Interaction of exogenous zirconium oxide nanophases with sulfur and tin in nickel melts

The interaction of exogenous refractory compound (ZrO₂) nanoparticles with sulfur and tin, which are present as surfactants in model nickel melts, is studied. Thermodynamic calculations are performed to consider the versions of removal of sulfur and tin from a melt in the form of S₂, SO₂, H₂S, Sn, and SnO. It is shown that the probability of their removal under melting conditions is low. Their contents is found to decrease when ZrO₂ nanoparticles are introduced: the degree of removal is α = 12–18% S in a model Ni–S alloy and 14–20% Sn in a model Ni–Sn alloy.     

Behavior of tin dissolved in liquid iron in the presence of refractory nanophases

Nanoparticles of the refractory phases Al₂O₃ and MgO are introduced in model Fe-Sn melt on the basis of thermodynamic analysis. The preparation of the composite consisting of a mixture of iron micropowder and oxide nanopowders is improved by producing a pressed composite, which is subjected to solid-phase refining before introduction in the melt. The reaction of nanoparticles with surfactant Sn is studied, and the heterophase interaction of Al₂O₃ and MgO with Sn is established. It is shown that, in the Fe-Sn-Al₂O₃ system, 17.1–22.8% (rel.) of the Sn is removed, depending on the isothermal holding time (5–20 min) and the content of nanoparticles in the melt (0.06–0.18 wt %); the corresponding result for the Fe-Sn-MgO system is 19.8–24.6% (rel.).     

Interaction of exogenous refractory nanophases with antimony dissolved in liquid iron

The heterophase interaction of Al₂O₃ refractory nanoparticles with a surfactant impurity (antimony) in the Fe–Sb (0.095 wt %)–O (0.008 wt %) system is studied. It is shown that the introduction of 0.06–0.18 wt % Al₂O₃ nanoparticles (25–83 nm) into a melt during isothermal holding for up to 1200 s leads to a decrease in the antimony content: the maximum degree of antimony removal is 26 rel %. The sessile drop method is used to investigate the surface tension and the density of Fe, Fe–Sb, and Fe–Sb–Al₂O₃ melts. The polytherms of the surface tension of these melts have a linear character, the removal of antimony from the Fe–Sb–Al₂O₃ melts depends on the time of melting in a vacuum induction furnace, and the experimental results obtained reveal the kinetic laws of the structure formation in the surface layers of the melts. The determined melt densities demonstrate that the introduction of antimony into the Fe–O melt causes an increase in its compression by 47 rel %. The structure of the Fe–Sb–O melt after the introduction of Al₂O₃ nanoparticles depends on the time of melting in a vacuum induction furnace.     

Extraction of Scandium and Zirconium from Their Oxides during the Electrolysis of Oxide–Fluoride Melts

The main features of scandium and zirconium extraction from their oxides to aluminum during the aluminothermic and electrolytic preparation of Al–Sc and Al–Zr alloys and master alloys in the KF–AlF₃, NaF–AlF₃, and KF–NaF–AlF₃ oxide–fluoride melts with Sc₂O₃ and ZrO₂ additives are studied. The influence of the melt composition and temperature, the synthesis time, the contents of oxides Sc₂O₃ and ZrO₂ in the melts, the mechanical stirring of aluminum, and the cathodic current density on the contents of scandium and zirconium in aluminum and on their extraction from the oxides is determined. The average values of scandium and zirconium extraction are 20–75 and 40–100%, respectively, depending on the synthesis parameters. The electrolytic decomposition of the oxides in the KF–AlF₃, NaF–AlF₃, and KF–NaF–AlF₃ melts results in the enhancement of scandium and zirconium extraction to aluminum. The parameters of the preparation of Al–Sc and Al–Zr alloys and master alloys with the scandium content to 10 wt % and zirconium content to 15 wt % during the electrolysis of oxide–fluoride melts are chosen as a result of the results obtained.     

