Materials Science Forum Vols. 838-839

Abstract: The superplasticity of high Nb Ti₃Al based alloy - Ti-23Al-17Nb (at.%) alloy sheet under the conditions of 940~1000°C and 5.5×10^-5s^-1~1.7×10^-3s^-1are studied. The results show the elongation changes as a parabola with the deformation temperature increasing, and the maximum elongation obtained at 960°C and 5.5x10^-5s^-1 is 1447.5%. Work hardening stage increases much more than softening stage when strain rate is decreased due to the increasing of element Nb. Compared with primary microstructure, the lath-like α₂ grains gradually disappeared, the α₂ grains became more equiaxed, and the content and size of α₂ grains are decreasing with increasing of deformation temperature. The volume fraction ratio of α₂ and β phase at the optimum deformation condition is 50:50%. The cavities mechanism at the fracture tip was discussed; it can be defined that the cavities could be avoided when deformation temperature is higher than 940°C.

Abstract: This study proposes a novel method of manufacturing composite vibration-damping steel sheet with Zn-22Al superplastic alloy using friction stir forming (FSF). Trials of mechanical interlocking of steel sheet with Zn-22Al superplastic alloy using FSF were carried out on a modified milling machine. The results are discussed in terms of residual microstructures and mechanical properties. We concluded that cladding steel sheet with Zn-22Al superplastic alloy using FSF results in superplastic forming and diffusion bonding.

Abstract: CAD models were built for a three-layer SPF/DB cylinder component. FEM method was employed to simulate the SPF/DB process with different girder structure at appropriate temperature/strain rate combinations. The results show that topology parameters of the structure influence the thickness of outer sheet and surface quality. When the thickness ratio of outer sheet to inner sheet exceeded 3:1 and the angle between adjacent ribs was great than 110 degree, ribs were formed and the cylinder surface was perfect. The simulation result was verified by experiment. The experimental results showed that the optimized cylinder structure can be formed at 920°C, 1×10^-4 strain rate perfectly, and the size of blank cylinder diameter can be controlled accurately by SPF/DB mold and the size deviation is less than 0.5mm.

Abstract: Ti₃Al intermetallic alloy is a light and high-temperature resistant material which substitutes for superalloy. It is promising for wide use in aerospace yield. In this paper, the Ti₃Al alloy was joined by diffusion bonding with and without Ti-6-4 alloy interlayer respectively. Diffusion bonding quality and shear strength of the joints were measured and compared. The results show that there was almost no defect found in joints with interlayer and maximum shear strength is 523 MPa in conditions of 940°C and 2.5 MPa pressure for 1.5h. In contrast, defect rate (percentages of sum of defects length in optical micrograph) of joints without interlayer exceeds 80% and maximum shear strength is only 150 MPa in same conditions. According to fracture analysis, the ductile fracture occurred at Ti-6-4 interlayer of joint with interlayer. Fracture of joint without interlayer belongs to mixed type of ductile fracture and brittle fracture.

Abstract: Using low gas pressure as a tool to form metal sheets is certainly feasible. However, the intrinsic flow properties of metal sheet are often a key factor in determining degree of formability, which has not been emphasized or explained well. Most metals, for examples aluminum alloys, can be either superplastic or non-superplastic depending on their original processing history or route (consequently, yielding suitable microstructure) and forming conditions, i.e. mostly temperature and strain rate. This superplasticity effect is clearly demonstrated by gas forming superplastic AA5083 and non-superplastic AA5052 into a V-shaped deep trough containing uneven concavities. The results show the superiority of superplastic material when harsh product standard is required.

Abstract: A novel superplastic dieless drawing technique with local heating and tensile deformation has been focused on for fabrication of zirconia ceramic tube. In this study, 3Y-TZP zirconia ceramic tube with outer diameter of 6mm and inner diameter of 4mm as a superplastic material is used experimentally. An apparatus of superplastic dieless drawing with rotary stage for circumferential uniform heating and acetylene burner for high temperature of 1700°C is developed. The superplastiac dieless drawing experiment is carried out to investigate the effect of the ratio of drawing speed to feeding speed on the flexible controllability of diameter after drawing process. As a result, the reduction in area after drawing process can be controlled by the ratio of drawing speed to feeding speed. In addition, a maximum reduction in area of 79.2% can be realized in this process. Consequently, the validity of developed apparatus of superplastic dieless drawing for Zirconia ceramic tube can be demonstrated.

Abstract: A broad research programme was conducted at the Advanced Forming Research Centre to study the impact of key process variables in the manufacture of superplastically formed aero-engine components. The paper highlights the innovative methods adopted to investigate the factors affecting SPF process cycle-time, tool/component instrumentation for in-process measurements, and tool life. An extensive programme of forming trials conducted on a large press on real-scale components was performed to closely monitor key process parameters and understand their influence on the component inflation and cycle-time. Advanced experimental trials were conducted by instrumenting components and tool to analyse process variable live measurements in the harsh environment of the press during the SPF process. An extensive investigation of the chemical and physical interactions at the tool/component interface and their influence on surface finish and tool life was also conducted by using a range of specialised equipment and a custom-built SPF simulator.

Abstract: Application of the conventional superplasticity (SP) allows producing the unique hollow structures. One remarkable example is the hollow titanium blade of the air engine fan produced by Rolls-Royce. However, high temperature titanium alloys processing (~ 927 °С) limits wide industrial application of the conventional SP. The solution of the mentioned issue can be found through the application of low-temperature SP. Ti-6Al-4V alloy with ultrafine grain structure at the temperature range of 600 ­ 800 °С has enough ductility resources for the superplastic forming (SPF) of the parts with the complicated shape. The formation of pores in Ti-6Al-4V alloy at uniaxial and biaxial tension at the temperature 600 °С is not observed. The effect of low-temperature SP also allows lowering pressure welding (PW) temperature essentially. Herewith, there is a possibility to produce the hollow parts by the combination of SPF and PW. The main goal is the optimization of the technological scheme and processing temperature. The use of the low-temperature SP provides high quality of hollow components such as blades.

Abstract: The results of development of new resource-saving technologies of local shape-forming under superplastic deformation conditions (SP) by means of roll-forming and rotary swaging are presented. These technologies are efficient for fabrication of discs, shells, rings up to 800 mm in diameter, as well as hollow shafts made of heat-resistant nickel-, titanium-and iron-based alloys that are used in aircraft engines and ground power installations. In particular, to implement innovative technologies a universal SRZhD-800 roll-forming mill has been developed for discs roll-forming made of heat-resistant alloys under SP. An efficiency of using of semi-finished products with prepared ultrafine grained (UFG) structure for generating precise complex geometry profile parts both homogeneous and regulated structure that changing in the radial direction of the disc and for obtaining high mechanical properties that are optimized taking operational conditions into account is proved. The technological process of rotary swaging under SP conditions has been developed for fabrication parts made of high alloy heat-resistant alloys using demountable mandrels. This method allows to obtain precise complex geometry profile parts such as disc with a thin cone flange which is characterized by homogeneous structure and high mechanical properties.

Abstract: This paper outlines the methods used to develop a full 3D Finite Element Model (FEM) capable of accurately predicting the superplastic forming (SPF) process of a complex multi-sheet structure. The geometry studied is a three-sheet pack consisting of an inner core sheet diffusion bonded in particular locations to two outer sheets to create a hollow internal structure when inflated. The pressure cycle implemented in the model is also used on the AFRC’s 200T press to produce parts which are compared to the model results. Comparison of 3D scans of the parts with the predicted process from the analysis reveals favorable results.