Band 105, Heft 6

The In–Pt–Sb system is modeled using the CALPHAD technique. The solution phases (liquid, fcc(Pt), rhom(Sb) and tetra(In)) are described as substitutional solution. The enthalpies of formation of the intermetallic compounds, Pt 7 Sb, Pt 3 Sb, Pt 3 Sb 2 , PtSb, PtSb 2 are calculated using first-principles calculations. In the In–Pt–Sb system, the compounds In 3 Pt 2 , In 2 Pt, In 7 Pt 3 in the In–Pt binary system and the compounds PtSb 2 and PtSb in the Pt–Sb binary system are treated as line compounds (In,Sb) m Pt n according to experimental solid solubility of the third component. The compound In 5 Pt 6 is treated as (In,Pt,Sb) 5 (In,Pt) 6 based on its thermodynamic model in the In–Pt system and experimental solid solubility of Sb in the In–Pt–Sb system. The thermodynamic model of compound InPt 3 keeps the order–disorder transition model with fcc(Pt) solid solution which was used in the In–Pt binary system, and is treated as (In,Pt,Sb) 0.25 (In,Pt,Sb) 0.75 . Other compounds InPt, In 9 Pt 13 , αIn 2 Pt 3 , βIn 2 Pt 3 , InPt 2 and InSb in the In–Pt–Sb system keep the same thermodynamic models as those in binary systems. Based on the published experimental isothermal sections, vertical sections and the liquidus surface projection, the In–Pt–Sb system is modeled, and a set of self-consistent thermodynamic parameters is obtained.

Two low-C steels, one microalloyed with Ti and the other with Ti and Mo were subjected to a classical controlled rolling schedule using torsion testing. The specific torsion schedules were a simulation of an industrial schedule adapted to the characteristic transformation temperatures of each steel. It is shown that such steels can develop a pancaked austenite, despite the fact that the alloys do not contain Nb. However, compared to Nb bearing steels, restoration between deformation passes is relatively rapid in the pancaking region. In order to reduce the loss of pancaking, the temperatures of the finishing rolling schedule were shifted to lower temperatures. This appeared to greatly reduce the restoration rates, but the transformation in the two phase region occurred towards the end of the final deformation pass. When comparing the two steels, it could be detected that Mo increases the temperature range for pancaking and reduces the restoration rates between deformation passes in the pancaking region.

Electrical discharge alloying was performed on AISI-D2 steel using Ni–W powder mixed dielectric in order to improve the hardness and to reduce the specific wear rate. The alloyed layer was characterized using optical microscopy, scanning electron microscopy, X-ray diffraction analysis and energy-dispersive spectroscopy. Wear tests were conducted based on L9 orthogonal array in a pin-on-disc tribometer and the alloying parameters were optimized using Taguchi's technique. Hard intermetallics based on Fe 7 C 3 , Cr 3 C 2 and Ni 2 W 4 C were formed by electric discharge alloying, which primarily contributed to the improvement in hardness up to 600 HV 0.5 . The specific wear rate of the alloyed layer was subsequently reduced by around a factor of eight compared to that of the base material. The pulse off-time was found to be predominant in obtaining higher hardness and lower specific wear rate among the alloying parameters, peak current, pulse on-time and off-time.

The fatigue-crack growth behavior of materials manufactured by means of selective laser sintering was studied. In the process, specimens were prepared from metal powders (316 steel) into the desired shape by additive manufacturing technology, followed by sintering and infiltration in a suitable molten metal. The latter process was aimed at eliminating the inherent porosity associated with powder metallurgy. Porosity is known to adversely affect the fatigue-crack growth rate behavior of powder metallurgy components. Carefully conducted fatigue-crack growth rate tests (single-edge-notch four-point bending type) were carried out on RapidSteel TM and the results were compared with data of infiltrated low carbon steel in the literature. Finite element analysis was carried out as an intermediate step in order to validate the geometry factor calculations provided by empirical formulae. It was found that the fracture resistance of RapidSteel was higher compared with low-carbon copper infiltrated steel tempered at 177 °C and 428 °C, and same as that tempered at 704 °C.

