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With the rapid development of the machinery industry, bearing materials with better tribological properties are demanded. Al alloys containing Erbium (Er) and Zirconium (Zr) have better comprehensive performance, whose tribological properties have hardly been reported before. In this work, dry sliding wear tests were performed on the Al–Sn and Al–Sn–Er–Zr alloys in two different annealing states to study the effect of trace Er, Zr on the tribological properties of the Al–Sn alloys. The Al–Sn–Er–Zr alloys showed better wear resistance than the Al–Sn alloys, which was mainly due to the higher hardness and strength of the Al–Sn–Er–Zr alloys. The wear losses of the alloys annealed at 375 °C for 100 h at the load of 70 N were significantly lower than those of the alloys annealed at 300 °C for 4 h. The wear coefficient K of the alloys annealed at 375 °C for 100 h decreased with the increasing load. The Al–Sn–Er–Zr alloys showed smoother worn surfaces than the Al–Sn alloys. With the load increasing, the wear mechanism changed from abrasive wear, mild adhesive wear and slight delamination wear to severe adhesive wear and delamination wear. The wear scars of different samples under the same load were similar, indicating that the addition of trace Er, Zr and annealing process did not change the wear mechanism. All samples experienced cracks and voids in the tribolayers. And oxygen accumulated in these defects. Most wear debris were lamellar, which was related to the adhesive wear and consist with the delamination theory.

The thermodynamics of five Al3Er compounds were investigated through first-principles density-functional theory (DFT) and experimental analysis. The Al3Er compounds with Al3Ho.hR20 (prototype Al3Ho, Pearson symbol hR20), Cu3Au.cP4, AlNd3.hP8, Ni3Ti.hP16 and Al3Gd.hR12 structures exhibited formation energies of −0.412(−0.417), −0.411(−0.416), −0.400(−0.413), −0.399(−0.345) and −0.342(−0.345) meV/atom when using DFT with “standard” potential (“frozen core” potential) of Er. The results indicated that the Al3Ho.hR20 structure was the thermodynamic stable phase and the other structures were metastable. The formation energy of Cu3Au.cP4 structure was only 1 meV/atom less than that of Al3Ho.hR20. Experimentally, the Al-30 wt.% Er alloys were cooled from 900 °C to 500 °C at the rate of 5 ± 2 °C/h and 60 ± 2 °C/h, respectively. The corresponding XRD analysis showed that the Al3Ho.hR20 was formed at the cooling rate of 5 ± 2 °C/h and the Cu3Au.cP4 was formed at the cooling rate of 60 ± 2 °C/h, which indicated that the Al3Ho.hR20 was in a thermodynamic stable phase and the Cu3Au.cP4 was in a metastable phase with high stability. The structural analysis indicated that the tiny energy difference between Al3Ho.hR20 and Cu3Au.cP4 might be attributed to a similar structure with varied stacking sequences.

The orientation, hardness and Young's modulus of Al3Yb single crystal were analyzed using the electron back scatter diffraction (EBSD) and nanoindentation techniques, combined with the first principles calculations. The Al3Yb single crystal of about 1 mm size could be obtained by heating hypereutectic Al-38.5 (wt%)Yb alloy to liquid state and cooling to room temperature at 60 °C/h. The results showed that the hardnesses of the Al3Yb single crystals oriented in (318), (023), (213), (112) and (122) directions varied between 5.4 ± 0.1 and 5.7 ± 0.1 GPa, and the reduced modulus were between 131.9 ± 1.6 and 140.5 ± 3.9 GPa. First principles calculations by assuming standard Yb pseudopotential with 4f electrons showed that the elastic constants of C11, C12 and C44 were 149.4, 32.94 and 66.59 GPa, respectively, and the Poisson's ratio was 0.161. Based on these calculated elastic constants and Poisson's ratio and the reduced modulus values, the Young's modulus of the Al3Yb single crystal was determined to be between 148.4 ± 2.3 and 154.9 ± 2.3 GPa for different orientations and the anisotropy coefficient (A) was 1.17 ± 0.01.

