TiB2 Platelets Research Articles

Microstructure and Properties of TiB2-TiC-SiC Ternary Phase Ceramics Produced by High-Gravity Field Activated SHS of Ti-Si-B4C Powders

TiB2-TiC-SiC ternary phase ceramics have been prepared by high-gravity activated combustion synthesis using (Ti-Si-B4C) mixing powders. XRD, FESEM and FETEM results show that the ceramic matrix was mainly composed of TiB2, TiC and β-SiC. Uniformly-distributed TiB2 platelets formed the skeleton of ceramics, and irregular TiC and β-SiC solids were embedded between TiB2 platelets. The relative density, Vickers hardness and fracture toughness of the ternary phase ceramics were measured with values of 97.9 %, 22.2 GPa and 10.1 MPa·m0.5. The high-fraction randomly-orientated TiB2 platelets were found to induce continuous crack deflection, and consumed more energy from the crack tip, thereby enhanced the strength and toughness of TiB2-TiC-SiC ceramics.

TiB2-TiC-SiC composites prepared through high-gravity field activated SHS

TiB2-TiC-SiC composites were prepared by high-gravity activated SHS using (Ti+B4C+Si) mixing powders. XRD, FESEM and FETEM results showed that the matrix of composites was mainly composed of TiB2, TiC and β-SiC. Uniformly-distributed TiB2 platelets formed the skeleton of composites, and irregular TiC and β-SiC solids were embedded between TiB2 matrix. It is supposed that TiB2 phases firstly precipitate prior to TiC from the molten reactive product in high-gravity field due to higher concentration of boron atom, and SiC solids solidify at final solidification stage and feed the TiB2 platelet skeleton, which effectively reduce the porosity and promote the relative density of composites.

Structure formation and densification of TiB2-TiC-Ni composites produced by chemical reaction of Ti-B4C system in high-gravity field

TiB2-TiC-Ni composites were achieved through direct reaction of Ti and B4C powder blends in a high gravity field of 1800 g with Ni binder. The microstructure of TiB2-TiC composites present pore-free with darker TiB2 platelets and the brighter TiC equiaxed grains easily distinguishable. Ti-B-C-Ni full-liquid SHS intermediate products immediately were formed following the reaction of Ti and B4C, which was considered to yield inherently fine-grained microstructures under the rapid cooling condition. The role of high gravity field was proposed as promoter of the final products densification and grain refinement of TiB2-TiC composites.

Synthesis Mechanism of TiB2-TiC-Ni Composites Produced by Combustion Reaction of Ti-Ni-B4C System in the High-Gravity Field

TiB2-TiC-Ni composites were fabricated through combustion reaction of Ti-Ni-B4C in a high gravity field. TiB2-TiC-Ni composites were pore-free with darker TiB2 phases and the brighter TiC easily distinguishable. The microstructure consisted of TiB2 platelets with an aspect ratio of 2 and equiaxed TiC grains. The reaction process was controlled by the high-gravity field, which was considered to accelerate decomposition of B4C and diffusion of boron and carbon atoms. The melting Ni and Ti increased the diffusion path for boron and carbon atoms, thereby promoting the reaction process. The rapid cooling of Ti-B-C-Ni full-liquid intermediate products immediately was expected following the reaction of Ti and B4C, which was responsible for fine-grained microstructure. The microstructural investigations have confirmed the role of high gravity field and Ni dilute as promoters of densification of the final products and grain refinement in this experimental.

TiB 2 -based Ceramic/1Cr18Ni9Ti Stainless Steel Composite Produced by Combustion Synthesis in Ultra-high Gravity Field

Abstract Based on fusion bonding and atomic interdiffusion between the ceramic and stainless steel, the TiB2-based ceramic/1Cr18Ni9Ti stainless steel composite with chemical composition gradient was produced by combustion system in ultra-high gravity field (CSUGF). The presence of chemical reaction in explosive combustion and the subsequent thermal-vacuum circumstance induced by liquid products in ultra-high gravity make stainless steel partially fused, resulting in fusion bonding. XRD, FESEM and EDS results show that the interface has a good bonding, and the intermediate exhibits three dimensional network ceramic-metal graded microstructure considered as a result of intensive interdiffusion of atomics. Vickers hardness profile reveals the quasi-parabola relationship of the hardness to the testing distance from the ceramic matrix to the steel substrate. Meanwhile, interfacial shear fracture of the composite presents the mixed mode consisting of intercrystalline fracture along TiB2 platelets and ductile fracture in Fe-Ni-Cr alloy, presenting interfacial shear strength (325±25) MPa.

