Abstract: 3D printing technology, with its "bottom-up" manufacturing concept of accumulating materials, has provided new ideas and new solutions for the manufacturing of complex structural parts, and opened up broader application scenarios for aviation, aerospace, automotive, medical, architecture, art and other fields.3D printing materials are divided into three categories: metal materials, organic polymer materials and inorganic non-metallic materials, commonly known as advanced materials, and the latest research results of advanced materials applied to 3D printing technology at home and abroad are summarized and elaborated respectively. It is found that, with the deepening of engineering application, 3D printed metal materials are gradually enriched and improved by alloying, modification and reinforcement materials can effectively improve the performance of wire materials, among which toughness and bending strength are important research indexes; most inorganic non-metallic materials are developed on process adaptability, and some materials have entered the performance improvement stage.

Key words: 3D printing; metal materials; organic polymer materials; inorganic non-metallic materials

Introduction

3D printing is also known as additive manufacturing (Additive Manufacturing, AM), based on the digital model file, through the software and numerical control system, the special metal materials, organic polymer materials, inorganic non-metallic materials and other types of materials according to extrusion, sintering, melting, light curing, injection and other ways layer by layer accumulation, so as to create the manufacturing technology of physical goods.3D printing is a "bottom-up" manufacturing concept, which provides new ideas and new solutions for the manufacturing of complex structural parts. It has been widely used in ² -5 in aviation, aerospace, automotive, medical, architecture, art and other fields.

At present, nearly 20 process types have been produced in the field of 3D printing both at home and abroad, among which 6 processes are the most mature and have the most applied processes

Including: laser selection melting (SLM), directional energy deposition

(DED), selective laser sintering (SLS), electron beam melting

Chemical (EBM), light curing technology (SLA), melt deposition

(FDM)。With the rapid development of 3D printing and related support industries

 Development, advanced 3D printing technology is constantly emerging, and the types of materials needed are also constantly updated and iterated. In this paper, advanced 3D printing materials are divided into three categories: metal materials, organic polymer materials and inorganic non-metallic materials, and expounds the latest research results of advanced 3D printing technology at home and abroad under each advanced material type, in order to make 3D in China The development of printing advanced materials industry plays a leading role in innovation.

 

1 Metal materials

 

3D printing of metal materials is a manufacturing technology with metal as raw material, in the form of metal powder and wire, quickly melting, solidification and forming under high temperature heat sources such as laser and electron beam. Metal materials commonly used in 3D printing include titanium alloy, high-temperature alloy, iron-based alloy, aluminum alloy and refractory alloy. By literature research: in metal material 3D printing, titanium alloy and iron alloy is more by adding enhanced phase improve performance, high temperature alloy, aluminum alloy is through alloy strength, and refractory alloy and 3D printing process adaptability is poor, often by thermal isostatic pressure (HIP) or temperature gradient improvement.

 

1.1 titanium alloy In 3D printing applications

 

Titanium is an important structural metal that was developed since the 1950s. Titanium alloy has high strength, good corrosion resistance and strong heat resistance. The titanium alloy used for 3D printing is mainly powder material. At present, TA1, TC4, TA15 and other brands are commonly used in domestic aerospace and medical fields, and the powder quality and batch stability have been filled Divide the verification. To meet the needs of the applications, researchers have continuously developed new titanium alloys and their composites. Large angle grain boundaries exist in the fiber organization of Ti-6.5Al-2 Zr-Mo o-V novel titanium alloy developed by Li et al, with hardness values ranging from 270 to 290 HV under different process parameters, Similarly, Ahmed et al. have developed a Ti-5A1-5Mo-5v-3 Cr, a new titanium alloy whose hardness is consistent with that of a traditionally processed alloy. In addition, the aviation field has put an urgent demand for titanium alloy oxidation resistance. Some scientific research units have carried out technical breakthroughs on high temperature titanium alloy such as Ti4822 and Ti2AINb, which is expected to replace some superalloy in engineering application, including TiAl alloy blades prepared by electron beam. With the development of the medical field, new medical-titanium alloy materials, such as Ti-Zr, Ti-Nb, Ti-Cu and Ti-Mb, have been developed successively, and domestic powder manufacturers have also actively invested in research and development. At present, the particle strengthening method has also attracted the attention and attempts of relevant scholars. Zhang et al. use the laser zone melting (SLM) process to mix titanium powder with a small amount of SiC nanoparticles to prepare nano Ti5Si3 new alloy coating in situ. The results show that the microhardness of the alloy coating is 706 HV, 51.5% compared than the original sample.

