Investigation of the density and microstructure homogeneity of square-shaped B4C-ZrB2 composites produced by spark plasma sintering method

Square-shaped monolithic B₄C and B₄C-ZrB₂ composites were produced by spark plasma sintering (SPS) method to investigate the effect of 5, 10, 15 vol% ZrB₂ addition on the densification, mechanical and microstructural properties of boron carbide. The relative density of B₄C increased with the increasing volume fraction of ZrB₂ and density differences in different regions of the sample narrowed down. Homogeneous density distribution and microstructure were accomplished with the increasing holding time from 7 to 20 min for the B₄C-15 vol% ZrB₂ composites, and the highest overall relative density was achieved as 99.23%. The hardness and fracture toughness of composites were enhanced with the addition of ZrB₂ compared to monolithic B₄C. The enhancement in fracture toughness was observed due to the crack deflection, crack bridging and crack branching mechanisms. The B₄C-15 vol% ZrB₂ composite exhibited the combination of superior properties (hardness of 33.08 GPa, Vickers indentation fracture toughness of 3.82 MPa.m^1/2).     

Spark plasma sintering of TiB2-based ceramics with Ti3AlC2

A TiB₂–Ti₃AlC₂ ceramic was manufactured by spark plasma sintering at 1900 °C temperature for 7 min soaking time under 30 MPa biaxial pressure. The role of Ti₃AlC₂ additive on the microstructure development, densification behavior, phase evolution, and hardness of the ceramic composite were studied. The phase characterization and microstructural investigations unveiled that the Ti₃AlC₂ MAX phase decomposes at the initial stages of the sintering. The in-situ formed phases, induced by the decomposition of Ti₃AlC₂ additive, were identified and scrutinized by XRD and FESEM/EDS techniques as well as thermodynamics principles. The sintered TiB₂–Ti₃AlC₂ ceramic approached a near full density of ~99% and a hardness of ~28 GPa. The densification mechanism and sintering phenomena were discussed and graphically illustrated.     

Spark plasma sintering and mechanical properties of compounds in TiB2-SiC pseudo-diagram

The influence of spark plasma sintering (SPS) parameters (temperature, time, pressure) and the role of particle size on densification, microstructure and mechanical properties of commercial additive-free TiB₂, SiC and composites thereof were studied by X-ray diffraction, scanning electron microscopy, the ultrasonic method and indentation. Three particle sizes of SiC and 2 of TiB₂ were processed. An optimal cycle was found for TiB₂ and SiC: 2000?°C, 3?min dwell time, and 100?MPa applied at 600?°C. The relative density of pure SiC increases linearly from 70% to 90% when the initial particle size decreases from 1.75?µm to 0.5?µm. Pure TiB₂ was densified up to 87%. Using 2.5?wt% SiC in TiB₂, the relative density increases to 97%. Young's modulus and the hardness of all samples were measured, with results discussed. The higher properties were obtained for additive-free TiB₂–5%SiC with a relative density of 97% and with the Young's modulus and Vickers hardness values being close to 378?GPa and 23?GPa, respectively.     

Spark plasma sintering of WC-Ti powder mixtures and properties of obtained composites

Three WC-Ti powder mixtures with 5, 10 and 15 wt% titanium were sintered by the spark plasma sintering technique. The microstructures and phase compositions of the samples were investigated by SEM, STEM, EBSD and XRD. The samples consisted of WC, W₂C and a (W_1-xT_x)C phases when the starting amounts of titanium were 5 and 10 wt%. At the titanium content of 15 wt% the microstructure of the samples included W₂C, (W_1-xT_x)C phases and elemental tungsten. The solubility of WC in TiC with the appearance of the (W_1-xT_x)C phase depended on the stoichiometry of the starting powder composition and sintering temperature. The results of EBSD phase mapping and the XRD investigation are in good agreement with the molar analysis. The best combination of hardness and fracture toughness was achieved with 5 wt% titanium. The appearance of elemental tungsten after sintering the WC-15Ti composition led to a significant reduction in hardness.     

