The research status and progress of the processing technology of titanium matrix composites (TiMMCs) were reviewed from the aspects of traditional mechanical processing, composite energy field processing, forging processing and additive manufacturing. Characteristics of TiMMCs processed by different processing techniques. Aiming at the main problems in current research, the development trend of TiMMCs processing technology in the future is prospected.
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Researcher-level senior engineer Wang Guangping
01
preamble
Titanium and its alloys are widely used in aerospace, petrochemical, marine and medical fields due to their excellent properties such as high specific strength, excellent chemical corrosion resistance and good biocompatibility [1-4]. However, the Young's modulus, wear resistance, and heat resistance of titanium alloys are lower than those of steel and nickel-based alloys, which limits their further applications in the automotive and aerospace fields [5-8]. The emergence of titanium matrix composites (TiMMCs) provides a new alternative to overcome the above problems. TiMMCs is a composite material composed of titanium and its alloys as the matrix and ceramics (particles, whiskers, short fibers and continuous long fibers) as the reinforcing phase (see Figure 1).
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a) Continuous long fiber reinforced titanium matrix composites
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b) Particle-reinforced titanium-based composites c) Whisker/short fiber-reinforced titanium-based composites
Figure 1 Schematic diagram of TiMMCs with different types of reinforcement phases
While maintaining the excellent properties of the matrix, TiMMCs can also obtain comprehensive properties that cannot be achieved by a single reinforcement phase or matrix through the complementarity and correlation of the properties of the fiber and the matrix. For example, the yield strength of (TiC+Ti5Si3)/Ti composite prepared by HUO et al. [9] is as high as 829MPa, which is 178% higher than that of pure titanium, while maintaining a high elongation of 8.1%, and having high strength and medium plasticity. Compared with the laminated TiC/Ti composites, the strength and ductility of TiMMCs are simultaneously enhanced, resulting in an excellent strength-ductility synergistic performance. The high specific modulus of TiMMCs is the main factor to promote its wide application in aircraft fuselage, while the high specific strength is the driving force to promote its application in the engine industry [10]. For example, the United States took the lead in using particle-reinforced titanium-based composites to manufacture aero-engine parts. The particle-reinforced titanium-based composite rotor blades developed by the United States have been successfully applied, which not only improves the performance of the rotor blades, but also reduces aviation. The manufacturing cost of the engine dropped by as much as $60,000 [11]. The Boeing Aircraft Company of the United States has developed a particle-reinforced titanium-based composite aircraft landing gear connecting rod, which not only has a significant increase in service temperature, but also reduces the mass by nearly 40% compared with that before the improvement, and has been successfully applied on the Boeing 787 aircraft[12] . The Atlantic Research Center of the United States successfully developed a particle-reinforced titanium-based composite material for helicopter landing gear, and it has been successfully applied. Compared with traditional materials, the weight is greatly reduced [13]. The French Aeronautical Research Center and the British Rolls-Royce company used particle-reinforced titanium matrix composites to prepare aero-engine blades and achieved success [14, 15]. In the automotive field, the requirements for lightweight structures are constantly increasing, which greatly promotes the application of TiMMCs. Toyota Corporation of Japan first used BTi/Ti composite materials for automobile exhaust valves, automobile engine exhaust valves and other parts, engine valves, etc. The total mass is reduced by nearly 40%, and it has the advantages of high life and low cost [16]. At the same time, countries such as Europe and the United States have also begun to use particle-reinforced titanium-based composite materials to replace traditional steel materials to manufacture main parts of automobiles, so as to reduce the weight of automobiles and further improve the performance of automobiles [17]. The application range of TiMMCs is shown in Figure 2.
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Figure 2 Application range of TiMMCs
Due to the complexity of material composition, TiMMCs is much more difficult to process than conventional engineering materials, and is a new type of difficult-to-process material. Meanwhile, although TiMMCs containing uniformly distributed reinforcements or discontinuous reinforcements generally exhibit higher strength, the ductility and toughness relative to the pure matrix are inevitably compromised [18]. For example, even with in-situ TiC and Ti5Si3, the tensile data show that the elongation at break drops sharply from 17.2% to 1.53% when the yield strength increment of the composite material reaches 410MPa, which places higher requirements on processing technology [19]. Therefore, how to achieve high-efficiency and low-damage processing of TiMMCs has become a research hotspot in the field of composite material processing.