Pressureless sintering of titanium carbide doped with boron or boron carbide

Abstract Titanium carbide ceramics with different contents of boron or B 4 C were pressureless sintered at temperatures from 2100 °C to 2300 °C. Due to the removal of oxide impurities, the onset temperature for TiC grain growth was lowered to 2100 °C and near fully dense (>98%) TiC ceramics were obtained at 2200 °C. TiB 2 platelets and graphite flakes were formed during sintering process. They retard TiC grains from fast growth and reduced the entrapped pores in TiC grains. Therefore, TiC doped with boron or B 4 C could achieve higher relative density (>99.5%) than pure TiC (96.67%) at 2300 °C. Mechanical properties including Vickers’ hardness, fracture toughness and flexural strength were investigated. Highest fracture toughness (4.79 ± 0.50 MPa m 1/2 ) and flexural strength (552.6 ± 23.1 MPa) have been obtained when TiC mixed with B 4 C by the mass ratio of 100:5.11. The main toughening mechanisms include crack deflection and pull-out of TiB 2 platelets.

Large-scale growth of TiB2 hexagonal platelets

Abstract This work reports on large scale growth of TiB2 hexagonal platelets on Ti3AlC2 samples prepared by pressureless sintering of Ti/Al/C green bodies in a graphite crucible coated with boron nitride. Single TiB2 platelet has a hexagonal shape with a particle size of less than 20 μm and a thickness of less than 1 μm. Some thicker platelet particles are composed of layer-stacking TiB2 thinner platelets. The growth mechanism of TiB2 hexagonal platelets has been discussed. The coexistence of exothermic reactions and liquid in the Ti-Al-C-BN system plays a key role in the hexagonal crystal growth of TiB2. Influence of Al content in the Ti-Al-C-BN system on the formation of TiB2 platelets has been also investigated. Phase composition was analyzed by X-ray diffraction, and microstructure of TiB2 hexagonal platelets was characterized by using scanning electron microscopy. The fabrication method developed here is a promising approach for preparing TiB2 platelet particles on a large scale.

Interfacial microstructure and mechanical properties of laminated composites of TiB2-based ceramic and 42CrMo alloy steel

Based on fusion and interdisffusion of the liquid ceramic and the molten steel, the laminated composite of TiB2-basedceramic and 42CrMoalloy steel consisting of 3-layer structure with the ceramic matrix, the intermediate and the steel substrate, was rapidly prepared by self-propagating synthesis with centrifugal-casting process, and within the intermediate the continuously-graded microstructures of span-scale-structured (micro-structured → micro-nanostructured → nano-structured) ceramic/alloy network developed while a conherent/particle-conherent relationship was kept in the interface of micro-nano/nanocrystalline TiB2 and Fe-Ni alloy base. Combining mechanical properties test with FESEM and HRTEM examination, it is considered that the in-situ achievement of the span-scale-structured continuously-graded intermediate of ceramic/alloy network microstructure not only presents the gradient joint with high flexural strength and high fracture toughness, but also presents the laminated composite with strong plastic deformation behavior and high ductility-like capacity during 3-point bending test. Meanwhile, the cooperative action of crack interlocking by fine Ni-based metallic films surrounding TiB2 platelets in the regions nearby the ceramic with precipitation strengthening by micro-nano/nanocrystalline TiB2 platelets in the intermediate was considered to contribute to the high interlaminar shear strength of 425±50 MPa.

Microstructure, Densification and Mechanical Properties of TiB<sub>2</sub>-TiC-NiAl Ceramic-Based Composite

By adjusting mass fraction of Ni-Al composite additive in Ti-B4C primary system, a series of TiB2-based ceramic composites were prepared by combustion synthesis in high gravity field. Because the adiabatic temperature of the whole reaction system maintained a constant in the presence of mass fraction of Ni-Al additive smaller than 18.55%, increasing mass fraction of Ni-Al additive to be 15% brought about the improved homogeneity in refined microstructure of the enhanced-densification TiB2-based composite, so flexural strength and fracture toughness of the ceramic composite increased simultaneously due to the enhanced self-toughening mechanisms contributed by a number of fine TiB2 platelets.

