CaO Crucible Research Articles

Influences of solid content of slurry on the microstructure of CaO crucible prepared by slip casting

AbstractCaO crucible was prepared from Ca(OH)2 slurry via a slip‐casting method in order to avoid hydration problem caused by free CaO during preparation process. The effect of solid content of Ca(OH)2 slurry on microstructure of CaO crucible was investigated. It was found that the rheological property of the slurry was significantly improved when the solid content of the slurry within a certain range. The change of solid content of slurry affects the microstructure of the final products. When the solid content of the slurry was 71 wt%, the manufactured CaO crucible was of smallest mean pore size (2.58 μm) after 1600°C heating treatment. The heated CaO sample was of lower apparent porosity (4.1%) and higher bulk density (2.93 g/cm3). And the size distributions of most CaO grains are between 10 and 40 μm.

Smelting high purity 55SiCr automobile suspension spring steel with different refractories

Abstract We performed a laboratory investigation at 1,873 K using a MoSi2 furnace to study the effect of refractories on inclusions in 55SiCr suspension spring steel. Three types of crucible materials (Al2O3, MgO·Al2O3, and MgO–CaO) were investigated. The results of this study indicated that SiO2, Al2O3, and MgO·Al2O3 were not suitable for making 55SiCr suspension spring steel. By contrast, MgO–CaO was a perfect choice for producing 55SiCr suspension spring steel. The advantages of using MgO–CaO crucibles to smelt 55SiCr spring steel were summarized in three aspects as follows: (i) the stability of MgO–CaO was quite good; (ii) a MgO–CaO crucible could act as a desulfurizer and dephosphorizer; (iii) finally, a MgO–CaO crucible could simultaneously remove Al2O3 inclusions.

Unveiling the Mechanism of Improved Oxidation Resistance for CaO Crucible Melting Using Ni-Al Alloy

Unveiling the Mechanism of Improved Oxidation Resistance for CaO Crucible Melting Using Ni-Al Alloy

Quantitative analysis of sulfur segregation at the oxide/substrate interface in Ni-base single crystal superalloy

Oxidation resistance of Ni-base single crystal superalloy is substantially improved when melted using a CaO crucible compared to that melted using an Al2O3 crucible. In order to understand the underlying mechanism, sulfur segregation at the oxide/substrate interfaces was characterized using aberration corrected scanning transmission electron microscope with energy dispersive X-ray spectroscopy (STEM-EDS) and three-dimensional atom probe (3DAP). Although sulfur segregation at the interface was detected in both samples, the peak concentration of sulfur was found to be much lower in the sample melted in the CaO crucible, and CaS inclusions were found near the sub-grain boundaries. These experimental results suggest that the improvement in the cyclic oxidation resistance using the CaO crucible is attributed to the suppression of S segregation at the oxide/substrate interface by the trapping of S by dissolved Ca.

Oxidation Resistance Improvement of Ni-Base Single-Crystal Superalloy Melted in a CaO Crucible

An advanced Ni-base single-crystal superalloy, TMS-238, has the highest temperature capability, but there is still potential to improve its high-temperature properties. In the present study, aiming for that further improvement, TMS-238 was melted in a CaO crucible, which replaced an Al2O3 crucible. Creep tests at 1100 °C/137 MPa and cyclic oxidation tests at 1100 °C were conducted to compare the high-temperature properties of TMS-238 melted in an Al2O3vs a CaO crucible. Regardless of the melting crucible, the creep properties of the samples were equivalent. Meanwhile, TMS-238 melted in a CaO crucible exhibited better oxidation resistance. Although the composition of the oxide scale was almost the same, the sample melted in an Al2O3 crucible had its oxide scale spalled, while a continuous oxide scale was formed on the sample melted in a CaO crucible. Dissolved Ca capturing S as CaS and preventing segregation of S at the metal-oxide interface is a possible reason for the improvement of the oxide scale adhesiveness. The results indicated that melting in a CaO crucible can improve the oxidation resistance of the original superalloys while maintaining their creep properties.

