rus
Issue #4/2021
D. V. Volosevich, S. A. Shalnova, A. M. Vildanov, I. S. Magidov, K. V. Mikhailovsky, O. G. Klimova-Korsmik
Direct Metal Deposition of Titanium-based Cermets
Direct Metal Deposition of Titanium-based Cermets
DOI: 10.22184/1993-7296.FRos.2021.15.4.296.306
The results of experimental studies of the macro- and microstructure, chemical and phase composition of a cermet alloy based on titanium are presented. The material is intended for laser methods of additive manufacturing using direct metal deposition. For analysis, samples were obtained with a ceramic powder content of 5 and 10 vol. % SiC. The introduction of ceramic particles turned out to be effective for refining the alloy grains. The grain size of pure titanium is about 3.5 mm, while the grain size of titanium reinforced with silicon carbide at a radiation power of 1400 W was 50 and 14 μm for 5 and 10% SiC, respectively. As a result of the introduction of ceramic particles into the titanium matrix, the microhardness of the composite material increases, the hardening increases, but the embrittlement of the material also increases due to the violation of the integrity of the material and the occurrence of a reaction at the phase boundary.
The results of experimental studies of the macro- and microstructure, chemical and phase composition of a cermet alloy based on titanium are presented. The material is intended for laser methods of additive manufacturing using direct metal deposition. For analysis, samples were obtained with a ceramic powder content of 5 and 10 vol. % SiC. The introduction of ceramic particles turned out to be effective for refining the alloy grains. The grain size of pure titanium is about 3.5 mm, while the grain size of titanium reinforced with silicon carbide at a radiation power of 1400 W was 50 and 14 μm for 5 and 10% SiC, respectively. As a result of the introduction of ceramic particles into the titanium matrix, the microhardness of the composite material increases, the hardening increases, but the embrittlement of the material also increases due to the violation of the integrity of the material and the occurrence of a reaction at the phase boundary.
Теги: dmd (direct metal deposition) dmd (прямое лазерное выращивание) slm (selective laser melting) slm (селективное лазерное плавление) sls (selective laser sintering) sls (селективное лазерное спекание) titanium-based cermets металлокерамические сплавы на основе титана
Direct Metal Deposition of Titanium-Based Cermets
D. V. Volosevich, S. A. Shalnova, A. M. Vildanov, I. S. Magidov, K. V. Mikhailovsky, O. G. Klimova-Korsmik
Institute of Laser and Welding Technologies, St. Petersburg State Marine Technical University, St. Petersburg, Russia
N. E. Bauman Moscow State Technical University, Moscow, Russia
The results of experimental studies of the macro- and microstructure, chemical and phase composition of a cermet alloy based on titanium are presented. The material is intended for laser methods of additive manufacturing using direct metal deposition. For analysis, samples were obtained with a ceramic powder content of 5 and 10 vol. % SiC. The introduction of ceramic particles turned out to be effective for refining the alloy grains. The grain size of pure titanium is about 3.5 mm, while the grain size of titanium reinforced with silicon carbide at a radiation power of 1400 W was 50 and 14 μm for 5 and 10% SiC, respectively. As a result of the introduction of ceramic particles into the titanium matrix, the microhardness of the composite material increases, the hardening increases, but the embrittlement of the material also increases due to the violation of the integrity of the material and the occurrence of a reaction at the phase boundary.
Keywords: SLM (Selective Laser Melting), SLS (Selective Laser Sintering), DMD (Direct Metal Deposition), titanium-based cermets
Received on: 26.04.2021
Accepted on:16.06.2021
INTRODUCTION
The active development of technologies for mechanical engineering, shipbuilding, aircraft and rocket engineering imposes new requirements on materials: high values of wear resistance, impact resistance, corrosion resistance, a combination of hardness and plasticity, etc. Traditional materials do not meet the standards that modern materials must meet. In this regard, of particular interest are composite materials consisting, as a rule, of a plastic matrix and solid strong fillers.
Traditional technologies for producing and processing materials, such as casting, forging, drawing and pressing, milling and turning, involve changing the shape and removing the material layer, which leads to a significant investment of time and labor. Moreover, the microstructure of the alloy and, as a consequence, its mechanical properties are sensitive to temperature and deformation rate, therefore, traditional methods of processing products face certain difficulties.
