Grzegorz Włoch

High-strength and thermally stable Al – CeO2 composite produced by means of mechanical alloying

Abstract The effect of temperature on both mechanical and structural features of a new Al-based metallic composite reinforced with fine CeO2 particles was the primary objective of the research work. Mechanically alloyed Al – CeO2 composite was manufactured from high purity Al and CeO2 powders. The powders were milled under argon atmosphere and then consolidated using hot pressing, vacuum degassing and hot extrusion methods. Hot compression tests revealed high mechanical properties of the material, which were ascribed to the very fine-grained structure of the composite. Transmission electron microscopy observations were performed on as-extruded material and samples annealed at 773 K. It was found that the composite structure is relatively stable at 773 K in comparison to Al-based composites reinforced with other heavy-metal oxides reported in literature.

Structure and properties of P/M material of AlMg - SiO2 system processed by mechanical alloying

New methods of material processing have been actively pursued in recent years in an attempt to extend current materials performance. Of particular interest are the powder metallurgy (P/M) techniques of mechanical alloying (MA). The MA process is generally used to create the materials with unique properties which give the material a wide spectrum of possible advanced applications. Light - metal based mechanically alloyed composites strengthened by heavy metal oxides addition (MeO) [1] have been examined according to bilateral research cooperation between Nihon University, Tokyo and AGH — University of Science and Technology.

Microstructure and mechanical properties of AA7039+20%SiC W composite.

Hot deformation tests were performed on an AA7039‐matrix composite reinforced with a 20% addition of SiC whiskers. The flow stress maximum was reduced with deformation temperature from 640 MPa to ∼8 MPa at 293 K and 823 K, respectively. TEM observations, performed on as deformed samples, revealed a highly recovered substructure of the matrix and a striated structure of the whiskers. The fringes, which are perpendicular to the whiskers’ longitudinal axis, were ascribed to nano‐sized twins and stacking faults formed during the crystal growth rather than to some effects of the deformation process.

Investigation of Homogenization Process of the 5019 Alloy Extrusion Billets

In the paper, the influence of homogenization parameters on the microstructure and properties of the 5019 alloy DC-cast billets was analysed. At the first stage, the microstructure of the alloy in as-cast state was investigated using SEM/EDS technique. Additionally, a DSC test and hardness measurements were performed. In the as-cast material, the presence of the dendritic microstructure with a pronounced microsegregation of magnesium in the dendrites cross-section was found. Subsequently, the specimens were subjected to laboratory homogenization experiments, with different soaking conditions and water quenching. The microstructural effects of the investigated variants of homogenization were evaluated using the same techniques as in the case of the as-cast alloy. It was found that after homogenization, with soaking at the temperature of 530 °C for 6 hours, the microsegregation is eliminated and the concentration of magnesium in the grains centres is over two times greater than in the dendrites cores before annealing. The solidus temperature rises by about 12 °C in comparison to the as-cast state. Neither extending the soaking time nor rising the temperature contributes to a further increase of the solidus temperature, or the magnesium concentration in the grains interiors. However, the tendency of dispersoids to grow and the change of Fe-bearing constituents chemical composition were observed after the high temperature, or prolonged annealing variants.

Preliminary study on the thermomechanical treatment of shape memory alloys for applications in clothing protecting against heat

Nowadays, a rapid growth of smart materials’ implementation in textiles and clothing can be observed as it allows attaining the functions and properties unachievable with conventional materials. Unique characteristics of shape memory alloys, in particular nickel–titanium (NiTi), place them in the focus of interest in this area. Despite numerous research works concerning the analysis of the NiTi alloys’ properties, a further investigation is still needed due to their sensitivity to thermomechanical treatment conditions. In this article, the results of preliminary study aimed at designing thermomechanical treatment procedure for NiTi elements intended for specific application in clothing protecting against heat are presented. The analysis of the influence of annealing temperature and thermomechanical cycling method on characteristic temperatures of martensitic transformation with use of differential scanning calorimetry was performed. Moreover, recovery rate characterizing two-way shape memory effect was evaluated. Test results indicate that by means of an appropriate selection of the alloy and choice of thermomechanical treatment conditions, it is possible to achieve a phase transition in the required temperature range and desired recovery rate of NiTi elements.

The Structure and Mechanical Properties of Plastically Consolidated Al-Ni Alloy

Mixed and preliminarily consolidated powders of aluminium and nickel (90 mass % Al and 10 mass % Ni) were hot extruded. As results the rod, 8 mm in diameter, was obtained. As-extruded material was subjected to the microstructural investigations using scanning electron microscopy (SEM/EDS) and X-ray analysis (XRD). The differential scanning calorimetry (DSC) and thermo-mechanical analysis (TMA) were also performed. The mechanical properties of as extruded material were determined by the tensile test and Vickers hardness measurements. In order to evaluate the thermal stability of PM alloy, samples were annealed at the temperature of 475 and 550 °C. After annealing Vickers hardness measurements and tensile tests were carried out. The plastic consolidation of powders during extrusion was found to be very effective, because no pores or voids were observed in the examined material. The detailed microstructural investigations and XRD analyses did not reveal the presence of the intermetallic phases in the as-extruded material. During annealing, the Al3Ni intermetallic compound was formed as the result of chemical reaction between the alloy components. The hardness of the alloy after annealing at the temperature of 475°C was found to be comparable to the hardness in as-extruded state. Annealing of the material at the temperature of 550°C results in hardness decreasing by about 50%, as the consequence of porosity formation and Al3Ni cracking.

Structural Characterization of Mechanically Alloyed AlMg-CeO2 Composite

A mechanical alloying and hot extrusion method was used to manufacture an AlMg-based composite reinforced by ~9 wt.% addition of CeO2. Structural features of as-extruded and re-melted samples were characterized by SEM/TEM observations and XRD analysis. Highly refined structure with uniform distribution of structural components has been received. It was found that during mechanical alloying and following hot pressing and extrusion of the material the decomposition of CeO2 oxides has been initiated. As result, formation of intermetallic grains of Al4Ce type was observed. Thermal analysis experiments combined with structural characterization allowed to determine the equilibrium state of the AlMg-CeO2 composite structure.

Extrusion of rapidly solidified 6061 + 26 wt% Si alloy

Due to low thermal expansion coefficient, high strength to weight ratio as well as high wear and corrosion resistance, high silicon aluminum alloys are commonly used in aerospace, automobile industry and many other practical applications [1]. The most common aluminum foundry alloys contain 5 – 12 wt % silicon. Higher content of silicon is not useful for commonly produced as-cast materials because of embrittlement effect resulted from the coarse primary silicon development. The most of mechanical properties of castings are determined by the silicon and eutectic structure morphology [2]. Some refining of the structure can be achieved by means of mechanical mold vibrations at high enough amplitudes [3], modifications with alkali or rare earth metals [4] and also by increasing the cooling rate during casting procedures [2]. However, the most effective refining of Al – Si alloy structure can be achieved due to rapid solidification (RS) combined with powder metallurgy (P/M) methods. Experiments described bellow were performed on RS powder of 6061 + 26 wt% Si alloy that was mechanically consolidated by vacuum hot compression and extrusion procedures. The RS powder was produced by air spray atomization at Toyo Aluminum Company. Chemical composition of the alloy is shown in Table 1. Table 1. Chemical composition of 6061+26%Si alloy Element Si Mg Cu Fe Cr Zn Al wt.% 26.0 0.69 0.16 0.21 0.11 0.11 in balance