Formation of metallic phase on reducing-gas injection in multicomponent oxide melt. Part 2. Density and surface properties

The density and surface tension of melts of ferronickel (0–100% Ni) and oxidized nickel ore are measured by the sessile-drop method, as well as the interface tension at their boundary in the temperature range 1550–1750°C. The composition of the nickel ore is as follows: 14.8 wt % Fetot, 7.1 wt % FeO, 13.2 wt % Fe₂O₃, 1.4 wt % CaO, 16.2 wt % MgO, 54.5 wt % SiO₂, 4.8 wt % Al₂O₃, 1.5 wt % NiO, and 1.2 wt % Cr₂O₃. In the given temperature range, the density of the alloys varies from 7700 to 6900 kg/m³; the surface tension from 1770 to 1570 mJ/m²; the interface tension from 1650 to 1450 mJ/m², the density of the oxide melt from 2250 to 1750 kg/m³; and its surface tension from 310 to 290 mJ/m². The results are in good agreement with literature data. Functional relationships of the density, surface tension, and interphase tension with the melt temperature and composition are derived. The dependence of the alloy density on the temperature and nickel content corresponds to a first-order equation. The temperature dependence of the surface tension and interphase tension is similar, whereas the dependence on the nickel content corresponds to a second-order equation. The density and surface tension of the oxide melt depend linearly on the temperature. The results may be used to describe the formation of metallic phase when carbon monoxide is bubbled into oxide melt.     

Effect of exogenous refractory nanophases on the structural properties of nickel melts

The surface tension and density of nickel and Ni-S melts containing Al₂O₃ and TiN refractory-phase nanoparticles (RPNPs) are studied by the sessile drop method using a digital camera and computer processing of images. The dependences of the structural properties of Ni, Ni-(Al₂O₃,TiN), Ni-S, and Ni-S-(Al₂O₃,TiN) melts on temperature and the type and size of RPNPs are determined. It is found that the surface tension decreases with increasing temperature, the temperature dependence of the surface tension is inverted, the degree of loosening in the Ni-S-(Al₂O₃,TiN) melts decreases, and Ni-S-RPNP ensembles affect the melt structure.     

The role of oxygen and zirconium in the formation and growth of Nb3sn grains

One method of producing Nb₃Sn is to react a molten tin alloy with a solid niobium alloy. Using this process, the addition of zirconium and oxygen to the niobium foil has been found to dramatically reduce the Nb₃Sn grain size and affect the Nb₃Sn superconducting critical current properties. Nb₃Sn grains grow semicoherently on the niobium alloy foil. The initial grain size is about 50 nm. These initial Nb₃Sn grains coarsen rapidly to become equiaxed grains about 0.2 μm in diameter. The equiaxed Nb₃Sn grains away from the Nb/Nb₃Sn interface are completely surrounded by a tin alloy phase that would have been liquid at the reaction temperature. Based on transmission electron microscopy observation and electrical property characterization, it is concluded that ZrO₂ clusters, less than 10 Å in size, form in the niobium alloy foil during processing. These clusters combine at the Nb/Nb₃Sn interface to form ZrO₂ precipitates. The ZrO₂ precipitates are found in all of the Nb₃Sn grains that have formed from a reaction between the liquid tin and the solid niobium at the Nb/Nb₃Sn interface. The precipitates are coherent with their host Nb₃Sn grains. During Nb₃Sn grain growth, the ZrO₂ precipitates dissolve in shrinking grains and reprecipitate in growing grains, as the migrating grain boundary intersects the precipitate. This dissolution/reprecipitation process slows the growth of Nb₃Sn grains. Formerly with GE Corporate Research & Development, Schenectady, NY,     

Oxidation processes for alloys in the Ni - Zr system. III. Oxidation of NiZr

We used the continuous weighing method to study the oxidation kinetics in air for the alloy NiZr at 500–1000°C. We used x-ray diffraction and metallography for layer-by-layer phase analysis of the scale. We have established that the oxidation kinetics is described by a parabolic equation q² = K_pτ (where q is the mass gain per unit area of the sample, K_p is the rate constant, τ is the time). The value of K_p periodically decreased on the kinetic isotherms. In the scale, the phase components are distributed over the layers as follows: top layer, cubic and monoclinic ZrO₂, NiO; inner layer, monoclinic ZrO₂, Ni, and (or) Ni₅Zr. At the boundary with the scale, the alloy layer (underscale) is depleted in zirconium. We have established that oxidation of NiZr is accomplished by predominant diffusion of oxygen through the oxygen vacancies in the lattice of monoclinic ZrO₂. The decrease in q and K_p as the temperature rises from 600°C to 850°C is explained by a reduced concentration of these vacancies and (or) slowdown of their mobility. For T ≥ 850°C, the oxidation mechanism changes: counterdiffusion of Zr⁴⁺ also occurs through interstices in the lattice of monoclinic ZrO₂. The outer layer (NiO), saturated by zirconium dioxide, loses any protective properties and diffusion of oxygen is facilitated. For this reason, both q and K_p increase as the temperature rises to 1000°C.     

