Effect of gelcasting conditions on quality of porous Al-Cu alloy

The porous A1-Cu alloy was prepared by the gelcasting process. And the effects of gelcasting conditions, such as monomer, the volume ratio of cross-linker and monomer, dispersant and redox initiating system on the height, gelling time and the quality of green body were investigated. （It was found that the dispersant and monomer played significant roles in the height and quality of green bodies, respectively.） The optimal conditions were 10% monomer, 2% cross-linker, 0.2% initiator （volume fraction）, and 1.2 g dispersant, in which the green body exhibited the best quality. The mechanisms of process conditions in eliminating the cracks and forming the pores of in the five stages were proposed. Mercury porosimetry provided a description of pore diameter ranging from 10 to 10000 nm and open porosity of 38.78 %.

Rheological property and drying mechanism of thermoresponsive gelcasting of ZnO

To solve the problem of drying gelcast green body, the thermoresponsive gel system which contains macromonomer graft chains was used in gelcasting of ZnO. The effects of the amount and length of graft chains macromonomer PIPAAm, the total amount of organic matters, and the solid loading on the rheological properties of suspensions were investigated, and the drying mechanism of gelcast green body was analyzed. The results show that ZnO suspensions with the gel system still display shear- thinning rheological behavior, but its viscosity increases with increasing the addition amount and relative molecular mass of PIPAAm graft chain, and the total organic matter content. The PIPAAm graft chains inhibit or even eliminate the formation of the ＂dense layer” on the surface of gelcast ZnO green bodies, and accelerate the drying of green bodies. The introduction of PIPAAm graft chains facilitates the shrinkage of the gelcast ZnO green bodies, which is a feasible method to increase the relative density of green bodies.

Porosity and mechanical properties of porous titanium fabricated by gelcasting

Porous Ti compacts with large size and complex shape for biomedical applications were fabricated in the porosity range from 40.5% to 53.8% by controlling gelcasting parameters and sintering conditions. The experimental results show that the total porosity and open porosity of porous titanium compacts gelcast from the Ti slurry with 34 vol.% solid loading and sintered at 1100℃ for 1.5 h are 46.5% and 40.7%, respectively, and the mechanical properties are as follows： compressive strength 158.6 MPa and Young＇s modulus 8.5 GPa, which are similar to those of human cortical bone and appropriate for implanting purpose.

Near-net shaped Al/SiCP composites via vacuum-pressure infiltration combined with gelcasting

To solve the problem of difficult machining, the near-net shaped Al/SiCP composites with high volume fraction of SiC particles were fabricated by vacuum-pressure infiltration. The SiCP preform with a complex shape was prepared by gelcasting. Pure Al, Al4Mg, and Al4Mg2Si were used as the matrices, respectively. The results indicate that the optimal parameters of SiCP suspension in gelcasting process are pH value of 10, TMAH content of 0.5 wt.%, and solid loading of 52 vol.%. The Al matrix alloyed with Mg contributes to improving the interfacial wettability of the matrix and SiC particles, which increases the relative density of the composite. The Al matrix alloyed with Si is beneficial to inhibiting the formation of the detrimental Al4C3 phases. The Al4Mg2Si/SiCP composite exhibits high relative density of 99.2%, good thermal conductivity of 150 W·m^-1·K^-1, low coefficient of thermal expansion of 10.1×10^-6 K^-1, and excellent bending strength of 489 MPa.

GELCASTING OF NANO-SIZE Y-TZP

The green specimens of nano-size Y-TZP are formed by gelcasting method. Using polymer electrolytes NaPAA and NH_4PAA, we have studied the rheological properties of slurry.The optimum pH range is between 8 to 10. The proper amount of dispersant changes with the solid content.The rheological measurements of suspension containing NH_4PAA show lower viscosity.The theoretical green density has been calculated.

