Residual stresses in a quenched superalloy turbine disc: Measurements and modeling

Abstract

A series of neutron diffraction measurements have been carried out to determine the elastic residual strains deep within a large, 40-cm-diameter, forged and water-quenched IN718 aeroengine compressor disc. Neutron path lengths of up to 6 cm were necessary to probe the thickest parts of the forging, and three-dimensional strain and stress components have been derived for the first time in such a large superalloy specimen. Measurements have been compared with the results from a coupled thermal-mechanical finite-element model of the quenching process, based upon appropriate temperature-dependent material properties, with some success. The general residual stress state in the disc is one of near-surface compression, balanced by tension within the disc interior. The steepest stress and strain gradients occur in the transition region from compression to tension, about 1 cm below the surface all around the disc. The largest stress component is in the disc tangential direction and reaches a magnitude of 400 to 500 MPa near the disc surface and at its core. This exceeds the effective yield stress because of the presence of significant hydrostatic stress.

In Situ Study of the Stress Relaxation During Aging of Nickel-Base Superalloy Forgings

“…direction the quench stresses are characteristically parabolic for Inconel 718, as is commonly seen for the through-thickness residual stresses upon quenching plates. [4][5][6] However, the maximum tensile stress values in Inconel 718 are found to be approximately 150 MPa higher in the present work than in References 4 through 6 where the maximum tensile stress values did not exceed 500 MPa. The reason for this may arise from the different geometry of quenched components as well as divergences in the quenching procedures such as variations in the transfer duration from the furnace to the quench tank.…”

“…In particular, processes such as forging followed by quenching/fast cooling generate very high level of residual stress in Ni-base superalloys. [4][5][6][7] Consequently, there is a requirement to precisely control and minimize the residual stress distribution because they can lead to distortion during machining and they superimpose on the operating stresses which can significantly reduce component life in-service. [8] Residual stresses are mitigated by means of thermal stress relaxation through the application of an annealing treatment, which also serves the purpose of an aging treatment precipitating or optimizing the distribution of the before mentioned strengthening phases, [9,10] A comparative study of residual stresses induced by inertia friction welding and subsequent thermal relaxation of these stresses by post-welding heat treatment (PWHT) was carried out by Preuss et al [11] The applied PWHTs were performed at temperatures close to the usual aging temperature.…”

Characterization of Plastic Flow Pertinent to the Evolution of Bulk Residual Stress in Powder-Metallurgy, Nickel-Base Superalloys

“…Converting the CRSS defined by Eq. [8] to the corresponding axial stress (under axisymmetric deformation conditions) using M = 3.06 and taking C APB to be 0.1 J/m 2 , [32] the strength increment associated with the fine or coarse precipitates was estimated to be 299 and 238 MPa, respectively. The difference (61 MPa) was approximately one-half the measured value for LSHR at 1144 K (871°C) and a strain rate of 10 À4 s À1 (Figure 7(a)).…”

“…[3][4][5][6][7][8][9] In addition to part geometry, initial temperature, and orientation relative to the quench medium, inputs to such models include the thermophysical properties of the part/quench medium, interface heat transfer coefficients, and the constitutive response of the workpiece, each of which must be input as a function of temperature.…”

Residual stresses in Inconel 718 engine disks

“…This step always starts with rheological tests required for different temperatures, strain rates and cooling rates. The model to be fitted can be quite simple (elasto-plastic formulation) [4,5] or much more sophisticated (kinematic hardening law) [6]. According to MATEC Web of Conferences the uncertainty of the current residual stress measurement methods, an elasto-plastic formulation is found sufficient for accurate residual stress prediction.…”