Correlation of Oxygen and Aluminum Contents of Molten Titanium-Aluminum Alloys in Alumina and Calcia Crucibles

As a key part of investigating a new proposed Ti-alloy production process, Ti-Al alloys were produced by aluminothermic reduction experiments at 1973 K in Al2O3 crucibles. Besides, pure Ti and Al were melted inside CaO crucibles at 1973 K to investigate the possibility of melt refining in equilibrium with CaO. The experiments were carried out in a vacuum induction furnace under argon gas at atmospheric pressure. The experimental results were proved by thermodynamic evaluations including also literature data. The correlation of oxygen and aluminum in Ti melt with 11 to 23 wt pct Al in contact with Al2O3 was assessed as $$ 3\ln X_{\text{O}} = -\,2\ln X_{\text{Al}} - 9.1 \pm 0.4. $$ This correlation in Ti melt with 3 to 10 wt pct Al in contact with CaO was $$ 3\ln X_{\text{O}} = - \,2\ln X_{\text{Al}} - 14.9 \pm 0.3. $$ Partial molar excess Gibbs free energies of mixing and combinations thereof in Ti-rich Ti-Al-O-Ca melt were assessed as $$ RT \ln (\gamma_{\text{Al}}^{2} \cdot \gamma_{\text{O}}^{3} ) = - 894 \pm 6\,({\text{kJ}}/{\text{mol}}) $$ , $$ RT \ln \left( {\gamma_{\text{Ca}} \cdot \gamma_{\text{O}} } \right) = - 195 \pm 4\,({\text{kJ}}/{\text{mol}}) $$ , $$ RT \ln \gamma_{\text{O}} = - 258 \pm 6\,({\text{kJ}}/{\text{mol}}) $$ , $$ RT \ln \gamma_{\text{Ca}} = 62 \pm 7\,({\text{kJ}}/{\text{mol}}). $$ The activity of Al2O3 in CaO-saturated slag was assessed as 0.003 ± 0.001. The changes of Gibbs free energy for the dissolution of 1 wt pct oxygen and 1 wt pct calcium in Ti-Al melt were estimated as −630 ± 6 and −11 ± 7 (kJ/mol), respectively. A model was developed and applied to calculate the basic data for refining Ti-Al alloy.

Correction to: Creep Property and Phase Stability of Sulfur-Doped Ni-Base Single-Crystal Superalloys and Effectiveness of CaO Desulfurization

The direct and complete recycling method for Ni-base superalloy is being developed and studied to reduce the material cost for cost-effective operation of gas turbine systems. Understanding the effect of sulfur contamination is important to determine allowable sulfur content after the recycling. However, in the case of single-crystal superalloys, this effect on material properties is not well known except for the detrimental effect on the oxidation resistance. In the present study, creep tests, aging tests, and cyclic oxidation tests have been performed on PWA1484 with varying sulfur content. The increasing sulfur content has been found to correlate with degradation of properties evaluated here. It is observed that the decrease in creep life in PWA1484 due to sulfur doping is primarily due to coarsening of the γ/γ′ interfacial dislocation network, increase in precipitation kinetics of topologically closed-packed phase, and decrease in oxidation resistance. For recycling purposes, a CaO crucible was used in the casting process, which successfully decreased the sulfur level in the alloy, and the resulting material showed comparable or even better properties in comparison to the low sulfur content material.

Desulfurizing Ability of the CaOsatd.-CaCl2-CaF2 Slags

Desulfurizing ability of the CaO-CaCl2-CaF2 slags saturated with CaO has been investigated from the viewpoint of the sulfide capacity and CaO solubility. The CaO-CaCl2-CaF2 slags containing small amounts of Cu2O and CaS were inserted in a CaO crucible with metallic copper. The CaO crucible was sealed in a nickel holder to prevent the evaporation of CaCl2, then heated up and kept at temperatures from 1573 K (1300 °C) to 1673 K (1400 °C) for 24 hours, which enabled the system inside the CaO crucible to reach the equilibrium. As expected, the sulfide capacity derived from the data obtained as well as CaO solubility of the slag increase with an increase in temperature at a constant ratio of CaCl2/CaF2. The solubility of CaO increases by the replacement of CaF2 with CaCl2, whereas the sulfide capacity slightly decreases and the activity coefficient of CaS (γ CaS) increases. This suggests that CaF2 has stronger interaction with CaS than CaCl2. The sulfur distribution ratio between carbon-saturated iron melts and the CaO-CaCl2 slag has been calculated to be about 10 000 at 1573 K (1300 °C) using the sulfide capacity obtained, which value is still large enough even with the replacement of CaF2 by CaCl2.

