Microstructure and Properties of Large Diameter Elbow of Ti75 Titanium Alloy with Short Radius Made by Expanded-Diameter and Pushed-Bend Method

The elbow made by expanded-diameter and pushed-bend method is feasible. Under the action of pushing force, expanding-diameter and bending moment of horn mould, the elbow generates composite deformation including bending and compressing deformation along axial direction and off-center expanding-diameter deformation along circumferential direction. The expanding-diameter deformation reduces wall thickness, while the compressing deformation of belly is greater than that of back, and result in thickening wall thickness on belly and eccentricity. The wall thickness flowed from belly to back along two sides of horn mould during expanding-diameter to compensate for thinned wall thickness on back of elbow during off-center expanding-diameter. The wall thickness uniformity of elbow was related to design of horn mould, pushing temperature and temperature field and pushing rate. The temperature of Ti75 titanium alloy elbow made by expanded-diameter and pushed-bend method was chosen in two phase region. It can reduce the deformation resistance and improve the alloy plasticity, and the elbow keeps the properties and microstructure consistent with pipe. The elbow made in β phase region easily produce grain over burning and overgrowing. The annealing of Ti75 titanium alloy elbow can be selected in two phases, which can keep elbow strength and microstructure homogenization.