Prospective for obtaining composite materials is additive manufacturing – layer-by-layer production of parts from CAD models. Additive technologies make it possible to obtain products of an almost unlimited configuration without unnecessary waste of material, time, and do not require additional equipment.
Products obtained using laser additive manufacturing methods such as SLM (selective laser melting), SLS (selective laser sintering), DMD (direct metal deposition) can achieve high density, and this, in turn, is directly related to mechanical, thermal and corrosive properties.
The characteristics of the initial powders are decisive for the quality of the final product: chemical and fractional compositions, the shape of the powder particles, as well as its morphology (pores, satellites, particle conglomerates). It is also important to select the optimal content of filler and matrix powders. In addition, the properties of the product depend on the parameters of the laser additive process, such as the power of the laser radiation, the scanning speed, the consumption of powders and shielding gases [1], [2]. Thus, the variety of chemical compounds that can be used as a matrix or filler, their various combinations, the effect of the content on the properties of the materials obtained, the dependence of the development of the structure on the parameters of the additive process open unlimited possibilities in the study of this direction.
Analysis of the starting powders
The morphology of the particles and the elemental composition of the metal powder BT6 and SiC were monitored. Table 1 shows the chemical composition of the powder according to GOST 19807-91 [3]. The content of chemical elements on the surface and on the powder cut was studied. Fig. 1 shows SEM images of BT6 powder and SiC.
The chemical composition of BT6 powder corresponds to GOST 19807-91. There are single satellites on the surface of the particles, which is an acceptable defect. The particle size is 50–150 microns. According to GOST 25849-83 [4], the powder particles are predominantly spherical, 3% of the particles are lamellar.
On average, the SiC powder contains 30.27 wt% C and 69.73 wt% Si, which corresponds to the composition of stoichiometric SiC; the powder contains no impurities of other elements. The particle size is 30–90 μm. According to GOST 25849-83, the powder particles have an angular shape.
Macro and microstructure, chemical and phase compositions
To study the structure, chemical and phase analysis, samples were obtained with a ceramic powder content of 5 and 10 vol% SiC, and for each content the value of the laser radiation power was varied in the range 1 400–2 200 W with a step of 200 W.
Fig. 2 shows panoramic SEM images of the samples. The study of the macrostructure revealed the presence of single pores with a size of about 2 microns. Also, many samples differ in the lack of fusion of the substrate and the base material. In addition, the samples have cracks that propagate deep into the material. As a rule, cracks originate at the sample boundary and propagate deeper into the material. The formation of cracks can be associated with the accumulation of heat as a result of layer-by-layer fabrication of the sample and the occurrence of thermal stresses.
It is known that the titanium matrix actively interacts with SiC particles with the formation of new TiC phases and titanium silicides (Ti5Si3, TiSi2). According to thermodynamic calculations [5], the free energy of such phases is lower than the free energy of silicon carbide, and such reactions can proceed spontaneously. On the one hand, new phases can increase microhardness and strength, and on the other hand, they violate the integrity of the structure, making the material more brittle. The C atoms penetrate more freely into the titanium matrix; therefore, the new TiC phase occurs both along the boundaries of the SiC particles and in the matrix. In fig. 3 shows a map of the distribution of chemical elements near the SiC particle.
It can be seen from the figure and the results of X-ray microscopy that the TiC phase is indeed precipitated along the boundaries of ceramic particles, which is also confirmed by chemical analysis by points. It was also found that the TiC phases in samples with 5 and 10% SiC have different structures. Fig. 4 shows a map of the distribution of chemical elements for a sample with 10% SiC.
Samples with a SiC content of 10% include TiC phases, which are dendritic structures. The point is that the amount of SiC in samples 1–5 containing 5 vol% SiC is insufficient for the formation of dendritic structures.
There are various variants of the reaction of the titanium matrix and silicon atoms, however, the reaction resulting in the formation of Ti5Si3 is energetically more favorable from the point of view of thermodynamics. Fig. 5 shows the results of mapping the region with the assumed Ti5Si3 phase. Chemical analysis showed that the phases with a «lamellar» structure are Ti5Si3 phases.
