bnsio2与nb的钎焊连接工艺及机理研究word格式论文.docxVIP

AbstractBN/SiO2 ceramic and Nb are always used as the material of attitude control engine injector for its excellent thermal performance. However, there exist some difficulties in the brazing of those two materials since their difference in coefficient of thermal expansion (CTE) would produce great thermal residual stress. Ti-Ni braze was introduced to join these two material for its high temperature properties.From the view of releasing residual stress, an interlayer of interpenetrating phase composites was added to improve the matching of CTE. The reinforced mechanism was primarily researched through theoretical analysis and finite element analysis.Ti-Ni braze was successfully adopted to join BN/SiO2 ceramic and Nb. The optimum processing parameters and Ti-Ni proportioning ratio were heating to 1140℃,holding for 5min with Ti/Ni=1. The maximum shear strength of the joint was 59MPa. The typical interfacial structure was: Nb/(βTi,Nb)-TiNi/TiNi+Ti2Ni/TiN+TiNi+TiNi3/ TiN+Ti3O5+TiB2+Ti5Si3/BN-SiO2. (Ti,Nb) solid solution aggregated and grew with the higher temperature. The dissolution of Nb increased and reaction layer thicken with the longer holding time. (Ti,Nb) content decreased and Ni3Nb was observed with the lower Ti/Ni.The mechanism of interfacial reaction was researched. The starting temperature was 1100℃. Nitrogen atom was always being the forward position. The [N] in TiN coulddiffuse forward continually in the braze. An dynamics model was created to research on the Nb dissolution. The relationship between the width of ternary eutectic zone and the holding time was researched.Interpenetrating phase composites was added as an interlayer between the BN/SiO2 and Nb. The shear strength of the joint could reaches 90MPa with a 50% improvment under the condition that the thickness is 100um and porosity is 50%. It was found that shear strength increased firstly and decreased then with the accretion of thickness and porosity. The braze infiltrated more thoroughly with th