Marta Mikuśkiewicz

Influence of planetary milling parameters on the properties of the activated silicon and aluminium nitride powders

Mechanochemical processing of the silicon nitride based powders by high energy milling in a planetary mill is reported. The particle size distribution, specific surface area and their morphology after milling were studied after a period of a short (30 min) or long (up to 360 min) grinding. It has been shown that mechanochemical processing with the high energy led to the considerable destruction of the component crystal lattice apart from particles diminution, and moreover, to decomposition of the applied surfactant. As a result, significant agglomeration of powder particles occurred after the given milling time.

Synthesis and thermal characterization of dysprosium zirconate

Results of investigations related to synthesis and thermal properties analysis of the Dy2Zr2O7 phase was presented in this article. This material was obtained during high temperature synthesis in an actual pressure of 15 MPa, in vacuum of 3×10-6 MPa, and at 1350°C with 2 hours of exposure. Feedstock materials were submicrocrystalline powders of dysprosia Dy2O3 and zirconia ZrO2. Both powders were mechanically blended in alcohol before the sintering process. The final product was analysed from the phase’s composition point of view. It was revealed that main constituent elements were dysprosium zirconate with an overall formula of Dy2Zr2O7 and others were Dy zirconates with a non-stoichiometric character. The presence of zirconia was found with tetragonal types of unite cell. This fact evidences that partial dissolution of Dy2O3 in ZrO2 took place. The obtained material was characterized by calorimetric investigations in the thermal range from 25 to 1450°C.

Study of Phase Transformation in Alloys of the Al-Fe System

In this paper, phase transformation in alloys of the Al-Fe and Al-Fe-Cr systems was investigated. The alloys were prepared by melting and gravity casting. The studies of phase transformation were carried out on samples after casting and annealing, using the differential thermal analysis (DTA) and dilatometric method. The knowledge on the phase transformations in these alloys including the information about order-disorder transition is very important from the point of view of obtained mechanical and physical properties of alloys of the Al-Fe system. These results are an important contribution in development of knowledge on iron aluminides. In the article, temperatures of phase transformations connected with a change in order type and transition into disordered solid solution were defined. Conformity of the recorded DTA results and dilatometric analysis was achieved.

Corrosion Resistance of Alumina-Sialon Refractories for Application in Aluminium Industry

This paper describes the manufacturing and corrosion resistance of sialon based ceramics for application in the modern aluminium industry. Sialon based ceramics are characterized by excellent mechanical properties at high temperatures, good corrosion and thermal shock resistance and low wettability, thus this material is suitable for the long term liquid aluminium contact. To obtain reaction bonded materials in this work, relatively cheap and commonly available components were used: fine Si and Al2O3 powders. The specimens were examined after heating in flowing nitrogen for the phase composition and dimension stability. Sintered materials were tested for corrosion resistance and wettability in liquid aluminium. The microstructure of the contact surface was examined by SEM/EDS methods.

Calorimetric study of Eu2O3–ZrO2 feedstock powders and sintered materials

The synthesis of ceramic materials based on europia–zirconia system and obtained by solid-state reaction in high-temperature vacuum press was investigated. Firstly, phase composition and calorimetric behavior of feedstock powders was investigated. The second part of the paper concerns the synthesis process of non-stoichiometric mixtures of feedstock powders prepared by four different methods of mixing. The influence of the homogenization method on the calorimetric behavior and phase composition of obtained sinters was studied. Finally, the influence of the additional high-temperature annealing was also investigated. From the obtained results, it can be concluded that the mixing procedure had a very strong influence on the morphology of obtained sinters. This is due to the structural inhomogeneity, as indicated by differences in phase composition. The synthesis process has a gradual character, and the obtaining of materials with different level of homogeneity allowed the determination of the order of subsequent intermediate phase formation.

Thermal parameters determination of Co–Al–W as-cast alloy homogenization by DTA analysis

The γ–γ′ Co-based superalloys are newly developed class of refractory alloys which may replace commercial Ni-based superalloys owing to their favorable properties at high temperature. In case of new Co-based superalloys, the heat treatment aims to obtain microstructure composed of appropriate volume fraction of small cuboidal γ′-Co3(Al,W) precipitates within the γ-Co matrix. However, due to a high tendency to interdendritic segregations of alloying elements, the alloys based on Co–Al–W system should be normally homogenized before further steps of heat treatment (solutionizing and aging). In this study, thermal analysis was applied for determination of temperature range for primary heat treatment of the Co–9Al–9W (at.%). The differential thermal analysis (DTA) measurements were carried out on the thermal analyzer NETZSCH STA 449 F3 Jupiter. On the base of obtained results, respectively, solvus of γ′ phase and solidus temperatures were determined, as well as the thermal range of Co3W (DO19) phase precipitation. As a consequence, the heat treatment without homogenizing (only solution and aging) was proposed as a most suitable way to obtain beneficial microstructure.

Microstructure and Thermal Conductivity Characteristics of Sm2Zr2O7+8YSZ Type TBCs

The article presents results of microstructural investigations of plasma sprayed ceramic thermal barrier coatings obtained using Sm2Zr2O7+8YSZ and 8YSZ powders in 50/50, 25/75 and 75/25 proportions. The coatings thickness is evaluated and spherical, horizontal and vertical porosity is quantitatively and qualitatively characterized. The results obtained in this investigation were used for adjusted values of thermal conductivity calculations on the basis of results obtained from thermal diffusivity measurements at temperatures between 20 and 1100°C.

Qualitative and quantitative description of microstructure of alloys from the Fe-Al system

The paper presents the test results of qualitative and quantitative analysis of the structure of alloys from Fe-Al system after casting and heat treatment. The analysis were carried out for three alloys, with different content of Al at.%: 36, 38, 48 at %, which were produced by melting and gravity casting. A quantitative evaluation of the structure was made with use of MET-ILO application on the basis of images acquired from a light microscope. Moreover the influence of the chemical composition and results of quantitative description of microstructure on the hardness of alloys from the aluminium – iron system were analysed. The obtained research will be used for the development of mathematical models determining the influence of primary structure on the opportunities for plastic deformation of alloys. Structural examination was carried out using scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). X-ray diffraction measurements were performed on this alloys.