Porous alumina ceramic via gelcasting based on2-hydroxyethyl methacrylate dissolved in tert-butyl alcohol

To obtain porous alumina ceramic with high strength,a novel gelcasting system based on 2-hydroxyethyl methacrylate(HEMA)dissolved in tert-butyl alcohol(TBA)was developed.The polymerization of the HEMA-TBA gelcasting system,the thermal behavior of obtained green body,and the microstructures and mechanical properties of the sintered bodies were investigated by rheometer,TG-DSC,SEM and bending strength testing,respectively.The results show that,(1)10 mg/mL of the initiator(benzoyl peroxide)is the optimal amount for polymerization of this gelscasting system at 25 ℃;(2)The alumina suspension of the HEMA-TBA gelcasting system showing shear-thinning behavior is sufficiently low for gelcasting process;(3)The bending strength of porous alumina ceramic samples,whose porosities range from 42% to 56%,is from(8±0.5)to(91±4.5)MPa.

Gelcasting of 316L stainless steel

A novel near-net process, gelcasting, was successfully used to prepare larger size 316L stainless steel parts with complex shape. In this study, the effects of process parameters on the viscosity of the slurry and the dry green strength were investigated. The results show that gas atomization （GA） powder is more suitable for gelcasting compared with water atomization （WA） powder. The maximum solid loading is 55vo1% for ball-milled slurry with GA powders. And the optimum amounts of monomers （acrylamide （AM）＋methylenebisacrylamide （MBAM）; the mass ratio, 30：1） and initiator in the AM system are 1.8% （based on the weight of metal powder） and 0.8%-1.4% （based on the weight of monomers）, respectively, at which, the maximum green strength obtained is 33.7 MPa. The mechanical properties of the sintered specimen are as follows： ultimate tensile strength, 493 MPa; yield strength, 162 MPa; and HRB, 72.

Near-net shape processing of spherical high Nb-TiAl alloy powder by gelcasting

Spherical Ti-45A1-8.5Nb-（W,B,Y） alloy powder prepared by an argon plasma process was near-net shape by gelcasting. In the non-aqueous system, methaerylate-2-hydroxy ethyl, toluene, benzoyl peroxide, and N,N-dimethylaniline were used as the monomer, solvent, initiator, and catalyst, respectively. To improve sintering and forming behaviors, many additives were included in the suspension. The concentrated suspension with a solid loading of 70vo1% was prepared. The high Nb-TiA1 powder was analyzed by electron microscopy and X-ray diffraction. It was found that the green bodies had a smooth surface and homogeneous microstructure, exhibiting a bending strength as high as 50 MPa. After sintering at 1480℃ for 2 h in vacuum, uniform complex-shaped high Nb-TiA1 parts were successfully produced.

Preparation and Properties of Sialon-SiC Suspension for Gelcasting

The raw materials of Al, Si, SiO2, and SiC were used to prepare Sialon-SiC suspeusion for gelcasting by adjuting the pH value and content of SiC particle and controlling the milling time. The result shows that the stable suspension for gelcasting coald be got by adding 40wt% SiC particle at pH = 8. Al would eusily hydralyze to deteriorate the suspension when the milling time was too long, so the optimum milling time should be less than 100 minutes. At last, a well-dispersed suspension with a viseosity of less than 0.32Pa· s was obtained and the solid looming was 54vol% .

Effect of Sintering Additive on the Properties of Sialon-SiC by Gelcasting

Sintering additives to gelcasting Sialon-SiC were decided by the optimizing experiments. The results show that Sialon-SiC can be sintered under 1450℃ and sintering temperature decreases by 100℃, when 2%～3% TiO 2 or Guangxi clay is used as sintering additive.

