Alloy Melt Research Articles

Preparation of a (Ca,Sr,Ba)ZrO3 Crucible by Slip Casting for the Vacuum Induction Melting of NiTi Alloy.

Vacuum induction melting is a more energy-efficient process for the preparation of a titanium alloy with good homogeneity and low cost. But the crucial problem for this technology is in developing a crucible refractory with high stability. In the present work, a novel (Ca,Sr,Ba)ZrO3 crucible was prepared by slip casting and its performance in melting NiTi alloy was studied. The results showed that a single solid solution was formed with a homogeneous distribution of metal elements after sintering at 1500 °C. It was found that the total content of oxygen and nitrogen remaining in the TiNi alloy after melting in the (Ca,Sr,Ba)ZrO3 crucible was 0.0173 wt.%, which fulfills the ASTM standard on biomedical TiNi alloys. The good resistance of the (Ca,Sr,Ba)ZrO3 crucible to molten NiTi has a relationship with the sluggish diffusion effect of high-entropy ceramics. This study provides insights into the process of designing highly suitable crucible material for melting a NiTi alloy.

Formation and Evolution of Interfacial Structure in Al–Si–Mg/Stainless Steel Bimetals during Hot-Dipping Process

Understanding trends in the formation of the intermetallic compound (IMC) layer in Al/Fe bimetallic composites can aid in significantly improving their mechanical properties. However, it is currently challenging to predict IMC layer formation during hot-dip aluminizing. Furthermore, the results from previous studies are difficult to compare owing to the variation in the process parameters used. Therefore, to understand how temperatures and holding times affect the thickness and hardness properties of IMC layers, we investigated the interfacial properties of aluminized stainless steel in molten Al-Si-Mg. AISI 420 stainless steel was hot-dip aluminized in an Al–Si–Mg alloy melt for 10–120 min at four different temperatures: 700, 750, 800, and 850 °C. Morphology, type, and element distribution of the phases formed in the reaction layer and the reduction rate of the aluminizing process were studied. Notably, while the reaction layer thickness increased with increasing aluminizing temperature when the holding time was low, long-term reaction caused the reaction layer to become thicker at lower temperatures. The mechanism of this morphological transformation is discussed. The results demonstrated effective trends in controlling the morphology of the intermetallic compound layer with respect to various hot-dip Al plating process parameters.

Study on Al Evaporation during AlV55 Melting and Alloy Preparation

Vacuum induction melting is a commonly used method for preparing AlV55 alloys. However, this method results in high Al evaporation losses, leading to poor cost control. Moreover, the influence of the process parameters on the alloy composition remains unclear. In this study, the evaporation pattern of Al in the melting and preparation processes of AlV55 alloys is studied, and measures for controlling the system pressure are proposed to effectively reduce Al evaporation. The experimental results show that smelting under an Ar gas atmosphere of 2000 Pa can reduce the evaporation loss of Al from 11.48% under vacuum conditions (60 Pa) to 0.58% of the amount of raw material added, effectively improving the metal utilization rate and reducing production costs. The influence of various process parameters on the alloy composition and Al volatilization are investigated to enable the effective control of the compositional uniformity and impurity content of the resulting alloys. Under optimal conditions, the impurity contents of C, O, and N are 0.03%, 0.0073%, and 0.013%, respectively; this reduces the amount of Al lost by evaporation compared to conventional methods, and the alloy produced meets commercial standards.

The role of the preparation route on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

Nearly equiatomic AlCoCrFeNi alloy samples were prepared by induction melting and mechanical alloying (MA) combined with spark plasma sintering (SPS). The cast sample showed a dendritic microstructure composed of spinodally decomposed nanometric constituents of the B2 and BCC phases. The spark plasma sintered sample exhibited an ultrafine-grained microstructure of B2 phase and FCC solid solution and Cr23C6 carbides. The MA + SPS sample was strengthened by compressive stress-strain test up to a yield strength of 2029 ± 5 MPa, resulting significantly higher compared to 1366 ± 32 MPa of the cast sample. In addition to the higher compressive yield strength, the sintered sample exhibited a hardness of more than 130 HV higher compared to the cast alloy. On the other hand, the cast alloy showed high plastic deformation (29%) and significantly high ultimate compressive strength of 3072 ± 122 MPa. Together with these mechanical characteristics, the MA + SPS sample showed good thermal stability while preserving the mechanical properties even after annealing at 800 °C. This was not the case with the cast sample, in which ductility and ultimate strength significantly decreased upon annealing at 800 °C. A substantial yield strength reduction of both MA + SPS and cast samples was recorded when tested at 800 °C. Nevertheless, stress-strain curve trends were observed to be quite different between the two samples, thus suggesting dissimilar deformation mechanisms under high-temperature compression.

