B4C-SiC Composites Research Articles

Densification of additive-free B4C-SiC composites by spark plasma sintering

Densification of additive-free B4C-SiC composites by spark plasma sintering

B4C-SiC composites with tuneable mechanical properties: Role of Al2O3 - Y2O3 sintering additives

B4C-SiC composites with tuneable mechanical properties: Role of Al2O3 - Y2O3 sintering additives

Enhanced mechanical properties of nanocrystalline B4C–SiC composites by in-situ high pressure reactive sintering

Enhanced mechanical properties of nanocrystalline B4C–SiC composites by in-situ high pressure reactive sintering

Microstructure and mechanical properties of carbon-precursor-added B4C and B4C−SiC ceramics subjected to pressureless sintering

Microstructure and mechanical properties of carbon-precursor-added B4C and B4C−SiC ceramics subjected to pressureless sintering

Tribological behaviors of B4C–SiC composites self‐mated pairs in seawater and pure water

AbstractIn this paper, the tribological behaviors of B4C–SiC composites self‐mated pairs in seawater and pure water were investigated, respectively. The results showed that the B4C–SiC composite with the content of 20%SiC has good mechanical properties. For the B4C–20%SiC self‐mated pair in seawater, the abrasive wear is greatly weakened, and the tribo‐chemical reactions between the composite surface and water molecules occurred. The tribo‐chemical polishing causes very smooth wear surfaces, and the sliding pairs enter to the status of liquid lubrication. An extremely low friction coefficient (0.038) and wear rate (both below the order of magnitude 10−5 mm3/N m) were obtained in this study. Due to the lower viscosity of pure water, the load carrying capacity of the liquid film reduces. So, in pure water, the sliding pair shows slightly higher friction coefficient and wear rate than that in seawater.

Unlubricated sliding wear of B4C composites spark-plasma sintered with Si aids and of their reference B4C monoliths

Two fully-dense B4C–SiC composites were fabricated by spark-plasma sintering (SPS) from B4C+Si powders, one superhard (i.e., ~28.7(8) GPa) with abundant SiC by SPS of B4C+20vol.%Si at 1400°C and the other ultrahard (i.e., ~35.1(4) GPa) with little SiC by SPS of B4C+4.28vol.%Si at 1800°C, and their unlubricated sliding wear was investigated and compared with those of the reference B4C monoliths. It was found that the two B4C–SiC composites underwent mild tribo-oxidative wear with preferential removal of the oxide tribolayer, with the one SPS-ed at 1400°C from B4C+20vol.%Si being, despite its lower hardness and greater proneness to form oxide tribolayer, only slightly less wear resistant than the one SPS-ed at 1800°C from B4C+4.28vol.%Si (i.e., ~1.0(5)·107 vs 1.37(8)·107 (N·m)/mm³). The reference B4C monolith SPS-ed at 1400°C is comparatively two orders of magnitude less wear resistant (i.e., ~1.70(6)·105 (N·m)/mm³), attributable to its undergoing severe purely mechanical wear by microfracture-dominated three-body abrasion due to its very poor sintering (i.e., high porosity of ~33.5%), poor grain cohesion, and low hardness (i.e., ~3.1(5) GPa). The reference B4C monolith SPS-ed at 1800°C, while equally or less hard (i.e., 28.4(9) GPa) and slightly porous (i.e., ~5.3%), is somewhat more wear resistant (~1.8(3)·107 (N·m)/mm³) than the B4C–SiC composites, attributable to its undergoing only mild purely mechanical wear by plasticity-dominated two-body abrasion without porosity-induced grain pull-out, but it requires SPS temperatures well above 1400°C. Finally, relevant implications for the ceramics and hard-materials communities with interests in tribological applications are discussed.

Improving fracture toughness of B4C – SiC composites by TiB2 addition

B 4 C-SiC composites can be used in many areas due to their superior properties. However, in order to be used as a body armor material in areas requiring high performance, their fracture toughness needs a degree of improvement. In this study, 0–20 wt% TiB 2 was added to B 4 C-SiC samples that were consolidated at 1950 °C by spark plasma sintering method. The contribution of TiB 2 to the microstructure, elastic and mechanical properties of B 4 C-SiC composites were investigated. The highest hardness was measured to be 29.5 GPa with 15 wt%TiB 2 addition. The highest fracture toughness was 3.08 MPa.m 1/2 found at sample made with 10 wt% TiB 2 . Addition of 10 wt% TiB 2 increased the fracture toughness by 28%, with only a 5% decrease in relative density. In addition, the fracture mode of B 4 C-SiC-TiB 2 composites is intergranular due to the addition of TiB 2 . • 0–20 wt% TiB2 added to B4C-SiC composites and evaluated the microstructure, elastic and mechanical properties. • 29.5 GPa hardness was obtained with the addition of 15 wt%TiB2. • The fracture toughness increased by 28% with the addition of 10 wt% TiB2 when compared samples without TiB2 addition.