Thus, the samples under study contain the following phases: metal matrix BT6, particles of SiC, TiC, and Ti5Si3. The phases of the titanium alloy, as well as the results of X-ray phase analysis, are shown in Fig. 6. X-ray diffraction patterns show that with an increase in the SiC content and with an increase in the laser radiation power, the TiC and Ti5Si3 content increases, which is associated with a more active dissolution of SiC particles and an increase in the number of free carbon and silicon atoms.
The introduction of ceramic particles turned out to be effective for refining the alloy grains. The grain size of pure titanium is about 3.5 mm, while the grain size of silicon carbide-reinforced titanium at 1400 W is 50 and 14 μm for 5 and 10% SiC, respectively. With an increase in power, the grains continue to grind and reach the minimum value – 10 and 4 microns for 5 and 10% SiC, respectively – at a power of 2200 W. It was also found that the grains near silicon carbide are smaller than the others. On average, the grain size near SiC is 1.5 times smaller than the grains located at a distance from the ceramic particles. The fact is that new TiC phases are precipitated along the boundaries of the titanium matrix; it is they that prevent further grain deposition.
Mechanical tests, fractographic analysis of fractures
To check the effect of the formation of new phases on the properties of the alloy, mechanical tests were carried out, as well as fractographic analysis of samples with a content of 1, 3, 5% SiC, obtained at a laser power of 1200 W.
The sample with a 1% SiC content is distinguished by an elongated grain, the boundaries of which are weakly expressed, which indicates the nature of fracture close to ductile. Samples with 3 and 5% SiC also have regions of elongated grains; however, the size of such regions decreases with increasing SiC content, which indicates a decrease in plastic properties and an approach to brittle fracture. Fracture occurred along grain boundaries, which indicates an intercrystalline fracture. The fact is that the reaction of a titanium matrix with silicon carbide is an interfacial reaction that violates the integrity of the alloy and increases the brittleness of the material. An increase in the SiC content leads to an increase in the brittle properties of the material. There are single cracks originating at the grain boundary and propagating deep into the material. Fractographic analysis of sample fractures confirmed that the introduction of ceramic particles into the titanium matrix and the formation of new phases of brittle intermetallic compounds and TiC leads to embrittlement of the material.
Fig. 7 shows the tensile curves of the samples, table 2 shows their mechanical properties. The results of tensile tests of the samples confirmed that the fracture is predominantly brittle, and the samples with 3 and 5% SiC have only proportional regions, while the sample with 1% SiC has a hardening region, in which the crystal lattice of the material is deformed. However, a comparison of the tensile strength of a pure alloy and an alloy containing 1% SiC proves the effectiveness of the introduction of ceramic particles. According to GOST 22178–76 [6], the average value of the ultimate strength of the BT6 alloy is ~980 MPa, ceramic particles increase the ultimate strength by 1.3 times. Also, with an increase in the SiC content, the yield stress decreases; nevertheless, the obtained values turned out to be higher than that of the pure BT6 alloy. The relative elongation of the BT6 alloy according to GOST 22178–76 is 8%, which is 8.5 times higher than the values for alloys reinforced with SiC particles.
In the course of the work, the dependences of the microhardness of the matrix on the power of laser radiation and on the content of ceramic particles were studied. Microhardness characteristic of BT6 alloy is ~350 HV [5]. With an increase in the power of laser radiation, the value of the microhardness of the titanium matrix increases. The maximum value of microhardness was achieved for a sample with 10% SiC at a power of 2200 W and amounted to 836.4 HV, which exceeds the value of microhardness characteristic of BT6 alloy without ceramic particles by 2.4 times.
CONCLUSION
MRSA and X-ray phase analysis confirmed the presence of new phases, and an increase in the SiC content and laser radiation power due to the more active decomposition of SiC particles into atoms leads to an increase in the intermetallic Ti5Si3 and TiC phases. Titanium carbide manifests itself in the structure in various configurations: acicular structures in samples with 5% SiC and dendritic structures for samples with 10% SiC. Intermetallic phases have a «lamellar» structure. Reinforcement of the titanium alloy with ceramic particles led to grain refinement to 10 and 4 μm for 5 and 10% SiC, respectively. The point is that the titanium carbide phase is precipitated along the grain boundaries, which prevents grain deposition.