Spark plasma sintering of Ti-diamond composites

Laser melting of Ti-diamond powders have been found to enhance the mechanical properties of technologically important material like titanium matrix composite (TMC). However, there is a tendency for the diamond to graphitise during the laser melting process. In order to overcome this fallacy, an alternate processing route, namely, spark plasma sintering (SPS) was adopted for fabricating the TMC's. A wide range of powder compositions varying from 5 to 50?wt percentage of diamond (0.25?μm) was added to titanium and the as-sintered compacts were investigated by X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscopy (EDAX). In-situ phase changes were observed with increase in diamond content in the composition. Addition of diamond upto 15% led to formation of a mixed Ti and TiC phase in the matrix. Interestingly there was no trace of metallic titanium with 20% diamond in the composition and a TiC-only phase was observed, corroborated by an abrupt increase in hardness to 1076 Hv. At even higher diamond percentages there was trace of unreacted carbon along with TiC. This work indicates, for the first time, the use of SPS as an alternate route for fabricating in-situ TMCs with enhanced mechanical properties.     

In-situ graphene platelets formation and its suppression during reactive spark plasma sintering of boron carbide/titanium diboride composites

Boron carbide composites with 10 vol.% TiB₂ were prepared by reactive sintering of B₄C, TiO₂, and carbon black powder mixture at the temperature of 1800 °C, under a pressure of 70 MPa in a vacuum. The combined effects of electric current and in-situ reactions led to a significant overheating of the central part of the sample, while no overheating was observed for hot press and non-reactive SPS processes. A lower electrical resistivity of TiB₂ produced a significant Joule heating of boron carbide, leading to its partial decomposition to form gaseous boron and graphene platelets. Homogenous, fully dense and graphene-free samples were obtained when employing an insulating Al₂O₃ paper during reactive SPS. A short dwell time (30 s after a degassing step of 6 min) and the uniform distribution of fine TiB₂ grains were the main advantages of isolated SPS over the reactive hot press and SPS processes, respectively.     

Spark plasma sintering of WC-based cermets/titanium and vanadium added composites: A comparative study on the microstructure and mechanical properties

In an attempt to develop the composition and properties of W₂C-(W,Ti)C-TiC and WC-WC_1-x-VC-V super hardmetals, spark plasma sintering (SPS) method was implemented. WC powders were mixed separately with 10?wt% Ti and 10?wt% V in a high energy mixer mill and sintering processes were performed at temperatures of 2150 and 2000?°C, respectively. XRD investigations revealed the formations of TiC and (Ti,W)C as the reaction products in WC-10?wt% Ti composite. Moreover, the interfacial reaction between WC and V led to the formation of WC1-x and VC compounds. A higher bending strength (613?±?25?MPa) and fracture toughness (4.1?±?0.58?MPa?m^1/2) were obtained for WC-10?wt% V samples compared to WC-10?wt% Ti, While the WC-10?wt% Ti composite showed a higher value of hardness (3128?±?42 Vickers) in comparison to WC-10?wt% V (2632?±?39 Vickers), which can act as a super hard cermet.     

Microstructure and properties of Al2O3-TiC-Ti3SiC2 composites fabricated by spark plasma sintering

Abstract

Abstract

Highly densified Al₂O₃-TiC-Ti₃SiC₂ composites were fabricated by spark plasma sintering technique and subsequently characterised. From fracture surface observation, it is found that Al₂O₃ is 0·2-0·4?μm, TiC is 1-1·5?μm and Ti₃SiC₂ is 1·5-5?μm in grain size. With the increase in Ti₃SiC₂ volume contents, Vickers hardness of the composites decreases because of the low hardness of monolithic Ti₃SiC₂. The fracture toughness rises remarkably when the contents of Ti₃SiC₂ increase, which is attributed to the pullout and microplastic deformation of Ti₃SiC₂ grains. At the same time, the flexural strength of the composites shows a considerable improvement as well. The electrical conductivity rises significantly as the Ti₃SiC₂ contents increase because of the formation of Ti₃SiC₂ network and the increase in conductive phase contents.     

