Reinforce
(entre
phase tra
poet! ’
ore
os ®
. 51 ¥
Fig. 1: SEM micrographs of alumina.
a) solid state sintered (SSS), b) of 0.5 wt.% MgSiOs containing LPS
Despite the markedly different microstructures, the variation of hardness and fracture toughness of
all specimens tested were within the range of an experimental error. Macroscopic-scale mechanical
characteristics fail to provide the hints on wear behavior of polycrystalline ceramic materials, since
the events responsible for wear take place at much lower — microscopic - scale of single grain
boundaries or several grains. The major mechanism of material loss during the wet erosive wear of
pure alumina of grain size > 1 pm is grain pull-out initiated by grain boundary microfracture and
crack interlinking. In the MgSiOs liquid phase sintered aluminas the intergranular silicate films
appear to have the main function of strengthening the grain boundaries, and material loss in these
materials occurs primarily by intragranular fracture at much reduced rates. [1] There may also be Fig. 3%
enhancement of the tribochemical component of wear. High fluctuating stresses (+ 450 MPa) in the So
MgSiO; sintered materials result from the thermal expansion coefficient differences between the a
alumina, the grain boundary magnesium aluminosilicate glass and the minor crystalline phases such a
as sapphirine, spinel and mullite that crystallise from the aluminosilicate glass upon cooling from The diffe
the processing temperature. These stresses appear to influence microcrack propagation rate by ITs
slowing the rate at which a transgranular crack can propagate across the boundary. Employing the with aspe
mechanisms mentioned, the addition of up to 10 wt.% of magnesium silicate sintering additives Same com
increased the wear resistance of alumina 2-3 times, compared to the pure alumina with the LEE
comparable mean grain size, Fig. 2.
Lavered
70: i
60-] 2 el -
. The Ze
504 i A Ine
- Sr Bi 3 TE
94% Thema
E or
~ 30 0 pure ALO, [1] nn nn
o —M— pure ALO, PrOpertie
= 20 MgSiO,: mons
ee —y—0.5wi.% Lo
104 a _ Om 1 Wh% layered
—@-—5wt.% | More ve
0 | ee . . =A— 10 wi.% m
0 2 ‘ 6 8 10 Nuit
D./pm wr
Tha ayn
Fig. 2: Wet erosive wear rates of the pure and LPS aluminas. hm
206
