Microstructure and Mechanical Properties of ZrB₂⁻HfC Ceramics Influenced by HfC Addition.

Yi Jing,Zisheng Lian,Hongbing Yuan

doi:10.3390/ma11102046

Abstract

ZrB2–HfC ceramics have been fabricated using the liquid phase sintering technique at a sintering temperature as low as 1750 °C through the addition of Ni. The effects of HfC addition on the microstructure and mechanical properties of ZrB2–based ceramics have been investigated. These ceramics were composed of ZrB2, HfC, Ni, and a small amount of possible (Zr, Hf)B2 solid solution. Small HfC grains were distributed among ZrB2 grain boundaries. These small grains could improve the density of ZrB2–based ceramics and play a pinning role. With HfC content increasing from 10 wt % to 30 wt %, more HfC grains were distributed among ZrB2 grain boundaries, leading to weaker interface bonding among HfC grains; the relative density and Vickers hardness increased, and flexural strength and fracture toughness decreased. The weak interface bonding for 20 and 30 wt % HfC contents was the main cause of the decrease in both flexural strength and fracture toughness.

Highlights

TheZrB2 ceramic is an ultrahigh-temperature ceramic with a high melting point, high electrical and thermal conductivity, high refractoriness, corrosion resistance, wear resistance, and ablation resistance [1,2,3]
ZrB2 –HfC–Ni ceramics with 10–30 wt % HfC content were sintered at 1750 ◦ C by hot pressing
ZrB2 –HfC–Ni ceramics were mainly composed of ZrB2, HfC, and Ni

Summary

Introduction

TheZrB2 ceramic is an ultrahigh-temperature ceramic with a high melting point (above 3300 ◦ C), high electrical and thermal conductivity, high refractoriness, corrosion resistance, wear resistance, and ablation resistance [1,2,3]. HfC is a potential candidate material for aerospace applications, owing to its high melting point and low self-diffusion coefficient. These applications include scramjet components and rocket nozzles serviced at above 3000 ◦ C [13,14,15]. It has emerged as a reinforcement phase to improve microstructure and mechanical properties for different ceramic matrix materials. HfC added into TiCN–based, TiB2 –based, and ZrO2 –based ceramics can form HfC particle dispersion that improves their microstructures, and enhances their mechanical properties [16,17,18]. Numerous studies on the influence of Co–WC [7], WSi2 [8], ZrO2 fiber [9], MoSi2 [19], B4 C [20], and SiC [21] additives on properties of ZrB2 –based ceramic have been reported, whereas few studies on the effects of the HfC additive on properties of ZrB2 –based ceramic have been undertaken

Methods

Results

Conclusion