Microstructures And Strength Of ZrO₂-Ti6Al4V Joints Using Crystalline And Amorphous Brazing Fillers

Zirconia is a beneficial ceramic material in many structures and devices due to its highstrength, fracture toughness and hardness. However, its brittleness and lack of flexibilitymake the fabrication of complex shaped and/or large-sized components difficult. Manystructural applications of zirconia demonstrate its reliable and durable joining to metals.Among these metals, Ti–6Al–4V alloy is most often introduced to bonding with zirconia.The combination of high specific strength, good tensile strength at moderate temperatureand excellent corrosion resistance make them widely be applied in the aerospace industries.One of the mostly widely used filler metal is based on the Ag–Cu–Ti system, namely onthe Ag–28wt.%Cu eutectic composition, with about2–5wt.%of titanium additions.Nevertheless, consumption of a large amount （60-70wt.%） of the noble metal, Ag, in thebrazing filler is the main disadvantage of these alloys. Recently, amorphous alloys have beenused as brazing fillers. The amorphous fillers have significant advantages such as unique offoil form combined with outstanding ductility and flexibility, wide range of width andthickness available. In particular, the amorphous fillers containing active Ti and Zr elementswith good glass forming ability may replace the traditional Ag–Cu–Ti filler alloys in somecases.In this paper, the interface reaction mechanism was studied, and the effect of brazingprocess parameters on microstructure and shear strength was investigated when the ZrO₂ceramic and Ti–6Al–4V alloy were brazed with Ag–Cu–Ti and Ti, Zr and Cu–based threekinds of amorphous fillers using by XRD, SEM, FESEM, EDS and the MTS material testingmachine and so on detection means. And then deduce the interface structure of control ordecision properties characteristics, and defines interface microstructure of the brazingprocess parameters. Establish the relationship of filler composition, brazing processparameters and interface microstructure. It provides a necessary theoretical basis andapplications for the development of novel amorphous fillers in the ZrO₂/Ti–6Al–4V joints.The major results of the present study are as follows:（1） Reveals the wetting of molten Ag–Cu–Ti metallic glass alloy on the ZrO₂substratebelongs to the reactive wetting. The reaction products are mainly TiO, Cu–Ti–O phases andCu–Ti intermetallic compounds. Study the Ti element content in the alloy filler （4–10at%） and temperature on the reaction system of wetting behavior, and wettability change rule.With the increase in the content of Ti, the wettability of Ag–Cu–Ti/ZrO₂systems areimproved significantly. It is the anomalous dependence of wettability of Ag₅₄Cu43Ti₄/ZrO₂system on the temperatures.（2） The ZrO₂/Ag₅₃Cu₄₁Ti6/Ti–6Al–4V system in the brazing process parameters affectthe performance of joint interface microstructure and joint are studied. The interfacestructure was ZrO₂/TiO+Ti₂O+Cu₂Ti₄O/Ag/CuTi+CuTi₂/Widmanst ten/Ti–6Al–4V withAg₅₃Cu₄₁Ti6filler. Brazing temperature, holding time and cooling rate is unfavorable higheror too fast, higher brazing temperature and holding time is too long, active element Ti in thealloy filler with parent metal reaction degree aggravate, easily lead to TiO+Ti₂O+Cu₂Ti₄Oreaction and Widmanst ten layer thickness increases. Cooling rate too fast, easy to producethe micro defects such as cracks and holes, have adverse effects on the interface strength.When the brazing temperature was1123K for10min, the cooling rate of5K/min for theoptimal parameters, the joint is better; the reaction layer thickness is moderate. The shearstrength was178MPa.（3） Reveals the wetting of molten Cu₅₀Ti₃₃Zr17, Ti₄7Zr28Cu14Ni11and Zr₅₅Cu₃₀Al₁₀Ni₅three amorphous alloys on the ZrO₂substrate belongs to the reactive wetting. The wettabilityof the amorphous fillers on the ZrO₂substrates obvious dependence on temperature, hightemperature helps the wetting. The reaction products are mainly TiO, Cu–Ti–O phases andintermetallic compounds. Due to the active elements of Ti, Zr in the fillers, enrichment andparticipate in the interface and reaction, greatly improve the wettability of the system. Buthigher element Zr concentration would inhibit Ti and ZrO₂reaction generated TiO+Ti₂Ocompounds, thereby weakening Ti wetting role in the reaction. But in the high temperature,high content of Ti and Zr will also generate a large number of brittle phases, resulting in thealloy droplets and ceramic substrate at the interface of micro–crack or even peel. Cu and Nielement can be infinite solid solution, amorphous fillers after the melt flow rate is enhanced.Wettability order: Cu₅₀Ti₃₃Zr17/ZrO₂>Ti₄7Zr28Cu14Ni11/ZrO₂> Zr₅₅Cu₃₀Al₁₀Ni₅/ZrO₂.（4） Set up three kinds of amorphous fillers brazing system of process parameters, theinterface microstructure and the inner link between and among joint shear strength. Overall,the brazing temperature, holding time and cooling rate determines the thickness of theinterfacial reaction layer, intermetallic compounds and Widmanst ten stucture and thenumber of distribution, and finally decided to the shear strength of joint. On the specificprocess, brazing temperature had a greater influence on the thickness of the interfacialreaction layer, is critical in shear strength. Holding time has a key role of intermetalliccompounds and Widmanst ten stucture distribution and the number. Slow cooling rate canreduce the residual stress, reducing the occurrence of the micro defects. Shear strengthmainly depends on the thickness of the interfacial reaction layer, the less of intermetalliccompound and Widmanst ten stucture and the slow cooling rate.（5） Summed up the brazing optimal parameters of the three systems:① ZrO₂/Cu₅₀Ti₃₃Zr17/Ti–6Al–4V system, when the brazing temperature was1173K for10min,the cooling rate of5K/min for the optimal parameters, the shear strength was162MPa.②ZrO₂/Ti₄7Zr28Cu14Ni11/Ti–6Al–4V system, when the brazing temperature was1173K for10min, the cooling rate of5K/min for the optimal parameters，the shear strength was85MPa.③ZrO₂/Zr₅₅Cu₃₀Al₁₀Ni₅/Ti–6Al–4V system, when the brazing temperature was1173K for10min, the cooling rate of5K/min for the optimal parameters, the shear strength was95MPa.