Volume 108, Issue 2

Structural anisotropy and excess volume in ultra-fine grained high-purity nickel prepared by equal-channel angular pressing (ECAP) is studied by means of dilatometry and compared with the processing route of high-pressure torsion. Both routes exhibit qualitatively similar three-stage behavior in length change upon defect annealing with a characteristic dependence on the measuring direction related to the deformation axes. Taking into account shape anisotropy of the crystallites, the length change in various directions can be quantitatively analyzed yielding direct access to the concentration of deformation-induced lattice vacancies, the vacancy relaxation, and the grain boundary expansion. The routes A12 and B C 12 of ECAP are compared.

The consequences of reducing the carbon concentration from 0.8 to 0.6 wt.% in a bulk nanostructured bainitic-steel have been investigated with the aim of enabling processing. We observed that the average thickness of the product phase plates increased from below 20–40 nm to about 100 nm after isothermal transformation at the same temperature. The increase in plate size led to decrease in hardness as expected. However the hardness reduction was not as large as might be expected, a transition to lower bainite at temperatures below 250°C may have provided additional strengthening. Transformation just below the martensite start temperature resulted in a mixture of martensite and bainite, with no observed increase in the rate of bainite transformation.

SA508Gr4 is a newly developed high-strength steel for nuclear reactor pressure vessels. Its welding characteristics remain largely unexplored. In this work, the simulated heat affected zone continuous cooling transformation (SH-CCT) diagram of SA508Gr4 steel was constructed and the high-temperature cooling phase compositions and the properties of the heat affected zone (HAZ) were characterized using dilatometry and microscopic tests. The results show that the phase transformation in the HAZ was divided into bainite and martensite transformation stages. When 4.6 ≤ t 8/5 (the HAZ cooling time from 800 °C to 500 °C) ≤ 15 s, lath-shaped martensite was fully developed, resulting in extensive hardening and cold cracking in the HAZ, while the cooling time required to form the bainite completely exceeds 1 200 s. Thus, to improve weld quality, preheating to 196 °C or higher is recommended.

The present study was carried out to investigate the effects of Ni, Mn, Zr, and Sc additions, individually or in combination, on the microstructure of 354 casting alloy (Al-9 wt.% Si-1.8 wt.% Cu-0.5 wt.% Mg). Microstructural examination and thermal analysis data showed that the main reactions detected during the solidification of the six 354 alloys (G1, G6–G10) investigated are: formation of the α-Al dendritic network; precipitation of Al-Si eutectic and post-eutectic β-Al 5 FeSi; Mg 2 Si phase; transformation of the β-phase into π-Al 8 Mg 3 FeSi 6 phase; and precipitation of Al 2 Cu and Q-Al 5 Mg 8 Cu 2 Si 6 phases. With 2 wt.% Ni addition, the formation of Al 9 FeNi and Al 3 CuNi phases is observed. In the base 354 alloy the main phases are restricted to Cu-, Mg-, and Fe-rich intermetallic phases. The Si particle characteristics and volume fraction of intermetallics are influenced by the solidification rate and Mg level, whereas addition of Fe and/or Mn has no significant influence. In alloy G9, Fe, Mn and Ni interact to form new intermetallic phases. An increased Fe content leads to formation of polyhedral/star-like sludge particles in addition to α-Fe and β-Al 5 FeSi phases; the presence of the hard sludge particles within the soft α-Al dendrites improves the alloy properties.

This paper presents the results of a microstructure and hardness investigation into the surface layer of cast aluminium–silicon alloys, after being alloyed by heat treatment and/or remelted with ceramic powders, using a high power diode laser (HPDL). The purpose of this work was to determine the appropriate laser treatment conditions for laser surface treatment of the investigated aluminium and magnesium alloys. For investigation of the obtained structure, optical and scanning electron microscopy was used with energy dispersive X-ray spectroscopy microanalysis. After the laser surface treatment was carried out on the heat-treated aluminium and magnesium cast alloys, there were visible structural changes concerning the microstructure, as well as distribution and morphology of the phases occurring in the alloy, influencing the hardness of the achieved layer. In the structure, three zones were discovered with different structures and properties. Concerning the laser treatment conditions for laser-surface hardening, the laser power and ceramic powder feed rate were also studied. The structure of the surface laser track changed so that two areas of the dispersing zone were detected, where the ceramic powder particles were present. This investigation, with the application of an HPDL for Al and Mg alloys, makes it possible to obtain or develop an interesting technology that is very attractive for the automobile and aviation industries, as a next step after laser surface treatment used for steels.

