Sintering and sliding wear studies of B4C-SiC composites

doi:10.1016/j.ijrmhm.2019.105124

International Journal of Refractory Metals and Hard Materials

Volume 87, February 2020, 105124

$International Journal of Refractory Metals and Hard Materials$

https://doi.org/10.1016/j.ijrmhm.2019.105124 Get rights and content

Highlights

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B₄C-10 wt% SiC-3 wt% Al₂O₃ and B₄C-10 wt% SiC-6 wt% Al₂O₃ composites prepared by spark plasma sintering.
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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.
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Microcracking, abrasion and pull-outs were major wear mechanisms.

Abstract

Dense boron carbide (B₄C) – silicon carbide (SiC) composites were obtained by spark plasma sintering technique at 1800°C with 3 wt% and 6 wt% aluminium oxide (Al₂O₃) additives. Addition of sintering additives results in formation of aluminium silicate (Al₂SiO₅) liquid phase which accelerates sintering kinetics and helps in obtaining high density ~ 99%. Microstructures reveal uniformly distributed SiC particles in B₄C 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 B₄C-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 mm³ to 16.1 × 10⁻² mm³ for B₄C-10 wt% SiC - 3 wt% Al₂O₃ and from 4.7 × 10⁻² mm³ to 14.8 × 10⁻² mm³ for B₄C-10 wt% SiC - 6 wt% Al₂O₃ 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.

Introduction

Design and development of high melting point ultra-hard materials is the most challenging task in processing and applications of ceramics. Boron carbide (B₄C) is an attractive structural material due to the combination of its superior properties like high hardness, low density, high melting point (∼2540 °C), good chemical stability, high elastic modulus, high wear resistance. Such outstanding properties are required for the applications in the armour ceramics, sand blasting nozzles, neutron absorber, lapping agent, polishing of high-speed steel and carbide tool tips etc. [1,2]. The major limitation in the development of wide range of applications of boron carbide is its low sinterability and fracture toughness. Low self-diffusion coefficient demands high temperature for sintering of B₄C powder to high density, while strong covalent bonding and lack of slip systems lead to high brittleness for the sintered B₄C ceramics. Small amount of additives such as TiB₂, CrB₂, Al₂O₃, Y₂O₃, ZrO_2, Fe₃Al etc. are effective in improving the sintering kinetics and enhancing the mechanical properties of B₄C [[3], [4], [5], [6], [7], [8], [9]]. Liquid phase formed with the additives facilitate sintering and is also responsible for increasing fracture toughness by changing the mode of fracture from transgranular to intergranular or combination [[7], [8], [9], [10], [11]]. Spark plasma sintering (SPS) has proved its ability for sintering boron carbide to high density at low temperatures, short dwell time and high heating rate than conventional sintering [[12], [13], [14], [15], [16], [17]]. Improved fracture toughness with high hardness and strength can only be achieved with a suitable combination of SPS processing parameters and additives [13]. In this regard, silicon carbide (SiC) is considered as an additive to improve sinterability as well as fracture toughness with less compromise on other mechanical properties of B₄C. Malmal et al. [18] sintered B₄C with 15 wt% SiC additive by SPS at 1700 °C and obtained a fracture toughness 5.7 MPa.m^0.5 and hardness of 36.2 GPa. Filiz et al. [19] observed that the addition of yttria (Y₂O₃) improves densification of B₄C-SiC composites by SPS. Further densification of B₄C-SiC is possible by adding small amount of low melting point additives like alumina (Al₂O₃).

Increasing demand of boron carbide for wear resistant applications requires systematic investigation of its performance under different tribological mating conditions. Results acquired from the literature on friction and wear of boron carbide in different sliding wear conditions are outlined as follows:

(1)
Dense monolithic B₄C ceramics were investigated in a various reciprocative sliding wear conditions against WC-Co cemented balls by Sonber et al. [20]. It is reported that the wear rate varied from 1.6 × 10⁻⁶ to 4.7 × 10⁻⁶ mm³/Nm and the coefficient of friction (COF) varied from 0.1 to 0.2. Also, abrasive and tribochemical wear mechanisms were not observed on the worn surface.
(2)
In a sliding wear study against chrome steel ball, Moshtaghioun et al. [21] observed lower wear rate for fully dense, coarse grained and harder B₄C ceramics compared to higher wear rate of for 94.7% dense and fine grained and less harder B₄C ceramics.
(3)
In other study Zorzi et al. [22] reported B₄C ceramics prepared with 4 wt% TiB₂ additive showed 95.5% density and a minimum wear rate of 2.2 × 10⁻⁵ mm³/Nm.
(4)
Sedlak et al. [23] reported wear rate decreased from 5 × 10⁻⁵ to 2.5 × 10⁻⁵ mm³/Nm with increase in graphene platelets content from 0 to 6 wt%. The COF varied from 0.34 to 0.58 with changing load from 5 to 50 N.
(5)
In a sliding test on B₄C ceramics at different temperatures ranging between 20 °C to 600 °C Lin et al. [24] observed reduced friction and wear with the addition of CNT. The COF and wear rate fluctuated from 0.2 to 0.8 and 5 × 10⁻⁸ g/Nm to 50 × 10⁻⁸ g/Nm, respectively.
(6)
Ortiz et al. [25] sintered B₄C ceramics to 95% density and studied wear behavior under lubrication with water, diesel and paraffine oil. Sliding wear rate was higher with water (8.6 × 10⁻⁷ mm³/Nm) than with diesel (6.0 × 10⁻⁸ mm³/Nm) and paraffin oil (2.9 × 10⁻⁸ mm³/Nm).