Common processing methods of TiMMCs include machining, forging, casting, and additive manufacturing [20]. Machining relies on mechanical force to change the shape of materials, which can efficiently carry out mass production and batch processing. It is one of the most commonly used cold processing methods. It can achieve high-precision dimensions and surface quality requirements, and is suitable for various types of materials including composite materials. material processing. Common machining operations include cutting, drilling, milling, and grinding. Forging, casting, and additive manufacturing are typical thermal processing processes that can improve the mechanical properties and structure of composite materials [21]. In addition, when choosing a suitable processing technology to process TiMMCs, it is necessary to comprehensively consider the different characteristics of each component in the composite material, as well as the wear and thermal expansion between the composite material and the processing tool, in order to obtain TiMMCs parts with excellent performance.
In this paper, the current processing technology of TiMMCs is reviewed, and the processing of TiMMCs in the future is prospected, in order to provide theoretical support for the high-performance application of TiMMCs.
02
Machining
Due to the limitations of the preparation technology of TiMMCs, machining is still an indispensable process in the manufacture of TiMMCs. Compared with the matrix material, reinforcement has higher hardness, higher strength, and more difficult processing, and there will be problems such as reinforcement phase fragmentation, pull-out and debonding during processing. The cutting process of TiMMCs has been comprehensively studied in terms of optimization and other aspects.
2.1 Machining
Aiming at the lack of systematic research on cutting performance such as tool wear mechanism, cutting force and cutting temperature changes in the cutting process of TiMMCs, Bian Weiliang [22] carried out research on the performance of different tool turning (TiCp+TiB w)/TC4. Single crystal diamond and cemented carbide are used in material processing. Under the same cutting conditions, the life of the PCD tool is longer. When the single crystal diamond tool cuts TiMMCs, the wear of the tool mainly comes from the repeated scraping of the high hardness enhancement relative to the tool. When cutting the TC4 alloy alone, the titanium alloy is bonded to the tool and The wear caused by the diffusion of processing material elements to the tool is more significant. When machining TiMMCs with cemented carbide tools, the diffusion and bonding of the workpiece material are also obvious.
In order to further explore the influence of cutting parameters and lubrication methods on machining characteristics, NIKNAM et al. [23] carried out dry and semi-dry turning experiments on particle-reinforced titanium matrix composites (PTMCs), and analyzed the cutting force under different cutting parameters. , surface roughness and particle removal behavior. The results show that the cutting force is greater under the semi-dry condition, and a film of lubricant will be produced, which hinders the smooth progress of cutting.
DUONG et al. [24] studied the initial tool wear behavior during TiMMCs turning, and found that wear is the most important mechanism in TiMMCs cutting, and diffusion and adhesion were found under all conditions. And a new wear form of hard thin layer was found in the process of machining, which in this case would lead to diffusion wear and mechanical tumor. Different from PTMCs, continuous fiber reinforced titanium matrix composites have unique anisotropy due to the continuity of fibers. In order to clarify the cutting mechanism of continuous fiber reinforced titanium matrix composites, ZAN[25] et al. The SiCf/Ti-6Al-4V orthogonal cutting test obtained the chip formation behavior and the deformation mechanism of the composite material at low temperature, room temperature and high temperature, and found that compared with the formation of adiabatic shear band during the cutting process of titanium alloy, SiCf/Ti The width of -6Al-4V sawtooth is larger. Figure 3 is a schematic diagram of SiCf/Ti-6Al-4V alternating layer cutting at different temperatures.
