Papers by Author: Hyun Hwi Lee

Abstract: Alumina (Al₂O₃)-zirconia (ZrO₂)-hydroxyapatite (HA) composite is used as biomaterials. Biomaterials must be bio-compatible to the body and should have excellent mechanical and tribological properties. 1 wt.% of rare earth oxide (Dy₂O₃) was added to the basic composition of composite Al₂O₃ -ZrO₂ (15wt.%)-HA(1wt.%). The powder mixture was hot-pressed at 1300°C in Ar gas environment under 30 MPa pressure for densification sintering. The microstructural analysis, phase transformation, surface morphology and mechanical properties like hardness, fracture toughness, mechanical strength of the composite were observed and evaluated by SEM , XRD, Vickers hardness, etc. The results demonstrated that the addition of 1 wt.% dysprosia has increased the mechanical properties of composite.

Abstract: Oxide ceramics such as alumina and zirconia are industrially utilized as cutting tools, a variety of bearings, biomaterials, and thermal and corrosion-resistant coatings due to their high hardness, chemical inertness, high melting point, and ability to retain mechanical strength at elevated temperatures. In this research, the effect of other ceramic additives (TiO₂) and h-BN within alumina(α-Al₂O₃) and yttria-stabilized tetragonal (Y-TZP) composite was studied with respect to the mechanical and tribological properties. The lowest coefficient of frction of 0.45 was observed for the ZTA ceramic composite with hBN-TiO₂. The highest hardness, fracture toughness and flexural strength were obtained as 15.7GPa, 5.2MPam^-1/2, 712MPa, respectively.

Abstract: The addition of h- BN to a polycrystalline Si3N4 was to increase the fracture toughness and other mechanical properties such as flexural strength and hardness of the material. The hot pressed samples were prepared from the mixture of α-Si3N4, AlN, MgO and h-BN. The composite contained from 0 to 2 wt.% BN powder with sintering aids (9% AlN + 3% MgO). The transparency, mechanical properties and microstructure of hot pressed polycrystalline Si3N4-BN composite materials were investigated by UV/VIS spectrophotometer, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The transparency decreased with increasing the content of h-BN into Si3N4.

Abstract: The ceramic channel is very important in SRL hot dipping system. High strength and fracture toughness of ceramic channel materials can improve the quality, productivity and economic feasibility of zinc plated steel. The purpose of this research was to find out the most suitable conditions of the ceramic channel that have best fracture strength and fracture toughness. The hot pressed composite materials was carried out by hot pressing Al2O3 with different content of ZrO2. The composite contained from 0-20 wt.% ZrO2. Hot pressed composite materials were observed for mechanical properties (density, hardness, fracture toughness and flexural strength) and microstructure.