Michał Stopyra

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.

The influence of section thickness on microstructure of Elektron 21 and QE22 magnesium alloys

The paper presents analysis of section thickness’ influence on microstructure of Elektron 21 and QE22 magnesium alloys in the form of a stepped casting test. Solid solution grain size and volume fraction of eutectic areas were measured using light microscope and sterological methods. The results showed the significant increase of grain size caused by wall thickness and its slight decrease connected with the distance beetwen analysed section and the gating system. This relationship was confirmed using statistical methods. QE22 alloy demonstrated finer grain structure than Elektron 21 alloy as well as lesser susceptibility of grain size to solidification conditions

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.

Cracking of 7CrMoVTiB10-10 (T24) Steel Weld Joints

7CrMoVTiB10-10 (T24) steel was designed for high temperature applications, especially for water wall panels in modern supercritical coal-fired boilers. However, welding of T24 steel caused many problems due to its cracking susceptibility. In the present paper the causes of T24 steel weld joints cracking have been discussed. Microstructural and fractographic analysis of weld joint were conducted and hardness was measured. It was found that the main causes of crack’s formation in weld metal are hot cracking susceptibility of T24, high deformation during welding process and weld metals’ hardenability. The mechanism of cracking was determined. It was concluded that cracks had been initiated in high temperature brittleness range, then propagated through the weld metal in transverse direction as the cold cracks. The reduction of weld metal’s ductility was due to too high cooling rate and excessive hardening of weld metal in relation to base metal.

The Corrosion Resistance of the Mg-Al-Ca-Sr Sand Casting Magnesium Alloys

In this paper, the corrosion resistance of two sand-casting creep resistant magnesium alloys Mg-9Al-1.5Ca-0.3Sr and Mg-9Al-2.2Ca-0.8Sr in the salt environment has been investigated. Specimens of each alloy has been immersed in 3.5% NaCl solution at room temperature and successively taken out after 1, 2, 4, 5 and 9 days. After immersion test, the microstructure and the appearances of the corroded structure were examined. The corrosion rates of both investigated alloys increased lineally with increasing the exposure time in both solutions. Mg-9Al-1.5Ca-0.3Sr alloy exhibits the higher corrosion rate during the immersion test than Mg-9Al-2.2Ca-0.8Sr. The corrosion layer of both alloys consists of MgO, MgOH and phases containing Cl, Na, Al and Ca. The increase of Ca content in the Mg-9Al-2.2Ca-0.8Sr alloy improved the corrosion resistance due to the formation of the reticular (Mg,Al)2Ca phase, which acted as an effective barrier against corrosion.

The Causes of Low Impact Strength of T23 Steel Weld Joints

T23 is modern bainitic steel designed for use in supercritical boilers. According to producer’s data weldability of this steel is good enough to avoid post-weld heat treatment. However, some of the T23 weld joints in as-welded condition have not met the minimal ductility requirement. The impact test revealed significant differences between the joints in as-welded and heat treated condition. Metallographic and fractographic examinations have been conducted in order to explain those differences. The specimens with low impact strength were characterized by brittle fracture and non-tempered martensite presence in weld metal. It was concluded that avoiding formation of disadvantageous structure in weld metal requires conducting of post weld heat treatment or applying multi-pass welding technique with annealing run.

Microstructural Stability of Long-Term Annealed AZ91 Magnesium Alloy Weld Joint

Welding and pad welding are widely used methods of repair and regeneration of defective magnesium alloys castings. AZ91 is one of the most popular magnesium alloys used at temperature up to 120°C. Therefore there is need to study the influence of welding and elevated temperature exposure on the microstructure and properties of AZ91 weld joints. This paper discusses microstructural stability of AZ91 gas tungsten arc weld joint in T6 condition (solution treated and aged). In order to examine the weld joints microstructural stability, the long-term annealing has been carried out at 120°C. Hardness of the base metal and fusion weld was measured after 250, 500, 750 and 1000h exposure respectively. Additionally, the base metals and the welds microstructure after 1000h annealing was investigated. Both in the base metal and in the weld, long-term annealing caused decrease in the intermetallic phases volume fraction. However, neither phase composition nor hardness of the weld joint were influenced by the heat treatment. Based on these results, it could be stated that the microstructure of investigated weld joint is stable at working temperature.

The Influence of Various Etchants on the Quantitative Analysis of Microstructure of Mg-Nd Alloy

The paper presents the results of the influence of various etchants on the quantitative analysis of microstructure of Mg-Nd master alloy. The methodology of quantitative analysis of these alloys’ microstructure were also presented. Qualitative analysis were done using light and scanning electron microscopes, chemical composition was investigated using EDS method. Seven types of etchants were used. Having chosen suitable images, quantitative analysis were done using Met-Ilo program. Comparison of results showed that chosen etchants didn’t make the significant influence on the quantitative analysis results of the microstructure, despite visible dissimilarities.

The Quality of Produced Sand-cast Engine Block Made from Elektron 21 Magnesium Alloy

The casting defects, microstructure and hardness of Elektron 21 Mg sand casting alloy was investigated. Visual and radiographic examination showed the presence of non-metallic inclusions and porosity. Quantitative analysis of microstructure was performed, no correlation between section thickness, grain size, volume fraction of eutectic areas and hardness was observed. Casting defects were responsible for cracking at magnesium casting/steel tube interface.

Corrosion Resistance of Mg-xAl-3Ca-0.8Sr Magnesium Alloys

The microstructure of Mg-xAl-3Ca-0.8Sr alloys consists of the α-Mg solid solution, irregular-shaped (Al,Mg)2Ca, bulky Al3Mg13Sr and lamellar (Al,Mg)4Sr phases. The results showed that aluminum has a positive effect on the corrosion resistance of Mg-xAl-3Ca-0.8Sr alloys. The main corrosion product is magnesium hydroxide Mg (OH)2 which forms a cracked layer on the surface of Mg-xAl-3Ca-0.8Sr alloys.