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Abstract
Al2O3 + 30 vol% ZrO2 matrix composites with 20 and 30 vol% cBN have been prepared with the optimized processing route, using spark plasma sintering (SPS) at temperatures of 1400 °C and 1250 °C. The influence of cBN addition on the microstructure characteristics, micro/nanohardness, elastic modulus, and crack-extension resistance of the composites and their constitutions have been investigated using scanning electron microscopy (SEM), statistical analyses of the individual grain size and micro/nanoindentation methods. The matrix consists of alumina and zirconia grains with grain sizes/diameter of approximately 220 and 160 nm with approximately 1.9 μm cBN grains in the Al2O3 + ZrO2 + cBN composites. The microhardness is slightly increasing with cBN addition from 16.2 to 17.1 GPa and the crack-extension resistance from 3.72 to 4.29 MPa.m1/2. The toughening mechanisms are in the form of crack deflection, crack branching, and crack bridging. The nanohardness and indentation modulus of the matrix are approximately 30 and 420 GPa, and the cBN grains 70 and 777 GPa, respectively.
Highlights
Alumina (Al2O3) ceramics, due to their excellent properties, such as high hardness, thermal stability, corrosion, and wear resistance, etc., are one of the most widely used advanced ceramics in different fields of industry, such as cutting tools, seal rings, components of bearings, etc. [1,2,3,4]
A slightly different situation is visible in the case of Al2O3 + ZrO2 + Cubic boron nitride (cBN) composites during the measuring of the hardness of Al2O3 + ZrO2 matrix where the behavior is influenced by the present cBN particles around, below the indents, at different distances, which is visible in the case of hardness–displacement but more significantly in the case of indentation modulus curves
The aim of the present contribution was the processing of Al2O3 + ZrO2 + cBN composites with an optimized processing route and to investigate the influence of cBN addition on their microstructure characteristics, microhardness, and crack-extension resistance
Summary
Alumina (Al2O3) ceramics, due to their excellent properties, such as high hardness, thermal stability, corrosion, and wear resistance, etc., are one of the most widely used advanced ceramics in different fields of industry, such as cutting tools, seal rings, components of bearings, etc. [1,2,3,4]. The cBN to hBN phase transformation has been investigated by many researchers, and according to the results, when sintering at a hightemperature, cBN is only stable at high pressures [16,17] These reports indicate that the fabrication of ceramic + BN composites with required properties under lower pressure is possible only at optimized processing conditions. Spark plasma sintering usually entails a pressure of up to 100 MPa, which is closer to ambient pressure than to the values of pressure in the cBN stability region, which are in the order of several GPa. During SPS, two opposing processes occur: Densification of the material (increase in density and Young’s modulus), and cBN to hBN transformation at higher temperatures (decrease in density and Young’s modulus). Further aims are to measure the nanohardness of the matrix and cBN grains
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