Preparing ZrO₂/LZAS Glass-ceramics Composite Materials By Sintering Method

Li2O-Al2O3-ZnO-SiO2 (LZAS) is widely used in industry because of its good combination of high temperature resistance, wear resistance, as well as corrosion resistance and adjustable coefficient of thermal expansion. However, the brittleness of this glass ceramic restricts its application in some fields. Therefore, that to improve the fracture toughness of LZAS glass ceramic is significant. The second phase particle toughening is one of the effective ways to improve the fracture toughness of glass ceramic. In this study, sintering process and the principle of sintering were investigated and zirconia particles toughened LZAS glass ceramic composite was obtained. The fracture toughness of LZAS glass ceramic is improved markedly by adding zirconia.In this thesis, the composition of LZAS glass ceramic is elaborately designed. The composite of ZrO2/Li2O-Al2O3-ZnO-SiO2 was prepared by orthogonal test, one-stage sintering processes and two-stage sintering processes, respectively. The effects of adding zirconia on phase composition, microstructure, crystallization kinetics and properties of the composite were investigated by XRD, DTA, SEM, etc. The effects and mechanisms of zirconia content on the composite of ZrO2/Li2O-Al2O3-ZnO-SiO2 were investigated.The results show that the LZAS glass ceramic used in this research has strong crystallization due to its low crystallization activation energy which is 88.14 kJ/mol. The influence degree of the parameters of heat treatment process on bulk density of LZAS glass ceramic is crystallization temperature> crystallization time> nucleation temperature> nucleation time. The main phase of the LZAS glass ceramic prepared by two-stage sintering processes at a crystallization temperature of 560 ℃ is Li3Zn0.5SiO4 and Li2ZnSiO4. For crystallization temperature over 580 ℃, the main phase changes into Li2Al2Si3O10 and Li2ZnSiO4. When LZAS glass ceramic was prepared by one-stage sintering processes, the main phase is Li3Zn0.5SiO4 and Li2ZnSiO4 at 580 ℃, Li2Al2Si3O10 and Li2ZnSiO4 at 650 ℃ or 710 ℃, respectively. With increasing zirconia content, the phase of the composite is hardly any changed, but the hardness, flexural strength and fracture toughness of the composite first increase and then unchange. When 15 vol% zirconia was added to LZAS glass ceramic, ZrO2/Li2O-Al2O3-ZnO-SiO2 composite has an increase of 20% in hardness,82% in flexural strength and 88% in fracture toughness compared to LZAS glass ceramic. Toughening mechanisms of zirconia on ZrO2/Li2O-Al2O3-ZnO-SiO2 composite were crack deflection and residual stress.