Izory® and Izory® gold are magnesia partially stabilized zirconia (Mg-PSZ) materials. They can also be described as tetragonally toughened or transformation toughened zirconia. Izory® is typically ivory colored, but Refractron also offers Izory® gold, which is yellow.
Yellow zirconia is typically an indicator of impurities, which lead to inferior properties, but Izory® gold bucks that trend. Refractron uses a proprietary process to offer customers a yellow MgPSZ with the same great properties as our ivory colored Izory®. The processing of both products is critical for developing the unique microstructure that helps create outstanding mechanical properties.
To achieve the microstructure that generates these properties it is important to know that zirconia exists as three different phases, monoclinic, tetragonal and cubic symmetry. With careful control of the process, specifically the firing, Refractron can optimize the balance and presence of these phases in Izory®. The ideal structure for Izory® includes tetragonal particles inter grown within cubic crystallites. The tetragonal phase is said to be metastable since it has not transformed to the monoclinic structure, the equilibrium phase of zirconia at room temperature.
The relationship between the two phases is unusual because monoclinic has a larger volume and a lower density than the tetragonal phase. In tetragonally toughened or transformation toughened zirconia, like Izory®, this provides the mechanism which toughens it against catastrophic fracture at room temperature. A crack generated in Izory® has a frontal stress field as it propagates. When this field encounters a metastable tetragonal crystallite, the phase responds by transforming to the larger volume monoclinic phase. The volume increase and associated strain oppose opening of the crack and act to increase the resistance of the ceramic to further crack growth.
Materials like Izory® exhibiting this behavior are said to be transformation toughened or tetragonally toughened and, therefore, have high fracture toughness. Izory® has approximately two times the fracture toughness of other structural ceramics such as alumina or Y-TZP (yttria stabilized zirconia). This is beneficial for many tough applications. It also means that Izory® is ideal for machining into complex shapes with tight tolerances without chipping. While, Izory® is known for its fracture toughness it also hard, strong and resistant to corrosion. It is an excellent choice for tough applications below 500°C like those found in wire drawing, oil drilling and chemical processing.