Crystallization Behavior Of Dy₂O₃-Al₂O₃-SiO₂ Glass-ceramics Filler And Its Application For Joining ZTA Ceramics

Zirconia toughened alumina（ZTA）possess many excellent properties,such as high strength,high toughness,excellent high temperature resistance and corrosion resistance.However,the inherent brittleness of ZTA ceramics makes it difficult to obtain complex and precise component through machining.Glass-ceramics joining technology is an important method to solve the these problems.RE₂O₃-Al₂O₃-Si O₂ glasses possess excellent chemical compatibility with ceramic substrate,high softening temperature and excellent chemical durability at high temperatures.Therefore,two kinds of glass-ceramics filler with high dysprosium oxide（60.5Dy₂O₃-13.8Al₂O₃-22.7Si O₂-3Ti O₂）and low dysprosium oxide（50Dy₂O₃-16Al₂O₃-29Si O₂-2Na₂O-3K₂O-RO）have been designed in this paper.The crystallization behavior,thermal expansion behavior and wetting behavior have been investigated in depth.Meanwhile,the system of glass was employed to join the ZTA ceramics,which optimizes the filler composition and joining parameters,and obtains a high strength joint.The crystalline phases formed in the 60.5Dy₂O₃-13.8Al₂O₃-22.7Si O₂-3Ti O₂ glass ceramic can be identified as Dy₂Si₂O₇ and Dy₂Si O₅.The large density difference between the glass and the crystalline phases and the crystallization mechanism of the glass is surface crystallization,which causes the formation of voids after crystallization in the high dysprosium glass filler.The thermal expansion results show that the softening temperature of the glass is as high as 902℃,and the thermal expansion coefficient is 6.67×10^-6/℃,which is close to ZTA ceramics.Joining experiments show that the fast cooling rate（50℃/min）can restrain the crystallization of the weld,which is helpful to obtain the joint without voids.As the joining temperature increases,the amount of Zr O₂ dissolved increases from the ZTA ceramic to the filler.The maximum flexural strength of 535 MPa is obtained when the joining temperature and cooling rate are 1475℃ and 50℃/min,respectively,which reaches the strength level of ZTA ceramic.The crystalline phases formed in the 50Dy₂O₃-16Al₂O₃-29Si O₂-2Na₂O-3K₂O glass ceramic can be identified as Dy₂Si₂O₇,Al₆Si₂O₁₃and Si O₂（tridymite）.The addition of Zn O promote the formation of Zn Al₂O₄ and the addition of Mg O results in the formed of Mg₂Al₄Si₅O₁₈.By reason of the content of Dy₂O₃ in the glass filler is reduced,the content of high-density crystals is decreased after the crystallization treatment,so obtained a joint without void.The thermal expansion consequence shows that the thermal expansion coefficient of the glass with adding Zn O ceramics is better matched with ZTA ceramics.The joining experiment shows that the crystal size in weld decrease with the increase of the joining temperature.When the joining temperature is 1500℃,the number of Zn Al₂O₄ and Al₆Si₂O₁₃ crystals in the weld was significantly reduced.The reason may be that due to the violent dissolution of weld filler and ZTA ceramic,which makes the composition of the weld glass seriously deviate from the original design composition.The joint flexural strength gradually increases first and then decreases with the increase of joining temperature.The maximum flexural strength of 358 MPa is obtained when the joining temperature is 1450℃.