Processing of Al2O3-AlN Ceramics and Their Structural, Mechanical, and Tribological Characterization

Abstract

The aim of this study is to present a novel, lower sintering temperature preparation, processing, structural, mechanical, and tribological testing of the AlN-Al2O3 ceramics. The precursor powder of AlN was subjected to oxidation in ambient environment at 900 °C for 3, 10, and 20 h, respectively. These oxidized powders were characterized by SEM and XRD to reveal their morphology, phase, and crystal structure. The SEM results showed coarse powder particles and the presence of aluminum oxide (Al2O3) phase at the surface of aluminum nitride (AlN). The XRD analysis has shown increasing aluminum-oxy-nitride conversion of aluminum nitride as the holding time of oxidation increased. The highest percentage of conversion of AlN powder to AlN-Al2O3 was observed after 10 h. Simultaneously the powders were compacted and sintered using the hot isostatic pressing (HIP) under inert environment (N2 gas) at 1700 °C, 20 MPa for 5 h. This led to the compaction and increase in density of the final samples. Mechanical tests, such as bending test and tribology tests, were carried out on the samples. The mechanical properties of the samples were observed to improve in the oxidized samples compared to the precursor AlN. Moreover, applying longer oxidation time, the mechanical properties of the sintered samples enhanced significantly. Optimum qualitative (microstructure, oxide percentage) and quantitative (tribology, hardness, and bending tests) properties were observed in samples with 10-h oxidation time.

Effect of the pressureless post-sintering on the hot isostatic pressed Al2O3 prepared from the oxidized AlN powder

“…3 b). Although the second phase of aluminum oxide can be observed only in the powders after 10 and 20 h of oxidation time 16 . These measurements are in agreement with Tabary et al 20 .…”

“…In the case of HIP_10 and HIP_20, the presence of α-Al 2 O 3 phase has been only observed. It can be explicable by the sintering process in nitrogen and high temperature disintegrated the non-stable θ-Al 2 O 3 phase 16 . As a post-sintering step pressureless sintering (PS) in hydrogen was applied to as processed HIP samples.…”

“…The sintered samples showed the presence of only α-Al 2 O 3 besides AlN proving that the sintering results in disintegration of θ-Al 2 O 3 phase. Their experiments also provided that the densification of sintered ceramics can be achieved by HIP at lower temperatures 16 .…”

“…Its presence can facilitate the liquid phase during sintering, which is beneficial for compacting and removing pores. Varanasi et al first oxidized AlN powders for 3, 10 or 20 h and after that sintered by HIP for the first time the dense AlN-Al 2 O 3 composite without Y 2 O 3 sintering additives 16 . The sintered samples showed the presence of only α-Al 2 O 3 besides AlN proving that the sintering results in disintegration of θ-Al 2 O 3 phase.…”

“…However, the strength of the composites is decreased significantly as the microcracks are formed 19 . Our previous study of the structural and mechanical characterizations of HIP sintered AlN-Al 2 O 3 was discussed in 16 . A combination of HIP and PS post-sintering is proposed in this paper to obtain high-density bodies with higher hardness.…”