Effects of process parameters on nonaqueous gelcasting for copper powder

An approach to fabricate sintered copper with high green strength and high sintered density using nonaqueous gelcasting technol- ogy is presented in this study. The effects of various gelcasting processing parameters such as monomer content, monomer/crosslinker ratio, initiator content, dispersant dosage, and temperature on the flexural strength of dried green bodies and the relative density of sintered bodies were studied to obtain better microstructures and properties. The appropriate process parameters obtained for copper gelcasting are as follows monomer content, 20vol%-30vol% （based on the total volume of reagents）; monomer/crosslinker ratio, 10：1 to 20：1; initiator content, 3vol%-4vol% （based on the volume of the monomer）; dispersant dosage, 1.5wt%-2.5wt% （based on the mass of the copper powder）; and reaction temperature, 65-75℃.

Research on Gelcasting Formation of SiC-Al_2O_3-Y_2O_3-La_2O_3 Systems

The rheological behavior and gelcasting of composite suspensions of SiC and synthesized Al 2O 3-Y 2O 3-La 2O 3 powder as sintering aid were investigated. It was found that the rheological behavior of SiC particles could be modified with a slightly oxidized surface that was similar to silica in colloidal behavior. The smaller the particles were, the more similar to silica the SiC powder was. The pH value of Al 2O 3-Y 2O 3-La 2O 3 synthesized powder slurry at isoelectric points (IEP) is higher than that of SiC powder. The dispersant PAA-NH 4 changes the IEP of both SiC and Al 2O 3-Y 2O 3-La 2O 3 powder slurry to higher pH values. The experimental results indicate that the composite suspension could possess satisfactory stability and lower viscosity at pH =10.1 and PAA-NH 4 as dispersant. The optimum solid loading was 550 0 in volume. Machinable green bodies with uniform complex shape are gained after molding.

Microstructure and properties of porous Si_(3)N_(4)ceramics by gelcasting-self-propagating high-temperature synthesis(SHS)

Porous silicon nitride ceramics have attracted a considerable attention due to their excellent overall performance,but poor porosity homogeneity and structural shrinkage induced by prolonged high temperature sintering limit its further application.Herein,as a three-in-one solution for the above issues,for the first time we develop a novel approach that integrates the merits of gelcasting-SHS(self-propagating high-temperature synthesis)to prepare porous Si_(3)N_(4)ceramics to simultaneously achieve high porosity,high strength,high toughness,and low thermal conductivity across a wide temperature range.By regulating the solid content,porous Si_(3)N_(4)ceramics with homogeneous pore structure are obtained,where the pore size falls inbetween 1.61 and 4.41 pm,and the elongated grains are interlaced and interlocked to form micron-sized coherent interconnected pores.At the same time,porous Si_(3)N_(4)ceramics with porosity of 67.83%to 78.03%are obtained,where the compressive strength reaches 11.79 to 47.75 MPa and fracture toughness reaches 1.20 to 6.71 MPa-m1/2.

Gelcasting of titanium hydride to fabricate low-cost titanium

In this work, low-cost titanium was fabricated by gelcasting of titanium hydride powder. The effects of morphology and grain composition of powder raw material and solid loading on the rheological behavior of gelcasting slurry were studied. The degreasing, dehydriding and sintering behaviors of gelcasted green body were investigated by differential thermal analysis （DTA） and dilatometer. The results show that the solid loading of titanium hydride slurry reaches 50 vol%. Combination of dehydriding and sintering in one process accelerates the densification, and the relative sintered density of the final part achieves 96.5 %. In order to test the ability of gelcasting process for fabricating structural materials, a resin handle produced by 3D printing technology was used as a model and a titanium handle was successfully fabricated. Higher solid loading and better sinterability of titanium hydride powder promote manufacture of bulk titanium with high relative density, complex shape and well-defined microstructure.

