Study On 3D Gel Printing Of Cemented Carbides

3D printing,also known as additive manufacturing,is any of rapid manufacturing technologies to make a three-dimensional object.Based on the dispersion-deposition fundamental,successive layers of material are laid down under computer control.In 3D printing,the objects can be made into almost any shape or geometry with maximizing material utilization,100%in theory.Most of the existing investigations focus on beam-based technologies,which are based on using a laser or electron beam to selectively melt powder layer and bind it together to create a solid structure.Beam-based technologies have been successfully used to directly fabricate pure titanium and titanium alloys,superalloy,magnalium alloy and so on.The powders used for 3D printing are generally required to be spherical with good fluidity and have fine grain size,narrow particle size distribution as well as high apparent density.However,there are several problems,including some materials cannot be made into spherical powder or wire,the components of metal or ceramic matrix composites have different melting points and the product performance is affected by high temperature and high energy rapid melting-solidification printing process,all of which restrict the application of 3D printing technologies.A non-beam-based process:3D gel printing(3DGP),which is the combination of 3D printing,slurry preparation and in-situ polymerization,is proposed in this paper.The metal/ceramic powder slurry with high solid loading is used as raw material.3D gel printing is a stereo deposition technique based on deposition and in-situ polymerization of slurry and shape formation by computer-controlled slurry extrusion.This study was supported by Beijing Science and Technology Ministry.Cemented carbides are widely used for cutting tools,excavating tools and wear parts due to the good combination of hardness,toughness and wear resistance.Nevertheless,the machining of cemented carbides is difficult due to their high hardness and strength-toughness as well as the waste of raw materials and high processing cost.New short process and near-net forming technology is urgently to be developed and researched.Fine and irregular shape cemented carbide powders cannot be rolled into a thin powder layer.What's more,there is a significance difference between the melting points of the hard phase and binder phase,which makes cemented carbides unsuitable for beam-based 3D printing technologies.Therefore,this paper focused on cemented carbides and conducted research on the development of cemented carbide slurry,3D gel printing equipment and technology,aiming to realize 3D printing for the near-net forming of complex cemented carbide parts.The research approach of "technologic analysis-device development-products manufacturing-new material/product design" is applied.This study started out with the analysis of the principle and procedure of 3DGP,by which the key technologic parameters and the general requests of slurry were concluded,providing guidelines and principles for the follow-up research.Then the 3D gel printing device was developed.Based on the properties of powder,the slurry of YG20 powder in a solution of organic monomers was prepared,of which the polymerization was controllable.And complicated cemented carbide part was printed.3DGP was further proposed to be applied on the design and manufacturing of metal matrix composites.TiC-high manganese steel cermet with a gradient distribution of TiC was successfully designed and fabricated by 3DGP.The main results are as follows:(1)3D gel printing was proposed.The slurry of metal/ceramic powder,which has high solid loading and good flowability,is used as raw material.In 3DGP process,based on the layered-manufacturing principle,successive layers of slurry are deposited and polymerized under computer control.The three-dimensional green body is produced from a 3D model at low temperature(20?80 ?).(2)3D gel printing device was developed.The device includes software control system and hardware system.By the open software system,in which all printing parameters could be adjusted,3D model is transformed into machine code and drives hardware system.After the hardware system,which consists of rectangular-pole structure,X-Y-Z movement device,screw-micro-extrusion,chemically and thermal induced systems,was operated,the slurry was extruded,deposited and polymerized on demand.The complicated metal or cermet parts can be printed layer-by-layer.The 3D gel printing device has a repeated positioning accuracy of ± 0.01 mm and a location error less than 2.2%.The maximum printing size of this system is 500 × 500 × 500 mm.The minimum of printing layer thickness is 0.1 mm while the printing speed reaches 90 mm/s.(3)Toluene-hydroxyethyl methacrylate gel system suitable for 3DGP process was developed.This gel system is applied as a low viscosity carrier,resulting in good flowability of slurry.The crosslinking property of the gel system is the real basis of 3DGP.By adding WC-20 wt%Co(YG20)powder and 0.2 wt%super dispersant Solsperse-6000,the YG20 slurry with a solid loading of 56 vol%and shear thinning behavior was prepared,which is conducive to the printing process.With the addition of 90 mmol/L initiator benzoyl peroxide(BPO),the polymerization reaction induction period of YG20 slurry was 2 min.After extruded,the YG20 slurry could be polymerized in 30 s at the catalyst(N,N-Dimethylaniline)concentration of 70 mmol/L.(4)WC-Co cemented carbide has been successfully printed.Depending on the rheological property and crosslinking property of YG20 slurry,the 3D gel printing process for YG20 parts has been developed.A bevel milling cutter with good shape and appropriate precision was printed under the optimal printing parameters,including 0.4 mm nozzle,0.34 mm layer height,1 cm3/min extrusion speed of slurry,20 mm/s printing speed and 92%filling rate and so on.After sintered at 1350 ?,the milling cutter maintained its shape and had homogeneous microstructure.The sintered density was 13.55 g/cm3,attaining 99.93%of theory density.The hardness and transverse rupture strength of sintered sample are 87.7 HRA and 2612.8 MPa,respectively.The mechanical properties of the samples printed by 3DGP are similar to those of specimens made by conventional press and sinter technology.(5)The integrated design and manufacturing of graded composites has been completed by 3DGP.3D gel printing device with multi-print-head was improved.Three TiC-high manganese steel cermet powders with TiC content of 20 wt%,30 wt%and 40 wt%were prepared.On the basis of toluene-hydroxyethyl methacrylate gel system,three slurries with solid loading of 60 vol%and well printability were prepared.The polymerization of these slurries can be controlled by adding 46 mmol/L initiator ammonium persulfate(APS)and 60 mmol/L catalyst tetramethylethylendiamin(TEMED).A cutting pick with a gradient distribution of TiC was successfully designed and fabricated.After sintering,the manufactured cutting pick had composition and structure gradient with corresponding graded mechanical properties.The density gradient was 6.79-6.5-6.22 g/cm3,indicating that the cutting pick was fully dense.The cutting pick had a hardness gradient of 45.6-52.8-59.9 HRC accompanied with the wear resistance improvement.The transverse rupture strength and impact toughness gradient were 2122.7-1711.3-1470.3 MPa and 19.14-13.35-9.75 J/cm2,respectively.3DGP has shown distinctive advantages and capabilities for the integrated design and manufacturing of graded composites.