カルシアるつぼによるTi-6Al-4V合金の溶解と鋳造欠陥

カルシアるつぼによるTi-6Al-4V合金の溶解と鋳造欠陥

Interfacial reactions between Ti-1100 alloy and CaO crucible during casting process

Ti-1100 alloys were melted in a controlled atmospheric induction furnace equipped with a CaO crucible. The microstructure, chemical composition, microhardness and metal–crucible interfacial reactions were systematically investigated. The results demonstrate that the primary solidification microstructure in the as-cast alloys was the typical Widmanstätten structure. The interactions between crucible and molten alloys are attributed to slight chemical dissolution and weak physical erosion. According to the line scanning analysis, the interfacial layer (α-case) thicknesses of Ti-1100 samples in the bottom and side wall are about 18 and 17 μm, respectively, which are slightly lower than those presented from microhardness tests (25 and 20 μm). The formation of α-case was caused by interstitial oxygen atoms. The standard Gibbs energy of reaction CaO(s)=Ca+O for Ti-1100 alloy was also determined. The equilibrium constant and the interaction parameter between calcium and oxygen were obtained as lg K=-3.14 and eCaO = 3.54.

Preparation of TiFe based alloys melted by CaO crucible and its hydrogen storage properties

The carbon contamination of alloys prepared by the electro graphite crucible is impossible to avoid due to the inherit reaction between the melt and the crucible. In this study, the TiFe-based alloy is prepared by VIM process using CaO crucible as well as the electro graphite crucible. The samples are examined by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Energy Dispersive Spectrometer (EDS), and the PCT curves are also measured. It is resulted that, the oxygen content of alloys melted by CaO crucible is almost equal to the one melted by graphite crucible and without the carbon contamination, meanwhile the carbon content of alloys obtained by the electro graphite crucible is 1860ppm, which exceeds the tolerance of the commercial alloy (1000ppm). The microstructure of the alloy melted by CaO crucible is dendrite, while it is composed of the equiaxed crystal with the lamellar structure and the spherical TiC particles distributed along grain boundaries or within the grain when melted by the graphite crucible; the interfacial reaction of the electro graphite crucible with TiFe alloy melt is serious and the interaction layer is formed up to 200μm in thickness, the carbon in TiFe-based alloys forms TiC. The hydrogen desorption plateau pressure of alloys melted by CaO crucible is (0.11–0.4)×105Pa, and that by the graphite crucible is (0.6–1)×105Pa. This may imply that the CaO crucible may be the promising candidate for melting the high performance TiFe based hydrogen storage alloys.

Microstructure and Hardness of High Temperature Alloy Ti-1100 Melted in CaO Crucible

A high temperature alloy Ti-1100 was produced by vacuum induction melting technology. The effects of casting modulus on the microstructure and hardness of the cast alloys were determined and the results were presented and briefly discussed. Results demonstrate that the microstructure of cast alloys with different modulus are all widmanstatten structure with basket weave features where individual α-laths are separated by a thin layer of retained prior β phase. The greater the modulus, the larger the prior β grain size and α-laths spacing, and the less the Vickers hardness. The roles of the casting modulus governing the microstructures and hardness of the alloys were also discussed.

Solubility of Calcium and Oxygen in Molten Iron Equilibrated with Slag in CaO, Al2O3 or CaO-stabilized ZrO2 Crucible at 1873 K

Solubility of Calcium and Oxygen in Molten Iron Equilibrated with Slag in CaO, Al2O3 or CaO-stabilized ZrO2 Crucible at 1873 K

Induction melting of γ-TiAl in CaO crucibles

In this work a Ti–48Al alloy was induction melted in a CaO crucible using different superheating temperatures. In the first stage, samples were allowed to cool to room temperature inside the crucibles, in order to simulate a low cooling rate, and in the second stage samples were centrifugally poured into a steel mould, in order to study the effect of the melting operation on the alloy contamination with oxygen. The effect of superheating temperature on the metal-crucible interaction, alloy chemical composition, microstructure and microhardness is evaluated. The CaO crucible was found to be slightly dissolved by the molten alloy and the extent of that dissolution depends on the superheating temperature. A relationship was found between oxygen concentration and microhardness profiles of the α 2 + γ microconstituent, from the surface to the inside of samples, which depends on the superheating temperature and cooling rate.

Dissolution of Dense Lime in Molten Slags under Static Conditions

Static dissolution of CaO into a CaO–SiO2–Al2O3 slag with fluxing agents (fluorspar, ilmenite and nepheline syenite) was studied using two experimental techniques. In one method, the slag was packed into dense CaO crucibles, and heated to 1500°C/1600°C. After reaction, the crucible was air cooled and cross-sectioned. In the second technique, slag with a piece of lime was heated in a platinum capsule. The development of the Ca2SiO4 phase at the lime/slag interface and the CaO dissolved in the slag from the lime specimen were examined by Electron Probe Micro Analysis and Scanning Electron Microscopy. Ilmenite and nepheline syenite were found to be effective substitutes for fluorspar, increasing the CaO dissolution rate in the slag.

