Synthesis, Structure, and Properties of Zirconia-Modified Aluminosilicate Glass-Ceramics
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hesis, Structure, and Properties of Zirconia-Modified Aluminosilicate Glass-Ceramics E. N. Kablova, A. S. Chainikovaa, *, N. E. Shchegolevaa, D. V. Grashchenkova, V. S. Kovalevaa, and I. O. Belyachenkova a
All-Russia Research Institute of Aviation Materials (State Scientific Center), Moscow, 105005 Russia *e-mail: [email protected] Received April 7, 2020; revised June 6, 2020; accepted June 8, 2020
Abstract—Strontium aluminosilicate glass-ceramics modified with zirconia additions in the presence of yttria as a stabilizing oxide and without it have been prepared by a sol–gel process. Increasing the zirconia content from 5 to 15 wt % has been shown to reduce the gelation time of the starting solutions, lower the gel crystallization onset temperature, activate the glass-ceramic sintering process, and increase the critical stress intensity factor (KIc) of the glass-ceramics by more than a factor of 2. The present results confirm that the increase in KIc on the addition of ZrO2 is due to transformation toughening. At the same time, the addition of yttria as a stabilizing oxide has been shown to hinder the martensitic transformation of tetragonal ZrO2 into the monoclinic phase. Keywords: glass-ceramic, strontium anorthite, SrO–Al2O3–SiO2, zirconia, gelation, crystallization, sintering, fracture toughness, transformation toughening DOI: 10.1134/S0020168520100064
INTRODUCTION The ability to increase the speed of aerial vehicles and improve their maneuver capability requires the use of novel high-temperature glass-ceramic materials for the fabrication of components of structures intended for service at high temperatures, under dynamic loads, and in aggressive media. From this point of view, there is great interest in strontium aluminosilicate glass-ceramics, in which the dominant crystalline phase is monoclinic strontium anorthite (SrAl2Si2O8), offering a unique combination of a high melting point (1650°C), a rather small linear thermal expansion coefficient ((26–48) × 10–7 K–1), and low density (3.08 g/cm3) [1–3]. At the same time, the low fracture toughness of these materials (KIc < 2.5 MPa m1/2) severely limits their potential applications. One possible approach to this problem is to modify strontium aluminosilicate glass-ceramics with reinforcing agents, that is, to produce glass-ceramic composite materials (GCCMs) [4–7]. Studies concerned with the incorporation of reinforcing agents into brittle glass-ceramics with the aim of improving their fracture toughness and strength were begun as early as the 1960s. Use was then made of metallic and ceramic reinforcements in the form of continuous fibers and whiskers, which allowed a high degree of toughening to be reached. The strongest
effect has been achieved using SiC fiber (Nicalon), with an increase in the KIc of the glass-ceramics by more than one order of magnitude. However, since such reinforcing agents and related composites are difficult to fabricate and expensive, more and more research effort has recently been focused on the use of particulate fillers [7]. Th
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