Multi-objective Optimization in Selective Laser Melting of AlSi10Mg Alloy Based on Response Surface Methodology

Multi-objective Optimization in Selective Laser Melting of AlSi10Mg Alloy Based on Response Surface Methodology

Effect of Calcium Addition on the Aluminum Alloy A201 Foam

To study the effect of calcium on the porosity, sphericity, and microstructure of Al–Cu foams, a gradient calcium content (0.5, 1.0, 1.5, and 2.0 wt%) is added into aluminum A201 alloy (Al–Cu alloy) for the cellular aluminum foam preparation via the melt foaming method (TiH2 is used as a bubbling agent). Thereafter, the porosity of the prepared Al foams and their pore size are found to increase, and the sphericity of pores tends to approach to unit with calcium addition. This phenomenon is then explained through the modified thermophysical properties (i.e., surface tension and viscosity) of A201 alloy melts caused by the calcium addition. After the microstructure analysis, a bunch of secondary phases in the A201 + Ca alloy foams, e.g., CalAl2Si2, Al2Cu, and Al20CaTi2 as well as an eutectic phase with a great copper content Al8CaCu4 are detected by means of scanning electron microscopy/energy‐dispersive X‐Ray spectroscopy and X‐Ray diffraction analysis.

Research Progress of Preparing Titanium Alloy By Molten Salt Method

Titanium alloy has excellent characteristics that cannot be compared with other metals such as light specific gravity, high specific strength, wide applicable temperature range, corrosion resistance, and hydrogen storage. The traditional titanium alloy smelting process is mainly based on titanium sponge as raw material, which has a long process, high energy consumption, heavy pollution, and other problems, which seriously restricts the sustainable development of titanium alloy in the world. The common methods of preparing titanium alloy are alloy melting, metal thermal reduction, powder metallurgy, and the gradually emerging molten salt electrolysis. Among them, molten salt electrolysis is recognized as the most promising method to replace the traditional titanium alloy production process, and certain achievements have been made in recent years in terms of both process and basic theory research. In this paper, the common processes of titanium alloy preparation by molten salt electrolysis at home and abroad, such as molten salt electrolytic co-deposition method, cathodic alloying method and liquid cathode method, new FFC method, and its derived SOM method, etc., will be summarized systematically, and the future research will be put forward.

سباكة الصلب عالي السبائكية AISI321 باستخدام السباكة الرملية

In this work, sand casting was used to obtain high-strength steel AISI-321 by melting alloy AISI304 using sand casting. This is in addition to titanium using an induction furnace, which is considered one of the metal forming processes that originated from the principle of casting in sand molds. In general, Ti will oxidize quickly in the melt if it is exposed to air in typical sand/investment casting processes; Titanium element provides greater resistance to inter granular corrosion. Stainless steel alloy 321, which differs from 304 in that it contains a percentage of titanium, which has given it the property of being used at high temperatures, which has increased the need or demand for stainless steel casting in some industries and due to the difficulty and complexity of producing some pieces or parts using SS304 (wrought) forging alloy by Machines, so that it became necessary to search for a way to improve quality and reduce time and cost, using plumbing technology, although information about this technology is not available in open references. The ability to cast stainless steel is affected by a variety of factors, such as the time and degree of melting, the types of additives, and the time of total solidification. In addition, there are some other casting factors that have a direct impact on the quality of casting stainless steel, such as the sand mold materials, their type, preparation of the sand mold, and the heat treatment steps. This research includes two parts, a theoretical part that includes the steps of sand casting, and the second part related to the practical side, where the effect of some casting factors was studied, which includes the weight and quantity of addition of titanium (300 to 1000 grams), the time of addition and pouring from (3 to 15 minutes), as well as a study of heat treatment and its effect. This is due to the quality of the stainless steel alloy under study. In each experiment, 100 kilograms were used on stainless steel 321 and 304. The practical experiments were completed in several experimental stages, and in each stage, some modifications were made so that they were based on previous results. The results of the chemical analysis of the last five samples showed a gradual increase in the amount of Ti% until it reached about 0.4%. The tensile strength and yield strength were at acceptable values compared to the Wrought SS321 and cast SS (CF) alloys, an austenitic stainless steel, where the lowest value was (200 and 198) MPa and the highest value was (559 and 315) MPa, respectively. The hardness values were between (145 to 149). Key words: sandcasting, Austenitic SS321, SS304, FeTi.

