Development of B4C Nanostructured Ceramics

Oleg Khasanov, Edgar Dvilis, Alexey Khasanov, Artem Kachaev, Zulfa Bikbaeva, Valentina Polisadova and Tamara Milovanova

TPU Nano-Centre, National Research Tomsk Polytechnic University, Tomsk, Russia khasanov@tpu.ru

Abstract—The B4C ceramic samples have been manufactured by SPS method using mixed micrometric and nano-scaled powder. The microstructure, density, microhardness, fracture toughness of sintered ceramics have been investigated. The optimal processing modes have been determined.

Keywords - nano-scaled powder, spark plasma sintering, B4Cceramics, manufacturing modes

I. INTRODUCTION

One of the promising method to improve the properties of advanced ceramics is making addition of superfine (nano-scaled, submicron) powder to a matrix of the micron-scaled powder.

The work goals were investigation of the properties of carbide ceramics produced by spark plasma sintering (SPS) method from nano-scaled (submicron) B4C powder mixed with micron-scaled B4C powder and determination of the optimal processing modes to manufacture high dense ceramics from mixed powders.

II. EXPERIMENTS

A. Preparation of mixed powder The pulverizing the commercial micron-scaled B4C powder

(М-5-P grade, GOST 3647-80) to obtain the powder with nano-scaled (submicron) particles was carried out by the pneumatic circulating installation [1].

The mean particle sizes measured by the scanning electron microscope JSM-7500FA JEOL were d50 = 4.7 microns for the initial commercial B4C powder and d50 = 0.88 microns (with d10 = 100 nm) for pulverized one (Figs. 1, 2). The specific surface SBET has been measured by the BET technique using “Sorbi-M” device: SBET = 0.99 m2/g for the initial commercial powder and SBET = 27.91 m2/g for pulverized one. XRD analysis (XRD-7000 Shimadzu) did not show impurities or additional phases in the pulverized submicron powder.

The homogeneous mixture of commercial powder (90wt%) and pulverized one (10wt%) was obtained using МТ-2 mixer (Fig. 3).

B. Sintering of ceramics Sintering of B4C ceramics from the commercial powder as

well as from the mixed powder was implemented by the SPS method using installation S515 (SPS SYNTEX INC.). The

sintered samples were pellets with diameter of 14 mm and thickness of about 3 mm.

The sintering temperature Ts and pressure P were varied in the range from 1850oC up to 1950oC and from 30 MPa up to 90 MPa correspondingly.

The SEM- images of microstructure of ceramics sintered from different powders (C- from commercial powder; M –from mixed one) are shown in Figs. 4, 5, 6.

Figure 1. SEM-image of the initial commercial B4C powder

Figure 2. SEM-image of the pulverized nano-scaled B4C powder

The work was supported by the Russian Ministry of Education and Science (contract №13.G25.31.0021; State assignment "Science").

978-1-4673-1773-3/12/$31.00 ©2013 IEEE

Figure 3. SEM-image of the mixed commercial and pulverized powder

Figure 4. The spall surface of C-ceramics (Ts = 1950oC ; P = 30 MPa)

Figure 5. The spall surface of M-ceramics (Ts = 1950oC ; P = 90 MPa); x2,000

Figure 6. The spall surface of M-ceramics (Ts = 1950oC ; P = 90 MPa); x3,000

C. Properties of sintered ceramics The density ρ has been determined by the weighing

technique using precision digital balance VLTE-150 and digital micrometer Mitutoyo ID-F150. The microhardness HV and fracture toughness K1c. have been measured by the method of indentation of Vickers pyramid using microhardness tester PMT 3M LOMO.

The results of measurements for ceramics sintered from the commercial powder (C) and from the mixed one (M) are presented in Table 1.

TABLE I. THE PROPERTIES OF SINTERED B4C CERAMICS

Ts, oC

P, MPa

HV, GPa

KIc, MPa*m1/2 ρrel, %

C M C M C M

1850

30 7.4 23.8 8.1 9.2 72 86

60 12.2 22.5 7.6 7.6 79 89

90 24.8 24.8 8.9 7.3 80 95

1950

30 17.2 32.5 4.4 4.4 98 97

60 22.3 35.6 6.7 6.5 99 99

90 32.9 42.7 9.9 9.5 98 98

III. DISCUSSION Abnormal high values of the microhardness (Hv=42.7 GPа)

in B4C ceramics sintered from the mixed powder and high density (98%) were obtained at SPS modes Ts = 1950°С; P = 90 МPа. In these samples the mean value of fracture toughness was К1с = 9.5 МPа*m1/2, that exceeds the values of К1с = 3.5…4.0 МPа*m1/2 in ceramics without submicron additives and produced by the method of hot pressing [2]. SEM-analysis of spall images has shown that B4C ceramics from the mixed powder sintered by SPS method under

optimum processing modes allows to produce the dense samples with perfect grain structure and qualitative intergrain boundaries.

IV. CONCLUSIONS 1) The largest density, microhardness, fracture toughness of

B4C ceramics from mixed commercial micrometric powder (90wt%) and nano-scaled one (10wt%) have been achieved by SPS at Ts = 1950oC and P = 90 MPa.

2) The high density (98%) with the combination of high microhardness (42.7 GPa) and fracture toughness (9.5 MPa*m1/2) have been achieved for В4С ceramics sintered from the mixed micrometric and nano-scaled powder.

3) Pulverizing the commercial В4С micrometric powder using the pneumatic circulating apparatus does not contaminate the powder.

ACKNOWLEDGMENT Authors thank Dr. Yury Biryukov (Tomsk State University)

for powder pulverizing and Ph.D. Serge Fomin (Tomsk Polytechnic University) for useful comments.

REFERENCES [1] N. N. Belov, Yu. A. Biryukov, A. T. Roslyak, N. T. Yugov, and S. A.

Afanas’eva, “Mechanism of the Crushing of Particles for Production of Submicron Powders of Refractory Compounds in a Pneumatic Circulation Apparatus”, Doklady Physics, vol. 49, No. 7, p.p. 436-440, February 2004.

[2] A. P. Garshin, V. M. Gropjanov, G. P. Zaitsev, and S. S. Semenov, Ceramics for mechanical engineering. Moscow: Nauchtekhlitizdat, 2003, 384 p. / Keramika dlya mashinostroeniya. Moskva: Nauchtekhlitizdat, 2003, 384 p. (in Russian).