Research On Process And Mechanism Of ZTA Ceramics Joining Based On In-situ Synthesized Whiskers

ZTA ceramic is one kind of composite ceramics, using Zr O2 toughening phase of Al2O3 ceramics, with a high melting point, high hardness, resistance to acid and alkali corrosion, and good toughness, becoming one of the widely used materials in high temperature structure ceramic. In the practical application, because the ceramic material has the disadvantage of poor machinability, It’s necessary to join the simple components to form complex structures. It will appear a few of problems when using the brazing method to join ceramics, such as, the large residual stress in joints, poor high temperature resistant performance and poor anti-corrosion resistance. The project propose a new method to join ceramics with the help of in-situ growth whiskers, for the purpose of reducing the residual stress in joints, with the advantage of similar thermal expansion coefficient between whiskers and ceramics. And the whiskers are epitaxial growth from ZTA ceramics, having good combination with the matrix. The morphology of whiskers and the microstructure of the joints, as well as the strength of the joints were researched by means of SEM, EDS, TEM, XRD and strength test.Different morphology of the whiskers were formed on the surface of ZTA ceramics when using five kinds of nonmetal powder, such as, B2O3, B2O3+Cu O, B2O3+K2SO4, B2O3+Mn O2, B2O3+Zn O. When using B2O3, the distribution of whiskers synthesized on the surface of ZTA ceramics is poor, and formed residual B2O3. The length-diameter ratio of whiskers is becoming shorter when using B2O3+Cu O as raw materials. When using B2O3+K2SO4, the morphology and the distribution of whiskers get improved, but the orientation of whiskers growth is close to the surface of ZTA ceramics. When using B2O3+Mn O2 and B2O3+Zn O as raw materials, the crystallinity, distribution and growth density of whiskers have been improved greatly. The diameter of whiskers is about 500 nm to 2μm, where as the length of the whiskers ranges from 20μm to 30μm. The direction of the whiskers on the surface of ZTA ceramics is vertical to ZTA ceramics approximately.Based on the study of whisker growth, It has realized the joining of ZTA ceramic itself by in-situ growth Al4B2O9 and Al18B4O33 whiskers in joints, when using B2O3, B2O3+Mn O2 and B2O3+Zn O as raw materials respectively. When using B2O3 separately, the volume fraction of whiskers in joints is less than 50 percent,and the highest strength is 78 MPa at the temperature of 1000℃,holding time of 4h. when using B2O3+Mn O2 and B2O3+Zn O as raw materials, the joint interface improved obviously and the volume fraction of whiskers in joints increased to about 80 percent. The highest strength of joints is 168 MPa and 163 MPa separately at the optimum technological parameter. After high temperature thermal cycling, the strength of joints decreased significantly. when the heat cycle temperature is 1200℃, the strength is less than 50 MPa.Adopting ABS microcrystalline glass layer can implement the joining of ZTA ceramics at high temperature. Through the crystallization behavior of ABS microcrystalline glass, whiskers composite of glass phase formed in joints. At temperature of 1400℃, holding time 1h, the joint consists of Al2 Si O5 glass phase and Al18B4O33 whiskers. The strength of joints has good high temperature performance. and after 1200 ℃ high temperature thermal cycle, the strength can retain 95 MPa.