Total Ankle Replacement with Built-in Antibiotic Spacer: A Paradigm Shift in the Management of Infected Ankles

Introduction/Purpose: Infection of an ankle fracture is a devastating complication that can lead to chronic pain, limited motion or amputation. Traditional treatment strategies after infection involve aggressive surgical debridement, implant removal and prolonged antibiotic therapy. Non-anatomic cement spacers for the tibiotalar joint have previously been described with mixed results. Articulating spacers have shown improved outcomes and may be used as definitive treatment. Currently, there are no prefabricated TAR spacers on the market. The use of 3D printing to create custom implants is emerging, however, there is a paucity of literature regarding their use. We present a case of post-infectious ankle arthritis in 14 year old patient treated with a 3D printed total ankle replacement with built in antibiotic spacer (TAR-AS). Methods: A CT scan was performed in accordance with computer aided design (CAD) parameters. Bilateral lower extremities were scanned to allow the unaffected side to be mirrored and be the basis for implant design. Slice spacing less than 1.25mm with pixel size of 0.5mm. The studies were in DICOM files and within a timeframe where no significant change in patient anatomy had occurred. The implants were fabricated by selective laser melting (SLM) of cobalt chrome alloy (CoCrMo) by Restor3d (Durham, NC). Our design incorporated a stacked gyroid component to facilitate antibiotic cement impregnation. In terms of surgical technique, the custom TAR-AS followed a similar approach to a patient specific TAR procedure. Prior to implantation, the gyroid component of the TAR-AS was filled with Simplex bone cement with tobramycin (Stryker). Results: At six months postoperatively, our patient reported no limitation in activities. AOFAS scores improved from 46/100 preoperatively to 83/100 at six months postoperatively. Radiographic parameters showed no signs of implant failure, loosening or change in alignment. Intraoperative cultures remained negative. Conclusion: We present a case demonstrating the utilization of 3D generated prostheses for treatment of post-infection ankle arthritis. The TAR-AS represents a significant advancement in the management of ankle infections. This innovative approach combines the benefits of joint replacement and continued antibiotic elution. With further research and continued technological advancements, the TAR-AS has the potential to become the gold standard for the treatment of infected TAR. Despite the promising results, challenges remain in the implementation of TAR-AS. Long term follow up studies are needed to evaluate the durability and longevity of the implant. Total ankle with built in antibiotic spacer Superior view of tibial tray with antibiotic cement packed in gyroid

Study on Structural Variation of Sn–20% Pb Alloy Melt Subjected to Ultrasonic Vibration: An Electrical Characterization

Study on Structural Variation of Sn–20% Pb Alloy Melt Subjected to Ultrasonic Vibration: An Electrical Characterization

Precise control of atomization initial stage to address nozzle clogging issue in the vacuum induction-melting gas atomization process

Vacuum induction-melting gas atomization (VIGA) is considered a widely applied method to prepare metal powders. However, the nozzle clogging problem in the VIGA process seriously affects the continuity of production and greatly increases the economic and time costs. In the atomization initial stage, the existence of unsteady state atomization mainly results in the nozzle clogging challenge. To understand the formation mechanism of nozzle clogging, a computational fluid dynamics (CFD) model was established to simulate the influence of unsteady state atomization sequence on the primary atomization of alloy melt. Typically, there are two kinds of sequence including starting the gas before pooling the alloy (namely, GA) and pouring the alloy before opening the gas (AG). The movement trajectory of the alloy melt droplet at the end of the delivery-tube was clarified. Based on CFD simulation, the atomization sequence of AG and GA was precisely controlled in the atomization pressure range of 2.5 MPa, 3.5 MPa, and 4.5 MPa to address the nozzle clogging issue. In the GA process, relatively finer powder was obtained at 3.5 MPa without nozzle clogging occurring. In contrast, the AG process greatly reduces the probability of nozzle clogging at 2.5–4.5 MPa, the final prepared powder is coarser. The predicted results of industrial experiments and numerical simulations are consistent. This study provides theoretical support for understanding the formation mechanism of nozzle clogging during the VIGA process.

