Fine TiB2 Platelets Research Articles

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.

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.

Microstructures and Toughening of TiC-TiB2Ceramic Composites with Cr-Based Alloy Phase Prepared by Combustion Synthesis in High-Gravity Field

Micro-nanocrystalline microstructures which are characterized by TiB2platelets of the average thickness close to or smaller than 1 μm can be achieved in nearly full-density solidified TiC-TiB2ceramic composites with Cr-based alloy phases by combustion synthesis in ultra-high gravity field of 2500 g. The filler phases in ceramic composites are actually Cr-based alloy with a little solidified solution of Ni atoms and Al atoms. The hardness, flexural strength, and fracture toughness of the materials are 18.5 ± 1.5 GPa, 650 ± 35 MPa, and 16.5 ± 1.5 MPa⋅m0.5, respectively. The improved fracture toughness of TiC-TiB2ceramic composites results from crack deflection, crack bridging, and pull-out by a large number of fine TiB2platelets and plastic deformation with some Cr-based alloy phases.

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.

Ceramic Coating of TiC-TiB<sub>2</sub> on 1Cr18Ni9Ti Substrate Achieved by Combustion Synthesis in High-Gravity Field

Based on fusion bonding of liquid TiC-TiB2ceramic film to stainless steel substrate of 1Cr18Ni9Ti, the ceramic coating on stainless steel substrate was achieved in graded composition by combusion synthesis in high-gravity field. XRD, FESEM and EDS results showed the ceramic coating was composed of a number of fine TiB2platelets, irregular TiC grains and a few of Cr metallic binder and the inclusions of Al2O3partilces, and physical and mechanical properties showed density, relative density, microhardness and fracture toughness of the ceramic coating were 4.25 g • cm-3, 98.2%, 24.6 GPa and 14.5 ± 3.5 MPa • m0.5, respectively. The joint of TiC-TiB2ceramic coating on stainless steel substrate consisted of 3-layer structures, i.e. the ceramic coating, the intermediate and stainless steel substrate, and within the intermediate of Fe-Cr-Ni-Ti metallic matrix Ti-Fe enriched carbides decreased gradually both in volume fraction and particle size from the ceramic coating to stainless steel substrate in the presence of atomic unidirectional diffusion of Ti and C, while some isolated α-Al2O3fine particles were also observed in the intermediate besides the presence of both some coarsened α-Al2O3inclusions nearby the ceramic coating and the barrier layers of Al2O3between the ceramic and the intermediate, so it is considered that the ceramic coating on stainless steel substrate is achieved partially by fusion bonding due to the poor incompatibilities between Al2O3inclusions and the intermediate, resulting in the moderate shear strength of 125 ± 35 MPa between the ceramic coating and stainless steel substrate.

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

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±1.5GPa and 860±35 MPa, whereas the maximum fracture toughness of 13.5±1.5MPam0.5 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.

Microstructures, Properties and Fracture Behavior of Solidified TiC-TiB<sub>2</sub> Composites with Increasing Content of TiB<sub>2</sub>

By adjusting the mole ratio of C and B elements in combustion system, solidified TiC-TiB2 composites with different TiB2 mole fraction were achieved by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that with increasing TiB2 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-50mol% TiB2 due to eutectic growth under rapid solidification of the ceramic. Properties showed that relative density, Vickers hardness and flexural strength of TiC-50mol%TiB2 simultaneously reached the maximum values of 21.5 ± 1.5 GPa and 860 ± 35 MPa , whereas TiC-66.7mol%TiB2 presented the maximum fracture toughness of 13.5 ± 1.5 MPa • m0.5. FESEM fractography analyses of the ceramics exhibited a mixed mode of transcrystalline fracture of TiC spherical grains and intercrystalline fracture of TiB2 platelets, and the tendency of intercrystalline fracture was obviously enhanced with increasing TiB2 content to be 66.7 mol%, resulting in enhanced toughening mechanisms of crack deflection, crack-bridging and pull-out by fine TiB2 platelets, thus, the highest flexural strength was achieved in TiC-50mol%TiB2 due to the achievements of both fine-grained microstructures and high fracture toughness in the full-density solidified ceramics.

