Unique mechanical properties of nanostructured transparent MgAl2O4 ceramics

Jie Zhang,Tiecheng Lu,Jianqi Qi,Xianghui Chang,Nian Wei

doi:10.1186/1556-276x-8-261

Abstract

Nanoindentation tests were performed on nanostructured transparent magnesium aluminate (MgAl2O4) ceramics to determine their mechanical properties. These tests were carried out on samples at different applied loads ranging from 300 to 9,000 μN. The elastic recovery for nanostructured transparent MgAl2O4 ceramics at different applied loads was derived from the force-depth data. The results reveal a remarkable enhancement in plastic deformation as the applied load increases from 300 to 9,000 μN. After the nanoindetation tests, scanning probe microscope images show no cracking in nanostructured transparent MgAl2O4 ceramics, which confirms the absence of any cracks and fractures around the indentation. Interestingly, the flow of the material along the edges of indent impressions is clearly presented, which is attributed to the dislocation introduced. High-resolution transmission electron microscopy observation indicates the presence of dislocations along the grain boundary, suggesting that the generation and interaction of dislocations play an important role in the plastic deformation of nanostructured transparent ceramics. Finally, the experimentally measured hardness and Young’s modulus, as derived from the load–displacement data, are as high as 31.7 and 314 GPa, respectively.

Highlights

Magnesium aluminate (MgAl2O4) spinel transparent ceramic has been considered as an important optical material due to its good mechanical properties and excellent transparency from visible light to infrared wavelength range [1]
Where S is the elastic constant stiffness defined as the slope of the upper portion of the unloading curve, as shown in Figure 1, hc is the contact depth, ε is the strain (0.75 for the Berkovich indenter), pause at a maximum load (Pmax) is the maximum applied load, A is the projected contact area at that load, Er is the Young’s modulus, and β is the correction factor that depends on the geometry of the indenter
The results showed that there was a higher degree of plastic deformation at a higher applied load, as shown in the inset of Figure 1

Summary

Introduction

Magnesium aluminate (MgAl2O4) spinel transparent ceramic has been considered as an important optical material due to its good mechanical properties and excellent transparency from visible light to infrared wavelength range [1]. There has been great interest in the investigation of ceramic materials with improved toughness [5,6,7,8]. It has been believed that nanostructured ceramics may have greatly improved mechanical properties when compared with their conventional large-grained counterparts [9]. In our previous work [10,11], we employed a novel technique to study the fabrication of nanostructured transparent ceramics.

Methods

Results

Conclusion