SPF/DB Processing Of Multi-layer Structure For Ti-23Al-26Nb Alloy

Ti2AlNb-based alloy has the higher temperature strength than other kinds oftitanium alloy and the lower density than Ni-based superalloy. As a result,Ti2AlNb-based alloy can greatly improve the thrust-weight ratio and fuel efficiency ofaerospace machinery, and the advantages also make Ti2AlNb-based alloy has higher usevalue than Ni-based superalloy. As Ti2AlNb-based alloy belongs to difficult formingalloy, it can not form well by conventional forming technology but by superplasticforming/diffusion bonding technology. To promote the application of Ti2AlNb-basedalloy, this paper studied the superplastic property and diffusion bonding property ofTi-23Al-26Nb alloy, and then explored the SPF/DB processing of three-layer structurefor Ti-23Al-26Nb alloy.First, the paper did unidirectional tensile test of Ti-23Al-26Nb alloy in differentstrain rate and temperature, the result shows that the optimum superplastic deformationtemperature and strain rate were980℃and5×10-4s-1respectively, and the calculatingdata indicates that the strain rate sensitivity coefficient and the material coefficient were0.31and507.1MPa·s respectively. The elevated-temperature diffusion bondingexperiments were taken to investigate the diffusion bonding property of Ti-23Al-26Nballoy, and the result shows that the diffusion bonding ratio can reach99%, the shearstrength of diffusion joint can be766.7MPa and the microstructure of the joint isuniform under the condition that the pressure was20.83MPa and the pressure holdingtime was2h.According to the results of the unidirectional tensile test, the three-layer structureforming process was simulated using the numerical simulation software Marc. Thesimulation results in different strain rate were analyzed and the results shows that theoptimal strain rate is5×10-4s-1. In this case, the thickness distribution is uniform and theforming time is proper, and the quality of the drip molding can meet the requiry. Thecorresponding time-pressure curve was obtained, which can provide a certain basis onthe subsequent SPF/DB forming process.Finally, doing the multi-layer structure diffusion bonding experiment by using the temperature and pressure parameters which confirmed by the results ofhigh-temperature diffusion bonding experiments. Then did the superplastic formingexperiments according to the results of simulation. The reasons of failure were analyzedand appropriate solutions were proposed in order to raise the quality of the three-layerstructure.