Advances and challenges in direct additive manufacturing of dense ceramic oxides

Ceramic oxides,renowned for their exceptional combination of mechanical,thermal,and chemical properties,are indispensable in numerous crucial applications across diverse engineering fields.However,conventional manufacturing methods frequently grapple with limitations,such as challenges in shaping intricate geometries,extended processing durations,elevated porosity,and substantial shrinkage deformations.Direct additive manufacturing(dAM)technology stands out as a state-of-the-art solution for ceramic oxides production.It facilitates the one-step fabrication of high-performance,intricately designed components characterized by dense structures.Importantly,dAM eliminates the necessity for post-heat treatments,streamlining the manufacturing process and enhancing overall efficiency.This study undertakes a comprehensive review of recent developments in dAM for ceramic oxides,with a specific emphasis on the laser powder bed fusion and laser directed energy deposition techniques.A thorough investigation is conducted into the shaping quality,microstructure,and properties of diverse ceramic oxides produced through dAM.Critical examination is given to key aspects including feedstock preparation,laser-material coupling,formation and control of defects,in-situ monitoring and simulation.This paper concludes by outlining future trends and potential breakthrough directions,taking into account current gaps in this rapidly evolving field.

Thermodynamic analysis of interactions between Ti-Al alloys and oxide ceramics

The thermodynamics of interactions between various oxides（CaO,MgO,Al2O3 and Y2O3） and molten Ti and Ti alloys was investigated.The dissolution mechanism of oxides in molten Ti alloys was provided and the stability of oxides in molten Ti alloys was investigated and predicted by thermodynamic analysis.Interactions between oxides and Ti-Al melts were studied by oxide crucible melting experiments.By quantitative analysis,it is indicated that impurity contents in alloys are proportionally decreased with increasing the Al content in alloys and decreasing the melt temperature,which is in agreement with the results of the predicting thermodynamic stability.

Influence of Metal Additives on the Electrical Conductivities of the Oxide Ceramics as an Electrode Material

The electrical conductivities are reported for various oxide ceramics and cermets at 1000°C.Adding metal can greatly enhance the electrical condnctivities of the oxide materials.The conductivity of the ceramic added with metal depends on:(1)the conductivity σ_o of the oxides;(2)the content of metal additives;(3)the dispersion of the metal phase among oxide phase.The conductivity of the metal added does not affect the con- ductivity of the metal-containing ceramic.Although the metal-containing ceramic has much higher conductivi- ty than oxide ceramic,the change rate of their conductivities with temperature is similar and is controlled by E_g of the oxide.

Interfacial reaction between zirconium alloy and graphite mold/yttrium oxide ceramic mold

Zirconium alloys are active in the molten state and tend to react with the mold during casting. The casting technology of zirconium is not yet well established; especially in selecting the mold materials, which are difficult to determine. In the present work, the interfacial reactions between zirconium casting and casting mold were studied. The zirconium alloy was melted in a vacuum arc skull furnace and then cast into the graphite mold and ceramic mold, respectively. The zirconium casting samples were characterized using SEM, EDS and XRD with an emphasis on the chemical diffusion of elements. A reaction layer was observed at the casting surface. Chemical analysis shows that chemical elements C, O and Y from the mold are diffused into the molten zirconium, and new phases, such as ZrC, Zr30, YO1.335 and Y6ZrO11, are formed at the surface. In addition, an end product of zirconium valve cast in a yttria mold has a compact structure and good surface quality.

Ab initio energetic study of oxide ceramics with rare-earth elements

Ab initio energetic calculations based on the density functional theory （DFF） and the projector augmented wave method （PAW） for determining the polymorphisms of lanthanide sesquioxides Ln2O3 （where Ln = rare-earth element, Y, and Sc）, LnMO3 perovskites （where M = AI and Ga）, and Ln2B207 pyrochlores （where B = Ti, Zr, and Hf） were reported. The relative lattice stabilities agreed well with the critically assessed results or the experimental results except the C-type Ln2O3 with a cubic structure, for which the calculated total energies were considerably more negative. With the increase of the Ln^3＋-cation radius, the polymorphic structures showed a degenerative tendency. The tendencies and quantities of the enthalpies of formation of the ternary oxide ceramics synthesized from their constituent binary oxides reasonably agreed with the available experimental results, and valuable thermodynamic properties were afforded to the compound, for which no experimental data is available. The enthalpies of formation of both perovskites and pyrochlores tend to become more negative with the increase of the Ln^3＋-cation radius.