Dense Ti 2 AlN/TiB 2 composite was successfully fabricated via in-situ hot pressing using Ti, Al, and BN powders as starting materials. The reaction path, microstructure and typical properties were systematically investigated. It was found that the crystallographic orientation relationship between Ti 2 AlN and TiB 2 could be expressed as: (0 0 0 1) Ti 2 AlN//(0 0 0 1) TiB 2 and [1 2¯$\bar 2$ 1 0] Ti 2 AlN//[1 2¯$\bar 2$ 1 0] TiB 2 for the first time. The composite exhibits high flexural strength (924 ± 45 MPa), high hardness (13.4 ± 0.3 GPa) and high electrical conductivity (6.5 ± 0.2 × 10 6 (Ω m) −1 ).

Metal matrix composite made from 6061 aluminum alloy matrix reinforced with titanium carbide particles was fabricated by stir casting. Titanium carbide particles were incorporated with varying proportions of 2, 4 and 6 percent weight fractions. Stirring was done to achieve uniform distribution of reinforcement and castings were made by pouring the mixture into graphite moulds. The composite was then studied with respect to its mechanical properties and microstructure. Tensile, compressive, impact and hardness specimens were machined to establish the mechanical properties of the composite. Comparative study for all the said composites is done with respect to yield strength, tensile strength, hardness, impact strength and compressive strength.

The present work focuses on the performance and properties of organomodified graphene nanoplatelet filled polysulfone nanocomposites prepared by solution casting. Morphology of the nanocomposites was investigated using atomic force microscopy and transmission electron microscopy. Contact angle measurements showed significantly increased hydrophobicity of the nanocomposites relative to the neat polymer. Mechanical properties of the nanocomposites showed marked improvement at low graphene loadings. Thermal properties measured using thermogravimetric analysis showed that the incorporation of graphene increased the thermal stability and the char yield of the nanocomposites. After immersing the samples in various solvents, the changes in weight and mechanical property were evaluated and the aging performance was found to be improved. The prepared polysulfone nanocomposites with desired hydrophobic, thermal, mechanical and barrier properties are usable for high performance applications.

The influence of the chemical composition of Zn-12Al- y Cu- x Mg ( y = 1, 5; x = 0.05–1.4 mass%) die casting alloys on age-related deterioration in mechanical strength and creep behavior was investigated. Tensile tests were performed after aging at room temperature for 1 day and at 100 °C for 1 week. Creep tests were carried out under tensile stresses of 25, 50 and 100 MPa at 100, 130 and 160 °C. Cu addition suppressed age-related deterioration of proof stress by suppressing the coarsening of the eutectic structure during the aging. Creep resistance was improved by the Mg addition, whereas the Cu addition has a deleterious effect on creep resistance. The results show that the age-related deterioration of Zn-12Al alloys can be improved without sacrificing creep resistance by the complex addition of Cu and Mg.

In this work, we investigated the effects of mixing speed on the tribological performance of a composite prepared with potassium titanate whiskers, palygorskites, and aramid fibers during the mixing process. The results showed that for the aramid fibers with a uniformity of 5–6 mm, 500 rad min −1 was the best speed compared with 800 rad min −1 and 1 000 rad min −1 , whereas for the uniformity of aramid pulp, 800 rad min −1 was the best speed. Furthermore, based on scanning electron microscopy analysis, it was demonstrated that the tribological performance of the composite, in particular, the friction coefficient with the aramid pulp exhibited a good stability, and its wear resistance was increased by 12%.