Microstructural development during directional solidification of α-seeded TiAl alloys

Microstructural selection during the directional solidification of binary TiAl alloys grown from Ti–43Al–3Si (at.%) seeds was examined. By using a seed crystal, the high-temperature hexagonal close packed α-phase can be correctly oriented so that an aligned lamellar TiAl/Ti 3Al microstructure results from the subsequent solid-state transformations upon cooling. From the equilibrium phase diagram, primary body-centered cubic β-phase solidification is expected in the compositional range for which the binary TiAl alloys were successfully seeded. Thus successful crystal growth of TiAl was found to be dependent upon the undercooling necessary for β nucleation. From these data, a microstructural selection map for the seeded growth of the α-phase was constructed and used to predict the compositional range for seeding TiAl alloys grown in CaO crucibles. The compositional range of the seeding criterion was then extended to multicomponent alloys by using an equivalent-Al concept to predict the shift in the liquidus surface for primary α and β solidification.

Single step centrifugal casting TiAl automotive valves

Centrifugal casting has been used to cast TiAl car valves. The casting has been carried out in vacuum using induction melting furnace coupled to a CaO crucible, which offers a maximum superheat of approximately 180 °C and much improved filling over normal cold wall induction furnace. In this work, the effects of the casting conditions, including superheat, rotation speed at one mould temperature have been investigated in terms of the product integrity and porosity and the microstructure of the valves. The mechanical properties and oxygen contents of cast stems with various degrees of superheat have been measured at room temperature. The as-cast car valves and some HIPped car valves have been successfully engine-tested. The feasibility for mass production of TiAl car valves and realistic costing for producing car valves using centrifugal casting and CaO crucible are currently also being assessed.

The effect of CaF2 on thermodynamics of CaO-CaF2-SiO2(-MgO) slags

To address the role of CaF2 in the CaO-CaF2-SiO2(-MgO) slag system employed for the production of low-pressure rotor steels, the thermodynamic aspects of the slag were investigated by equilibrating it with liquid iron at 1873 K in CaO or MgO crucibles. Presaturation of slag with an oxide block piece of CaO or MgO in a Pt crucible and application of a carbon paste to the outside of an oxide crucible were designed to prevent crucible failure during the slag-metal experiments. The liquidus isotherm and phase boundary of the preceding slag system were investigated using the slag-metal equilibria. Also, the effect of CaF2 on the sulfide capacity and the activity coefficient of Fe t O were of particular interest in controlling the sulfur level and cleanliness of low-pressure rotor steels.

Investigation into deoxidation during vacuum induction melting refining of nickel base superalloy using CaO crucible

The influence of carbon and aluminium on deoxidation during vacuum induction melting (VIM) of a Ni-6Cr-2Mo-6W-5Co alloy using a CaO crucible has been studied. It has been found that carbon plays a dominant role in deoxidation during the melting stage, and about 50-70% of the initial oxygen can be removed. Thermodynamics calculations show that the C-O reaction is far from the equilibrium state, and experimental results for carbon and oxygen contents in the liquid alloy correspond with those when the CO partial pressure pCO is 103-102 Pa. Aluminium addition can further reduce the oxygen content to below 6 ppm. Thermodynamics calculations for the C-Al, Al-CaO and C-Al2O3 reactions demonstrate that they can all take place during the melting process. These reactions bring about reductions in the amounts of carbon and aluminium, respectively, of about 1.3-3.5 times and 20-50 times those required for deoxidation only.

Effect of boron on high temperature embrittlement of a high purity Fe-S alloy

It is well-known that the properties of iron are affected by impurities. With a small amount of sulfur, a drastic hot ductility drop appears near 1000 K. Boron in Fe-P alloy improves the grain boundary brittleness at room temperature by intrinsic cohesion mechanism and competition mechanism. In the present research, the intrinsic effect of boron on the hot ductility drop of Fe-S alloy has been investigated. High purity Fe-60 mass ppm S alloys doped with boron (0 to 70 mass ppm) were melted in a CaO crucible using a high vacuum induction furnace. It is found, for example, by tensile tests at 973 K that the reduction in area (RA) increases from 20% to 50% by the addition of about 20 mass ppm boron to a high purity Fe-60 mass ppm S alloy. However, by adding more boron, the RA decreases and then becomes constant with boron contents higher than 35 mass ppm. It is observed that excess sulfur and boron precipitates as iron-sulfide and iron-boride uniformly distributed in the matrix. The decrease in RA by adding more than 10 mass ppm boron is caused by the strengthening of the matrix due to the increase in the number of iron-boride particles. It should be emphasized that experimental research using highly purified specimens is significant to clarify the inherent properties of metals.