 

1.2 Supertemperature alloy In 3D printing applications

Superalloy is a kind of alloy served in high temperature environment above 600℃, can withstand harsh mechanical stress and has good tissue stability. Superalloy is the main material of turbine blade, turbine disk, combustion chamber and other thermal end components of aero engine. At present, the superalloy raw materials used by domestic 3D printing manufacturers are mainly nickel-based and cobalt-based alloy powder, with brands including GH3230, GH3536, GH3625, GH4169, GH4099, GH5188, et al. With the deepening of the engineering application degree, the superalloy materials with good oxidation resistance and casting performance gradually enter people's vision. Wen et al. developed a gradient alloy of GH1469 and CoCrMo, with uniform alloy composition, tissue and texture, and found that the CoCrMo end was mainly composed of y-fcc phase columnar subcrystal and a small amount of sheet-mounted ε -hcp phase, and the antioxidant properties were significantly improved, including the sheet-mounted ε -hcp phase. Ghoussoub Through the study (Nb + Ta) / Al ratio, successfully developed a new alloy with good antioxidant performance and creep resistance slightly lower than CM247LC alloy. Chen et al. successfully designed the casting superalloy K418 laser constituency melting (SLM) process, The room temperature strength of the superalloy is 1078 MPa and 600℃ The intensity of 946 MPa.

 

1.3 Iron-based alloy In 3D printing applications

   Most of the iron-based alloys used in 3D printing are stainless steel and die steel powder, which are common in SLM and DED process products in the field of nuclear power. At present, domestic and foreign scholars focus on iron-based alloys by strengthening their wear resistance. Zou et al. studied the feasibility of mixing silicon carbide (SiC) particles with stainless steel 316L, and found that with the increase of SiC content, the microorganization changed from isoaxial to dendrites and led to grain refinement. After laser treatment, the strength and tribological properties were significantly improved [. Tanprayoon The feasibility of mixing titanium nitride (TiN) particles with stainless steel 316L was studied, and we found that the nanoscale TiN particles were strengthened and increased the alloy hardness by 70 HV.os。Some enterprises have also developed a high Mn-Ni type double-phase stainless steel alloy powder, which greatly improves the corrosion resistance and wear resistance of stainless steel.

 

1.4  aluminum alloy In 3D printing applications

The room temperature strength of aluminum alloy used for 3D printing is only about 300 MPa, and the addition of some trace elements can significantly improve the room temperature strength of aluminum alloy. Medium strength and high strength aluminum alloy is expected to replace structural titanium alloy and stainless steel as an important component in the aerospace field. A school-enterprise cooperation project has developed isotropic Al-Mn-Sc-Zr series aluminum alloy, which makes the multi-directional limit tensile strength of aluminum alloy higher than 500 MPa and the elongation rate higher than 10%. There are also school-enterprise cooperation projects that have jointly developed medium strength Al-Mg-Si-Mn-Ti printed materials, which have excellent performance of tensile strength of more than 450 MPa and elongation rate of more than 9%. There is also a school-enterprise cooperation project to develop the ceramic in-situ enhanced aluminum alloy powder, and the maximum tensile strength of the print piece is more than 540 MPa, Maximum break elongation exceeds 15%. The tensile strength of ZYHL-2 high-strength aluminum alloy developed by an enterprise and a scientific research institute is stable at 550~560 MPa, and the elongation rate is 12%~14%. At the same time, the tensile strength can still reach 250 MPa at a high temperature of 215℃ The rate can reach more than 18%. Wang et al. developed an Al-Mg-Sc-Zr alloy. After implementing the laser selection melting process, it not only has a good combination of strength and toughness, but also the ultrafine second-phase particles also show obvious heterogeneous A-A1 matrix organization, which is comparable to the traditional 7075-T651 forged aluminum alloy [1. Wang et al. developed the new Al-Zn-Mg-Cu aluminum alloy and explored the microtissue stability and mechanical properties of the alloy. They found that the yield strength and ultimate tensile strength of the alloy were improved by 171 MPa and 143 MPa respectively due to the combined effect of grain refinement, dislocation enhancement and precipitation reinforcement.

