Desenvolvimento de vitrocerâmicos transparentes resistentes ao impacto

Abstract

Transparent glass-ceramics (GCs) can replace glasses traditionally used as ballistic windows and electronic displays due to their better mechanical properties. This improvement is obtained by the crystallization of phases with better mechanical properties and/or by stresses induced by the phases. In this doctoral thesis, bulk-crystallized GCs from MgO.Al2O3.SiO2 system - MAS - and surface-crystalized GCs from Li2O.Al2O3.SiO2 system - LAS - with a low thermal coefficient phase were developed. The parent glasses were melted, cast into copper moulds and subsequently controlled crystallized. TiO2 e CeO2 were added to the MAS to reduce the time for nucleation and maintain transparency. The MAS glass-ceramics obtained up to 10 GPa of hardness and approximately 70% of light transmission (4 mm thickness). These values are similar to glass-ceramics developed for the same application. The 1.5% addition of TiO2 reduced the nucleation time from 72h to 8h, and the obtained hardness was up to 9 GPa. For LAS glass-ceramics, the β-spodumene surface crystallized layer led to the compression stress of ~400 MPa, according to analytical and finite element methods (FEM), with up to 3% of error. The failure stress on the biaxial flexure Ball-on-Three-Balls test (B3B) increased from 180 MPa to 680 MPa with a 56 μm layer. The material demonstrated suppression of radial cracks in the indentation and scratch tests and absorbed 14x higher energy than parent glass in Charpy impact tests. The dynamic fatigue tests in MAS and LAS glasses and glass-ceramics demonstrated that crystallization enhances subcritical crack growth (n). Parent glasses showed n-coefficient values from 10 to 21, while GCs was from 17 to 56. The GCs studied in this thesis are promising materials for their application based on mechanical properties and transparency.