Spark plasma sintering of TiN ceramics codoped with SiC and CNT

In this research, we investigated the effects of SiC and multi-walled carbon nanotube (MWCNTs) addition on the densification and microstructure of titanium nitride (TiN) ceramics. Four samples including monolithic TiN, TiN-5?wt% MWCNTs, TiN-20?vol% SiC and TiN-20?vol% SiC-5?wt% MWCNTs were prepared by spark plasma sintering at 1900?°C for 7?min under 40?MPa pressure. X-ray powder diffraction patterns and scanning electron microscope (SEM) micrographs of the prepared ceramics showed that no new phase was formed during the sintering process. The highest calculated relative density was related to the TiN ceramic doped with 20?vol% SiC, while the sample doped with 5?wt% MWCNTs presented the lowest density. In addition, the SEM investigations revealed that the addition of sintering aids e.g. SiC and MWCNTs leads to a finer microstructure ceramic. These additives generally remain within the spaces among the TiN particles and prohibit extensive grain growth in the fabricated ceramics.     

Microstructure and mechanical properties of spark plasma sintered TiB2 ceramics combined with a high-entropy alloy sintering aid

A high-entropy alloy (HEA), CoCrFeNiMn_0.5Ti_0.5, is used as a sintering aid for the densification of TiB₂ sintered by spark plasma sintering. The HEA content in the starting TiB₂-HEA mixture is varied from 0 to 10?wt-%. The microstructure and mechanical properties of the sintered samples are analysed and the optimum HEA content of 10% is found for the preparation of the TiB₂-HEA ceramics, allowing combining high mechanical properties (Vickers hardness of 2174.64?HV and flexural strength of 427.69?MPa) and high relative density of 99.1%.     

Effect of solid solution formation on densification of spark plasma sintered ZrC ceramics with TiC as sintering aid

The densification of ZrC ceramics doped with different contents of TiC prepared by spark plasma sintering at the temperatures between 1750 and 1850°C has been investigated. The microstructure and mechanical properties of the ceramics have been characterised. It was shown that TiC additions effectively promoted the densification process by forming (Zr,Ti)C solid solution. The relative densities and mechanical properties of ZrC samples increased with the increasing of TiC content or the sintering temperature. Ceramic with the content of TiC up to 10 vol.-% sintering at 1850°C showed an excellent combination of properties including a relative density of 98.7%, hardness of 20.8?GPa and flexural strength of 605?MPa.     

Preparation of mullite-TiB2-CNTs hybrid composite through spark plasma sintering

A near fully dense mullite-TiB₂-CNTs hybrid composite was prepared successfully trough spark plasma sintering. 1 wt%CNT and 10 wt%TiB₂ were mixed with nano-sized mullite powders using a high energy mixer mill. Spark plasma sintering was carried out at 1350 °C under the primary and final pressure of 10 MPa and 30 MPa, respectively. XRD results showed mullite and TiB₂ as dominant crystalline phases accompanied by tiny peaks of alumina. The microstructure of prepared composites demonstrated uniform distribution of TiB₂ reinforcements in mullite matrix without any pores and porosities as a result of near fully densified spark plasma sintered composite. The fracture surface of composite revealed a proper bonding of TiB₂ with mullite matrix and also areas with CNTs tunneling and superficies as a result of pulling-out phenomenon. The flexural strength of 531 ± 28 MPa, Vickers harness of 18.31 ± 0.3 GPa, and fracture toughness of 5.46 ± 0.12 MPa m^−1/2 were achieved for prepared composites as the measured mechanical properties.     