 

1.5 Infusion refractory alloy In 3D printing applications

      The molten metals include tungsten, molybdenum, tantalum, niobium and other metals, its biggest common feature is high melting point, and each metal also has its own characteristics. Tungsten has high hardness and good radiation shielding performance, and is widely used in the electronics industry, nuclear industry and medical industry. Tantalum has corrosion resistance and excellent electrical properties, and is mainly used in tantalum electricity, capacitor manufacturing and medical implants, among which pure tantalum implants are shown in Figure 5. Using 3D printing method production of CT equipment tungsten collimator has been long batch application abroad, the key performance has exceeded the traditional process of collimator, refractory metal melting point is higher, forming energy input is higher, will form more hole defects, generally by adjusting the process parameters and thermal isostatic pressure. By studying the process parameters, Gu et al. and Song et al. found that dense alloy [7-18] is easier to form at low energy density. Chen et al. used laser selective melting (SLM) technology to successfully develop a new refractory alloy of Nb-5W-2Mo-1 Zr, and prepared high density parts. The alloy is almost completely compact with a tensile strength of (678.7 ± 1.1) MPa and an extension rate of (5.91 ± 0.32)%.

In the 3D printing process, the metal powder quality is one of the key factors affecting the structure and performance of the final printing parts. Combined with China's 3D Printing metal materials problems and need to solve the key technology discovery, need to enrich 3D printing metal material system, strengthen the 3D printing metal alloy and innovative structure function integration material research, through the combination of theory and engineering practice, developed disruptive new materials and new structure, realize metal 3D printing technology innovation in China.

2 Organic polymer materials

Organic polymer materials include special resin, ultra-high molecular weight polymer and other materials, mainly wire, through a specific heat source form accomplish. Domestic and foreign material manufacturers use polylactic acid (PLA), PETG, etc 3D printing the mechanism of wire synthesis, chemical modification of traditional wire, improve the toughness and strength of the material. The modification of polyether ether ketone (PEEK) material adopts the composite treatment of enhancement groups such as carbon fiber.

 

2.1  polylactic acid (PLA) In 3D printing applications

Polylactic acid (PLA) is a new type of biodegradable material, the product made of polylactic acid in addition to can be biodegraded, biocompatibility, gloss, transparency, feel and heat resistance is also very good, also has certain antibacterial, flame resistance and ultraviolet resistance, mainly used for service Decoration, construction, agriculture, forestry, paper making and health care. Recently, the domestic mainstream PLA wire manufacturers have modified and upgraded the traditional materials, and have achieved great results. ESUN can broaden its application range after hardening it, and the eSUN PLA wire products are shown in Figure 7. Polymaker By mixing the PLA and polyacrylic acid microspheres, improve the mechanical properties of polylactic acid materials, especially the toughness, Polymaker polylactic acid wire products. A new material enterprise uses methyl methacrylate-butyl acrylate copolymer to improve the impact resistance of the material.

Foreign researchers adopt the methods of strengthening PLA by combining material compound and adding enhancement base. Reverte et al. added short fibers as reinforcing materials to PLA and obtained a new composite material with increased tensile strength by nearly 50%. Zerankeshi et al. prepared a new type of PLA-graphite wire composite material, which can significantly improve the mechanical strength of PLA and bring the mechanical strength of PLA to 47 MPa².

 

2.2 PETG In 3D printing applications

The PETG material is a transparent amorphous type copolyester that can be used Traditional extrusion, injection, blowing and suction forming methods can also be used in 3D printing forming, its secondary processing performance is excellent, is widely used in plastic products, medical health care products, packaging products and other fields. The PETG raw material used for 3D printing is mainly FDM wire material. The high melting point of PETG puts forward high requirements for the printing temperature, but the mechanical performance of the material forming is low and the heat resistance is poor, which is seriously blocked in the actual application process, so PETG Modification is usually required to improve its mechanical properties and printing properties. Domestic and foreign 3D printing consumables manufacturers have introduced PETG consumables with their own characteristics by enhancing and strengthening PETG. Taulman 3D Launch a guideline wire, good biocompatibility, thermal deformation temperature of more than 70℃.3DxTech: a Nanotube wire, which is made by PETG and carbon nanotubes, and has excellent chemical corrosion resistance, heat resistance, extremely low hygroscopicity and excellent size stability. At present, there are few researchers on PETG, and only on the aspect of toughness and modification. Rubans and Santosh carbon fiber (CF) and shape memory alloy (Ni-Ti) as reinforced material mixed with PETG, found that the hardness, tensile strength and impact strength of CF-PETG composite sample strength and other mechanical properties improved, the dynamic mechanical properties of Ni-Ti-PETG composite material significantly improved, and compared with the short fiber reinforced composite, composite wire has higher damping performance 

