Mechanical Behavior of Alumina–Silicon Carbide „Nanocomposites”

Abstract

The fracture behavior of Al,O, containing 5 vol% 0.15 pm SIC particles was investigated using indentation techniques. A significant increase in strength was achieved by the addition of SIC particles to the base AI,O,. Specifically, the strength increased from 560 MPa for A1,0, to 760 MPa for the composite samples (average values for unindented hotpressed bars tested in four-point bending). After annealing for 2 h at 1300°C, the average strength of the composite samples increased to about 1000 MPa. Toughness was estimated using indentation-strength data. While there was a slight increase in toughness, the increase was not sufficient to account for the increase in the unindented strength on Sic particle addition. It is suggested that the observed strengthening and apparent toughening were due to a machining-induced compressive surface stress.

Prediction of fracture strength in Al2O3/SiCpceramic matrix nanocomposites

“…4 with different volume fractions of SiC nanoparticles, where the following data reported recently by Sun et al [26] are used: It should be pointed out that while the above analysis exhibits a fairly good agreement with the experimental results reported in the literature [9][10][11]24,26], the dislocation activities in the CMNCs are different from those in the precipitation-hardened metallic materials. For example, unlike aluminum alloys and nickel-based sueralloys, the dislocations in ceramics can hardly move on the slip plane and be stopped by the barrier to form the conventional Orowan loops at room temperature.…”

“…1 shows a comparison of the model prediction with the experimental data for SiC particulate-reinforced alumina nanocomposites [9]. In this figure, the following data for Al 2 O 3 /SiC p nanocoposites are used [9]: annealing. Fig.…”

“…Nano-sized particles present within matrix grains strengthen the grain boundaries due to compressive radial stresses, where the alumina matrix has a larger thermal expansion coefficient than that of silicon carbide particles [5,8]. Others include flaw-healing mechanisms [9,10].…”

Electron microscopy of crack/particle interactions in Al2O3/SiC nanocomposites

“…Zhao et al, 1993;Piciacchio et al, 1994;. However, the scale of the improvements, if any, in strength and toughness remains controversial, and the toughening mechanisms have not been identified with confidence.…”

Nanocomposites—a new material design concept

“…Several researchers have reported a moderate enhancement of fracture toughness with improved strength in nanocomposites, for instance, Niihara [1], Davidge et al [11], Carroll et al [14], Zhao et al [19], and Gao et al [20], in spite of the well-known trade-off relations between the strength and the fracture toughness of monolithic ceramics [8]. Several mechanical properties were also improved, such as hardness [14,20,21], wear resistance [1,5], thermal shock resistance [1], and creep resistance [1,5].…”