From available studies, it is clear that the additives and lubrication helps in reducing wear but it is difficult to compare the scattered results in wear or friction due to differences in material processing, microstructural and mechanical characteristics as well as sliding test parameters. Furthermore, the influence of sintering additives on wear behavior of highly dense (≥96%) B₄C ceramics is rarely reported.

In the present study, the powder mixtures of B₄C-10 wt% SiC-X Al₂O₃ (X: 3 wt% or 6 wt%) composites were sintered to high density (~99%), and tribological behaviour of sintered B₄C-SiC composites in dry sliding wear conditions against SiC ceramics was studied. Alumina content and sliding loads were varied in this study, to observe their effects on sliding wear behaviour.

Section snippets

Materials and characterization

Powder mixture batches of B₄C, 10 wt% SiC and 3 wt% Al₂O₃ (designated as BSA3), and B₄C, 10 wt% SiC and 6 wt% Al₂O₃ (designated as BSA6) were respectively mixed in a polypropylene jar using WC balls in toluene for 24 h. X-ray diffraction (XRD, D8 Discover, Brukeer AXS GmbH, Germany), was used to study phase analysis of powder mixtures. Both the mixtures were dried, sieved and then sintered at 1800 °C with heating rate of 150 °C/min for 10 min by spark plasma sintering (Dr. Sinter, SPS-625, Fuji

Phase analysis and microstructure

Fig. 1 shows Z-axis displacement vs. temperature plot for sintering of BSA3. Displacement curve shows real-time shrinkage profile of the powder mixture during densification of the sample. Shrinkage occurred when temperature reached to 1500 °C, while sharp elevation is attributed to the generation of liquid phase aluminium silicate (Al₂SiO₅). In SiC-Al₂O₃ system, liquid phase of Al₂SiO₅ is known to form at 1600 °C (Eq. (4)). $A l_{2} O_{3} + {SiO}_{2} \to {Al}_{2} {SiO}_{5}$

The liquid phase fills the pores, decreases

Conclusions

High density (~99%) B₄C-10 wt% SiC-3 wt% Al₂O₃ and B₄C-10 wt% SiC-6 wt% Al₂O₃ were successfully sintered by spark plasma sintering. The phase evolution, microstructural features and mechanical properties were studied. Effect of alumina content on friction and wear of B₄C-SiC composites in sliding contacts against commercially available counterbody of SiC balls at 5 N, 10 N and 15 N loads, was investigated using a ball on disk tribotester. The following are major conclusions:

a)
Alumina additive

Declaration of Competing Interest

Authors declare that they have no conflict of interest.

This work has no involvement of the funding sources/agencies from the public, commercial and non-profit sections. There is no involvement of peer human resource other than mentioned, as well.

Acknowledgement

B₄C powder received from Materials Processing & Corrosion Engineering Division, BARC, Mumbai, India.

Sonali Jamale is currently pursuing her Ph.D. degree from Indian Institute of Technology (IIT) Roorkee. She obtained her master degree in nanotechnology from National Institute of Technology (NIT) Calicut in 2014. She received her bachelor's in mechanical engineering from S.R.T.M University Nanded. She works in understanding mechanical and tribological behaviour of ceramics.

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B. V. Manoj Kumar is currently working as Associate Professor at the Department of Metallurgical and Materials Engineering, Indian Institute of Technology (IIT) Roorkee. Dr. Manoj works in understanding the microstructure mechanical property-wear relation of important ceramics/cermets and composites prepared using advanced sintering techniques.

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Sintering and sliding wear studies of B4C-SiC composites

Highlights

Abstract

Introduction

Section snippets

Materials and characterization

Phase analysis and microstructure

Conclusions

Declaration of Competing Interest

Acknowledgement

J. Nucl. Mater.

Ceram. Int.

Ceram. Int.

Ceram. Int.

J. Eur. Ceram. Soc.

Scripta Material

Ceram. Int.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Ceram. Int.

J. Refract. Met. Hard Mater.

J All Comp

Ceram. Int.

J. Eur. Ceram. Soc.

Sintering and sliding wear studies of B₄C-SiC composites