the toughening mechanism of ZTA ceramic

ZTA陶瓷的增韧机理       ZTA陶瓷的增韧机理是晶须及纤维增韧,第二相弥散强化增韧, ZrO2相变增韧,以及与金属复合形成金属基复相陶瓷，残余应力增韧等等。以下简单介绍几种研究较热的增韧途径的机理。  
1、应力诱导相变增韧        对于ZrO2/Al2O3体系,主要的增韧方式是由ZrO2产生的相变增韧.李世普等人将其解释为：zro2颗粒弥散在Al2O3陶瓷基体中，由于两者具有不同的热膨胀系数，烧结完成后，在冷却过程中，zro2颗粒周围则有不同的受力情况，当它受到基体的抑制，zro2的相转变也将受到抑制。此外，zro2还有另一个特性，是相变温度随着颗粒尺寸的降低而下降，一直可降到室温或室温以下。党基体对zro2有足够的压应力，而zro2的颗粒度有足够小，则其相变温度可降至室温以下，这样在室温时zro2仍可以保持四方相。当材料受到外应力时，基体对zro2的抑制作用得以松弛，zro2颗粒即发生四方相到单斜相的转变，并在基体中引起裂纹，从而吸收了主裂纹扩展的能量，达到增加断裂韧性的效果，这就是zro2的应力诱导相变增韧。 

2、微裂纹增韧 毫无疑问，在大多数情况下，陶瓷体内存在有裂纹，包括表面裂纹，工艺缺陷，环境条件下诱发的缺陷，当受外力或存在应力集中时，裂纹会迅速扩展导致陶瓷体破坏。因此，应防止裂纹扩展，消除应力集中，是解决增韧问题的关键。      部分稳定的zro2在发生t-zro2到m-zro2马氏体相变时，相变出现了体积膨胀而导致产生微裂纹。这样不论是zro2陶瓷在冷却过程中产生相变诱发微裂纹，还是裂纹在扩展过程中在其尖端区域形成的应力诱导相变导致的微裂纹，都将起到分散主裂纹尖端能量的作用，从而提高了断裂能，达到增韧效果。         但是，要实现Al2O3陶瓷的增韧效果，zro2颗粒的尺寸也很重要，其颗粒细度要小，要不大于室温临界相转变直径约0。7微米,而且粒度范围要窄，目的是为了使ZTA陶瓷中同时获得应力诱导相变增韧和微裂纹增韧两种机制。 

One, the toughening mechanism of ZTA ceramic,      toughening mechanism of ZTA ceramics is whisker and fiber reinforced and dispersed second phase strengthening and toughening, ZrO2 phase transformation toughening, and with metal complex formation of metal matrix composite ceramics, residual stress toughening and so on. Following is a brief description of several research hot way to toughen mechanism.

1, the stress induced transformation toughening for the ZrO2/Al2O3 system, the main toughening methods is transformation toughening produced by ZrO2 Li Shipu et al. Interpreted as: ZrO2 particles dispersed in Al2O3 matrix, due to the different thermal expansion coefficient between the two, after the completion of sintering, during the cooling process, a force of around ZrO2 particles the situation is different, when suppressing it by the matrix, the phase transition will also be inhibited by ZrO2. In addition, ZrO2 has another characteristic, is the phase transition temperature decreases with decreasing particle size, has been reduced to room temperature or below. The party matrix has enough compressive stress on the ZrO2 and ZrO2 particles is small enough, the phase transition temperature can be reduced to below room temperature at room temperature, so ZrO2 can still maintain a tetragonal phase. When a material is subjected to external stress, inhibition of matrix of ZrO2 relaxation, ZrO2 particle is the four phase to the The transition of the single phase and the crack in the matrix, which absorbs the energy of the main crack growth, can achieve the effect of increasing the fracture toughness, which is the stress induced phase transformation toughening of ZrO2.

2, micro crack toughening without doubt, in most cases, there is a ceramic body including crack, surface crack, process defects, induced defects under the environmental conditions, when the external force or the existence of stress concentration, the crack will lead to the rapid expansion of ceramic body damage. Therefore, we should prevent crack propagation, eliminate stress concentration that is the key to solve the problem. The toughening stabilized ZrO2 in t-ZrO2 to m-ZrO2 martensitic transformation, transformation the volume expansion caused by micro cracks. So whether the ZrO2 Ceramics produced transformation induced during the cooling process of micro cracks, micro cracks or cracks formed in the tip region in the expansion process should be stress induced transformation result, will play the role of the main crack tip energy dispersion, thus improving the fracture energy, achieve the toughening effect. However, in order to realize Al2O3 ceramic toughening effect, ZrO2 particle size Inch is also very important, the fineness of the particles should be small, otherwise than room temperature critical phase transition diameter of about 0.7 m and narrow particle size range to in order to make the ZTA ceramics at the same time, the stress induced phase transformation toughening and microcrack toughening mechanism.