Characterization and machinability properties of glass-ceramic materials produced from vermiculite

Machinable glass-ceramic materials are produced by controlled crystallization heat treatment performing to the glasses obtained by melting and casting processes. They can be processed into complex shapes and precision parts with conventional metalworking tools quickly and economically. In this study, production possibilities of glass and machinable glass-ceramic materials from vermiculite ore were investigated. The vermiculite from SİVAS/Yıldızeli region was calcined at 1050 ℃, then SiO2, Al2O3, K2O, MgF2 and B2O3 were added to prepare machinable glass-ceramic compositions. The prepared compositions were milled and mixed in the alumina ball mill for 1 hour. Homogeneously mixed powders were melted in alumina crucible at 1500 ℃ for 1 hour and cast into graphite mold and glass production was realized. In order to eliminate the internal stresses in the glass structure after casting, annealing was performed for 1 hour at 600 ℃. As a result of XRD analysis, the produced glasses were found to be amorphous. The glass transition and crystallization heat treatment temperatures were determined by DTA / DSC. The glass-ceramic transformation was realized by stepped and direct heat treatment at the determined temperatures. In the glass-ceramic materials, phase analysis with XRD, microstructure characterization with SEM, crystallization kinetics calculations with thermal analysis were performed. In order to determine the mechanical properties of glass and glass-ceramics, hardness, fracture toughness measurements and machinability tests were applied. In addition, the density of glass and glass-ceramics were calculated by using Archimedes principle. As a conclusion of the studies, it has been determined the glass-ceramic coded B0 exposed to stepped heat treated and the glass-ceramic coded B10 in direct heat treatment (1100 ℃ 10 hours) having the best machinability performance. These glass-ceramics can be recommended for machinability applications.