluxing agent to prevent the Cu particles form oxidation. The distribution of phosphorus shows higher concentration at grain boundaries due to low solubility of P in Cu. A case study on SLS of this powder system to fabricate a gear was carried out. The relative density of 82% and radial dimension error of 1.9% were achieved.

Abstract: New Cu-based bulk amorphous alloys exhibiting a large supercooled liquid region and good mechanical properties were formed in a quaternary Cu-Ni-Zr-Ti systems consisting of only metallic elements. The compositional range for the formation of the amorphous alloys that have high glass forming ability (GFA) (> 3 mm diameter) and large supercooled liquid region (> 50 K) is defined in the pseudo-ternary phase diagram Cu-Ni-(Zr, Ti). A bulk amorphous Cu₅₄Ni₆Zr₂₂Ti₁₈ alloy with the diameter of 6 mm can be prepared by copper mold casting. The Cu₅₄Ni₆Zr₂₂Ti₁₈ alloy shows glass transition temperature (T_g) of 712 K, crystallization temperature (T_x) of 769 K and supercooled liquid region (ΔTx) of 57 K. The Cu₅₄Ni₆Zr₂₂Ti₁₈ alloy exhibits high compressive fracture strength of about 2130 MPa with a plastic strain of about 1.5 %. The new Cu-based bulk amorphous alloy with high GFA and good mechanical properties allows us to expect the extension of application fields as a new engineering material.