The formation of new phases has the following consequences: the Ti5Si3 and TiC phases have a microhardness that significantly exceeds the microhardness of the BT6 alloy, therefore, as a result of the introduction of ceramic particles into the titanium matrix, the microhardness of the composite material will increase; hardening of the material; embrittlement of the material due to the violation of the integrity of the material and the occurrence of a reaction at the phase boundary. Mechanical tests were carried out to check the influence of interfacial reactions on the properties of the alloy. The samples with 1.3.5 and 7% SiC were obtained by direct metal deposition at a power of 1200 W. It became clear already at the stage of preparing blades for mechanical tests, that an excessive SiC content (7% for this work) leads to a significant decrease in the plastic properties of the material: the sample has cracks that do not allow making a blade. Fractographic analysis showed that the samples have areas of ductile and brittle fractures; however, the size of the viscous fracture region with weakly pronounced grain boundaries decreases with an increase in the SiC content, which indicates that the properties of the material approach brittle. The tensile curves confirmed the results of fractography: the samples with 3 and 5% SiC have a curve typical for brittle materials, while the sample with 1% SiC has a hardening region characterized by deformation of the crystal lattice of the material.
With an increase in the SiC content, the yield stress and plasticity decrease, the maximum values were achieved at a 1% SiC content and amounted to 1110 MPa and 1300 MPa, respectively, which on average exceeds the corresponding values of pure BT6 alloy by 1.3 times.
The maximum value of the relative elongation was 2.1% for the sample with 1% SiC, which is 8.5 times less than the corresponding value for the unreinforced BT6 alloy. Measurement of the microhardness of the alloy grains also proved the efficiency of introducing SiC particles: both an increase in the laser radiation power and an increase in the SiC content lead to an increase in the microhardness of the composite material. The maximum value was achieved for a sample with 10% SiC at a power of 2200 W and amounted to 836.4 HV, which is 2.4 times higher than the BT6 microhardness.
With the financial support of the Department of Education and Science of the Russian Federation the creation and development of the world-class scientific center “Advanced Digital Technologies” (Grant Agreement № 075-15-2020-903 from 16.11.2020).
ABOUT AUTHORS
Volosevich D. V., dasha.volosevich@mail.ru, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-2288-2935
Shalnova S. A., sveta-net07@mail.ru, Engineer, Materials Research Department. Institute of Laser and Welding Technologies, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-9535-3137
Vildanov A. M., wildam92@mail.ru, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-7319-0605
Magidov IS, j-bright@mail.ru, Master’s student, Department of Rocket and Space Composite Structures, Moscow State Technical University N. E. Bauman, Moscow, Russia.
ORCID: 0000-0003-1168-7066
Mikhailovsky K. V., MSTU named after M.V. N. E. Bauman, Moscow, Russia.
ORCID: 0000-0003-3424-3775
Klimova-Korsmik O.G., Cand. of Eng. Sc., Head of Materials Research Department.Institute of Laser and Welding Technologies, o.klimova@ltc.ru, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-2619-8874
Contribution by the members of the team of authors
The article was prepared on the basis of the work of all members of the author collective.
Conflict of interest
The authors declare that they have no conflicts of interest. All authors took part in writing the article and supplemented the manuscript in part of their work.
D. V. Volosevich, S. A. Shalnova, A. M. Vildanov, I. S. Magidov, K. V. Mikhailovsky, O. G. Klimova-Korsmik
Institute of Laser and Welding Technologies, St. Petersburg State Marine Technical University, St. Petersburg, Russia
N. E. Bauman Moscow State Technical University, Moscow, Russia
The results of experimental studies of the macro- and microstructure, chemical and phase composition of a cermet alloy based on titanium are presented. The material is intended for laser methods of additive manufacturing using direct metal deposition. For analysis, samples were obtained with a ceramic powder content of 5 and 10 vol. % SiC. The introduction of ceramic particles turned out to be effective for refining the alloy grains. The grain size of pure titanium is about 3.5 mm, while the grain size of titanium reinforced with silicon carbide at a radiation power of 1400 W was 50 and 14 μm for 5 and 10% SiC, respectively. As a result of the introduction of ceramic particles into the titanium matrix, the microhardness of the composite material increases, the hardening increases, but the embrittlement of the material also increases due to the violation of the integrity of the material and the occurrence of a reaction at the phase boundary.