The aging strengthening behavior and coarsening process of Al 3 Er precipitates were investigated in Al–0.045Er (in at.%) alloys aged isothermally at 300–400 °C, using Vickers micro-hardness measurement and transmission electron microscopy (TEM) observation. The isothermal hardness curves showed that the peak hardness decreased slightly with the increase of temperature. From the TEM observations, the radius of Al 3 Er precipitates at peak hardness was measured to be 2.4 ± 0.4 nm. The coherency of Al 3 Er precipitates started to get lost at the radius of 8.0–9.1 nm, which were much larger than the predicted value. The difference was speculated to be due the reduction of misfit between Al 3 Er precipitates and matrix when particles were very small. From the analysis of the coarsening of coherent Al 3 Er particles using LSW theory, the diffusion activation energy and the diffusivity pre-exponential constant of Er in Al were deduced to be 77.2 ± 5.3 kJ/mol and (4.3 ± 2.2) × 10 −12 m 2 s −1 , respectively. Finally, the strength increment caused by Al 3 Er particles was evaluated using precipitation strengthening theory. It was found that when the particle radius was larger than 2.4 nm, the Orowan bypass mechanism dominated. In radius of 0–1.4 nm, a less coherency strengthening contribution indicated a reduction of lattice misfit between particles and matrix. From the strength plateaus in radius of 1.4–2.4 nm, the anti-phase boundary (APB) energy of Al 3 Er precipitates was deduced to be 0.60 ± 0.03 J/m 2 .

The solubilities of Er and Yb in Al at high temperature were evaluated from the electrical resistivity measurement, from which the Δ S and Δ H were estimated to be 3.0 ± 0.1k and −0.86 ± 0.01 eV for Al–Er alloys, 3.7 ± 1.0k and −0.93 ± 0.07 eV for Al–Yb alloys, respectively. The solubility curves of Er and Yb therefore could be obtained. According to the solubility curves of Er and Yb, on the one hand, the largest volume fractions of Al 3 Er, Al 3 Yb at room temperature were calculated to be 0.18%, 0.10%, respectively, which were obviously less than that of Al 3 Sc, i.e., 0.92%. On the other hand, the free energy per unit volume for the nucleation of trialuminides was evaluated with the consideration of Gibbs–Thomson effect. According to the obtained chemical driving force, the corresponding critical radius, critical nucleation energy and the steady state nucleation rate could be further calculated. The results indicated that in the binary alloys with the same concentration at the same temperature, comparing with Al 3 Sc, Al 3 Yb and Al 3 Er showed smaller critical radius and larger steady state nucleation rate, which implied that in Al–Yb and Al–Er alloys, higher number density of fine precipitates would be possibly existed.

The intergranular corrosion and β phase evolution of 5083 aluminum alloy containing Er and Zr during annealing at 100–230 °C were studied using mass loss tests and transmission electron microscopy. The mass loss curves showed that when annealing temperature changed from 200 to 220 °C, the alloy was subjected to a transition from sensitized state to stabilized state, corresponding to the change of nucleation position of β precipitates from grain boundaries to triple junctions. Particularly, when the annealing temperature was at 210 °C, this transition could also happen when the annealing time was increased from 0.5-10 h to 15-24 h, associated with the change in the shape of β precipitates. The classical nucleation analysis with the consideration of Mg segregation showed the nucleation rates at grain boundary and triple junction were 1013 and 1011 m−3 s−1 at sensitization temperature 150 °C, but 109 and 1010 m−3 s−1 at stabilization temperature 220 °C, suggesting the change of nucleation site with increasing temperature. The analysis of diffusion flux of Mg around β precipitate suggested that the shape change of β precipitates from elongate to spheroidal at 210 °C was attributed to the dominant interface diffusion over the grain boundary diffusion with the increase of time. Keywords: Aluminum alloy, Microstructure, Corrosion, Classical nucleation theory, Diffusion

The recrystallization behaviors of Al-Er and Al-Er-Zr alloy at different aging states have been investigated. The results indicate that the recrystallization temperature of Al-Er-Zr alloy is significantly higher than that of Al-Er alloy. Al-Er-Zr alloy at over aged state after 60% cold rolled has the highest recrystallization temperature.

We have studied the electronic structure of the interface between 6H-SiC{0001} and graphite. On n-type and p-type 6H-SiC(0001) we observe Schottky barriers of Phi_b,n^Si= 0.3+-0.1eV and Phi_b,p^Si=2.7+-0.1eV, respectively. The observed barrier is face specific: on n-type 6H-SiC(000-1) we find Phi_b,n^C=1.3+-0.1eV. The impact of these barriers on the electrical properties of metal/SiC contacts is discussed., Comment: 6th European Conference on Silicon Carbide and Related Materials, ECSCRM 2006, Newcastle upon Tyne, UK, September 3rd - 7th, 2006. Revised version. Proceeding will appear in Materials Science Forum