Mechanical behavior of mullite-zirconia composites

Abstract

In this work, mechanical properties of mullite-zirconia composites synthesised through reaction sintering of Algerian kaolin, Į-Al 2 O 3 , and ZrO 2 were characterized. Phases present and their transformations were characterized using x-ray diffraction. Hardness H and fracture toughness K IC were measured by Vickers indentation using a Zwick microhardness tester. The flexural strength was measured through three point bending test using an Instron Universal Testing Machine. It was found that the increase of ZrO 2 content (from 0 to 32wt.%) decreased the microhardness of the composites from 14 to 10.8 GPa. However, the increase of ZrO 2 content (from 0 to 24wt.%) increased the flexural strength of the composites from 142 to 390 MPa then decreased it with further increase of ZrO 2 content. Also, the fracture toughness increased from 1.8 to 2.9 MPa.m 1/2 with the increase of ZrO 2 content from 0 to 32 wt.%; and the rate of the increase decreased at higher fractions of ZrO 2 content. The average linear coefficient of thermal expansion (within the range 50 to 1450°C) for samples containing 0 and 16 wt.% ZrO 2 sintered at 1600°C for 2 hours was 4.7 x10 -6 K -1 and 5.2 x 10 -6 K -1respectively.

Synthesis and characterization of mullite–zirconia composites by reaction sintering of zircon flour and sillimanite beach sand

“…However, if t→m transformation exceeds a certain value, it has negative impact on mechanical strength. 34 For the samples containing 20 wt% zirconia, tetragonal to monoclinic transformation is around 62.67%. This transformation (t→m) creates microcracks, which increases the flexural strength and fracture toughness.…”

Additive manufacturing and mechanical characterization of high density fully stabilized zirconia

“…Groups 3 and 6 had the highest hardness values (15.3±0.4 GPa and 15.4±0.2 GPa, respectively). To compare the fracture toughness, the equation proposed by Liang et al [21] was chosen due to its popularity for zirconia [22][23][24][25][26][27][28][29][30][31][32]. According to their method, the value of fracture toughness is estimated from the following equation: (1) where K IC is the fracture toughness in MPa•m 0.5 , H is the hardness in MPa, E is the Young's modulus in MPa, φ is a constant equal to 3, and a and c are the half diagonal length of the indent and half length of the crack in m, respectively.…”

“…where ν is Poisson's ratio which was assumed to be 0.29 [22][23][24][25][26][27][28][29][30][31][32].…”

Thermal decomposition and reaction sintering for synthesis of mullite-zirconia composite using kaolin, γ-alumina and zirconia

“…TEC of the pure mullite was low, so the effect of ZrO 2 content led to a slight increase of this coefficient for the mullite-ZrO 2 composite. The TEC of mullite-zirconia increased in a small amount with increasing temperature, possibly due to the increase of the densification of composite material and the phase transformation behavior of the partially stabilized zirconia from tetragonal to monoclinic phase [13,19].…”