Mechanical and electrical performances of ternary Cu-2.8%Ni-0.7%Si alloy modulated by ultrasonic solidification

One-dimensional (1D) and three-dimensional (3D) ultrasounds were introduced into the solidification process of ternary Cu-2.8wt%Ni-0.7wt%Si alloy together with the in-situ measurements of acoustic fields. In the case of 1D ultrasound, stable cavitation was the main form of acoustic energy transmission. The grain size of α-Cu dendrites was reduced because stable cavitation improved the wetting between impurities and alloy melt, which further promoted nucleation process. When 3D ultrasounds were applied, transient cavitation was the dominant mode of acoustic energy dissipation. This induced local high undercooling in alloy melt, causing a significant increase in bulk nucleation rates and the formation of numerous tiny α-Cu equiaxed grains. Meanwhile, as ultrasonic dimension increased, the strengthened acoustic streaming accelerated solute and thermal diffusion and weakened the preferred orientation of growing α-Cu grains. The proportion of low-angle grain boundaries (LAGBs) increased consequently, which suppressed the nucleation and growth of δ-Ni2Si discontinuous precipitates (DPs) during subsequent annealing treatment. The tensile strength and electrical conductivity of 3D ultrasonically solidified alloy after annealing reached 688.2 MPa and 2.7×107 S/m respectively, showing obvious advantages in synergetic mechanical and electrical performances.

Evolution behavior of Fe and Fe-rich phases in high-Fe concentration Al-Si-Mg alloy with Mn, Cr, and Co alloyed

In this work, we report the evolution behavior of Fe and Fe-rich phases in the high-Fe concentration recycled Al-Si-Mg aluminum melt with and without alloying elements (Mn, Cr, Co) introduced. Firstly, the thermodynamic calculations reveal that the addition of Mn, Cr, and Co could improve the nucleation temperature of the Fe-rich phase. Moreover, four solidified ingots for Al-10Si-0.5Mg-1Fe alloy(base alloy) and the base alloy with 1.3 wt% Mn, 0.8 wt% Cr, and 0.8 wt% Co added, respectively, were prepared by holding the melt for 30 min at 610 ℃ after all the raw materials were fully melted. Microstructure examination revealed that the addition of Co resulted in the formation of the needle-like Fe-rich phase, which further leads to a poor settling effect and low iron removal efficiency. In contrast, the addition of Mn and Cr favors converting β-AlFeSi into α-AlFeMnSi, and forming the Chinese script and fish-bone Fe-rich phase. The size of the Fe-rich phase formed after adding Cr is smaller, while the residual Fe content after adding Mn is less. Also, the sludge phase at the bottom of the ingot presents a polygonal shape and long rod shape after adding Mn and Cr, respectively. Further, the Mn alloying increases the particle size of the sludge, while Cr refines the sludge phase and increases the aspect ratio (length/width ratio) of the sludge. Particularly, for Al-Si-Mg alloy with 1.0% Fe content, the superior mechanical properties are obtained by adding 0.8 wt% Cr, and the tensile strength reaches 136 MPa. After adding 1.3 wt% Mn, the Fe content of the upper section is reduced to 0.37 wt%, and the Fe removal rate achieves 63%. The obtained results provide some guidelines for achieving high iron separation efficiency in recycled aluminum-silicon alloy melts.

Laser Melting of Mechanically Alloyed FeNi: A Study of the Correlation between Microstructure and Texture with Magnetic and Physical Properties.