Manufacturing of WC–Co composites using the electroless precipitation method at different sintering temperatures of 1 100, 1 250, 1 350 and 1 500 °C was successfully achieved. The chemical composition of the investigated materials was 90 wt.% WC with 10 wt.% Co, and 80 wt.% WC with 20 wt.% Co. The specific density, densification, and Vickers microhardness measurements were found to increase with increased sintering temperature for both the WC–Co compositions. The composites of tungsten carbide with 10 wt.% Co had a higher specific density and Vickers microhardness measurements than those for the composites of tungsten carbide with 20 wt.% Co. Composites with WC-10 wt.% Co had better wear resistance. The stress–strain and transverse rupture strength increased monotonically with the increase in sintering temperatures, agreeing with the material hardness and wear resistance behavior. Fractographical scanning electron microscopy analysis of the fracture surface demonstrated a rough characteristic conical shape failure in the direction of the maximum shear stress. A proposed mechanism for the formation of the conical fracture surface under compression testing is presented.

In the present study, the molecular level mixing method has been extended to fabricate carbon nanotube based silver nanocomposite. Here, the influence of types of carbon nanotubes and their functionalization on the coefficient of thermal expansion was examined. Covalently and non-covalently functionalized single wall as well as multiwall carbon nanotubes were used in the synthesis process. The microstructural features of the composite revealed that the carbon nanotubes decorated with silver nanoparticles were dispersed embedded and anchored in the silver matrix. Experimental results confirmed that the coefficient of thermal expansion of the composite reduces in relation to that of pure silver, with increasing content of carbon nanotubes in the silver matrix. The thermal expansion of nanocomposites, up to 6 volume percent of nanotubes, reduces to 50 – 60 % that of pure silver. However, more reduction in thermal expansion of silver nanocomposite with single wall carbon nanotube than with multiwall nanotubes has been observed, which is correlated with high aspect ratio and large effective surface area of single wall nanotubes. Moreover, covalently functionalized multiwall nanotubes exhibit more reinforcing effect than non-covalently functionalized. We believe that strong bonding between carbon nanotubes and metal matrix due to covalent functionalization is responsible for effective reduction in thermal expansion.

This paper presents experimental results on four thermophysical properties of pure polycrystalline rhodium samples over a wide temperature range. Specific heat capacity and specific electrical resistivity were measured from 300 to 2 200 K, while hemispherical total and normal spectral emissivities were measured from 1 200 to 2 200 K. All the properties were obtained by means of the electrical pulse calorimetry technique using specimens in the form of a thin rod, of about 2 mm in diameter and 200 mm in length. For necessary corrections, literature data on thermal linear expansion have been used. All the results are compared with available literature data and discussed.

In this study, 0 – 15 wt.% Co 3 O 4 powders were added to 8 mol.% yttria-stabilized cubic zirconia (8YSZ) powders in order to determine the effect of Co 3 O 4 addition and amount on the microstructure, sintering, and electrical properties of yttria-stabilized cubic zirconia. Colloidal processing was used to ensure uniform mixing of the powders and to obtain a homogeneous microstructure. X-ray diffraction results showed that the average lattice parameter of the yttria-stabilized cubic zirconia decreased from 5.146 Å to 5.135 Å upon Co 3 O 4 addition, and that the lattice parameter did not change above a Co 3 O 4 content of 1 wt.%. The initial decrease in the lattice parameter is attributable to the smaller ionic radius of Co 3+ dissolved in the yttria-stabilized cubic zirconia matrix. The electrical conductivity of the specimens was measured using a frequency response analyzer in the range of 100 mHz – 13 MHz and 300 – 800 °C. Grain boundary conductivity of yttria-stabilized cubic zirconia was found to be enhanced with increasing Co 3 O 4 addition, with the presence of electronically conductive cobalt oxide at grain boundary triple points increasing the grain boundary conductivity, due to an increase in the Co 3+ and Co 2+ electronic charge carrier ions.