Reaction Fusion and Spatial Span-Scale Microstructure Evolution of TiB<sub>2</sub>-Based Ceramic and Metal Achieved by High Gravity Field

The plates of 1Cr18Ni9Ti stainless steel were selected as metal substrates, and CrO3+Al thermites were introduced into B4C+Ti primary system for enhancing adiabatic temperature of reaction system. By improved processing route, i.e. respectively preparing, ball-milling and compacting B4C+Ti blends and CrO3+Al thermites and subsequently filling them one by one into the crucibles, TiB2ceramic to 1Cr18Ni9Ti graded composites were prepared by reaction joining in high-gravity field. it was found that refined TiB2 platelets were embedded in or around the irregular TiC grains, and Fe-Cr-Ni metallic phases were distributed between TiC and TiB2 phases, and Al2O3 inclusions disappeared completely at the intermediate between TiB2ceramic and 1Cr18Ni9Ti, the thickness of which reached 1.05 mm. The 3D net ceramic-metal composite microstructure (3DNCMCM) existed at the intermediate. The Vickers hardness distribution of the intermediate appeared the parabolic gradient composite feature, and the shear strength of the intermediate reached 325±15 MPa because of the increasing thickness of intermediate, at which 3D net ceramic-metal composite microstructure (3DNCMCM) existed.

Reaction Fusion and 3D-Network Span-Scale Graded Microstructure Evolution in Laminated Composite of TiB2-Based Ceramic and 42CrMo Steel

Based on liquid fusion and atomic interdiffusion of TiB2-based ceramic and 42CrMo steel, the ceramic-metal laminated composites with interfacial 3D-network span-scale graded microstructures were achieved by combustion synthesis in high gravity field. The presence of respective atomic concentration gradient of Ti, B, C, Fe and the others between the ceramic and the steel reasoned for continuously-graded interfacial microstructure in which the TiB2 and TiC phases transform sub-micrometer, micro-nanometer grains from the micrometer ones. The Fe-based liquid flow from the ceramic to the steel substrate resulted in the 3D-network distribution of Fe-based alloy phases from the ceramic to the steel substrate. Hence, interfacial shear fracture presented the mixed mode consisting of intercrystalline fracture along fine TiB2 platelets and ductile fracture in Fe-based alloy phases, presenting interfacial shear strength 415 ± 25 MPa of the laminated composite.

Fusion bonding and microstructure formation in TiB2-based ceramic/metal composite materials fabricated by combustion synthesis under high gravity

The novel ceramic/metal composite materials were successfully fabricated by combustion synthesis in high gravity field. In this paper, the Ti-B4C was selected as the main combustion reaction system to obtain TiB2-TiC ceramic substrate, and the 1Cr18Ni9Ti stainless steel was selected as the metal substrate. It was found that the TiB2-TiC/1Cr18Ni9Ti composite materials exhibited continuously graded composition and hybrid microstructure. The TiC1−x carbides and TiB2 platelets decreased gradually in size and volume fraction from the ceramic to stainless steel. Due to the rapid action of thermal explosion as well as the dissolution of the molten stainless steel into TiB2-TiC liquid, the diffusion-controlled concentration gradient from the ceramic liquid to the alloy liquid was observed. Finally, as a result of the rapid sequent solidification of the ceramic liquid and the melt alloy surface, the laminated composite materials were achieved in multilevel, scale-span hybrid microstructure.

Microstructure modification and fracture behavior of solidified TiC–TiB2 ceramic prepared by combustion synthesis in ultra-high gravity field

A series of solidified TiC–TiB2 were fabricated by combustion synthesis integrated with ultra high gravity, and the ceramics were comprised of TiB2 primary phases, irregular TiC secondary phases, a few of Al2O3 inclusions and Cr-based metallic phases. Obviously, the increased high gravity field promoted phase separation of Al2O3 droplets from the molten reaction products, which resulted in not only the rapidly reduced Al2O3 inclusions but also the refined microstructure and the improved homogeneity. When high gravity acceleration reached 2500 g, the ultrafine-grained microstructure with the average thickness of TiB2 platelets smaller than 1 μm was achieved. More and more fine TiB2 platelets with aspect ratio of 4–6 participated in the toughening mechanism of crack bridging and subsequent pullout, the maximum fracture toughness could amount to 16.5 ± 1.0 MPa m0.5. Because of rapidly reduced Al2O3 inclusions, the refined microstructure and the improved homogeneity were obtained in the near full-density composite, the maximum flexural strength of 982 ± 20 MPa was also simultaneously achieved in the solidified TiC–TiB2 composite at 2500 g.