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a) Cryogenic (CT)
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b) Room temperature (RT)
Fig.3 Cutting diagram of alternating layers of fiber-reinforced titanium matrix composites at different temperatures
2.2 Grinding
Grinding relies on many abrasive grains on the surface of the grinding wheel to simultaneously cut the workpiece to remove material, which is suitable for precision and ultra-precision machining of materials. DING et al. [26, 27] established a three-dimensional finite element model of the grinding process in order to understand the material removal behavior of TiCp/Ti-6Al-4V during conventional grinding and high-speed grinding, and based on the finite element model, discussed the material removal behavior. The removal behavior and the effect of grinding speed on the formation of machined surface features (see Figure 4). The results show that the material removal behavior during grinding of TiCp/Ti-6Al-4V can be divided into ductile removal of metal matrix material and brittle removal of TiC reinforced particles. Similarly, LIU et al. [28] concluded that material removal in high-speed grinding of PTMCs can be divided into four stages: plastic removal of alloy matrix, crack initiation in enhanced particles, crack propagation in enhanced particles, and brittle failure of enhanced particles. Compared with grinding speed, undeformed chip thickness has a greater influence on the formation of machined surface defects. On this basis, LI et al. [29, 30] studied the grinding performance of single-layer electroplated CBN grinding wheel and brazed CBN grinding wheel for PTMCs (see Figure 5). The results showed that single-layer brazed CBN grinding wheel is more suitable than electroplated grinding wheel for high-speed grinding of PTMCs. Liu Chaojie et al. [31] analyzed the grinding force model of PTMCs side grinding by means of simulation. When removing the matrix, the fluctuation of the grinding force is regular. When removing the TiC reinforced particles, cracks will appear and expand on the surface of the material. There are also massive chips removed on the surface, and the fluctuation of the grinding force in the area where the reinforced particles are removed is large. In addition, the normal and tangential grinding forces both increase with the increase of single abrasive chip thickness.
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a) Ordinary grinding PTMCs simulation
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b) Test results of ordinary grinding PTMCs
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c) Simulation of high-speed grinding PTMCs
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d) Experimental results of high-speed grinding of PTMCs
Fig. 4 Simulation and test results of PTMCs removal behavior at different speeds
(vs=3m/min, ap=0.010mm)
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a) Grinding with electroplated CBN grinding wheel
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b) Grinding with brazed CBN grinding wheel
Figure 5 Comparison of electroplated CBN grinding wheel and brazed CBN grinding wheel for grinding PTMCs
03
Composite energy field processing
Ultrasonic vibration assisted grinding is a compound processing technology that introduces ultrasonic vibration to the traditional grinding technology to reduce the cutting temperature and improve the grinding quality. In ultrasonic vibration-assisted machining, the contact state between the tool and the workpiece changes due to high-frequency vibration, and the tool and the workpiece are in intermittent contact, accompanied by cavitation effects and high-frequency impacts, so that the contact between the workpiece and the tool The friction force is reduced, thereby reducing the cutting heat and cutting force, and can increase the service life of the tool and improve the processing quality. Ultrasonic vibration assisted machining technology has been widely used in difficult-to-machine materials such as nickel-based alloys, TiMMCs, and ceramic matrix composites.
WU et al. [32] carried out an axial ultrasonic vibration-assisted grinding test on PTMCs, and found that under the action of ultrasound, the cutting trajectory of abrasive grains increases, and the abrasive grains repeatedly press on the surface of the workpiece to reduce the surface roughness value. YUE et al. [33] carried out the ultrasonic vibration assisted grinding test of PTMCs single abrasive grain, compared the influence of ordinary grinding and ultrasonic grinding on the material removal rate at different grinding speeds and different feed rates, and established the ultrasonic The cutting thickness model of a single abrasive grain under the action shows that the ultrasonic vibration is more likely to cause micro-breaking of the abrasive grains, which can continuously update the state of the cutting edge and maintain the sharpness of the abrasive grains at all times. ZHAO et al. [34] used a self-made radial vibration platform (see Figure 6) to conduct an ultrasonic vibration-assisted grinding test on PTMCs, and compared it with the ordinary grinding test. Compared with ordinary grinding, ultrasonic vibration assisted grinding can reduce the grinding temperature by 24.2% to 51.8%, and at the same time, the material removal rate can be increased by 2.8 times.
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Figure 6 Radial Vibration Ultrasonic Platform and Vibration Measuring Device
BEIJANI et al. [35] used laser-assisted machining (LAM) to process TiMMCs for the first time on the basis of traditional turning (see Figure 7). The results show that compared with conventional machining, although the surface roughness value of the workpiece increases by 15%, the total cutting volume of the LAM tool increases by 180%, and the tool life is effectively improved, which is attributed to the transfer of particles in the matrix rather than fracture.
