Wetting Behavior of the Ag-5CuO Brazing Alloy on ZTA Composite Ceramic with/without CuO Coating in Air

The wetting of Ag-5 wt.% CuO (Ag-5CuO) alloy on initial/CuO-coated zirconia toughened alumina (ZTA) composite ceramic in air was studied in detail. The results showed that the contact angle of the Ag-5CuO/ZTA system rapidly decreased from 81° at 970 °C to 45° at 990 °C during the heating process, however, moderate reductions in contact angle were observed in the subsequent heating and temperature holding stages. In comparison with the contact angle of pure Al2O3, an increment of about 4° of the stable contact angle of Ag-5CuO alloy on the heterogeneous ZTA was observed. The reaction between Al2O3 and CuO can reduce the damage of the CuO-rich liquid to ZrO2 in the ZTA substrate. Both oxygen and CuO were helpful in reducing the contact angle of Ag on ZTA and enhancing the bonding of the Ag/ZTA interface. The continuous CuO coating on ZTA and the monotectic liquid containing more CuO in the region near the triple line induced reductions of more than 40° and about 10° in the contact angle, respectively, between the initial and the CuO coating-improved wetting systems.

Low velocity drop weight impact behaviour of Al2O3-Ni-ZrO2 and Al2O3-Ni-Cr2O3 ceramic composites

Particulate Al2O3 matrix nanocomposites containing 1 vol.%Ni were prepared by the heterogeneous precipitation method and the addition of 5 vol.% ZrO2 (ANZ) or 1 vol.% Cr2O3 (ANC). The prepared samples were subjected to the low energy drop weight impact tests to compare the behaviour of the composites under low energy impact and to investigate the damage mechanisms. The pure Al2O3, Al2O3/Ni, Al2O3/ZrO2 and Al2O3/Cr2O3 compositions with the same additive ratios were also produced to make the comparison systematically. Also, the Vickers hardness measurements were carried out and a significant increase in hardness was attained for both ANZ and ANC composites. The average hardness value around 24.8?1.0GPa was measured for the ANZ and ANC composites which means ~15% improvement compared to the pure Al2O3. Between all the compositions, the maximum force (Fmax) value was obtained for the ANZ (for 12 J impact energy level Fmax = 26617N) according to the low energy drop weight impact test results. Tensile radial crack network formation, cone formation, fracture and crushing of the cone structure were observed as damage mechanisms for all compositions. The volume of conical frustum structure was evaluated for each composition and the effect of microstructure on possible ballistic performance was also discussed.

Effect of Nitrogen Content on the Formation of Inclusions in Fe-5Mn-3Al Steels

The effect of N content on the characteristics and formation of inclusions in the Fe-5Mn-3Al steels was investigated in this study. Two synthetic steel melts were produced by two different methods—N2 gas purging and injecting—to introduce nitrogen into the melt. The N content of steel melt varied from 2 to 54 ppm. An increase in the N content to 47 ppm (for 533N-P) and 58 ppm (for 533N-I) increased the total amount of inclusions from 13 to 64 mm−2 and from 21 to 101 mm−2, respectively. The observed inclusions were Al2O3(pure), Al2O3-MnS, AlN(pure), AlN-MnS, AlON, AlON-MnS, and MnS. When the N content was less than 10 ppm, AlN-MnS inclusions were the primary type of inclusions and they formed as solidification products. With an increase in the N content, AlN(pure) inclusions became the dominant type of inclusions as AlN was stable in the liquid steel. These findings were confirmed by thermodynamic calculations. The influence of cooling rate on the types of inclusions was studied and a higher number of AlN-MnS inclusions were observed in samples with slow cooling rate.

The microstructure and selected mechanical properties of Al2O3 + 3 wt.% TiO2 plasma sprayed coatings

The Al2O3+TiO2 coatings are of the interest of surface engineering due to their high hardness and wear resistance but also increased toughness, when compared to pure Al2O3 ones. This article describes the deposition of Al2O3+3 wt.% TiO2 coatings by Atmospheric Plasma Spraying (APS) technique. The commercial AMI 6300.1 powder (-45 + 22 μm) was used as a feedstock. The 2k+1 spraying experiment, based on two variables, namely spray distance and torch velocity, was designed. The samples were characterized in the terms of morphology, microstructure, microhardness and roughness. It was observed that the shorter spray distance resulted in lower porosity, higher microhardness and lower roughness of coatings.

