I have some technical development where we want to use PSZ (Ytrium type).
However, in the application, temperature will have a temperature cyclic
between 150 to 300°c. I heard problem of phase transformation but without
clear information for such temperature level (phase tetragonal & monoclinic)
If youhave some information on this phenomena & case of problem, please let
Since you are trying to use partially stabilized zirconia I am
assuming you have some knowledge of the tranformation toughening
effect. Partially stabilized zironia is also referred to as
transformation toughened zirconia in which a dopant, typiclly 3mol%
yttria, is used to partially stabilize the cubic phase resulting in a
mix of stable cubic phase zirconia and metastable tetragonal zirconia.
Microstructurally this appears as elliptical tetragronal precipitates
in a cubic matrix. Dont confuse this with tetragonal zirconia
polycrystal in which the entire material consists of metastable
tetragonal phase at low temperatures with precise control of yttria
content and cooling rates. Heres where it gets interesting. As the
PSZ is cooled the tetragonal phase wants to expand into the monoclinic
form below 1000C, however, the stabilized cubic phase provides a
compressive stress that prevents this expansion. When a propagating
crack hits one of these precipitates, the energy of the crack is
dissipated by the energy of the phase transformation back into the
monoclinic form. Here is where your problem lies. Typically, PSZ
ceramics are used at elevated temperatures where the thermodynamic
driving force for the phase transformation is not so great. Your
problem is referred to as low temperature degredation of PSZ, and is
due to the spontanteous transformation of tetragonal zirconia to the
monoclinic phase in the 100 - 300C range. The interaction of
microcracks accompanied by the spontaneous phase transformation
results in larger macrocracks, which significantly lowers the strength
of PSZ which can initially have a bending strength of 1200MPa. This
low temperature degredation has been noted when using PSZ in bio
applications. I believe the addition of alumina particles or Nb as a
co-dopant with yttria have been used to alleviate low temperature
degredation. There may even be zirconia suppliers of PSZ for medical
applicaitons that could solve your problems.
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