Microstructure and mechanical properties of reaction-bonded B4C-SiC composites

Microstructure and mechanical properties of reaction-bonded B4C-SiC composites

Effect of Co addition on microstructural and mechanical properties of WC–B4C–SiC composites

In this study, the effect of Co addition on microstructural and mechanical properties of WC-B 4 C–SiC composites sintered by spark plasma sintering (SPS) method was investigated. For this purpose, three batches of WC-B 4 C–SiC with different contents of Co (10 vol%, 15 vol%, and 20 Vol %) were sintered at 1400 °C. The results of X-ray diffraction (XRD) analysis of the samples indicated the formation of W 2 B 5 , W 3 CoB 3 as well as the remained C phases and unreacted SiC phase. It was observed that by increasing the Co content, the amount of W 2 B 5 phase reduces and W 3 CoB 3 and C contents increase. Therefore, W 2 B 5 peaks were not detected in the sample containing 20vol% Co. Relative density values above 97% were obtained for all the composites. However, a decrease was observed in relative density by increasing the Co content in the composites. The highest flexural strength (510 ± 42 MPa), fracture toughness (10.34 ± 0.82 MPa m 1/2 ), and hardness (20.63 ± 0.75 GPa) were also obtained for the sample containing 10vol% Co compared to the other samples. In addition, Transgranular fracture of SiC as well as pulling out of W 3 CoB 3 and W 2 B 5 particles were observed in the fracture surface micrographs of the samples. The presence of micro-cracks in the SiC grains, fracture of W 3 CoB 3 grains, and crack deflection was reported as dominant toughening mechanisms.

Evaluating the role of uniformity on the properties of B4C–SiC composites

Fully dense boron carbide-silicon carbide composites were successfully produced by spark plasma sintering method at 1950 °C under 50 MPa applied pressure. The effect of dry and wet mixing methods on uniformity was observed. Density, elastic modulus, microstructure, Vickers hardness and fracture toughness were evaluated. The results showed that dry mixing did not provide uniformity on composites properties. On the other hand wet mixing provided uniformity in microstructure and consistency in material properties. The hardness of the sample containing 50 wt% B4C was measured to be 30.34 GPa hardness value was found at 50 wt% B4C content sample. The increase in the B4C content of the composites decreased the Young's modulus, shear modulus, bulk modulus and fracture toughness. The highest values were found at 10 wt% B4C sample which were 415 GPa (E), 177 GPa (G), 209 GPa (K), and 2.89 MPa m1/2 fracture toughness (KIc).

Mechanical properties of B4C–SiC composites fabricated by hot-press sintering

Abstract We fabricated boron carbide-silicon carbide (B4C–SiC) composites by hot-press sintering without additives and evaluated the crystal phase, relative density, microstructure, and mechanical properties of the sintered body. When B4C and SiC were uniformly dispersed in the composite, crystal growth was inhibited, and a sintered body with a fine and uniform microstructure, with improved mechanical properties, was fabricated. The relative density of B4C–SiC composites sintered at temperatures lower than 2000 °C and 40 MPa of pressure exceeded 99.8%, and the bending strength and Vickers hardness at B4C 50 wt% were 645 MPa and 30.6 GPa, respectively.

Sintering and sliding wear studies of B4C-SiC composites

Dense boron carbide (B 4 C) – silicon carbide (SiC) composites were obtained by spark plasma sintering technique at 1800°C with 3 wt% and 6 wt% aluminium oxide (Al 2 O 3 ) additives. Addition of sintering additives results in formation of aluminium silicate (Al 2 SiO 5 ) liquid phase which accelerates sintering kinetics and helps in obtaining high density ~ 99%. Microstructures reveal uniformly distributed SiC particles in B 4 C matrix. Increase in alumina from 3 wt% to 6 wt% results in decrease in hardness from 35.1 ± 0.8 to 33.7 ± 0.9 GPa, and increase in fracture toughness from 5.9 ± 0.4 to 6.5 ± 0.4 MPam 0.5. Using a ball-on-disk tribo tester under dry unlubricated conditions at 5, 10 or 15 N load, influence of alumina content on friction and wear properties of B 4 C-SiC composites was investigated against SiC counterbody with a linear speed of 0.08 m/s for 60 min. The coefficient of friction (COF) increased from 0.25 to 0.65 with load, and the influence of alumina on frictional behaviour appeared to be negligible. With increase in load, wear volume of the composites increased from 7.5 × 10 −2 mm 3 to 16.1 × 10 −2 mm 3 for B 4 C-10 wt% SiC - 3 wt% Al 2 O 3 and from 4.7 × 10 −2 mm 3 to 14.8 × 10 −2 mm 3 for B 4 C-10 wt% SiC - 6 wt% Al 2 O 3 composites. Microcracking, abrasion and pull-outs contributed as major wear mechanisms of composites in selected wear conditions. The relation between wear behaviour and mechanical properties of sintered composites is discussed. • B 4 C-10 wt% SiC-3 wt% Al 2 O 3 and B 4 C-10 wt% SiC-6 wt% Al 2 O 3 composites prepared by spark plasma sintering. • Hardness of the composites decreased and fracture toughness increased with increase in alumina content. • In sliding against SiC ball, the average COF and wear volume increased with increase in load. • Microcracking, abrasion and pull-outs were major wear mechanisms.