Microstructures and Properties of Solidified TiC-TiB<sub>2</sub> Composites Prepared by Combustion Synthesis in Enhanced High-Gravity Field

By taking combustion synthesis to prepare a series of solidified TiC-TiB2composites under the increased high-gravity acceleration from 500g to 2500g, then in the near-full-density composite the ultrafine-grained microstructure with the matrix of TiB2platelets smaller than 1 μm in thickness was achieved, and all TiB2 platelets almost shared in the contributions of bridging and pullout to toughening ceramic, thereby presenting fracture toughness of 16.5 ± 1.0 MP · m0.5and flexural strength of 982 ± 20 MPa.

Microstructures and Crack Propagation in the Joint of Solidified TiC-TiB<sub>2</sub> to Ti-6Al-4V Prepared by Reactive Fusion Bonding in Ultrahigh Gravity Field

By taking combustion synthesis in ultrahigh gravity field to prepare solidified TiC-TiB2 composite ceramic, laminated composite of the ceramic to Ti-6Al-4V was achieved by fusion bonding and atomic inter-diffusion, and within the joint there formed the unique microstructure of multiscale (micrometer-micro/nanometer-nanometer) and multilevel characterized by size and distribution of TiB2 and TiB due to the presence of a series of metallurgical reaction including peritectic reaction of solidified and Ti liquid, direct growth of TiB solids from liquid Ti and subsequent eutectic reaction of TiB solids and liquid Ti. FEMSEM images of crack propagation paths at the joint showed despite the contribution from crack bridging of micro-nanometer TiB2 and TiB platelets to crack propagation resistance, residual stress toughening and subsequent crack pinning by micro-nanometer TiB2 ,TiB platelets and needle-like nanometer TiB grains as well as ductile phase toughening and bridging toughening by Ti metallic phases became the primary resistances to crack propagation, thereby presenting the delayed fracture behavior in the joint, so that shear fracture usually occurred at the solidified Ti alloy rather than the joint, and shear strength of 375 ± 55 MPa was achieved between the solidified ceramic and Ti alloy.

Composition Modification and Mechanical Properties of Solidified TiB<sub>2</sub>-Based Ceramic Prepared by Combustion Synthesis in Ultra-High Gravity Field

The solidified TiC-TiB2 ceramics with excessive Ti mole content were prepared through adjusting the Ti additional agent in combustion system with ultra-high-gravity of 2000 g, and the ceramics were comprised of TiB2 primary phases, irregular TiC1-x secondary phases, a few of Al2O3 inclusions and Cr-Ti-Al metallic phases. The additional Ti content resulted in not only the rapidly-reduced Al2O3 inclusions but also the refined microstructure and the improved homogeneity in the solidified microstructure. As the Ti additional agent was increased, more and more Ti atoms could participate in the formation of nonstoichiometric TiC1-x phases and Cr-Ti-Al metallic phases. The maximum fracture toughness of 18.5 ± 1.0 MP · m0.5 in current solidified TiC-TiB2composite was achieved because of the less Al2O3 inclusions, the refined microstructure and the Ti-rich Cr-Ti-Al metallic phases obtained in the near-full-density composite. The high fracture toughness contributed from not only mechanism of crack deflection, crack-bridging and pull-out by a large number of fine TiB2 platelets, but also the ductile fracture toughening result from plastic deformation of Cr-Ti-Al metallic phases.

Fracture Behavior of Solidified TiC-TiB<sub>2</sub> Ceramic Prepared by Combustion Synthesis in Ultra-High Gravity Field

A series of TiC-TiB2 ceramics were prepared by combustion synthesis in ultra-high gravity field, the microstructure, fracture behavior and toughening mechanism of the composite ceramic are discussed. The maximum fracture toughness of 13.1 MPa · m0.5 is achieved in TiC-66.7%TiB2, very close to the values (10~15 MPa · m0.5) of fiber-reinforced ceramic composite, contributed from the intensive coupled toughening mechanisms of crack deflection, frictionally crack-bridging and pull out by a large number of fine TiB2 platelets and ductile phase toughing caused by a few Cr-Al metallic phases.

