Intermetallic coumpound formation at metal–metal interfaces was observed for thin film couples of Al and transition metals such as Cr, Ti, Hf, Zr, Co, Ta, Pd, and Pt. The Al–Cr system was investigated in some detail using a conductance method and nuclear backscattering for reaction‐rate measurements. The compounds CrAl7 and Cr2Al11 were identified and their growth was found to be diffusion controlled. The temperature dependence of the rate constant for CrAl7 obeyed an Arrhenius plot from 300° to 450 °C with an activation energy of 1.91±0.1 eV. The Al‐rich phases of the remaining transition metals were investigated; the compounds either exhibited a planar interface with parabolic growth kinetics or an irregular interface with nonparabolic growth. An empirical relationship involving the melting point and stability of the compounds was proposed to explain the different growth kinetics.

KINETICS OF COMPOUND FORMATION IN THIN FILM COUPLES OF Al AND TRANSITION METALS.

Constitutive flow behavior and hot workability of the powder metallurgy processed 20 vol.%SiC(P)/2024Al composite were investigated using hot compression tests. The modified Arrhenius-type constitutive equations were presented with the values of material constants in consideration as a function of strain. Dynamic material model (DMM) and modified DMM were used to construct the power dissipation efficiency maps, and Ziegler's instability criterion and Gegel's stability criterion were used to build instability maps. The presence of finer SiC(P) and more boundaries resulting from smaller 2024Al powders shifted the dynamic recrystallization domain of the 2024Al matrix to higher strain rate and lower temperature ranges and decreased the peak value of power dissipation efficiency. Large instable regions were found in the form of flow localization and cavitations located at the matrix/SiC(P) interfaces and within the SiC(P) clusters. By comparison, the Gegel's stability criterion was more sensitive to the instability zones than the Ziegler's instability criterion for this material. (c) 2010 Elsevier B.V. All rights reserved.

Constitutive flow behavior and hot workability of powder metallurgy processed 20 vol.%SiCP/2024Al composite

Study on hot deformation behavior and workability of squeeze-cast 20 vol%SiCw/6061Al composites using processing map

Cu (400 A)/polyimide was mixed with 80 keV Ar+ and N2+ from 1.0×1015 to 2.0×1016 ions/cm2. The same processes were repeated for the Cu (400 A)/Al (50 A)/polyimide system which has Al as a buffer layer. The quantitative adhesion strength was measured by a standard scratch test. X-ray photoelectron spectroscopy was employed to investigate the change in the chemical bonds of the ion beam mixed polyimide substrate and the intermediate effects for the adhesion enhancement in Cu/Al/polyimide. Two distinct tendencies are observed in the adhesion strength: Cu/Al/polyimide is more adhesive than Cu/polyimide after ion beam mixing, and N2+ ions are more effective in the adhesion enhancement than Ar+. The formation of an interlayer compound of CuAl2O4 accounts for the former, while the latter is understood by the fact that N2+ ions produce more pyridinelike moiety, amide group and tertiary amine moiety which are known as adhesion promoters.

Adhesion enhancement of ion beam mixed Cu/Al/polyimide

Irradiation experiments were conducted on multilayer (ML) and coevaporated (CO) thin films in order to examine the role that the heat of mixing ({Delta}H{sub mix}) has in ion-induced grain growth Room temperature irradiations using 17 MeV Xe were performed in the High Voltage Electron Microscope at Argonne National Laboratory The alloys studied (Pt-Ti, Pt-V, Pt-Ni, Au-Co and Ni-Al) spanned a large range of {Delta}H{sub mix} values Comparison of grain growth rates between ML and CO films of a given alloy confirmed a heat of mixing effect Differences in grain growth rates between ML and CO films scaled according to the sign and magnitude of {Delta}H{sub mix} of the system (with exception of the Pt-V system) Substantial variations in growth rates among CO alloy films experiencing similar irradiation damage demonstrated that a purely collisional approach is inadequate for describing ion-induced grain growth and consideration must also be given to material-specific properties Results from CO alloy films were consistent with a thermal spike model of ion-induced grain growth The grain boundary mobility was observed to be proportional to the thermal spike-related parameter, (F{sub D}{sup 2})/({Delta}H{sub coh}{sup 3}), where F{sub D} is the deposited damage energy and {Delta}H{sub coh} is the cohesive energy