Fabrication of dense B4C-preceramic polymer derived SiC composite

Abstract B4C-SiC composites were fabricated via the preceramic polymer (PCP) route combined with pressure-assisted sintering. Fully dense bodies were achieved by controlling surface oxide on B4C powder and pyrolysis conditions for PCP coated powder. We elucidate i) the microstructure and phase developments observed in the process of fabricating dense B4C-PCP derived SiC composites and ii) the mechanical properties and crack deflection behavior of dense bodies. The incorporation of PCP derived SiC to B4C decreases hardness due to the lower hardness value of SiC compared to B4C and the residual carbon accompanied by SiC formation. Instead, the PCP derived SiC improved indentation fracture toughness. The main toughening mechanism supposed is a combination of crack impeding by SiC grains and crack deflection within SiC grains, likely due to the presence of subgrains or layered microstructure in the PCP derived SiC grains.

Microstructure and mechanical properties of reaction bonded B4C-SiC composites: The effect of polycarbosilane addition

Abstract Reaction bonded B 4 C-SiC composites were prepared by infiltrating silicon melt into porous B 4 C-SiC green preforms at 1500 °C in vacuum. The porous green preform was obtained from a mixture of polycarbosilane (PCS) and particle size graded B 4 C after pre-sintering at 1600 °C. For the first time, PCS was used to adjust the phase composition and microstructure of the reaction bonded boron carbide composites. It is indicated that the addition of PCS and its content has a significant influence on the microstructure as well as the mechanical properties of the subsequent reaction bonded B 4 C-SiC composites. For the B 4 C-SiC composite with 5 wt% PCS added, a flexural strength of 319±12 MPa, and an elastic modulus of 402±18 GPa can be achieved, which is 23% and 15% higher than those of the composite without PCS addition, respectively. While, with the higher content of PCS addition, the mechanical properties of the composites are decreased drastically due to the large amount of residual Si agglomeration in the composites. The reaction mechanisms as well as their microstructure evolution processes correlated with the mechanical properties of the reaction bonded B 4 C-SiC composites are further discussed in our work.

Densification behaviour and mechanical properties of B4C–SiC intergranular/intragranular nanocomposites fabricated through spark plasma sintering assisted by mechanochemistry

Abstract High-performance B 4 C–SiC nanocomposites with intergranular/intragranular structure were fabricated through spark plasma sintering assisted by mechanochemistry with B 4 C, Si and graphite powders as raw materials. Given their unique densification behaviour, two sudden shrinkages in the densification curve were observed at two very narrow temperature ranges (1000–1040 °C and 1600–1700 °C). The first sudden shrinkage was attributed to the volume change in SiC resulting from disorder–order transformation of the SiC crystal structure. The other sudden shrinkage was attributed to the accelerated densification rate resulting from the disorder–order transformation of the crystal structure. The high sintering activity of the synthesised powders could be utilised sufficiently because of the high heating rate, so dense B 4 C–SiC nanocomposites were obtained at 1700 °C. In addition, the combination of high heating rate and the disordered feature of the synthesised powders prompted the formation of intergranular/intragranular structure (some SiC particles were homogeneously dispersed amongst B 4 C grains and some nanosized B 4 C and SiC particles were embedded into B 4 C grains), which could effectively improve the fracture toughness of the composites. The relative density, Vickers hardness and fracture toughness of the samples sintered at 1800 °C reached 99.2±0.4%, 35.8±0.9 GPa and 6.8±0.2 MPa m 1/2 , respectively. Spark plasma sintering assisted by mechanochemistry is a superior and reasonable route for preparing B 4 C–SiC composites.

Effects of silicon addition on the microstructure and properties of B4C–SiC composite prepared with polycarbosilane-coated B4C powder

Abstract Dense, fine grained B 4 C–SiC composites were successfully fabricated with the hot-pressing pyrolyzed mixtures of polycarbosilane-coated B 4 C powder and the Si additive at 1950 °C for 1 h under 30 MPa. The addition of Si not only improved the densification process due to the formation of liquid phase Si, but also greatly enhanced the mechanical properties of B 4 C ceramics. However, the added Si showed no significant effect on fracture toughness. The improvement in mechanical properties was attributed to the decrease of porosity and the elimination of free carbon derived from polycarbosilane and B 4 C powder. The introduction of Si improved the microstructure homogeneity and further refined the layer structure of in-situ SiC grains. The flexural strength, Vickers hardness, and fracture toughness of the sample prepared with 11.4 wt% Si, respectively, reached 389 MPa, 33.2 GPa, and 5.64 MPa m 1/2 .