Optical and electrical properties of room temperature preparedα-IGZO thin films using an In_(2)Ga_(2)ZnO_(7) ceramic target

In this study,a high-purity In_(2)Ga_(2)ZnO_(7) ceramic target was used to deposit indium gallium zinc oxide(IGZO)films by RF magnetron sputtering technology.The microstructure,growth state,optical and electrical properties of the IGZO films were studied.The results showed that the surface of the IGZO film was uniform and smooth at room temperature.As the substrate temperature increased,the surface roughness of the film gradually increased.From room temperature to 300℃,all the films maintained amorphous phase and good thermal stabilities.Moreover,the transmission in the visible region decreased from 91.93%to 91.08%,and the band gap slightly decreased from 3.79 to 3.76 eV.The characterization of the film via atomic force microscope(AFM)and X-ray photoelectron spectroscopy(XPS)demonstrated that the film prepared at room temperature exhibited the lowest surface roughness and the largest content of oxygen vacancies.With the rise in temperature,the non-homogeneous particle distribution,increase in the surface roughness,and reduction in the number of oxygen vacancies resulted in lower performance of theα-IGZO film.Comprehensive analysis showed that the best optical and electrical properties can be obtained by depositing IGZO films at room temperature,which indicates their potential applications in flexible substrates.

Zero sintering-induced shrinkage of porous oxide ceramics

Porous oxide ceramics are widely used in extreme working conditions owing to their excellent resistance to high temperatures and corrosion.However,sintering is an inevitable process applied to ceramics,from the green body to the final product.The highly complex structures exacerbate the shrinkage-induced ir-regular deformation and crack formation in the sintering process.A pioneering approach is developed in this study to achieve zero shrinkage for porous alumina ceramics during multistep sintering,using a combination of active fillers-ZrAl 3 and Al 75 Si 25.The response surface method is used to optimize the material compositions and sintering process,to achieve shrinkages of less than 0.05%for the entire pro-cess.The sintering expansion mechanism is investigated by analyzing the pyrolysis and microstructures of samples at different temperatures.The combination of ZrAl 3 and Al 75 Si 25 can attain the continuous expansion of the matrix in a wide temperature range of 600-1400°C.Furthermore,typical alumina com-ponents are fabricated and used to verify the effectiveness of the proposed approach.Owing to shrinkage suppression,the profile deviation of the samples is less than 0.1 mm,and the proportion of microcracks is reduced by 97.8%.The suggested approach shows potential applications in near-net,low-defect fabrica-tion of complex fine ceramic components.

The Synthetic and Mechanical Properties of a Silica Matrix Cermet Composite

A cermet composite was prepared by employing thermal spraying flame onto stainless steel surfaces of(304)type.Hence 25,50%of aluminum was mixed with matrix of(10%Al_(2)O_(3)-SiO_(2)).A spray system consistis of oxygen barrel,acetylene and spray gun that contains powders feeder at different spray distances(5,10,15,20 and 25 cm).The thermal treatment of the samples resulting from spraying was performed at 1100℃for 1.5 hr.Some physical examinations(porosity and adhesion),mechanical tests(hardness and wear rate)and Atomic Force Microscope(AFM)test were performed before and after thermal treatment.The test results showed that the best mixing rate was(50%)and the best spray distance was(15cm)where the quality of coating layer improved after thermal treatment at 1100℃for 1.5 hr with a porosity ratio reduced from 11.2%to 6.6%,and adhesion strength improved with the increase in the alumina content to 50%.The results demonstrated that the best adhesion value after thermal treatment was 30.98 MPa.The hardness of coating layer increased from 45.78 to 54.88 HV;while the lowest rate of wear was at 50%of alumina with a spray distance of 15cm.Also,there was a clear improvement based on AFM within grain size,root mean square and roughness rate.