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a) Schematic diagram
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b) Actual device
Figure 7 Laser-assisted processing test device
04
Additive Manufacturing Processing
Laser additive manufacturing technology can directly manufacture complex structural parts, showing great application prospects in the manufacture of TiMMCs. BANERJEE et al. [36] successfully processed TiB/TC4 composites using laser stereoforming processing technology (LENSTM), and used scanning electron microscopy and transmission electron microscopy to characterize the microstructure of the as-deposited composites in detail. The results showed that the method prepared The TiB/TC4 composite microstructure is significantly refined and is thermodynamically stable. Similarly, GU et al. [37] used selective laser melting (SLM) to process the prepared TiC/Ti composite powder, and obtained TiC particle-reinforced TiAl3 (main phase) and Ti3AlC2 (secondary phase) matrix composites. Despite slight grain growth relative to the milled powder, the SLM-treated composite still exhibits a fine microstructure. [38] used direct metal deposition (DMD) laser processing technology to prepare PTMCs containing different volume fractions (TiB+TiC) from powder raw materials composed of pre-alloyed (Ti-6Al-4V+B4C) powder mixtures. Mechanical studies have shown that at 20-600 °C, the Vickers hardness of particle-reinforced TiMMCs containing B4C increases by 10%-15%, and the Young's modulus increases by 10%. The preparation of TiMMCs by DMD laser processing technology is shown in Figure 8.
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Fig.8 Schematic diagram of TiMMCs prepared by DMD laser processing technology
05
Forging
Forging can eliminate the loose defects of materials during the smelting process, effectively refine the microstructure, and obtain high-quality forgings that match the structure and performance.
Relevant foreign scholars have studied the effect of hot forging on the microstructure and tensile properties of Ti-TiB matrix composites. Studies have shown that the room temperature elongation of the forged Ti-13.3B and Ti-7B composites reaches 6.1% and 5.2%, respectively, and the material properties are effectively improved. Domestic scholar Hu Jiarui et al. [39] forged PTMCs of sintered TiC generated in situ, and the structural defects of PTMCs after forging were eliminated, dynamic recrystallization occurred, and the mechanical properties at room temperature were improved. The tensile fracture SEM morphology of TiC particle reinforced TiMMCs is shown in Fig. 9. At the same time, due to the improved matrix structure, the wear resistance of PTMCs after forging is improved. same
[40] compared and analyzed the mechanical properties of 5% (TiB+TiC)/Ti-1100 composite materials. At 500-650 °C, the as-cast composite material was brittle fracture, and the forged composite material was ductile fracture, and The strength and elongation of the composite material after forging are significantly increased.
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a) Sintering (matrix penetrating cracks) b) Sintering (intergranular cracks and grain cracks
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c) β-forging d) (α+β)-forging
Fig.9 Tensile fracture SEM morphology of TiMMCs reinforced by TiC particles
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conclusion
Due to the presence of reinforcing phases, TiMMCs exhibit different mechanical properties and processing mechanisms from traditional titanium alloys. Looking ahead, the processing of TiMMCs will develop in the following aspects.
(1) Processing technology improvement The processing technology of TiMMCs will be continuously improved to improve production efficiency and product quality. New cutting tools and processing methods will be developed to reduce cutting forces and tool wear, and to realize the synergistic removal of TiMMCs heterogeneous components.
(2) Combination of multiple processing technologies TiMMCs have poor room temperature plasticity, and the comprehensive processing of TiMMCs by using various thermal processing methods such as high-temperature superplastic deformation, hot forging and hot extrusion deformation can maximize the application potential of TiMMCs in various fields.
(3) New material development With the advancement of science and technology, new TiMMCs will be developed with higher performance and wider application fields. For example, nano-TiMMCs, multifunctional TiMMCs and high-temperature durable TiMMCs will further promote the development of TiMMCs.
(4) Sustainability and environmental protection Sustainability and environmental protection will become key considerations when processing TiMMCs. The development of more environmentally friendly processing methods, the recycling of waste composite materials and the reduction of energy consumption will be the future direction of development.
(5) Multi-field application TiMMCs will be applied in more fields. In addition to the existing aerospace and automotive industries, the medical, energy and construction fields will also continue to explore the application potential of TiMMCs.