Keywords: SLM (Selective Laser Melting), SLS (Selective Laser Sintering), DMD (Direct Metal Deposition), titanium-based cermets
Received on: 26.04.2021
Accepted on:16.06.2021
INTRODUCTION
The active development of technologies for mechanical engineering, shipbuilding, aircraft and rocket engineering imposes new requirements on materials: high values of wear resistance, impact resistance, corrosion resistance, a combination of hardness and plasticity, etc. Traditional materials do not meet the standards that modern materials must meet. In this regard, of particular interest are composite materials consisting, as a rule, of a plastic matrix and solid strong fillers.
Traditional technologies for producing and processing materials, such as casting, forging, drawing and pressing, milling and turning, involve changing the shape and removing the material layer, which leads to a significant investment of time and labor. Moreover, the microstructure of the alloy and, as a consequence, its mechanical properties are sensitive to temperature and deformation rate, therefore, traditional methods of processing products face certain difficulties.
Prospective for obtaining composite materials is additive manufacturing – layer-by-layer production of parts from CAD models. Additive technologies make it possible to obtain products of an almost unlimited configuration without unnecessary waste of material, time, and do not require additional equipment.
Products obtained using laser additive manufacturing methods such as SLM (selective laser melting), SLS (selective laser sintering), DMD (direct metal deposition) can achieve high density, and this, in turn, is directly related to mechanical, thermal and corrosive properties.
The characteristics of the initial powders are decisive for the quality of the final product: chemical and fractional compositions, the shape of the powder particles, as well as its morphology (pores, satellites, particle conglomerates). It is also important to select the optimal content of filler and matrix powders. In addition, the properties of the product depend on the parameters of the laser additive process, such as the power of the laser radiation, the scanning speed, the consumption of powders and shielding gases [1], [2]. Thus, the variety of chemical compounds that can be used as a matrix or filler, their various combinations, the effect of the content on the properties of the materials obtained, the dependence of the development of the structure on the parameters of the additive process open unlimited possibilities in the study of this direction.
Analysis of the starting powders
The morphology of the particles and the elemental composition of the metal powder BT6 and SiC were monitored. Table 1 shows the chemical composition of the powder according to GOST 19807-91 [3]. The content of chemical elements on the surface and on the powder cut was studied. Fig. 1 shows SEM images of BT6 powder and SiC.
The chemical composition of BT6 powder corresponds to GOST 19807-91. There are single satellites on the surface of the particles, which is an acceptable defect. The particle size is 50–150 microns. According to GOST 25849-83 [4], the powder particles are predominantly spherical, 3% of the particles are lamellar.
On average, the SiC powder contains 30.27 wt% C and 69.73 wt% Si, which corresponds to the composition of stoichiometric SiC; the powder contains no impurities of other elements. The particle size is 30–90 μm. According to GOST 25849-83, the powder particles have an angular shape.
Macro and microstructure, chemical and phase compositions
To study the structure, chemical and phase analysis, samples were obtained with a ceramic powder content of 5 and 10 vol% SiC, and for each content the value of the laser radiation power was varied in the range 1 400–2 200 W with a step of 200 W.
Fig. 2 shows panoramic SEM images of the samples. The study of the macrostructure revealed the presence of single pores with a size of about 2 microns. Also, many samples differ in the lack of fusion of the substrate and the base material. In addition, the samples have cracks that propagate deep into the material. As a rule, cracks originate at the sample boundary and propagate deeper into the material. The formation of cracks can be associated with the accumulation of heat as a result of layer-by-layer fabrication of the sample and the occurrence of thermal stresses.
It is known that the titanium matrix actively interacts with SiC particles with the formation of new TiC phases and titanium silicides (Ti5Si3, TiSi2). According to thermodynamic calculations [5], the free energy of such phases is lower than the free energy of silicon carbide, and such reactions can proceed spontaneously. On the one hand, new phases can increase microhardness and strength, and on the other hand, they violate the integrity of the structure, making the material more brittle. The C atoms penetrate more freely into the titanium matrix; therefore, the new TiC phase occurs both along the boundaries of the SiC particles and in the matrix. In fig. 3 shows a map of the distribution of chemical elements near the SiC particle.
