Site-Dependent Tension Properties of Inertia Friction-Welded Joints Made From Dissimilar Ni-based Superalloys

Abstract

Microstructure, tensile properties, and fracture behavior of the inertia friction weld joints of dissimilar superalloys, cast Mar-M247 and wrought LSHR, were studied to assess the weld quality. Tensile tests were conducted at 23 and 704°C on the samples containing different areas of the weld interface of the same welded material. The stress-strain curves were registered at different axial distances from the weld interface. In all tested samples, plastic deformation was localized on Mar-M247 side, outside the heat-affected zone (HAZ), and the resistance to plastic deformation of Mar-M247 increased with a decrease in the distance from the weld interface inside HAZ. Only elastic deformation occurred on the LSHR side. Fracture occurred on the Mar-M247 side, outside HAZ, or at the weld interface. In the latter case, welding defects in the form of clusters of nanometer-sized oxide and carbide particles were observed at the fracture surfaces. These results revealed that the IFW process is capable of producing the weld joints between Mar-M247 and LSHR with the fracture strength higher than that of Mar-M247. However, optimization of the IFW processing parameters is required to minimize clustering of oxide/carbide particles at the weld interface in this alloy pair.

Effect of Process Variables on the Inertia Friction Welding of Superalloys LSHR and Mar-M247

“…The yield strength of LSHR is approximately 50 pct higher as that of Mar-M247 at temperatures to 1023 K (750°C); at yet higher temperatures, Mar-M247 exhibits higher yield strength. [4,7] LSHR samples measuring 12.7-mm diameter 9 51-mm length were extracted from the center section of a 330-mm-diameter 9 51-mm-thick pancake forging using electrical discharge machining (EDM). The longitudinal direction of the extracted samples was parallel to the short transverse direction of the pancake; the end surfaces of each sample coincided with the surfaces of the forging.…”

“…Details of this procedure were reported previously. [7] A 2-D axisymmetric finite element model of the IFW process using the DEFORMä software was utilized to explore the effect of the weld process parameters (including process efficiency) on weld upset and peak interface temperature. Trends in predicted upset and peak interface temperature from the computer simulations were compared to experimental results to aid in the interpretation and analysis of the welding process.…”

“…This is an important finding in that straight/flat weld interfaces in these materials often indicate a lack of plastic deformation, are usually decorated with fine carbide and oxide particles, and typically yield poor bond quality. [4,7] It is also important to note that all three of the welds had the same applied axial load and initial flywheel kinetic energy, thus indicating that bond quality depended primarily on the flywheel moment of inertia and its impact on the weld duration. This observation is intuitive in that the weld times are longer, and therefore, the weld interface is held at an elevated temperature longer with a larger moment of inertia.…”

“…[4] The various welds exhibited two different types of mechanical behavior during post-weld tension testing [7] : (1) plastic deformation and fracture on the Mar-M247 side outside the heat-affected zone (HAZ) or (2) fracture at the weld interface. For the latter failure mode, microstructural analysis revealed defects that weakened the weld interface.…”

“…These flaws included submicron agglomerated/clustered oxide and carbide particles and/ or films at the weld interface and circumferential cracks at or near the interface on the Mar-M247 side. [4,7] The carbide and oxide particles were deduced to have been produced by friction-induced milling of large carbide particles and oxide film(s), respectively. Furthermore, particle clustering was concluded to have resulted from insufficient radial plastic flow of Mar-M247 during IFW.…”