Layered Composite of TiC-TiB2 to Ti-6Al-4V in Graded Composition by Combustion Synthesis in High-gravity Field

By taking combustion synthesis to prepare solidified TiB2 matrix ceramic in high-gravity field, the layered composite of TiC-TiB2 ceramic to Ti-6Al-4V substrate in graded composition was achieved. XRD, FESEM and EDS results showed that the bulk full-density solidified TiC-TiB2 composite was composed of fine TiB2 platelets, TiC irregular grains, a few of α-Al2O3 inclusions and Cr alloy phases, and α'-Ti phases alternating with Ti-enriched carbides constituted the matrix of the joint in which fine TiB platelets were embedded, whereas some C, B atoms were also detected at the heat-affected zone of Ti-6A1-4V substrate. The layered composite of the solidified ceramic to Ti-6Al-4V substrate in graded composition with continuous microstructure was considered a result of fused joint and inter-diffusion between liquid ceramic and surface-molten Ti alloy, followed by TiB2-Ti peritectic reaction and subsequent eutectic reaction in TiC-TiB-Ti ternary system.

TiC-TiB<sub>2</sub> Coating on Ti-6Al-4V Alloy Substrate in Graded Composition Achieved by Fusion Bonding and Atomic Interdiffusion under Combustion Synthesis in High-Gravity Field

Based on fusion bonding of liquid TiC-TiB2 ceramic film and molten Ti-6Al-4V substrate to induce the surface alloying of Ti-6Al-4V substrate, the TiC-TiB2 ceramic coating on Ti-6Al-4V substrate was achieved in graded composition by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that TiC-TiB2 ceramic coating was composed of fine TiB2 platelets, TiC irregular grains, Cr metallic phase and a few Al2O3 inclusions. The mechanical properties showed that the relative density, microhardness and fracture toughness of TiC-TiB2 ceramic coating reached 98.5%, 25.8 ± 3.5 GPa and 16.5 ± 2.5 MPa • m0.5, respectively. The fusion-bonding area and heat-affected zone of Ti alloy were obviously observed between the ceramic coating and Ti alloy substrate, and within the fusion bonding area a number of ultralfine TiB platelets and fine Ti-enriched carbides were embedded in the matrix of α’-Ti martensite, whereas at the heat-affected zone of Ti-6A1-4V substrate some C, B atoms were also detected. As a coupled result of fusion bonding and inter-diffusion between liquid ceramic film and molten Ti alloy substrate, followed by TiB2-Ti peritectic reaction and subsequent eutectic reaction in TiC-TiB-Ti ternary system, the ceramic coating of TiC-TiB2 on Ti-6Al4V substrate was achieved in continuously-graded composition, presenting the transitional change in microhardness from the ceramic coating to Ti alloy substrate with high shear strength of 450 ± 35 MPa between the coating and the substrate.

Microstructure transformation and mechanical properties of TiC–TiB2 ceramics prepared by combustion synthesis in high gravity field

Abstract By conducting combustion synthesis in high-gravity field, the solidified TiC–TiB2 with a series of TiB2 mole content were prepared through adjusting the mole ratio of C and B elements in combustion system. XRD, FESEM and EDS results showed that with increasing TiB2 mole content, the matrix of TiC–TiB2 composite ceramics transformed a number of fine TiB2 platelets from the TiC spherical grains, and fine-grained even ultrafine-grained microstructures were achieved in solidified TiC–50%TiB2 due to the coupled quasi-eutectic growth under rapid solidification of the ceramic. Properties showed that relative density, Vickers hardness and flexural strength of TiC–50%TiB2 simultaneously reached the maximum values of 98.7%, 21.5 ± 1.5 GPa and 860 ± 35 MPa, whereas the maximum fracture toughness of 13.5 ± 1.5 MPa m0.5 was achieved in TiC–66.7%TiB2. FESEM fractography analyses of the solidified ceramics indicated that the highest flexural strength achieved in TiC–50%TiB2 benefits from not only the lowest content of Al2O3 inclusions and Cr–W–Ti borides, but also the achievements of fine-grained microstructure in the near-full-density ceramic and high fracture toughness contributed from a intensive coupled mechanism of crack deflection, crack-bridging and pull-out by a large number of fine TiB2 platelets.