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Ion-induced grain growth in multilayer and coevaporated metal alloy thin films

A dynamic Monte Carlo simulation (MCS) program was developed to discribe the processes of interfacial modification of materials by ion beam mixing and applied to the bilayer and multilayer Al/Pd system. For the bilayer system, the MCS results for the dependence of the mixing rate on the film thickness of top layer (Al) show that the optimum film thickness for ion beam mixing corresponding to the mean damage depth in the Al layer. The dynamic MCS results show that the number of moved Pd atoms is larger than that of Al for small Al overlayer thickness due to collisional nature. In the case of multilayer system, the mixing rate depends on the structure of the multilayered system, and differs from the bilayered system. The mixing rate has a maximum value at the second interface with no dependence on structure. The maximum mixing rate for the multilayer system is larger than that of the bilayer system by a factor of 2. The energy deposition due to the nuclear collisions at the interface and the total number of intermixed atoms across the interface are found to play an important role for these interfacial mixing characteristics.

Dynamic Monte Carlo simulation for cascade interfacial mixing

Atomic transport in the radiation enhanced diffusion (RED) region has been studied from the shifts of a marker layer in ion beam mixed Pd Co and Pd Au bilayers 80 keV Ar+ with a dose of 15 × 1016 ions/cm2 were irradiated into the bilayers at temperature region from 90 K to 700 K In the Pd Co system, the atomic flux of Pd (JPd) transported across the interface is nearly same with JCo in the thermal spike region, while JPd is always larger than JCo in the RED regio However, in the Pd Au system, JPd is nearly same with JAu in both of the thermal spike and RED regions We have developed a model to describe the atomic transport in the RED region, which predicts that the atom with small cohesive energy has more mobility than that with large cohesive energy

Cohesive energy effects on the atomic transport induced by ion beam mixing

Evaporated Al/Cr bilayer thin films were irradiated by 80 keV Ar+ at doses in the range from 1 × 1015 to 2 × 1016 Ar+/cm2 at room temperature in order to investigate the Ar+ induced interfacial mixing behavior and the phase formation and transition by Ar+ bombardment. Ion bombardment induces intermixing across the Al/Cr interface and mixing variance increases with increasing ion dose. Cascade and thermal spike models are found to be not adequate for the ion beam mixing mechanism at room temperature in this system. The Al13Cr2 phase is formed as an initial phase by ion beam mixing and then transforms into the Al11Cr2 or Al4Cr phases at subsequent ion bombardment. This result is discussed in terms of the enhanced atomic mobility and the thermodynamical driving force by introducing the concept of an effective heat of formation.

Ar + induced interfacial mixing and phase formation in the Al/Cr system

Ion-beam mixing in Al-Pd, Al-Cr, Pd-Cu, Ag-Cu and Ag-Fe bilayers has been studied using Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES) over an ion dose range between 1 × 1015 and 1 × 1016 Ar+ cm−2 at room temperature. RBS and AES results show that the mixing efficiency of the light elements is higher than that of the heavy elements. The mixing efficiency of a heavy element is independent of the heat of mixing energy, while that of a light element has a close relation with the heat of mixing. The experimental results are discussed in terms of cascade mixing and thermal spike mixing.

Ar+-induced mixing mechanisms in metal-metal bilayer systems

Evaporated A1/Pd bilayered thin films have been irradiated using 80 keV Ar+ with doses in the range of 1 × 1015 to 1 × 1016 Ar + cm 2 at room temperature. Auger electron spectroscopy depth profiles show that intermixing has occurred through the Al/Pd interface as a result of Ar+ bombardment. The mixing variances of Al and Pd are far from being constants, and the mixing efficiency of Al is higher than that of Pd. A strong dependence of the mixing variance on the nuclear energy deposition was observed. The experimental results are discussed in terms of the damage controlled atomic motion.

J.J. Woo

Papers

Dynamic Monte Carlo simulation for cascade interfacial mixing

Cohesive energy effects on the atomic transport induced by ion beam mixing

Ar + induced interfacial mixing and phase formation in the Al/Cr system

Ar+-induced mixing mechanisms in metal-metal bilayer systems

Ion beam mixing variance profiles of A1 and Pd in A1/Pd bilayers