The current study attempts to establish the interrelation between microstructure and magnetic properties induced during laser melting of the FeNi alloy. This study demonstrates the optimization of laser parameters for defect-free, uniform, and chemically homogeneous FeNi alloy synthesis. Mechanically alloyed FeNi (50-50 atom %) powders obtained after 12 and 24 h milling, with average particle sizes of 15 and 7 μm, were used as starting materials. It was found that the optimum range of laser power density for synthesis of dense and defect-free solids is between 1 and 1.4 J/mm2. For laser melting under similar conditions, 12 h milled FeNi powder produces a larger grain (∼100 μm) with a preferred texture of (001), compared to 25 μm grain size in 24 h milled FeNi, with random texture. Smaller grain size is correlated with higher resistance to domain wall movement, resulting in higher coercivity and remanence in the laser-melted samples prepared from 24 h of milled powder. The presence of microtexture in laser-melted samples prepared from 12 h milled powder is related to a higher anisotropy.

STUDY OF THE TECHNOLOGY FOR OBTAINING A MIXTURE OF SILICOFLUORIDE AND SODIUM FLUORIDE FROM A BY-PRODUCT OF HYDROFLUORIC ACID PRODUCTION

The article presents the results of research on the technology of processing and utilization of by-product of hydrofluoric acid production – a mixture of fluorosilicic and hydrofluoric acids using sodium hydroxide and sodium chloride (local mineral raw materials) to obtain fluoride salts – a mixture of silicofluoride and sodium fluoride. As a result of laboratory studies, the optimal parameters of the process of acid mixture processing using sodium hydroxide and sodium chloride to obtain a mixture of SSF and sodium fluoride were determined: temperature – 20-25 °C, duration – 10-20 min, concentration of sodium hydroxide and sodium chloride – 20-25%; in this case the maximum degree of extraction of SSF and sodium fluoride is achieved. The product obtained when sodium hydroxide was used under these optimum conditions was chemically analyzed and found to consist of 67.8% Na2SiF6 and 31.5% NaF. In the case of sodium chloride, the resulting mixture contains 95.8% of Na2SiF6 and 3.5% of NaF. To confirm the reliability of the results of chemical analysis and the found optimal parameters, as well as to determine the mineralogical composition of the obtained fluoride salts, X-ray phase analysis was carried out using an upgraded Dron-2 unit. The obtained product can be used in electrolysis production for obtaining aluminosilicon alloy (silumin) and electrolyte melt, as well as for fluoridation of drinking water and in the production of acid-resistant cements. On the basis of the conducted laboratory studies, the basic technological scheme of processing of the mixture of FSA and hydrofluoric acid with the use of sodium hydroxide and sodium chloride was developed.

Achieving superior grain refinement efficiency for Al–Si casting alloys through a novel Al–La–B grain refiner

Conventional Al–Ti–B and Al–Ti–C refiners fail to refine Al–Si casting alloys with high Si content due to the well-known “Si-poisoning” effect. Developing a novel grain refiner with superior grain refinement efficiency for Al–Si casting alloys is the research focus in recent years. In this work, a superior anti Si-poisoning α-Al grain refiner Al–2La–1B alloy with fine LaB6 particles was successfully fabricated via the aluminum melt reaction method. The microstructural evolution, grain refinement performance and refinement mechanisms of the Al–2La–1B alloy were comprehensively investigated based on the experiment results and first-principles calculations. The currently designed Al–2La–1B refiner presents supreme grain refinement efficiency on Al–Si casting alloys. The average grain size of Al–7Si alloy inoculated with 0.5% Al–2La–1B alloy can be refined to 67 ± 5 μm. The superior grain refinement performance can be attributed to the presence of fine LaB6 particles in the refiner. These particles are highly stable in Al–Si alloy melt and can directly act as the potent nucleation sites for α-Al due to the small lattice misfit and low interfacial energy. Moreover, the nucleation potency of the LaB6 particles will not be influenced by the solute Si element. Our work provides an effective strategy for designing a superior α-Al grain refiner for Al–Si casting alloys.

Investigation of effects of process parameters on microstructure and fracture toughness of SLM CoCrFeMnNi