Spark plasma sintering of B4C and B4C-TiB2 composites: Deformation and failure mechanisms under quasistatic and dynamic loading

Spark plasma sintering (SPS) was employed to consolidate powder specimens consisting of B₄C and various B₄C-TiB₂ compositions. SPS allowed for consolidation of pure B₄C, B₄C-13 vol.%TiB₂, and B₄C-23 vol.%TiB₂ composites achieving ≥99 % theoretical density without sintering additives, residual phases (e.g., graphite), and excessive grain growth due to long sintering times. Electron and x-ray microscopies determined homogeneous microstructures along with excellent distribution of TiB₂ phase in both small and larger-scaled composites. An optimized B₄C-23 vol.%TiB₂ composite with a targeted low density of ～3.0 g/cm³ exhibited 30–35 % increased hardness, fracture toughness, and flexural bend strength compared to several commercial armor-grade ceramics, with the flexural strength being strain rate insensitive under quasistatic and dynamic loading. Mechanistic studies determined that the improvements are a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B₄C matrix in compression and TiB₂ phase in tension, and c) TiB₂ phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB₂ serves as a toughening and strengthening phase, and scaling of SPS samples show promise for the manufacture of ceramic composites for body armor.     

Ultra-high elevated temperature strength of TiB2-based ceramics consolidated by spark plasma sintering

Spark plasma sintering of TiB₂–boron ceramics using commercially available raw powders is reported. The B₄C phase developed during reaction-driven consolidation at 1900 °C. The newly formed grains were located at the grain junctions and the triple point of TiB₂ grains, forming a covalent and stiff skeleton of B₄C. The flexural strength of the TiB₂–10 wt.% boron ceramic composites reached 910 MPa at room temperature and 1105 MPa at 1600 °С. Which is the highest strength reported for non-oxide ceramics at 1600 °C. This was followed by a rapid decrease at 1800 °C to 480–620 MPa, which was confirmed by increased number of cavitated titanium diboride grains observed after flexural strength tests.     

Transmission electron microscopy characterization of spark plasma sintered ZrB2 ceramic

Microstructures of ZrB₂ ceramics consolidated by hot-pressing and spark plasma sintering were investigated by transmission electron microscopy (TEM), combining energy dispersive X-ray spectroscopy (EDX). The microstructures of both ceramics were compared. Amount of impurities was lower for ZrB₂ consolidated by spark plasma sintering than for hot-pressed ZrB₂. In particular, oxygen impurity was not detected even at the grain-boundaries in ZrB₂ consolidated by spark plasma sintering. The cleaning effect generated on the powder surfaces during spark plasma sintering cycle was displayed. In addition, dislocations were present only in the spark plasma sintered ZrB₂ ceramic, as a result of localized high stresses.     

Effect of LaB6 additions on densification,microstructure, and creep with oxide scale formation in ZrB2-SiC composites sintered by spark plasma sintering

A comparative study has been carried out on densification, microstructure, and creep with oxide-scale formation in ZrB₂-20 vol.% SiC-(7, 10 or 14 vol.%) LaB₆ composite containing B₄C and C as additives, and prepared by spark plasma sintering at 1800 °C under 70 MPa ram pressure. Addition of LaB₆ has promoted densification of composites by scavenging oxygen impurity, thereby increasing their hardness. Constant load compressive creep tests at 1300 °C under 47 and 78 MPa stresses have shown the lowest creep rate in the 10 vol.% LaB₆ composite. The stress exponents obtained for composites having 10 vol.% LaB₆ (～1.3 ± 0.1) and 14 vol.% LaB₆ (～2.6 ± 0.2) suggest respectively, grain boundary diffusion with intergranular glassy phase formation and dislocation glide as operating mechanisms. Intergranular cracking caused by grain boundary sliding appears as the damage mechanism. Oxide scales formed during creep exhibit greater thickness and defect concentration than those by isothermal exposure at 1300 °C within similar duration.     

Densification and toughening mechanisms in spark plasma sintered ZrB2-based composites with zirconium and graphite additives

The densification behavior and toughening mechanisms of ZrB₂-based composites with in-situ formed ZrC were investigated. The composites were spark plasma sintered at 1700 °C for 7 min under the applied pressure of 40 MPa. Metallic zirconium and graphite flakes were used as precursors to achieve ZrC reinforcement. Microstructural and phase analyses as well as mechanical characterizations were carried out on the near fully-dense composite samples. Results indicated ZrC as the only secondary phase in composite with 5 vol% of metallic Zr and graphite flakes. However, higher volume fractions of precursor materials led to the formation of ZrO₂ as the dominant secondary phase. Whereas decreasing trend of the hardness number versus volume fraction of the precursors was observed, the highest indentation fracture toughness was achieved in sample with 15 vol% metallic Zr/graphite flakes. Finally, the formation of secondary phases and their effects on densification, and mechanical behavior of the composites were discussed.     

