Zirconia ceramics constitute a major proportion of the World’s Zirconium demand. Naturally obtained Zirconia or Baddeleyite (ZrO2) is used to make Engineering Zirconia. Since structural stability is the fundamental lookout in modern science, the information on the fracture toughness of zirconia decides the material’s suitability for a particular application.
Mechanical Properties of Materials
The life of a material, how it deforms, resists failure and ultimately fails are gauged using material properties. Ductility is a material property for which it can undergo large amount of plastic deformation before failure. Toughness stands for the material’s strength and also extent of ductility. The maximum resistance of the material to any applied stress is tensile strength. Metal fatigue is the phase preceding fracture where the metal becomes weak due to repeated applied loads.
Fracture is the final phase of a material when tit succumbs to the stress applied. The classical study on the topic ever has been Griffith’s theory of fracture developed during the world war. The study speaks about science of energy conservation during the material’s lifespan.
Fracture Strength, stress and Energy
Before knowing Fracture toughness, it’s important to understand Fracture strength. Fracture strength gives an idea of how much strength a material possess. Fracture strength is a function of the atomic or interatomic bonding in materials, expressed Pressure units.
The stress associated with deformation is fracture stress and Fracture energy is the energy absorbed by a material during cracking. Fracture mechanics delineates two major ideas about energy. Fracture energy, indicating the resilience of the material and Fracture energy release rate, the driving force that helps in the propagation of cracks. Both the energy holds analogous relationship.
What is Fracture toughness?
Since the Complete avoidance of manufacturing flaws is hypothetical, knowing fracture toughness helps in assessing the behaviour of the material. The fracture toughness unit is given as Megapascals times meter squared (MPam2) and is generally calculated as unit force times area.
Fracture toughness Equation
Fracture toughness is also known as the Critical stress intensity factor . Knowing the critical stress intensity factor is crucial to know the stress value at which a material breaks if a void exists. The fracture toughness formula to calculate the critical stress intensity factor is:
Were,
is fracture toughness
is the geometric factor
is the stress applied
is the crack length
More than being a mathematical expression, this helps the scientist to anticipate the behaviour of a material under pressure.
How to measure fracture toughness
There are several ways to measure fracture toughness. The widely used test among all is the Charpy V notch test method where a sample with a V or U notch is subjected to an Impact.
Fracture toughness of Ceramics
Engineering materials have been made competitive in terms of Fracture toughness with development in science and technology. Let’s compare the fracture toughness factor of different ceramic materials. The Critical stress intensity factor (KIC) of fine ceramics is typically low. In other words, a fissured Fine ceramic is more prone to failure under applied stress. Given the shortcomings, advanced ceramics have been found as a better alternative with superior Fracture toughness values.
Comparing fracture toughness of Zirconia and other ceramics
Fracture toughness of Alumina: The fracture toughness of alumina ranges from 3.3 to 4.5 MPam1/2. Depending on the grain size and sintering, the values would generally have deviations. For example, the densely sintered alumina is comparatively brittle than the other counterparts.
Fracture toughness of Glass: The properties of glass vary concerning the type and thickness of the glass material. The fracture toughness of glass would be as low as 0.6 and as high as 0.8 MPam1/2.
Fracture toughness of Zirconia: Zirconia offers extreme durability and wear resistance. For instance, a Zirconia ceramic knife that is made from solid-state sintering is currently used as an alternative to steel knives. Fracture toughness of Zirconia depends upon factors such as grain size, Yttria content, Sintering and Post sintering operating parameters. The fracture toughness of Zirconia as indicated is around 17 MPam1/2.
Zirconia Ceramic applications
Zirconia products find a place in a variety of engineering applications due to their unmatchable fracture toughness and other superior properties.
Zirconia in Dentistry
Zirconia is used in dentistry for several applications such as implants, crowns and other orthodontic materials.
Zirconia ceramic Crown: It is generally used for tooth preservation in cosmetic dental treatments. Zirconia dental crowns have higher fracture resistance even at a thickness of 0.5 mm. This is relatively higher than the maximum biting force value of 1000. Zirconia ceramic crown has advantages such as stain resistance, biocompatibility, tooth preservation without metal and numerous other benefits. However, Zirconia crown problems include immediate tooth wear, fracture, patient sensitivity and minimum translucence.
Picture showing Zirconia Crown before and After
Zirconia Vs porcelain bridge
Zirconia bridge has higher lifespan around 20 years than porcelain bridge. In appearance, Zirconia bridges generally are more appealing due to their translucent appearance. Zirconia are stronger and have fewer chipping and grinding problems when compared to porcelain bridges.
Yttrium stabilized zirconia
Yttrium-stabilized zirconia is made when Yttrium iii oxide (Y2O3) is used to stabilize the crystal cubic structure of ceramic. The Yttrium stabilized zirconia (YSZ) offers numerous properties such as superior mechanical strength, and excellent optical and ionic properties. It is also used to manufacture Zirconia plates that can handle temperatures of 2000 degrees or above. With 8 mol% of Yttria, polished zirconia plates are chemically inert and abrasion-resistant.
Zirconia diamonds
Zirconia diamond is cost-effective and is a better alternative to real diamond. Although diamond tends to sparkle more profoundly Zirconia diamonds are no less an alternative for a better jewellery material.
Conclusion
Zirconia ceramics are high-end advanced ceramic with superior fracture resistance or fracture toughness. They remain to be dominant in the industry due to their unmatchable thermophysical properties and high end durability. Since the impact resistance offered is high, they can be deployed successfully in hard-wearing and high-temperature engineering scenarios.