| The joining of sapphire and TC4 is sorted to the joining of ceramic and metal,of which the significant residual stress in the joint is the greatest problem.Brazing has always been the leading technology in the joining of ceramic and metal.So in this research brazing is used to join sapphire and TC4 alloy.The technologies of in-situ synthesizing and interlayer brazing are used.The feasibility of Ag based Ag-28Cu+x Ti composite fillers wetting on sapphire has been studied,which are conducted on the <001> plane of sapphire.When the percentage of Ti reaches 9wt.%,the best wetting angle is obtained.Then Ag-28Cu+9wt.%Ti are used to brazing sapphire to sapphire.By analyzing t he microstructures and phases of the joint,the interfacial microstructured are determined.The thermo-dynamic conditions and mechanism of the brazing process has also beed studied.In order to ease the residual stress in the joint of sapphire and TC4,in-situ synthesizing technology is used to brazing sapphire and TC4.Due to the study in Chapter 3,the typical microstructures has been determined,which is sapphire/Ti3(Cu,Al)3O/Ti2(Cu,Al)+Ti2Cu/Ti B+Ti B2+Ag(s.s)+Ti2Cu+Ti(Cu,Al)/(αTi+Ti2Cu)+Ti3Al+Ti2Cu/TC4.The influence to the phases and microstructures of temperature and Ti B2 ’s percentage are both studied.The mechanism of the brazing process is: physical contact of composite filler and base metal;the Ti B whisker and Ti3(Cu,Al)3O forms;the Ti B whiskers continue to grow,Ti2 Cu and Ti2(Cu,Al)form;Ti Cu and Ti(Cu,Al)form,(αTi)+Ti2Cu and Ag(s.s)separate out.When the in-situ synthesizing technology is used to braze sapphire and TC4 alloy,the strength of the joint is not strengthened properly,and cracks form in the sapphire.So the interlayer technology is used to brazing sapphire and TC4 alloy.Mo interlayer and Ag-28Cu+9wt.%Ti+Mo composite filler are both used to braze sapphire and TC4.A brief discussion of the microstr uctures of the joint is conducted.Shear strength test are performed with the samples.The reason of the fracture of the joint has been discussed.By showing the influence of the thickness of Mo interlayer to the joint,the suitable thickness of the Mo int erlayer is abtained.As the thickness of the Mo interlayer grows,the cracks reduce and disappear.The highest strength falls at the thickness of 300μm,which is 13.25 MPa. |