 

 

2.3 Polyether ether ketone (PEEK) In 3D printing applications

Polyether ether ketone (PEEK) is a high temperature thermoplastic special engineering plastic, with high strength, high temperature resistance, chemical corrosion resistance, wear resistance, self-lubrication, biocompatibility, flame retardant and other excellent performance, in the automobile, aircraft manufacturing, electronic appliances and medical and other fields have certain applications. Yan et al. used carbon fiber (CF) to prepare the new composite material with PEEK powder, and the results showed that the preheating temperature of the new material decreased, and the problems of shrinkage and warping of parts were significantly improved [2. Zheng et al developed a new material mixed hydroxyapatite (HA) and PEEK, and using fuse manufacturing (FFF) process prepared bone tissue scaffold, the study results showed that cell adhesion, proliferation, osteogenic differentiation and mineralized bone marrow mesenchymal stem cells on PEEK / HA stent, and PEEK / HA stent pure PEEK stent has better fusion effect and bond strength [2]. Fluoryl poly was designed and synthesized by Shang et al EE (FD-PEEK), study results, 15 mol% Introduction of the group (15% -FD-PEEK) causes interlayer strength and fracture Strain was 400% and 500% higher than PEEK, respectively, as reached 67 MPa and 11.23%, indicating that the interlayer strength of the material was significantly improved by [26].

The demand for organic polymer materials is large, which puts forward higher requirements for the strength, wear resistance, high temperature resistance, weather resistance, antistatic resistance, flame retardant and cost. Therefore, the performance of organic polymer materials still has a lot of room for improvement, which is still far from being widely used in the industrial field.

 

3.Inorganic and nonmetallic materials 

The inorganic non-metallic materials mentioned in this chapter are mainly sand-type materials and ceramic materials commonly used in the 3D printing process. Due to the late start of domestic binder injection and ceramic light curing processes, most of the research on sand materials and some ceramic materials is mainly focused on process verification. At present, most of the materials of the corresponding process are still in the state of breakthrough, and the research on SiC ceramics and three calcium phosphate ceramics and other materials has entered the stage of composite reinforcement.

 

3.1 Sand-type material In 3D printing applications

The sand type materials are mainly divided into coated sand for selective laser sintering (SLS) technology and resin sand for adhesive injection (BJP) technology. SLS coated sand material is a kind of selective laser sintering (SLS) process printing casting core or shell forming material, printed sand material combined with the traditional casting process, can quickly cast metal parts. BJP resin sand mainly includes silica sand for casting, furan resin binder, phenolic resin binder, inorganic binder and other casting sand forming materials. Sand core and sand shape are formed through BJP process, which greatly improves the casting production efficiency. Covered sand has excellent sintering performance, especially suitable for the rapid casting of complex structure metal parts, and is widely used in aerospace, automotive manufacturing and other fields. The tensile strength of the coated sand material developed by an enterprise can reach 4~6 MPa, the gas generating rate is 12 ~ 13 mL/g, high fire resistance, good dispersion, better sand resistance than the traditional process, making the castings easy to demmold, and the surface roughness of the castings can reach 3.2~6.3 μ m.

Huazhong University of Science and Technology uses coated sand to directly sintered sand and combined with melting mold, precision casting process successfully cast the motorcycle cylinder block, cylinder head and turbine casting. Domestic related scholars have improved the process of adhesive jet resin sand. Chen rui for 3D printing sand compaction low problem, put forward a space grid sand 3D printing method, using circular, rectangular two base shape, according to different grid size and different skeleton size between grid mesh, reduce the sand strength 10%~50%, improve the sand type permeability more than 100%, reduce the binder dosage of 10%~50%2. Lin Feng proposed an analysis model for the influence of printing process parameters on sand carbon emission sources, established an optimization model with three objectives, and took a certain type of impeller casting as an example study. The results showed that the carbon emission was reduced by 33.1%, the printing efficiency was increased by 38.35%, and the bending stress was only reduced by 1.02%2.

