The phase relations in the ZrO2–La2O3–Gd2O3 ternary system were experimentally studied and thermodynamic modeling was performed. Selected compositions were synthesized using the co‐precipitation method, equilibrated at 1673 and 1873 K, and analyzed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM/EDX). The phase transformations were investigated using differential thermal analysis (DTA), and the heat capacities of (La1 − xGdx)2Zr2O7 (x = 0.25, 0.50, 0.75) compounds were measured using differential scanning calorimetry (DSC). Experimental studies showed a substantial extension of the fluorite phase into the ternary system and solid‐state transformations involving phases A (hexagonal), fluorite, B (monoclinic), and pyrochlore at 1845 K (DTA). Additionally, thermodynamic modeling was performed using the CALPHAD (CALculation of PHAse Diagrams) approach. Comparing the new experimental data and the calculations based on ternary extrapolations of the binary systems revealed major inconsistencies. One source of inconsistencies was related to the calculated phase equilibria in the binary La2O3–Gd2O3 system. Additional experimental investigation of the binary system indicated an underestimated solubility of La2O3 in the B phase in the temperature range 1673‐1873 K. Based on these new data, the mixing parameters of the B phase were re‐assessed. The new experimental results for the ternary system were used to optimize the mixing parameters of the fluorite, B and C (cubic) phases. All new experimental data were well reproduced by the improved thermodynamic description of the ternary system.

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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.

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A 2 B 2 O 7 oxides with pyrochlore or defected fluorite structure are among the most promising candidates for insulation layer material in thermal barrier coatings. The present paper presents the procedure of synthesis of holmium zirconate Ho 2 Zr 2 O 7 and praseodymium zirconate Pr 2 Zr 2 O 7 via Polymerized-Complex Method (PCM). Thermal analysis of precursor revealed that after calcination at relatively low temperature (700°C) fine-crystalline, single-phase material is obtained. Thermal diffusivity was measured in temperature range 25-200°C, Ho 2 Zr 2 O 7 exhibits lower thermal diffusivity than Pr 2 Zr 2 O 7 . Additionally, PrHoZr 2 O 7 was synthesized. The powder in as-calcined condition is single-phase, but during the sintering decomposition of solid solution took place and Ho-rich phase precipitated. This material exhibited the best insulating properties among the tested ones.