High-Temperature Buckling Analysis of Titanium Cans Under External Pressure

Abstract

Powder metallurgy techniques are often used in the fabrication of finished and semi-finished articles. At the CEA, a cold followed by a hot isostatic pressing method is used to produce solid forms from various types of powder. Occasionally, during the hot isostatic pressing part of the process, buckling of the titanium envelope near to the sealed end leads to fracture of the can and incomplete powder consolidation. The aim of this paper is to investigate by numerical finite element simulation the fracture process. A 2-D shell element model with Fourier series taking into account plastic deformation of the can material has been considered and used to determine the buckling critical pressure and the corresponding buckling mode. The simulation has been used to eliminate failure of the can by modifying the temperature-pressure schedule or by changing the can design. The calculations show that reducing the sharp angles of the initial titanium can near the rupture area can resolve the buckling problem; however, this solution is not totally satisfactory due to the development of a zone of constriction (breaks and irregularities) in the compacted powder just behind the modified can wall. This geometrical defect leads to difficulties in machining the final product. A better solution to the problem is to increase the initial can temperature prior to application of the pressure. This leads to a can of enhanced ductility with a better ability to deform. This latter solution, which can be employed with or without can modifications, eliminates both the can’s buckling and the zone of constriction. These numerical results have been validated by recent tests performed in our laboratories.