Laser assembly nanostructured Al2O3/TiO2 coating on cast aluminum surface

CO2 laser quick assembly technology is adopted on the surface of cast aluminum ZL104 to form a dense ceramic coating containing a great deal of nanometer Al2O3/TiO2 particles which eliminate cracks and porosities.The major phases of the coating are α-Al2O3 andβ-TiO2. The micro-hardness distribution of the coating is 1 813,1 504, 1 485 and 1 232 (HV0.05). The bonding strength of the coating LC1 is 11.4 N, which is 7.26 times higher than that of the conventional hot-spraying Al2O3/TiO2 coating. It has been proved by analysis that the bonding strength is achieved because of the effects of both super-quick laser consolidation and the nanometer effect of nanometer ceramic material.

3D nonlinear photolithography of tin oxide ceramics via femtosecond laser

As a wide band gap semiconductor material,tin oxide(SnO_(2))has been widely used in gas sensing,optoelectronics and catalysis.The complex micro and nanoscale threedimensional(3D)geometric structures endow the conventional SnO_(2)ceramics with novel properties and functionalities.Nevertheless,ceramics cannot be cast or machined easily due to their high mechanical toughness and resistance.The additive manufacturing opens a great opportunity for flexibly geometrical shaping,while the arbitrary shaping of SnO_(2)ceramics at micro and nanoscale is always a challenge.Herein,preceramic monomers which can be polymerized under ultrafast laser irradiation,were utilized to form complex and arbitrary 3D preceramic polymer structures.After calcination treatment,these green-body structures could be converted into pure high-dense SnO_(2)ceramics with uniform shrinkage,and the feature size was down to submicron.Transmission electron microscopy(TEM)analysis displays that the printed SnO_(2)ceramic nanostructures can be nanocrystallized with grain sizes of 2.5±0.4 nm.This work provides the possibility of manufacturing 3D SnO_(2)ceramic nanostructures arbitrarily with sub-100 nm resolution,thus making it promising for the applications of SnO_(2)in different fields.

Laser melted oxide ceramics:Multiscale structural evolution with non-equilibrium features

Compared with the versatility in metal industry,application of laser on oxide ceramics is quite limited due to the intrinsic features of ceramics and limited understanding in laser-ceramic interaction mechanism,especially for high-energy laser that causes melting of materials.In this research,a study into general behaviors of several oxide ceramics melted by laser under inert atmosphere is presented.Key factors in determining state transformation,chemical reduction and phase structure are summarized,with further investigation into the evolution in microstructure at multiscale and the corresponding novelty and metastability.It is found that laser melting does show great potential in introducing deep reduction,unique microstructure,and notable increase in structure complexity and total entropy,and those features could contribute to some unconventional functional performance with brand-new structure-property relationship.

Ultrasonic investigations on elastic properties of (Bi,Pb)-Sr-Ca-Cu oxide ceramic superconductors

Ultrasonic velocities have been measured in single phase Bi_1.7 Pb_0.3Sr2CaCu2O8+x and Bi1.7Pb0.3Sr2Ca2O10+x polycrystalline samples. Anomalous changes of both longitudinal and transverse velocities were observed near 200K, which indicates that some structural phase transitio might occur. The elastic constants of these samples have been determined from the measured ultrasonic velocity data, which are much smaller than those of YBa2 Cu3 O7-y and BaTiO3, manifesting that the interlayer coupling will dramatically decrease when the c - axes of the unit cells of these perovstite-like multilayer ceramics increase. The values of Poisson ratio, however, of those ceramics are very close, implying similar interatomic bonding forces. Corrected to void-free state, the Debye temperature of these materials is estirnated as 270 ±20k. The temperature dependence of Debye temperatures for these materials is also calculated by using the same method and reported for the first time.

