Investigation of Indentation Fracture Toughness (KIC) and Weibull Parameters of 0.25Li2O.2SiO2-0.75BaO.2SiO2 Glass-Ceramic

In the present study, mechanical properties of 0.25Li2O.2SiO2-0.75BaO.2SiO2 glass-ceramic were investigated. The trans-formations‘ temperatures were determined by DTA instrument. The optimum nucleation temperature was found to be 540°C. This suggested the crystallization temperatures as 675, 720 and 800°C. After carrying out crystallization heat treatments, Vickers indentation test was applied. In order to determine the indentation fracture toughness (KIC), crack half-length ‚c‘ of the samples was measured. To calculate KIC, Young’s modulus, E and the measured hardness, Hv were used. Using KIC and probability of fracture ‚P‘, ln ln[1/(1 − P)] – ln KIC graph was drawn based on the Weibull distribution equation. Consequently, Weibull modulus, ‚m‘ and scale parameter, ‚K0‘ were determined and compared with each other

The Effect of Milling Time and Sintering Temperature on Crystallization of BaFe₁₂O₁₉ Phase and Magnetic Properties of Ba-Hexaferrite Magnet

Barium hexaferrite samples were prepared by mechanical alloying using the stoichiometric amounts of BaCO₃ and Fe₂O₃ precursors followed by heat treatment applied in the temperature range 700-1150°C. It was found that the high energy ball mill with a milling rate enabled to obtain powders with the finer particles at the reduced milling time mechanical alloying of the initial powders linked to the formation of barium hexaferrite phase. The exothermic reaction peaks corresponding to the formation of BaFe₁₂O₁₉ phase shift from 928°C to 793°C for the increased milling time up to 6 h. This was resulted in improved magnetic properties that the Mₛ value of the as-blended sample sintered at 800°C rised from 31.16 emu/g to 53.46 emu/g after milling for 6 h. The saturation magnetization and remanence values of the samples mechanically alloyed for 3 h and sintered at 1150°C also increased to 63.57 emu/g and 31.26 emu/g, respectively, more than for 800°C and 900°C. The increase in the annealing temperature favours the formation of BaFe₁₂O₁₉ phase in the samples