Crystal Growth, Fracture Behavior and Toughening of Rapidly-Solidified TiC-TiB<sub>2</sub> Prepared by Combustion Synthesis in High-Gravity Field

Micro-nanocrystalline microstructures characterized by TiB2 platelets of the average thickness close to or smaller than 1 μm, were achieved in full-density solidified TiC-TiB2 composites by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that a large number of fine TiB2 platelets were uniformly embedded in irregular TiC grains, a few Cr-Al metallic phases or in between those phases. The achievement of micro-nanocrystalline microstructures results from low-velocity faceting growth of TiB2 crystal, high-velocity non-faceting growth of TiC solid and high diffusion rate of C relative to B in liquid TiC-TiB2. The relative density, Vickers hardness, flexural strength and fracture toughness of TiC-TiB2 composites measured 99.3%, 21.5 ± 1.5 GPa, 845 ± 35 GPa and 16.8 ± 1.5 MP • m0.5, respectively. High flexural strength of the materials benefits mainly from the achievement of micro-nanocrystalline microstructure in the full-density solidified ceramic and high fracture toughness contributed from intensive coupled toughening mechanisms by a large number of fine TiB2 platelets and a few Cr-Al metallic phases.

Microstructures and Properties of Solidified TiC-TiB<sub>2</sub> Ceramic Composites with Increasing Cr Metallic Binder Prepared by Combustion Synthesis in High-Gravity Field

By increasing addition amount of (CrO3 + Al) subsystem in (B4C + Ti) system, the solidified TiC-TiB2 composites with a series of mass fraction of Cr binder were achieved by combustion synthesis in high-gravity field. The microstructures of the solidified ceramics presented a number of fine TiB2 platelets embedded in TiC grains, Cr-Ti alloy or between TiC grains and Cr-Ti alloy. The increased Cr binder in the ceramic not only brought about the enhanced densification of the ceramic due to fill-up of Cr-Ti liquid in shrinkage cavities between solidified TiC and TiB2 phases, but more importantly made fine-grained even ultrafine-grained microstructure achieved because of the accelerated nucleation and the decelerated growth of TiB2 at initial stage of material solidification. As a result of the achievement of fine-grained even ultrafine-grained microstructure along with the enhanced toughneing mechanisms contributed by the refined TiB2 platelets and the increased plastic phases of Cr-Ti alloy, the solifidied TiC-TiB2 composite containing 20.7 % Cr binder presented the maximun values of 1045 ± 25 MPa and 21.5 ± 1.6 MPa • m 0.5, simultaneously, in flexural strength and fracture toughness along with the moderate hardness of 17.5 ± 2.2 GPa.

Preparation and Properties of Solidified TiC-TiB<sub>2</sub> with Hypoeutectic, Eutectic and Hypereutectic Microstructures

By using combustion synthesis under high gravity, TiC-TiB2 fine-grained composite ceramics with hypoeutectic, eutectic and hypereutectic microstructures were prepared through rapid solidification. XRD, FESEM and EDS results show that with increasing TiB2 content, TiC-TiB2 composite ceramics transform the microstructures consisting of fine TiB2 platelets from ones composed of fine TiC spherical grains, whereas when TiB2 content reaches 50mol%, the ceramics develop the eutectic microstructures that small aspect-ratio TiB2 platelets were embedded in TiC matrix. Mechanical properties show that relative density, Vickers hardness and flexural strength of TiC-50mol%TiB2 all reach the maximum values (respectively as 98.6 % ,18.4 GPa, 840 MPa) due to eutectic reaction during solidification, meanwhile TiC-50mol%TiB2 has the maximum fracture toughness of 11.5 MPa∙m0.5 due to the cooperative action of crack deflection, crack-bridging and pull-out toughening by fine TiB2 platelets.

Ultra-High-Hard Composites of TiC-TiB<sub>2</sub> Prepared by Combustion Synthesis under High Gravity

The large-bulk solidified TiC-TiB2 composites were prepared by combustion synthesis in high-gravity field. XRD, FESEM, SEM and EDS results showed that TiC-TiB2 composites were mainly composed of TiC matrix in which a number of fine TiB2 platelets were embedded, surrounded by the boundary regions consisting of (Cr, Ti) C0.63 carbides. The hardness, flexural strength and fracture toughness of TiC-TiB2 composites measured 28.5GPa, 750±25MPa and 6.2±0.5MPa•m1/2. High hardness of the composites benefits from the absence of the intermediate borides and the achievement of stoichiometric TiC phases due to rapid solidification, whereas the achievement of high strength benefits the refinement and homogeneity of the microstructures due to rapid separation of liquid oxides in high-gravity field and rapid coupled growth of TiC and TiB2 phases.

Microstructures and properties of large bulk solidified TiC–TiB 2 composites prepared by combustion synthesis under high gravity

Large bulk solidified TiC–TiB2 composites with full density were prepared by combustion synthesis in a high-gravity field. The materials presented unique solidification microstructures in which a number of fine TiB2 platelets were embedded in TiC matrix. The hardness, flexural strength and fracture toughness of the materials were 28.5 GPa, 750 ± 25 MPa and 6.2 ± 0.5 MPa m1/2, respectively. The materials’ high hardness resulted from the absence of intermediate borides and the achievement of stoichiometric TiC phases due to rapid solidification.