Showing papers by "Gürel Çam published in 1999"

Characterisation of electron beam welded aluminium alloys

Abstract: Electron beam (EB) welding was performed on three different aluminium alloys, namely alloys 2024, 5005, and 6061 (plate thickness 5 mm except alloy 5005 which was 3 mm in thickness), to establish the local microstructure–property relationships that would satisfy the service requirements for an electron beam welded aluminium alloy component with weld zone strength undermatching. Microstructural characterisation of the weld metals was carried out by optical and scanning electron microscopy. A very low level of porosity was observed in all EB welds owing to surface cleaning before welding and the vacuum environment of the EB welding process. Extensive microhardness measurements were also conducted in the weld regions of the joints. Global tensile properties and fracture toughness properties (in terms of crack tip opening displacement, CTOD) of the EB joints were determined at room temperature. The effects of strength mismatch and local microstructure on fracture toughness of the EB joints are discuss...

Determination of mechanical and fracture properties of laser beam welded steel joints

Abstract: Laser beam (LB) welding is increasingly being used in welding of structural steels. The thermal cycles associated with laser beam welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone that usually exhibits a high hardness for C-Mn structural steels due to the formation of martensite. It is rather difficult to determine the tensile properties of a laser weld joint area due to the small size of the fusion zone. Complete information on the tensile and fracture toughness properties of the fusion zone is essential for prequalification and a complete understanding of the joint performance in service, as well as for conducting the defect assessment procedure for such weld joints. Therefore, an experimental investigation on the mechanical properties of laser welded joints using flat microtensile specimens (0.5 mm thick, 2 mm wide was carried out to establish a testing procedure to determine the tensile properties of the weld metal and heat-affected zone (HAZ) of the laser beam welds. In the present work, two similar joints, namely, ferritic-ferritic and austenitic-austenitic and one dissimilar ferritic-austenitic joint were produced with a CO 2 laser using 6-mm-thick steel plates. In addition to the testing of flat microtensile specimens, the mechanical properties were examined by microhardness survey and conventional transverse and round tensile specimens. The results of the microtensile specimens were compared with standard round tensile specimens, and this clearly showed the suitability of the microtensile specimen technique for such joints. The crack tip opening displacement (CTOD) tests were also performed to determine the fracture toughness of the LB welds using three-point bend specimens. The effect of strength heterogeneity (mismatchingj across the weld joint and at the vicinity of the crack tip on the CTOD fracture toughness values was also discussed.

Diffusion bonding of investment cast γ-TiAl

Abstract: Intensive alloy development studies on intermetallic gamma (γ) based alloys in recent years has led to the development of several aerospace engine components using advanced γ-TiAl based alloys by ingot and powder metallurgical routes. These materials are of great interest to the aerospace industry owing to their very low density and good high temperature properties. Further application of this material will require the development of successful joining and cost effective fabrication methods. Joining of this intermetallic alloy by fusion joining processes, however, requires very careful process controlling, i.e. low cooling rates and very high preheat temperatures. On the other hand, solid state joining processes, particularly diffusion bonding, brazing, and friction welding, can readily be used to join this material. In the present work, successful application of solid state diffusion bonding to weld investment cast γ-TiAl alloys has been demonstrated. A series of diffusion bonds were produced without using an interlayer at temperatures ranging from 950 to 1100°C with different pressure levels and holding times. Bonds have been characterized using optical and scanning electron microscopy. Defect-free bonds were achieved for all the conditions studied. The bond qualities were assessed by shear testing at room temperature. Reasonable shear strength levels were obtained by bonding at 1000 and 1100°C for 3 h at pressures of 20 and 40 MPa, respectively. The bonds were also post bond heat treated at 1430°C for 30 min, which improved the bond quality in all cases.