Densification,microstructures, and mechanical properties of (Zr,Ti)(C,N) ceramics fabricated by spark plasma sintering

Dense (Zr, Ti) (C, N) ceramics were fabricated by spark plasma sintering (SPS) at 1900–2000 °C using ZrC, TiCN and ZrH₂ powders as raw materials. A single Zr-rich (Zr, Ti)(C, N) solid solution was formed in Zr_0.95Ti_0.05C_0.975N_0.025 and Zr_0.80Ti_0.20C_0.90N_0.10 ceramics (nominal composition). A Ti-rich solid solution appears in Zr_0.50Ti_0.50C_0.75N_0.25 ceramics. The coaddition of TiCN and ZrH₂ promoted the densification of (Zr, Ti) (C, N) ceramics by forming solid solutions and carbon vacancies, which could reduce critical resolved shear stress (CRSS) and promote carbon and metal atom diffusion. ZrC-45 mol% TiCN-10 mol% ZrH₂ (raw powder composition) possesses good comprehensive mechanical properties (Vickers hardness of 24.5 ± 0.9 GPa, flexural strength of 503 ± 51 MPa, and fracture toughness of 4.3 ± 0.2 MPa·m^1/2), which reach or exceed most ZrC-based (Zr, Ti) C and (Zr, Ti) (C, N) ceramics in previous reports.     

A novel ZrB2-based composite manufactured with Ti3AlC2 additive

A novel ZrB₂–Ti₃AlC₂ composite was densified using spark plasma sintering at 1900 °C under pressure of 30 MPa for 7 min. The effect of Ti₃AlC₂ MAX phase on the densification behavior, microstructural evolutions, phase arrangement, and mechanical properties of the composite were investigated. The phase analysis and microstructural studies revealed the decomposition of the MAX phase at the initial steps of the SPS process. The structural characteristics and surface morphology of the in-situ synthesized reinforcements were verified using X-ray diffraction and scanning electron microscopy, respectively. The formation mechanism of each reinforcement phase was also investigated using thermodynamical assessments. The prepared ZrB₂–Ti₃AlC₂ composite not only possessed a near fully-dense characteristic having an excellent hardness of 31 GPa, but also unexpectedly presented high fracture toughness. The indentation fracture toughness of the composite was calculated as 7.8 MPa m^1/2, which is unprecedented compared with the same class of hard ZrB₂-based composites. Indeed, the superior mechanical properties of the composite achieved in this study was obtained by the homogenous distribution of Al-based reinforcements, formation of hard interfacial ZrC grains, and solid solutions provided by Ti-based phases. The correlations between the phase arrangement, microstructure, and the attained mechanical properties of the composite were comprehensively discussed.     

Densification mechanism,microstructure and mechanical properties of ZrC ceramics prepared by high-pressure spark plasma sintering

The traditional way of densifying high-melting-point ceramics at high temperatures with long soaking time leads to severe grain coarsening, which degrades the mechanical properties of ceramics. Here, highly dense (∼98%) zirconium carbide (ZrC) ceramics with limited grain growth were obtained by spark plasma sintering (SPS) at relatively low temperatures, 1900 ℃, with a high pressure up to 200 MPa in a reliable carbon-fiber-reinforced carbon composite (C_f/C) mold. Subgrains and high-density dislocations formed in the high-pressure sintered ceramics. The hardness and fracture toughness of the prepared highly dense ZrC ceramics reached 20.53 GPa and 2.70 MPa·m^1/2, respectively. The densification mechanism was mainly plastic deformation under high pressure. In addition, ZrC ceramics sintered at high pressure possessed a high dislocation density of 7.30 × 10¹² m⁻², which was suggested to contribute to the high hardness.