It can be seen from the figure and the results of X-ray microscopy that the TiC phase is indeed precipitated along the boundaries of ceramic particles, which is also confirmed by chemical analysis by points. It was also found that the TiC phases in samples with 5 and 10% SiC have different structures. Fig. 4 shows a map of the distribution of chemical elements for a sample with 10% SiC.
Samples with a SiC content of 10% include TiC phases, which are dendritic structures. The point is that the amount of SiC in samples 1–5 containing 5 vol% SiC is insufficient for the formation of dendritic structures.
There are various variants of the reaction of the titanium matrix and silicon atoms, however, the reaction resulting in the formation of Ti5Si3 is energetically more favorable from the point of view of thermodynamics. Fig. 5 shows the results of mapping the region with the assumed Ti5Si3 phase. Chemical analysis showed that the phases with a «lamellar» structure are Ti5Si3 phases.
Thus, the samples under study contain the following phases: metal matrix BT6, particles of SiC, TiC, and Ti5Si3. The phases of the titanium alloy, as well as the results of X-ray phase analysis, are shown in Fig. 6. X-ray diffraction patterns show that with an increase in the SiC content and with an increase in the laser radiation power, the TiC and Ti5Si3 content increases, which is associated with a more active dissolution of SiC particles and an increase in the number of free carbon and silicon atoms.
The introduction of ceramic particles turned out to be effective for refining the alloy grains. The grain size of pure titanium is about 3.5 mm, while the grain size of silicon carbide-reinforced titanium at 1400 W is 50 and 14 μm for 5 and 10% SiC, respectively. With an increase in power, the grains continue to grind and reach the minimum value – 10 and 4 microns for 5 and 10% SiC, respectively – at a power of 2200 W. It was also found that the grains near silicon carbide are smaller than the others. On average, the grain size near SiC is 1.5 times smaller than the grains located at a distance from the ceramic particles. The fact is that new TiC phases are precipitated along the boundaries of the titanium matrix; it is they that prevent further grain deposition.
Mechanical tests, fractographic analysis of fractures
To check the effect of the formation of new phases on the properties of the alloy, mechanical tests were carried out, as well as fractographic analysis of samples with a content of 1, 3, 5% SiC, obtained at a laser power of 1200 W.
The sample with a 1% SiC content is distinguished by an elongated grain, the boundaries of which are weakly expressed, which indicates the nature of fracture close to ductile. Samples with 3 and 5% SiC also have regions of elongated grains; however, the size of such regions decreases with increasing SiC content, which indicates a decrease in plastic properties and an approach to brittle fracture. Fracture occurred along grain boundaries, which indicates an intercrystalline fracture. The fact is that the reaction of a titanium matrix with silicon carbide is an interfacial reaction that violates the integrity of the alloy and increases the brittleness of the material. An increase in the SiC content leads to an increase in the brittle properties of the material. There are single cracks originating at the grain boundary and propagating deep into the material. Fractographic analysis of sample fractures confirmed that the introduction of ceramic particles into the titanium matrix and the formation of new phases of brittle intermetallic compounds and TiC leads to embrittlement of the material.
Fig. 7 shows the tensile curves of the samples, table 2 shows their mechanical properties. The results of tensile tests of the samples confirmed that the fracture is predominantly brittle, and the samples with 3 and 5% SiC have only proportional regions, while the sample with 1% SiC has a hardening region, in which the crystal lattice of the material is deformed. However, a comparison of the tensile strength of a pure alloy and an alloy containing 1% SiC proves the effectiveness of the introduction of ceramic particles. According to GOST 22178–76 [6], the average value of the ultimate strength of the BT6 alloy is ~980 MPa, ceramic particles increase the ultimate strength by 1.3 times. Also, with an increase in the SiC content, the yield stress decreases; nevertheless, the obtained values turned out to be higher than that of the pure BT6 alloy. The relative elongation of the BT6 alloy according to GOST 22178–76 is 8%, which is 8.5 times higher than the values for alloys reinforced with SiC particles.