Pd electrocatalysts supported on antimony tin oxide and Vulcan XC-72 were both synthesized via a modified sodium borohydride reduction method. The catalysts were characterized by means of powder X-ray diffraction and cyclic voltammetry. Linear sweep voltammetry, open circuit potential curves and chronoamperometry were employed to evaluate the activities of the catalysts. The results show the particle size of Pd in the Pd electrocatalysts supported on antimony tin oxide catalyst is about 2.5 nm, which is smaller than that of the Pd electrocatalysts supported on Vulcan XC-72 (about 6.3 nm), and the surface area of the Pd electrocatalysts supported on antimony tin oxide electrode is larger than that of the Pd electrocatalysts supported on Vulcan XC-72 electrode. The Pd catalyst supported on antimony tin oxide shows superior performance to the catalyst supported on Vulcan XC-72.

Amorphous LaAlO 3 thin films were deposited on bare Si substrates using RF-magnetron sputtering at room temperature. A post-annealing process was performed in O 2 atmosphere at 650 °C for 30 min. The annealed films have a high-quality amorphous structure with faceted surface and uniform thickness. Smaller roughness of about 0.197 nm was observed. By analyzing the interfacial structure of the films, we confirmed that O 2 annealing causes the formation of a low k (∼ 6.57) La and Al silicate phase with high-quality interface and surface. Unlike most previous studies, our results show the possibility of the formation of a relatively low k interfacial layer for LaAlO 3 thin films during the thermal processing required by complementary metal oxide semiconductor applications.

Upon application of nano-sized metallic Ni particles as catalyst, the in-situ synthesis mechanism of spinel whiskers in MgO–C refractories was studied. Their phase composition and morphology were determined by means of X-ray diffraction and scanning electron microscopy supported by energy dispersive spectroscopy. The results show that when the catalyst of nano-sized Ni was added in MgO–C refractories, the granular MgAl 2 O 4 (MA) spinels transformed into the shape of whiskers at 1 200 °C. The presence of Ni catalyst can accelerate the generation of Mg vapor, which can react with Al vapor to form MA spinel whiskers. Through dissolution and precipitation, MA spinel crystals nucleate directly and grow into whiskers from the catalytic droplets of nano-sized metallic Ni particles. The growth of spinel whiskers follows a typical vapor–liquid–solid (V–L–S) growth mechanism.

Boron nitride can be used as a good catalyst carrier because of its high thermal conductivity and chemical stability. However, a high specific surface area of boron nitride is still desirable. In this work, a carbon fiber composite coated with boron nitride villous nano-film was prepared, and was also characterized by means of scanning electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller analysis. The results indicated that the carbon fibers were covered by uniform villous boron nitride films whose thickness was about 150 – 200 nm. The specific surface area of the boron nitride/carbon fiber composite material was 96 m 2  g −1 , which was markedly improved compared with conventional boron nitride materials

The effects of applied torque on the corrosion behaviour of W.-Nr. 1.4404 and 1.4462 stainless steels and W.-Nr. 2.4605 and 2.4858 nickel alloys with crevices were investigated using the cyclic potentiodynamic polarization method. Crevice corrosion (material-to-polytetrafluoroethylene) was tested in 3.5 % NaCl solution at 22 °C. The corroded surface was examined using scanning electron microscopy. The results indicate similar trends in susceptibility to crevice corrosion with increasing torque. Among the four specimens, the W.-Nr. 1.4404 is the most susceptible to crevice corrosion.

Various grain sizes of an Mg-4Y-3Nd-0.5Zr alloy were obtained by changing the cooling rate in a casting with wall thickness from 10 to 70 mm, and the effect of grain size on the microstructure and mechanical properties was investigated. When the cooling rate increased from 23.6 to 240.2 K min −1 , the grain size of as-cast specimens decreased from 115 to 42 μm, and the sizes of the eutectic phase morphology decreased. The ultimate tensile strength and tensile yield strength for heat-treated materials decreased 12 %–14 % due to the increase in grain size by decreasing the cooling rate. Meanwhile, both the ultimate tensile strength and yield strength showed a linear relationship with d −1/2 ( d is the grain size).