Application of external gear pump in water-hydraulic system

The ceramic coating technology of microarc oxidation (MAO) was utilized to modify surface properties of the movable endplate of a high pressure gear pump used in water-hydraulic system, which is made of aluminium alloy. A coMPact ceramic layer of more than 130 μm was developed on the movable endplate with the hardness up to HV1000 by means of microarc oxidation. A trial of tests conducted in a water power transmission system show that the maximum outlet pressure of the gear pump with the movable endplate treated by microarc oxidation, can reach 16 MPa. It is pointed out that the ceramic coating developed by microarc oxidation technology on the surface of aluminium alloy, is economical and feasible.

Preparation of large-size Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod by laser directed energy deposition and its microstructure homogenization mechanism

Laser 3D printing based on melt growth has great potential in rapid preparation of Al_(2)O_(3)-based eutectic ce ramics.In this work,la rge-scale Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod with diameter of 4-5 mm and height higher than 250 mm was additively manufactured by laser directed energy deposition.Especially,heat treatment was applied to eliminate the microstructure heterogeneity in the as-deposited eutectic ceramic,and the microstructure homogenization mechanism was studied in depth.The results indicate that colonies and banded structures completely disappear after the heat treatment,producing a homogeneous network eutectic structure.The microstructure homogenization is revealed to experience three stages of discontinuous coarsening,continuous coarsening and microstructure coalescence.Additionally,it is found that the eutectic spacing linearly increases with the heat treatment time,meaning that the coarsening behavior of the laser 3D-printed Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)eutectic ceramic satisfies well with the Graham-Kraft model.

A sol-gel method to synthesize indium tin oxide nanoparticles

Transparent conductive indium tin oxide （ITO） nanoparticles were synthesized by a novel sol-gel method. Granulated indium and tin were dissolved in HNO3 and partially complexed with citric acid. A sol-gel process was induced when tertiary butyl alcohol was added dropwise to the above solution. ITO nanopartides with an average crystallite size of 18.5 nm and surface area of 32.6 m^2 ]g were obtained after the gel was heat-treated at 700 ℃, The ITO nanoparticles showed good sinterability, the starting sintering temperature decreased sharply to 900 ℃, and the 1400 ℃ sintered pellet had a density of 98.1% of theoretical density （TD）.

Formation mechanism and roles of oxygen vacancies in melt-grown Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) eutectic ceramic by laser 3D printing

Laser three-dimensional(3D)printing has become a significant technique to fabricate high-performance Al_(2)O_(3)-based eutectic ceramics based on melt growth.However,oxygen vacancies are inevitable crystal defects during this process,and their formation mechanism and roles in the as-deposited ceramics are still unclear.In this paper,Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) ternary eutectic ceramics were prepared by laser 3D printing,and the formation mechanism of the oxygen vacancies was revealed by conducting a well-designed annealing experiment.In addition,the effects of the oxygen vacancies on the structure and mechanical property of the as-solidified eutectic ceramic were investigated.The formation of oxygen vacancies is revealed to be a result of the transfer of oxygen atoms from the oxide ceramic to the oxygen-deficient atmosphere by means of vacancy migration mechanism.Besides,the presence of oxygen vacancies has no obvious effects on crystalline structure and microstructure of the additively manufactured eutectic ceramic.However,the chemical bond property changes to some extent due to the formation of these crystal defects,which may affect the mechanical property of the as-deposited eutectic ceramic.It is found that the hardness decreases by 3.9%,and the fracture toughness increases by 13.3%after removing the oxygen vacancies.The results may provide a potential strategy to regulate the mechanical property of the oxide ceramic materials.

Phase transformation of ZrO2 doped with CeO2

Thermal barrier coatings（TBCs） protection is widely used to prolong the lifetime of turbine components.The outermost layer of TBCs is ceramic layer, whose function is heat insulation, and the main composition of the ceramic layer is ZrO2. In this study, the micro-Zr02 and the nano-ZrO2 doped with 10 wt% CeO2 as well as microZrO2 and nano-ZrO2 were prepared by air plasma spraying（APS） to study the advantages of the addition of rare earth element. The effect of CeO2 on the phase transformation of ZrO2 was studied. The results show that there are few cracks in micro-and nano-ZrO2 doped with 10 wt% CeO2,and rare earth oxides can affect the phase transformation significantly. The morphologies, hardness and elastic modulus of the four ceramic layers were also discussed.