Fabrication of porous titanium carbide ceramics by gelcasting process

Titanium carbide ceramics with high porosity were fabricated by gelcasting process with methacrylamide as a chain forming monomer,methylenebisacrylamide as a cross-linker monomer and tetramethylammonium hydroxide as a dispersant.The stability of suspension,mechanical properties,phase composition and micro structure were investigated by zeta potential,bending and compressive strengths,X-ray diffraction and scanning electron microscopy(TEM) analyses,respectively.The results show that the optimal concentration of dispersant for the best homogeneous unagglomerated microstructures is 0.4 wt%at pH 9.The highest green strength of 33 MPa is obtained from the suspension with 40 vol% solid loading and25 wt% monomer.The porosity increases with the increase in monomer content and the decrease in solid loading.Also,the strength of porous TiC ceramic decreases with the content of pores increasing in the sintered ceramics.

Effect of agarose content on microstructures and mechanical properties of porous silicon nitride ceramics produced by gelcasting

Porous Si3N4 self-reinforce ceramics were prepared by gelcasting using agarose solutions. By changing the agarose content in the slurries, the porous silicon nitride ceramics with different porosities, α→β-Si3N4 phase transformation, and mechanical properties were obtained. When the agarose content changed from 0.2% to 0.8% (w/w, based on powder), the porosities increased from 10.3% to 21.4%, while the fracture strength decreased from 455 to 316 MPa and the fracture toughness decreased from 6.6 to 5.5 MPa·m1/2. Many fibrous β-Si3N4 grains grown from the internal wall of the round pores is the typical microstructure of the gelcasting porous silicon nitride ceramic. Both elongated β-Si3N4 grains and suitable interfacial bonding strength contributes to high fracture toughness by favoring crack deflection and bridging. The growth mechanisms of fibrous grains resulted from the synergy of solution-diffusion-reprecipitation and vapor-liquid-solid (VLS).

陶瓷的凝胶注模成型及其研究现状

阐述了陶瓷凝胶注模成型 (gelcasting)的工艺过程及关键影响因素 ,介绍了最近几年该技术的研发动态 ,指出环境友好型凝胶体系的开发 。

Liquid drying of BeO gelcast green bodies using ethanol as liquid desiccant

BeO gelcast green bodies were dried by liquid drying method with liquid desiccant ethanol.Effects of ethanol concentration,solids loading and aspect ratio of green body on the moisture and shrinkage of green bodies were studied through measuring mass and dimension.Additionally,liquid drying stress was analyzed and a model of the initial stage drying stress was established.The results show that higher ethanol concentration,lower solids loading and higher aspect ratio of gelcast green bodies increase the drying rate.Increasing the ethanol concentration decreases the shrinkage rate.Liquid drying stress is generated due to a non-uniform drying rate.During the process of liquid drying,the inner drying stress of the green body changes from compressive stress to tensile stress,while the outer drying stress changes from tensile stress to compressive stress.

Preparation of porous Si_(3)N_(4) ceramics via tailoring solid loading of Si_(3)N_(4) slurry and Si_(3)N_(4) poly‐hollow microsphere content

Porous Si_(3)N_(4) ceramics were prepared by aqueous gelcasting using Si_(3)N_(4) poly-hollow microspheres(PHMs)as pore-forming agent.The effects of solid loading of Si_(3)N_(4) slurry and Si_(3)N_(4) PHM content on the properties of porous Si_(3)N_(4) ceramics were investigated.Onlyβ-Si_(3)N_(4) phase is observed in porous Si_(3)N_(4) ceramics,and Si_(3)N_(4) PHMs distribute uniformly both in Si_(3)N_(4) green samples and porous Si_(3)N_(4) ceramics.Results show that solid loading of Si_(3)N_(4) slurry and Si_(3)N_(4) PHM content could considerably influence the properties of porous Si_(3)N_(4) ceramics.With the increase of solid loading of Si_(3)N_(4) slurry(decrease of Si_(3)N_(4) PHM content),the distributing state of Si_(3)N_(4) PHMs changes from contacting with each other to just embedding in the matrix,thus their porosity decreases,while their shrinkage,flexural strength,and fracture toughness increase.