Band 95, Heft 2

The Rh–Zr system has been critically assessed by means of the CALPHAD technique. The solution phases (liquid, body-centered cubic (Zr), face-centered cubic (Rh) and hexagonal close-packed (Zr)) were modeled with the Redlich – Kister equation. The intermetallic compounds Rh 3 Zr, Rh 5 Zr 3 , Rh 4 Zr 3 , and RhZr, which have a homogeneity range, were treated by the formulae (Rh, Zr) 3 (Rh, Zr), Rh 5 (Rh, Zr) 3 , (Rh, Zr) 4 Zr 3 , and Rh(Rh, Zr) by a two-sublattice model with Rh and Zr or Rh on the first sublattice, Rh and Zr or Zr on the second one, respectively. The intermetallic compound RhZr 2 was treated as a stoichiometric compound. A set of self-consistent thermodynamic parameters of the Rh–Zr system was obtained.

63 Ni grain boundary (GB) diffusion in polycrystalline γ-Fe – Ni alloy was measured by the conventional radiotracer method. The double product P = δ x D gb ( δ is the GB width and D gb is the GB diffusivity) was found to follow the Arrhenius relationship P =1.31×10 −13 × exp(−157 kJ mol −1 / RT ) m 3 /s, where R is the gas constant and T is the temperature. The results in the coarse-grained material (grain size d ≈ 0.5 mm) were discussed in comparison with our previous investigation of Ni diffusion in a nanocrystalline alloy ( d ≈ 100 nm) of the same composition.

Differential scanning calorimetry and transmission electron microscopy (TEM) were employed to investigate the crystallization kinetics of an amorphous Zr 70 Cu 20 Ni 10 alloy. It has been found that the crystallization process is mainly controlled by three-dimensional nucleation and growth with an increasing nucleation rate. The activation energy for crystallization is approximately 388 kJ/mol. TEM observations confirmed that the primary precipitation phase during the isothermal crystallization process is the Zr 2 Ni phase, which can be partly attributed to the stronger binding nature between Zr and Ni atoms than that between Zr and Cu atoms.

Previously, it has been established that oxidation-induced cavitation of binary NiAl alloys occurs primarily when Nirich compositions are oxidized. In this work it is shown that at 1100 °C cavities form principally during the very early stages of oxidation for these compositions. During this time, the growing oxide is a transient, theta-alumina whereas on the Al-rich compositions the growing oxide rapidly transforms to alpha alumina. It is concluded that cavity formation is associated with tensile stresses generated by the flux divergence created by the outward diffusion of Al during the growth of theta-alumina and the inward diffusion of nickel. Once the transient oxide transforms to alpha alumina, the outward flux of aluminum is decreased and with it the flux divergence. Values for the inter-diffusion coefficients for the alloys investigated, derived from the diffusion profiles, are also reported.

The influences of counterface materials and reinforcements on the sliding wear behavior of copper matrix composites have been investigated. Experiments were performed using a block-on-ring type wear machine on which SiC/Cu and (SiC+Gr)/Cu hybrid composites were slid against various counterfaces, i. e. GCr15 bearing steel, 45 medium carbide steel and AlSi alloy. Experimental results show that increasing counterface hardness is in favor of the establishment of a wear resistant mechanically mixed layer (MML) on SiC/ Cu composite, while massive materials transfer and seizure take place when tested against soft counterface. The wear resistance of hybrid composite is improved by forming a graphite-rich MML, and the hardness of steel counterfaces does not influence the wear behavior obviously. The graphite film formed on the two sliding surfaces alleviates materials transfer and avoids the occurrence of seizure with soft counterface.

An artificial neural network was applied to slag glass-ceramic complex data analysis. A three-layer feedforward network was built with a new robust learning algorithm based on a concept of entire error modifying . These studies indicate that the network has an excellent learning ability when its topology is M –(2 M + 1) – 1 and when an appropriate study error was chosen. Research shows that this slag glass-ceramic neural network is robust, accurate and stable in complex data analysis, and can disclose the relationship of elemental compositions, processing parameters and material properties of slag glass-ceramic effectively.

Single-spark erosion experiments were conducted in different pure metal samples. The samples were used as the cathode, and a platinum electrode was used as the anode. The sparks were produced at high pressure and room temperature, having at this conditions a breakdown phase (ca. 100 ns) and an arc phase (several hundreds of μs). The crater volumes on the different materials were correlated with several properties of materials, in view of different models of material erosion related to melting enthalpy, vaporization enthalpy and sublimation energy. It was found that the quotient between the eroded volume and the spark energy correlates well with a function of the energy necessary to heat the material up to the melting point and to melt it. The particle ejection model can be used to explain this process. Moreover, it was found that the crater shape is related to the surface tension of the molten material. These investigations may be relevant for the development of high-performance materials for electrode and contact applications.

The influence of silicon and other alloying elements of plastic-molding steels on machinability in face-milling and ball-nose end-milling was investigated. Increase of silicon content decreased the adhesion of chips to a tool and as a result, tool life increased in a dry cutting condition. Vanadium had a similar effect, especially at relatively low cutting speed. To understand these phenomena, the chip surface was analyzed. From these results, it is proposed that low melting temperature oxides of the Fe–Si–O and Fe–V–O systems are formed on the chip surface of high-silicon steel and vanadium-added steel; these oxides lubricate the interface between chip and tool. On the other hand, manganese and chromium that on believed to are form the Fe–Mn–O and Fe–Cr–O oxide film of high melting temperature reduced the lubrication effect. Carbon also decreased tool life due to an increase of pearlite, while the addition of sulfur did not influence tool life.

The documented experimental results show that grain refinement can not substantially improve the elongation but the strength of low carbon steels, particularly when the grain size is smaller than 1 μm. A simple model of geometrically necessary dislocations and statistically-stored dislocations is proposed to account for the effects of grain refinement on the yield strength and uniform elongation of ultrafine grained low carbon steels. In this model, both grain boundary and precipitate strengthening mechanisms were considered. It is shown that both grain and precipitate refinements are necessary to improve the strength and elongation of materials.