Interfacial IMC Layer and Tensile Properties of Ni-Reinforced Cu/Sn–0.7Cu–0.05Ni/Cu Solder Joint: Effect of Aging Temperature

Thermal aging behavior on the intermetallic compounds (IMCs) layer and mechanical properties of Cu/Sn–0.7Cu/Cu and Cu/Sn–0.7Cu–0.05Ni/Cu joints has been investigated from aging temperature of 60–180 °C for 100 h. Layer thickness increases as aging temperature rose for both the joints. Mechanical properties deteriorates with increase in aging temperature. After aging at 180 °C, any signs of ductile fracture surface with a large amount of dimples are absent. Instead, an intergranular fracture surface is obtained for both the joints, indicating that the process transformes from ductile to brittle behavior. However, brittle Cu₃Sn layer is observed between Cu₆Sn₅ layer and Cu substrate for Cu/Sn–0.7Cu/Cu joint after aging at 60 °C, while (Cu, Ni)₃Sn IMC layer is detected until aged at 140 °C for Cu/Sn–0.7Cu–0.05Ni/Cu. Compared with Cu/Sn–0.7Cu/Cu joint, the interfacial morphology directly changes from scallop-shaped into layer-shaped structure with lower Gibbs free energy, and the layer thickness is obviously suppressed after addition of Ni particle. Excellent mechanical properties, including UTS, elongation, and hardness, are obtained for Cu/Sn–0.7Cu–0.05Ni/Cu because of the slight increase in layer thickness and dense layer-shaped interfacial morphology. Thermal aging reliability is enhanced for the Cu/Sn–0.7Cu–0.05Ni/Cu solder joint after doping with 0.05 wt% Ni particle.     

Oxidation Processes for Alloys in the Ni – Zr System. Part 2. Phase Composition of Scale Formed on Ni7Zr2

We have used x-ray and metallographic layer-by-layer phase analysis to study the structure and composition of scale formed on the alloy Ni₇Zr₂ during its oxidation in air over a period of 1 h and 10 h in the temperature range 500-1200°C. In the scale we find NiO, the cubic and monoclinic modifications of ZrO₂, and also Ni and Ni₅Zr. The phase components are nonuniformly distributed over the thickness of the scale. The outer scale consists of the oxides NiO and ZrO₂, while the composition of the inner scale includes Ni and Ni₅Zr in addition to monoclinic ZrO₂. Cubic ZrO₂ is formed on the surface of the specimen in the initial stages of its oxidation at 500-700°C. For T ≥ 900°C, on the surface of the scale we find both modifications of ZrO₂, while the nickel phase is itself a solid solution Ni(Zr). We note that the mechanisms for the formation of low-temperature (T ≤ 800°C) and high-temperature (T ≥ 900°C) scales are different. It is hypothesized that these differences are determined mainly by the fact that at high temperatures, diffusion of zirconium ions toward the outer boundary of the scale is superimposed on diffusion of oxygen toward the scale – alloy boundary.     

Ni–ZrO2 Composite Coating by Electro-Co-Deposition

In the present investigation Ni–ZrO₂ metal matrix composite coatings were prepared on steel substrate using watt’s type solution through electro-co-deposition process with different weight percentages of zirconia powder dispersed in the bath. In the coating, nickel is present with faceted appearance along with ZrO₂. The microhardness and wear resistance of the coatings increase with increasing weight percentage of particles content in the coating. The hardness of the resultant coatings was found to be 325 VHN for pure Ni coating whereas 401VHN for Ni–ZrO₂ (15 g/l ZrO₂) coating depending on the particle volume in the Ni matrix. The results also showed that the wear resistance of the composite coatings was improved as compared to unreinforced Ni deposited material. Strengthening of the coating was attributed to the ZrO₂ dispersion and partially favorable texture.     

Oxygen activities in Cr-containing Fe and Ni-based melts

Plug-type, ZrO₂-based oxygen sensors have been used for long-term measurements of oxygen activity in Fe–O–Cr and Ni–O–Cr melts. In these melts, equilibrated with chromium oxide, oxygen activities a_O were determined as a function of Cr content. From the experimental results, data were derived for activity coefficients f_O and of 1st and 2nd order interaction parameters e_O^Cr and r_O^Cr. Cr₂O₃ has been identified as the oxide phase in equilibrium with the metal melt at ≥ 5 wt.% Cr in the case of iron and at ≥ 0.2 wt.% Cr in the case of nickel. Oxygen activities and oxygen contents in Cr-containing iron melts are lowered with increasing additions of nickel. Further investigations were directed to a_O determination in Fe–O–Cr–C and Fe–O–Cr–Al melts.     