In the course of the work, the dependences of the microhardness of the matrix on the power of laser radiation and on the content of ceramic particles were studied. Microhardness characteristic of BT6 alloy is ~350 HV [5]. With an increase in the power of laser radiation, the value of the microhardness of the titanium matrix increases. The maximum value of microhardness was achieved for a sample with 10% SiC at a power of 2200 W and amounted to 836.4 HV, which exceeds the value of microhardness characteristic of BT6 alloy without ceramic particles by 2.4 times.
CONCLUSION
MRSA and X-ray phase analysis confirmed the presence of new phases, and an increase in the SiC content and laser radiation power due to the more active decomposition of SiC particles into atoms leads to an increase in the intermetallic Ti5Si3 and TiC phases. Titanium carbide manifests itself in the structure in various configurations: acicular structures in samples with 5% SiC and dendritic structures for samples with 10% SiC. Intermetallic phases have a «lamellar» structure. Reinforcement of the titanium alloy with ceramic particles led to grain refinement to 10 and 4 μm for 5 and 10% SiC, respectively. The point is that the titanium carbide phase is precipitated along the grain boundaries, which prevents grain deposition.
The formation of new phases has the following consequences: the Ti5Si3 and TiC phases have a microhardness that significantly exceeds the microhardness of the BT6 alloy, therefore, as a result of the introduction of ceramic particles into the titanium matrix, the microhardness of the composite material will increase; hardening of the material; embrittlement of the material due to the violation of the integrity of the material and the occurrence of a reaction at the phase boundary. Mechanical tests were carried out to check the influence of interfacial reactions on the properties of the alloy. The samples with 1.3.5 and 7% SiC were obtained by direct metal deposition at a power of 1200 W. It became clear already at the stage of preparing blades for mechanical tests, that an excessive SiC content (7% for this work) leads to a significant decrease in the plastic properties of the material: the sample has cracks that do not allow making a blade. Fractographic analysis showed that the samples have areas of ductile and brittle fractures; however, the size of the viscous fracture region with weakly pronounced grain boundaries decreases with an increase in the SiC content, which indicates that the properties of the material approach brittle. The tensile curves confirmed the results of fractography: the samples with 3 and 5% SiC have a curve typical for brittle materials, while the sample with 1% SiC has a hardening region characterized by deformation of the crystal lattice of the material.
With an increase in the SiC content, the yield stress and plasticity decrease, the maximum values were achieved at a 1% SiC content and amounted to 1110 MPa and 1300 MPa, respectively, which on average exceeds the corresponding values of pure BT6 alloy by 1.3 times.
The maximum value of the relative elongation was 2.1% for the sample with 1% SiC, which is 8.5 times less than the corresponding value for the unreinforced BT6 alloy. Measurement of the microhardness of the alloy grains also proved the efficiency of introducing SiC particles: both an increase in the laser radiation power and an increase in the SiC content lead to an increase in the microhardness of the composite material. The maximum value was achieved for a sample with 10% SiC at a power of 2200 W and amounted to 836.4 HV, which is 2.4 times higher than the BT6 microhardness.
With the financial support of the Department of Education and Science of the Russian Federation the creation and development of the world-class scientific center “Advanced Digital Technologies” (Grant Agreement № 075-15-2020-903 from 16.11.2020).
ABOUT AUTHORS
Volosevich D. V., dasha.volosevich@mail.ru, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-2288-2935
Shalnova S. A., sveta-net07@mail.ru, Engineer, Materials Research Department. Institute of Laser and Welding Technologies, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-9535-3137
Vildanov A. M., wildam92@mail.ru, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-7319-0605
Magidov IS, j-bright@mail.ru, Master’s student, Department of Rocket and Space Composite Structures, Moscow State Technical University N. E. Bauman, Moscow, Russia.
ORCID: 0000-0003-1168-7066
Mikhailovsky K. V., MSTU named after M.V. N. E. Bauman, Moscow, Russia.
ORCID: 0000-0003-3424-3775
Klimova-Korsmik O.G., Cand. of Eng. Sc., Head of Materials Research Department.Institute of Laser and Welding Technologies, o.klimova@ltc.ru, St. Petersburg State Marine Technical University, St. Petersburg, Russia.
ORCID: 0000-0002-2619-8874
Contribution by the members of the team of authors
The article was prepared on the basis of the work of all members of the author collective.
Conflict of interest
The authors declare that they have no conflicts of interest. All authors took part in writing the article and supplemented the manuscript in part of their work.
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