An Investigation of Non-Metallic Inclusions in Different Ferroalloys using Electrolytic Extraction

Ferroalloys are integral constituents of the steelmaking process, since non-metallic inclusions (NMIs) from ferroalloys significantly influence the transformation of inclusions present in liquid steel or they are directly involved in casted steel. In this study, the characteristics of inclusions (such as the number, morphology, size, and composition) in different industrial ferroalloys (FeV, FeMo, FeB, and FeCr) were investigated using the electrolytic extraction (EE) technique. After extraction from the ferroalloy samples and filtration of the solution, the inclusions were investigated on a film filter. The three-dimensional (3D) investigations were conducted using a scanning electron microscopy in combination with energy dispersive spectroscopy (SEM-EDS). The characteristics of inclusions observed in the ferroalloys were compared with previous results and discussed with respect to their possible behaviors in the melt and their effects on the quality of the cast steels. The particle size distributions and floatation distances were plotted for the main inclusion types. The results showed that the most harmful inclusions in the ferroalloys investigated are the following: pure Al2O3 and high Al2O3-containing inclusions in FeV alloys; pure SiO2 and high SiO2-containing inclusions in FeMo alloys; Al2O3 and SiO2-containing inclusions in FeB alloys; and MnO-Cr2O3, Al2O3, and Cr2O3-based inclusions in FeCr alloys.

О ВЛИЯНИИ ДОЛИ КАРБИДА ТИТАНА НА ОБРАЗОВАНИЕ НАНОСТРУКТУР В ТВЕРДЫХ СПЛАВАХ (AL2O3 И TIC) ПРИ РАЗНОМ ИХ СООТНОШЕНИИ

The volume of nanostructures that are realized under the action of a number of ions (boron, nitrogen, zirconium, hafnium) is determined using the example of studying the influence of the fraction of components in a solid alloy containing Al2O3 and TiC at their different ratio of the fraction of components. Conditions (component ratios) are obtained for which the minimum grain sizes are realized, i.e., the hard alloy surface has the best physical-mechanical characteristics at 50Al2O3 and 50TiC. It is shown that when processing pure Al2O3 and TiC, it is also possible to obtain rather low grain size values. At the ratios of components 20-80 and 80-20, larger grain sizes are realized than in the previous cases. Nonequilibrium states can also be used after studying the physical and mechanical characteristics of hard alloys. It is shown that under the action of light ions (nitrogen), the temperature stresses do not reach the necessary values for the formation of nanostructures, and under the action of heavy ions (hafnium) there is a high probability of realization of nanostructures at an energy of 20 keV and insignificant under the action of ions with an energy of 200 eV.

The Effect of the Addition of Y2O3 on the Microstructure of Polycrystalline Alumina Ceramics

In the scope of this study, a powder mixture was prepared that contained 3 Al2O3-Y2O3 consisting of 99.99% pure Al2O3 and aluminum oxide of 65–67% and 70% by weight of 99.999% pure Y2O3 powders. After the powders were weighed on a precision scale, the milling process was carried out in a vibratory disc mill. For the granulation, 3 powder mixtures that were subject to sintering were sieved to a size of less than 106 µm in a powder sieve shaker. The powders were shaped with a cold isostatic press after this step and the 3 acquired samples were sintered for 12 h under a temperature of 1923 K. Selected physical and mechanical behaviors were taken by evaluating microhardness measurements, bending strength XRD analysis and electron microscope images of the 3 sintered samples. The changes in the Y2O3 additive and phase composition, microstructure, and mechanic properties were examined.

Influences of Adding Aluminum on Inclusions in H13 Steel through P–ESR

Reducing oxide inclusions’ number and size by aluminum deoxidization is an effective way for improving working life of high strength steel. For this purpose, during inert gas protection electro–slag remelting (P–ESR) process and H13 steel as electrodes, the deoxidizer being made of aluminum grains, iron powder and calcium fluoride powder mixture was added into slag pool with different addition rates. Results of experiment indicated that, by P–ESR remelting, oxygen content reduced from 0.0045 to 0.0010 with different aluminum addition rates. Based on the SEM and EDS analysis, inclusions transformed from CaO–MnO–SiO2–Al2O3 particles in electrode to pure Al2O3 particles, and number and size of particles modified obviously. Finally, action mechanism of the deoxidizer during P–ESR process was discussed by analysis results and thermodynamic calculation.