Elsevier

Ceramics International

Volume 42, Issue 9, July 2016, Pages 11486-11489
Ceramics International

Short communication
Improvement of densification and mechanical properties of Al2O3–B4C ceramics

https://doi.org/10.1016/j.ceramint.2016.04.025Get rights and content

Abstract

Al2O3–B4C ceramics had poor densification, due to the formation of Al18B4O33 phase by reaction between Al2O3 and B2O3 on the surface of B4C. In the present work, Y2O3 or Ti additive together with ZrO2 from milling media were introduced into Al2O3–B4C ceramics. Results showed that Y2O3 reacted with B2O3 to produce YBO3 phase, and removed Al18B4O33 phase, resulting in the improved densification and the coarse microstructure. However, Ti and ZrO2 reacted with B2O3 to produce hard TiB2 and ZrB2 phases, removed the most of Al18B4O33 phase, refined microstructure by pinning effect of hard particles, and improved densification and mechanical properties.

Introduction

Al2O3 has been widely used for various applications, due to the unique combination of strength, hardness, thermal stability, and corrosion resistance [1], [2]. B4C has promising properties of low density, high hardness, and good wear resistance [3]. The addition of B4C as second phase into monolithic Al2O3 inhibited the grain growth by grain-boundary pinning effect, increased the hardness and fracture toughness, and improved cutting performance [2], [4], [5], [6]. Therefore, Al2O3–B4C ceramics would be especially promising for cutting tools and wear resistant materials [4].

On the other hand, B4C suppressed the sinterability of Al2O3 [7]. Al18B4O33 phase could be formed by the reaction between Al2O3 and B2O3 [8]:9Al2O3+2B2O3Al18B4O33

Due to the inevitable existence of surface oxide (B2O3) in the B4C powders, the secondary Al18B4O33 phase formed by Reaction (1) could be detected in the sintered Al2O3–B4C ceramics [1], [9], [10]. Previous studies have confirmed that the secondary Al18B4O33 phase inhibited the densification and decreased mechanical properties [1], [10], [11]. So, the removal of secondary Al18B4O33 phase would be expected to enhance the properties of Al2O3–B4C ceramics.

Previous study has shown that Ti additive could improve the densification of B4C ceramics, and lead to the formation of TiB2 which acted as very efficient B4C grain-growth inhibitors [12]. It were reported that Y2O3 could improve the densification of B4C ceramics [13]. In addition, Y2O3 could reduce the grain growth of Al2O3 ceramics [14]. Therefore, it would be possible that Ti or Y2O3 additive could enhance the sinterability of Al2O3–B4C ceramics and inhibit its grain growth.

In the present work, the effects of Y2O3 or Ti additive together with ZrO2 coming from milling media on phase composition, densification, microstructures, and mechanical properties of Al2O3–B4C ceramics were investigated. The aim of present work was to inhibit the formation of Al18B4O33 phase, and further improve the densification and properties of Al2O3–B4C ceramics.

Section snippets

Experimental procedure

Raw materials were available α-Al2O3 (TM-DAR, particle size of 0.2 μm, purity of 99.99%, Taimei Chemicals Co., Nagano, Japan), B4C (particle size of 2.5 μm, purity of 99.9%, Aladdin Co., Shanghai, China), Y2O3 (particle size of 1 μm, purity of 99.5%, Aladdin Co., Shanghai, China), and Ti powders (particle size of 1 μm, purity of 99.5%, Aladdin Co., Shanghai, China). The Al2O3–15 wt% B4C containing 0 wt%, 5 wt% Y2O3 and 5 wt% Ti were named as AB15, AB15Y5, and AB15T5, respectively, as shown in Table 1.

Results and discussion

Fig. 1 presents the XRD patterns of hot-pressed AB15, AB15Y5, and AB15T5 ceramics, as well as milled AB15 powders. Only Al2O3 as main phase and B4C as secondary phase were observed in the milled AB15 powders. Table 2 summarizes the results of XRD phase identification of hot-pressed AB15, AB15Y5, and AB15T5 ceramics. In all hot-pressed ceramics, minor ZrB2 phase was detected, in addition to Al2O3 and B4C phases. The ZrO2 was introduced by wear of the milling media during ball milling. After hot

Summary

Effects of Y2O3 or Ti additive together with ZrO2 coming from milling media on phase composition, densification, microstructures, and mechanical properties of hot-pressed Al2O3–B4C ceramics were investigated. Secondary Al18B4O33 phase was formed in the Al2O3–B4C ceramics without additive by the reaction between Al2O3 and B2O3 on the surface of B4C, and inhibit the densification. The Y2O3 additive reacted with B2O3 to produce soft YBO3 phase, inhibit the formation of Al18B4O33 phase, and

Acknowledgments

This work was financially supported by the research fund of Introduction of Leading Talents of Guangdong Province (No. 400120001) and Guangdong Innovative and Entrepreneurial Research Team Program (No. 2013G061).

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