Microstructure and phase identification in type 304 stainless steel-zirconium alloys

Stainless steel-zirconium alloys have been developed at Argonne National Laboratory to contain radioactive metal isotopes isolated from spent nuclear fuel. This article discusses the various phases that are formed in as-cast alloys of type 304 stainless steel and zirconium that contain up to 92 wt pct Zr. Microstructural characterization was performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and crystal structure information was obtained by X-ray diffraction. Type 304SS-Zr alloys with 5 and 10 wt pct Zr have a three-phase microstructure—austenite, ferrite, and the Laves intermetallic, Zr(Fe,Cr,Ni)_2+x. whereas alloys with 15, 20, and 30 wt pct Zr contain only two phases—ferrite and Zr(Fe,Cr,Ni)_2+x. Alloys with 45 to 67 wt pct Zr contain a mixture of Zr(Fe,Cr,Ni)_2+x and Zr₂(Ni,Fe), whereas alloys with 83 and 92 wt pct Zr contain three phases—α-Zr, Zr₂(Ni,Fe), and Zr(Fe,Cr,Ni)_2+x. Fe₃Zr-type and Zr₃Fe-type phases were not observed in the type 304SS-Zr alloys. The changes in alloy microstructure with zirconium content have been correlated to the Fe-Zr binary phase diagram.     

Specific features of the initial stages of the aluminothermic reduction of zirconium from ZrO2

The phase composition of the products of the low-temperature stage of the reaction of ZrO₂ with aluminum is studied. The influence of charge compacting and particle size of the reagents is revealed. The onset temperatures for the reaction of zirconium oxide (TsrO-1 and TsrO-S trade marks) and aluminum (APZh and PA-4 trade marks) are determined by differential scanning calorimetry. A high dispersity of ZrO₂ and the presence of zircon ZrSiO₄ in zirconium oxide (TsrO-S) are found to provide a decrease in the onset temperatures for the reaction. Intermetallic compound ZrAl₃ is predominantly formed at the low-temperature stage of the reaction of ZrO₂ with aluminum. Zirconium is reduced from ZrO₂ by aluminum stage by stage through the formation of lower oxides ZrO and Zr₃O. Suboxide AlO is detected in the products of reaction of ZrO₂ with aluminum. The heat flow rates are estimated, according to which the reduction of zirconium from ZrO₂ by aluminum is formally characterized by the first order, and the activation energy is E = 160–170 kJ/mol.     

Nanocrystallization and magnetic properties of Fe-30 weight percent Ni alloy by surface mechanical attrition treatment

A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attrition treatment (SMAT). The microstructure of the surface layer after SMAT was investigated using optical microscopy, X-ray diffraction, and transmission electron microscopy. The analysis shows that the nanocrystallization process at the surface layer starts from dislocation tangles, dislocation cells, and subgrains to highly misoriented grains in both original austenite and martensite phases induced by strain from SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The saturation magnetization (M _s ) and coercivity (H _c ) of the nanostructured surface layers increase significantly compared to the coarse grains sample prior to SMAT. The increase of M _s for SMAT Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced martensitic transformation. Meanwhile, H _c was further increased from residual microstress and superfined grains. These were verified by experiments on SMAT pure Ni and Co metal as well as liquid nitrogen-quenched Fe-30 wt pct Ni alloy.     

Structure and properties of the slags of continuous converting of copper nickel-containing mattes and concentrates: III. Influence of the slag composition on the surface tension and density of slag melts

The surface tension and density of the slags that form during the continuous converting of copper mattes and concentrates into blister copper are determined. The slag melt compositions are varied over a wide range of (Fe + Ni) concentrations and SiO₂/CaO and (Fe)/(Cu + Ni) ratios. The surface tension and density are measured by the bubble pressure technique. The concentration of iron and nickel in a slag and the (Fe)/(Cu + Ni) and SiO₂/CaO ratios affect the density and surface tension.     

