Development of Ti PVD Films to Limit the Carburization of Metal Powders during SPS Process

Spark plasma sintering technique is used for the fabrication of dense materials with a fine-grained microstructure. In this process, a powder is placed into a graphite mold and a uniaxial pressure is applied by two graphite punches. A graphite foil is inserted between the punches and the powder and between the mold and the powder to ensure good electrical, physical and thermal contact. One of the major drawbacks during sintering of metal powders is the carburization of the powder in contact with the graphite foils. In this study, a PVD coating of titanium was applied on the graphite foils in contact with the metal powder (pure iron). The results are promising, as the investigations show that the application of a Ti PVD film of 1.5 and 1.1 µm thickness is effective to completely avoid the carburization of iron powder. Carbon diffuses inside the PVD film during sintering. In parallel, iron diffusion was revealed inside the Ti coating of 1.5 µm thickness. On the other hand, a Ti PVD film of 0.5 µm thickness provides a protection against carbon diffusion just on the sides in contact with the mold, proving that the coating thickness represents an important parameter to consider.

Analysis of oxide scale thickness and pores position of HCM12A steel in supercritical water

More attention has been paid to the exfoliation of oxide scale on high-temperature heating surface of utility boiler. The oxidation mechanism of HCM12A steel in supercritical water is proposed and the growth of oxide film is simulated. The duplex scale contains an outer magnetite layer and an inner Cr-rich spinel layer. According to the data of Backhaus and Töpfer, the diffusion coefficient values of iron in magnetite layer are discussed and the function of R V, R I {R}_{\text{I}} for oxygen activity can be used for calculation of iron diffusion coefficients in Cr-rich spinel layer. Based on Wagner’s oxidation theory, the oxidation rate constants of HCM12A are calculated at 500 and 600°C in supercritical water, compared with experimental data of the relevant literatures. The oxygen activities at the interfaces of alloy/Cr-rich spinel oxide and magnetite/supercritical water are estimated. The simulation results of weight gain are matched with the test data. The iron diffusion mechanisms inside the magnetite layer and the Cr-rich spinel layer are analyzed. The iron diffusion coefficient at the interface of Cr-rich spinel/magnetite is discontinuous, while the oxygen activity is continuous in the whole double layer. The thickness of oxide scale on inner tube walls of the final superheater coils (T91) of a 600 MW supercritical boiler is calculated by using the calculation method provided by the paper. The modeling results, the measured data, and the calculation results by the method are compared. Accurate calculation of the thickness of the inner and outer oxide scales can provide a necessary basis for predicting the stress and exfoliation of oxide scales.

SIMULATION OF IRON CORROSION IN LEAD-MAGNESIUM EUTECTIC (LME) USING OXYGEN INHIBITOR

SIMULATION OF IRON CORROSION IN LEAD-MAGNESIUM EUTECTIC (LME) USING OXYGEN INHIBITOR. Lead-magnesium (Pb-Mg) is a metal that considered to have potential as a coolant raw material in the heat transfer system of nuclear reactors. However, the coolant in the form of Pb-Mg eutectic is corrosive to structured materials (eg steel cladding) used in reactors. In this research, steel material is represented by pure iron to simplify the simulation and calculation. This research aims to determine the effect of temperature on iron corrosion and the effect of adding oxygen as an inhibitor to reduce the iron corrosion rate in LME. In this study, corrosion was observed by looking at (coefficient) the diffusion of iron atoms into LME. A large iron diffusion coefficient represents high iron corrosion. To see inhibition effectivity with oxygen, the most effective oxygen concentration that can reduce the iron diffusion coefficient is searched. Simulations of iron corrosion and inhibition are performed using molecular dynamics simulation. The result of this research showed that oxygen concentration mixed into LME for effective inhibition of iron corrosion was in the range of 0.125 wt% - 0.135 wt% (for temperatures of 973K). Thus, oxygen is believed that able to inhibit iron corrosion in Pb-Mg eutectic up to 98.44%

Change of Mechanical Properties of Zinc Coatings After Heat Treatment

Hot-dip galvanized coatings represent a protection based on passivation of the single zinc layer. It is one of the most commonly used surface treatments of steel. However, pure zinc forms merely an insignificant upper layer. Coating crosscut is formed by intermetallic phases that can cause decrease in the level of anticorrosion protection. This results from an iron diffusion from the base material. Goal of this paper is to analyse the changes in the mechanical properties of these phases in relation to zinc coating heat treatment. For the experiment, annealing temperatures of 200 °C and 300 °C were used, and the staying time was set at 1, 3 and 5 hours. Furthermore, samples without any heat treatment were subjected to comparison as well. Moreover, following tests were conducted: bending test in compliance with the ČSN EN ISO 1519 standard, and tearing test (in accordance with the ČSN EN ISO 4624 standard). On the basis of performed tests, the changes in mechanical properties of the zinc coating after heat treatment could be analysed.

Влияние отжига в газообразном цинке на люминесценцию в видимом и среднем ИК диапазонах ZnSe : Fe-=SUP=-2+-=/SUP=-

The study results of the effect of annealing in a zinc vapor atmosphere on the defect and impurity composition of iron diffusion-doped ZnSe:Te plates on the characteristics of cathodoluminescence (CL) in the IR range are described. The formation of precipitates at the boundaries of twin faults was found. It is shown that in structures with a surface iron concentration of more than 1 at%, a significant increase in the CL intensity in the IR range is observed as a result of annealing in a zinc vapor atmosphere. A partial recovery of interband luminescence in regions with a high iron concentration as a result of annealing was found.

Bioactive hydrogel coatings of complex substrates using diffusion-mediated redox initiation

Iron diffusion-mediated hydrogel crosslinking is a facile method to generate conformable hydrogel coatings with tunable thickness, multilayer structures, and bioactivity.