Selective Laser Melting (SLM) of multi-component alloy (MCA) such as CoCrFeMnNi is gaining significant attention due to its potential to exhibit an intriguing blend of mechanical properties, particularly strength-ductility combinations. However, limited attention has been directed toward the critical aspect of fracture toughness, which is indispensable for various engineering applications. This study delves into obtaining the fracture toughness of SLMed CoCrFeMnNi MCA, with a focus on the influence of microstructure, densification, and key printing parameters (volumetric energy density (VED), laser power, and scan speed). Experimental findings revealed that individual printing parameters rather portray better insights on the densification as opposed to the VED. Notably, slow scan speed of 800 mm/s significantly enhances densification irrespective of the VED. The alloy presents complex cellular structures with the morphology reflecting a non-linear dependence on VED. The presence of cellular dislocations analogous in scale to the cellular structures was observed with dark nanoprecipitates, recognized as Mn-rich oxides. Microhardness evaluations portrayed a non-linear relationship with varying VED, with values spanning between 230 HV and 280 HV. The fracture toughness did not exhibit a linear correlation also with VED, but better fracture toughness values were achieved at 200 W. Additionally, a notable observation of late crack initiation was observed on the load-displacement curves, indicative of the material's intrinsic ductility. The fracture toughness values ranged between 320 and 220 MPa.m−0.5. A correlation between the microstructure and densification with the fracture toughness was made. The paper also presents a comprehensive discussion on the mechanisms underpinning microstructure formation and their consequential effects on the fracture toughness of the material.

Quantification of melt pool dynamics and microstructure during simulated additive manufacturing

The dynamics of laser spot melting and metallic alloy solidification are investigated through synchrotron x-ray radiography, 3D electron backscatter diffraction data, and computational fluid dynamics (CFD) simulations on a model NiMoAl alloy. Solidification velocities are measured from in-situ images to validate a CFD model of the spot melt. TriBeam tomography is used to reconstruct the melt pool in 3D, characterize the microstructure, and validate the CFD model melt pool dimensions. 3D geometrically necessary dislocation (GND) density calculations reveal extensive deformation at the sample surface. GND calculations integrated with the CFD model reveal that the halo of small, equiaxed grains adjacent to the fusion line is a result of recrystallization that occurred in the heat affected zone. By combining in-situ and ex-situ data modalities across a variety of temporal and spatial length scales, the microstructure formation mechanisms and their relationship to melt pool solidification are quantified.

Effect of ultrasound treatment on the performance and segregation of Al–Cu alloy with different Cd contents

By applying ultrasonic treatment to ZL205A aluminum alloy melt containing different Cd contents and then using a tensile test, a scanning electron microscope experiment, and a metallographic experiment, the influence of ultrasonic treatment to ZL205A aluminum alloy melt on the properties of aluminum–copper alloy with different Cd contents in the liquid phase high-temperature region was studied. The effect of ultrasonic treatment on the solidification structure of ZL205A aluminum alloy was investigated. The results showed that there was no significant difference in the form of Cd and the solid solution rate of the aluminum alloy with different Cd contents in ultrasonic-assisted casting. However, the effect of ultrasonic waves on the high-temperature liquid phase of the melt of ZL205A aluminum alloy can effectively reduce the porosity defects in the solidification structure of the casting, refine the solidification structure, and make the structure more uniform. The ultrasonic cavitation effect can promote the formation and uniform distribution of Al–3Ti and improve the nucleation rate, and the effect can continue after heat treatment. This can solve the problem that increasing Cd content in ZL205A greatly reduces the toughness of castings while increasing the strength. The sample with a Cd content of 0.20% and with ultrasonic treatment has the highest strength, the average tensile strength is 475.5 MPa, and the yield strength is 381.75 MPa. However, compared with the conventional casting samples with the same Cd content, the decrease in elongation was significantly reduced.

Hot-dip aluminizing of Fe–Cr–B cast steel in Al–Ti–B alloy melt

The periodic layered structure (PLS) composed of alternative arrangement of Cr–Al–B MAB phase and FeAl3 was formed at the (Cr, Fe)2B/Al interface during hot-dip aluminizing (HDA) of Fe–Cr–B cast steel in molten Al. However, the effect of alloying element in the Al melt on the PLS was still unknown. This work focused on the effect of Ti on the interfacial reaction between Fe–Cr–B cast steel and molten Al–Ti–B alloy. The Ti atoms in Al–Ti–B alloy melt could partially replace the Cr atoms in the M-sites of the Cr–Al–B MAB phase contained in the PLS after it formed in-situ, leading to the formation of (Cr, Ti)–Al–B MAB phase solid solution. The B atoms in the melt absorbed by the Cr–Al–B MAB phase also accounted for the blackening of the Cr–Al–B MAB phase. It was the first time that the M-site MAB phase solid solution in the Cr–Al–B system was prepared by hot-dip aluminizing.