Brazing of zirconia with AgCuTi and SnAgTi active filler metals

The self-brazing of partially stabilized zirconia using Ag27Cu3Ti and Sn10Ag4Ti active filler metals is investigated. It was shown that the contact angles of Ag27Cu3Ti and Sn10Ag4Ti on zirconia decreased with the increase of brazing temperature and remained constant at about 34 deg and 44 deg above 900 °C, respectively. The flexural strengths were 227 and 137 MPa for ZrO₂/Ag27Cu3Ti/ZrO₂ and ZrO₂/Sn10Ag4Ti/ZrO₂, respectively, after brazing at 900 °C for 10 minutes. In these brazing systems, the titanium in the filler metals segregated at the interface and formed a TiO reaction layer responsible for the wetting and bonding when a ZrO₂ ceramic is brazed with Ag27Cu3Ti and Sn10Ag4Ti filler metals. Interfacial analyses by electron probe microanalysis (EPMA) showed that such TiO reaction layers of ZrO₂/Ag27Cu3Ti and ZrO₂/Sn10Ag4Ti possessed similar thicknesses at the same brazing condition, implying that the TiO interfacial reaction layers of both brazing systems were of the same nature and formation kinetics.     

Evaluation of the Inertness of Investment Casting Molds Using Both Sessile Drop and Centrifugal Casting Methods

The investment casting process is an economic production method for engineering components in TiAl-based alloys and offers the benefits of a near net-shaped component with a good surface finish. An investigation was undertaken to develop three new face coat systems based on yttria, but with better sintering properties. These face coat systems were mainly based on an yttria-alumina-zirconia system (Y₂O₃-0.5 wt pct Al₂O₃-0.5 wt pct ZrO₂), an yttria-fluoride system (Y₂O₃-0.15 wt pct YF₃), and an yttria-boride system (Y₂O₃-0.15 wt pct B₂O₃). After sintering, the chemical inertness of the face coat was first tested and analyzed using a sessile drop test through the metal wetting behavioral change for each face coat surface. Then, the interactions between the shell and metal were studied by centrifugal investment casting TiAl bars. Although the sintering aids in yttria can decrease the chemical inertness of the face coat, the thickness of the interaction layer in the casting was less than 10 μm; therefore, these face coats still can be possible face coat materials for investment casting TiAl alloys.     

Some Thermophysical Properties of Liquid Cr‐Mn‐Ni‐Steels

In the last years new Cr‐Mn‐Ni‐TRIP/TWIP steels have been developed at the Institute of Iron and Steel Technology, Freiberg University of Mining and Technology. Within the Collaborative Research Center SFB 799, the ZrO₂‐ceramic‐TRIP‐steel composite materials are produced using the infiltration of open foam ceramics with liquid steel and using powder metallurgy with small additions of ceramic powder before sintering. The thermophysical properties of liquid steel play an important role in both production routes. They affect the infiltration efficiency in one process and the produced powder size in the other, and therefore finally determine the composite properties. In this work some of these properties were estimated, as they are not available in literature. The investigated steels contain approximately 16% chrome, 7% manganese and 3% to 9% nickel. The surface tension was estimated using two methods: the drop weight method and the maximum bubble pressure method. In the drop weight method similar conditions at the gas/metal interface exist as during the atomization or the infiltration process, where liquid metal is exposed to high volume of inert gas. In all these cases the evaporation of manganese affects the surface tension. For comparison of results and for estimation of the liquid steel density the maximum bubble pressure method was used where the evaporation of manganese is limited. The wettability on partially MgO‐stabilized ZrO₂ ceramic substrates and its change with contact time was determined using the sessile drop method.     

Effect of Surface Tension on Gas Atomization of a CrMnNi Steel Alloy

The aim of the current research is the experimental investigation of the mass median particle size d₅₀ as a function of surface tension for liquid Cr–Mn–Ni steel alloy with 16% Cr, 7% Mn, and 9% Ni. To modify the liquid steel design sulfur was add to the Cr–Mn–Ni steel in five steps up to a 1000 mass ppm. The surface tension of the liquid steel alloy was measured using maximum bubble pressure method and yttria stabilized capillary in a temperature range from 1701 to 1881 K. In addition, the same steel charges were sprayed to steel powder using a vacuum inert gas atomization using pure argon gas. The increase of sulfur in Cr–Mn–Ni steel will decrease the surface tension to 0.91 N m^?1. The temperature coefficient of surface tension is positive for all investigated Cr–Mn–Ni alloys due to a sulfur content ≥100 mass ppm. The final mass median particle size d₅₀ decreases from 54.3 µm for AISI 304 reference steel alloy to 17.1 µm for Cr–Mn–Ni steel alloy (16‐7‐9 S10) with the highest sulfur content and the lowest surface tension of all investigated liquid steels. It is concluded from the present work that surface tension is the decisive factor in adjusting d₅₀ at a constant spraying parameters.