Investigation on the Behaviours of TiB2 Reinforced B4C-SiC Composites Against Co-60 Gamma Radioisotope Source

In the present study, the gamma attenuation behaviours of the Titanium diboride (TiB2) reinforced boron carbide (B4C)-silicon carbide (SiC) composite materials were investigated against Co-60 gamma radioisotope source. In the experiments TiB2 unreinforced and 2% and 4% TiB2 (by volume) reinforced B4C-SiC composite materials were used. In the composite materials B4C/SiC ratio has been realized as 6/4 by volume. The linear and mass attenuation coefficients of the samples were carried out for Co60 gamma radioisotope source which has two energy peaks (1.17 and 1.33 MeV). Then mass attenuation coefficients and half-value thicknesses (HVT) of the materials were calculated. Experimental mass attenuation coefficients were compared with the theoretical values which were calculated from XCOM computer code. Furthermore HVTs of the samples were evaluated and compared each other. It has been seen that the experimental and theoretical mass attenuation coefficients are closed to each other and differences are under 10 percent. In addition, TiB2 reinforced B4C-SiC composites have smaller HVTs than unreinforced one. Moreover 4% TiB2 reinforced B4C-SiC composite has smaller HVT than the 2% reinforced sample. Reinforcing TiB2 and increasing TiB2 ratio increase the gamma attenuation property of the B4C-SiC composites against Co-60 gamma radioisotope source.

Microstructure and properties of B4C-SiC composites prepared by polycarbosilane-coating/B4C powder route

Abstract B4C-SiC composites with fine grains were fabricated with hot-pressing pyrolyzed mixtures of polycarbosilane-coated B4C powder without or with the addition of Si at 1950 °C for 1 h under the pressure of 30 MPa. SiC derived from PCS promoted the densification of B4C effectively and enhanced the fracture toughness of the composites. The sinterability and mechanical properties of the composites could be further improved by the addition of Si due to the formation of liquid Si and the elimination of free carbon during sintering. The relative density, Vickers hardness and fracture toughness of the composites prepared with PCS and 8 wt% Si reached 99.1%, 33.5 GPa, and 5.57 MPa m1/2, respectively. A number of layered structures and dislocations were observed in the B4C-SiC composites. The complicated microstructure and crack bridging by homogeneously dispersed SiC grains as well as crack deflection by SiC nanoparticles may be responsible for the improvement in toughness.

Preparation of B4C–SiC composite ceramics through hot pressing assisted by mechanical alloying

Abstract In order to prepare dense B4C–SiC composites under relatively low temperature without any additive, stacking disordered B4C–SiC ultrafine composite powders were fabricated by mechanical alloying firstly. Subsequently, hot pressing sintering was applied to produce a dense B4C–SiC composite under relatively low temperature (1800–1950 °C) without any additive. For the samples sintered at 1950 °C for 30 min, the obtained relative density, Vickers hardness, flexural strength and fracture toughness were 96%, 24 GPa, 430 MPa, and 4.6 MPa.m1/2, respectively. The microstructural characterization showed that the main fracture mode was transgranular. The transgranular facture is caused by the powerful interfacial bonding between B4C and SiC. The density of the samples sintered with composite powders was 13% higher than the density of the samples sintered with mixed powders under the same conditions, indicating that the composite powders had an improved sintering activity due to their disordered structure. Meanwhile, the role of disorder–order transformation-driven sintering of ceramics was demonstrated.

Sintering of B<sub>4</sub>C-SiC Composites with ALN-Y<sub>2</sub>O<sub>3</sub> Addition

One suitable material candidate to improve B4C mechanical properties is SiC. B4C-SiC ceramic composites are very promising armor materials because B4C and SiC are intrinsically very hard. In this work a pressureless sintering study of B4C-SiC ceramics was made. B4C-SiC mixtures were prepared with SiC concentration from 10 to 50 wt%. Without the external applied pressure during sintering it was necessary to add sintering aid. The additive system AlN-Y2O3 was investigated as sintering aid. Samples were densified by pressureless sintering at 2000 °C/30 min in an argon atmosphere. B4C-SiC composites were analyzed by XRD and SEM. Bulk density and total weight loss were also measured. Density higher than 93 % of the theoretical value was determined and microhardness of 30.3 GPa was achieved for composite with 10 wt% of SiC sintered with AlN-Y2O3 additive.