3.2 Ceramic materials In 3D printing applications

Among the ceramic materials used for 3D printing ceramic materials, the most studied and most mature ceramic materials are mainly oxides (Al ₂ O ₃,

ZrO ₂), SiC, tricalcium phosphate (TCP), etc. Powder bed forming technology generally requires the powder to have high fluidity; the raw materials used in curing forming technology are composed of ceramic powder, dispersant and additives.

Oxide ceramics are widely used in the manufacture of cutting tools, grinding wheels, ball valves, bearings, etc., among which, with Al₂O₃ and ZrO ₂, ceramic cutting tools are the most widely manufactured. The properties of this material concerned by research scholars are mainly wear resistance and strong toughness. Hofer et al. developed a lithography-based additive manufacturing technology of alumina ceramics, using the speed of 300~450℃ / min, and generated the alumina with high mechanical strength and high toughness of 810 MPa 129). Shen et al. directly prepared Al ₂ O ₃ / GdAIO₃ (GAP) composite ceramics, with microhardness and fracture toughness (17.1 ± 0.2) GPa and (4.5 ± 0.1) MPam'230, respectively.

SiC Ceramics have the best high-temperature mechanical properties among known ceramic materials (high bending strength, excellent corrosion resistance, high wear resistance and low friction factor, etc.), and their antioxidant performance is also the best among all non-oxide ceramics. Chang, et al. proposed a route for printing high performance SiC ceramics by introducing low light absorption SiO ₂ powder and a two-step sintering process, and prepared SiC ceramics with higher flexural strength (268.66 MPa) [31. Lu et al. used to realize the preparation of SiCw / SiC sintering (SLS) technology. When the particle size of Sic was 60~80 μ m, the number of SiCw was the largest, and the formation and growth mode followed the traditional steam-liquid-solid (V-L-S) mechanism 3]. Xu et al. proposed a new type of water-based slurry composed of silicon carbide, toner and silicon carbide whiskers (SiCw), and the maximum bending strength of the specimen was 239.3MPa³.

The chemical composition of triccalcium phosphate ceramic (Tricalcium phosphate, TCP) is widely found in human bones, so it is widely used in the medical field as a good three-dimensional scaffold for bone repair. TCP stent is one of the hot research topics at home and abroad. For a long time, researchers have been constantly improving the performance to improve the treatment effect of TCP stent on bone injury and other aspects. Li et al. developed a new composite of β -calcium phosphate ceramic / 58S biological glass (β -TCP / BG) and prepared β -TCP / BG ceramic slurry stent. The results showed that the maximum viscosity of β -TCP / BG resin slurry was 85.92 Pas, and the compression of the stent

Degree reaches the maximum (11.43 ± 0.4) MPa³4. Yin et al. and Qi et al. discussed the feasibility of recombining alloy and TCP ceramics, and their studies showed that the biodegradation and mechanical stability of TCP ceramic stents with alloy elements were greatly improved.

 

4 Conclusions and the outlook In 3D printing 

In this paper, 3D printing advanced materials are divided into three categories: metal materials, organic polymer materials and inorganic non-metal materials, and the latest research results of advanced 3D printing technology at home and abroad are expounded respectively, and the following new understanding is obtained:

(1) With the deepening of engineering application, the types of 3D printing metal materials are gradually enriched, and the performance is improved by means of alloying, enhancement and reinforcement.

(2) Based on the principle of synthesis, modification and material composite to improve the performance of wire, and toughness and bending strength are important research indicators.

(3) Most of the research on 3D printing inorganic nonmetallic materials such as sand and ceramics is carried out around process adaptability, and some materials have begun to enter the stage of performance improvement.

 

At present, 3D printing advanced materials industry has become a research hotspot at home and abroad. New advanced materials can be obtained through raw materials and reinforcing foundation, mixed preparation into composite materials and optimizing material composition. Next, also should be from new material application technology theory and mechanism of shape method, draw lessons from successful experience, improve the application scenario, in the rapid development of 3D printing advanced materials industry to grasp the opportunity, stimulate the performance of the material, processability, function diversification of development, gradually promote 3D printing advanced materials industry more healthy and orderly development.