D.C. Fernando

Bio: D.C. Fernando is an academic researcher from Gas Turbine Research Establishment. The author has contributed to research in topics: Superalloy & Deformation (engineering). The author has an hindex of 2, co-authored 3 publications receiving 21 citations.

Tensile deformation micro-mechanisms of a polycrystalline nickel base superalloy: From jerky flow to softening

Abstract: In this study, efforts were made to elucidate the tensile deformation micro-mechanisms of a polycrystalline nickel-base superalloy used for the fabrication of critical rotating and stationary components of the gas turbine engine under relevant service conditions. The microstructural evolutions during the investigated temperatures and strain-rates are explicitly indicating the divergence in associated tensile responses. The alloy exhibits serrated or jerky flow behavior at 300 and 400 °C, whereas, yield strength anomaly (YSA) is observed at 750 °C. With further increase in testing temperature, softening mechanisms start dominating and dynamic recrystallization occurs at 930 °C. TEM investigation revealed that the serration in the flow curve at 300 °C is attributed to the disordering of the secondary γ′-precipitates by the leading a/2 dislocation super-partial and refurbishment of order through thermal activation before the trailing super-partial arrives. The YSA observed at 750 °C is essentially due to the cross-slip of dislocation super-partials and the presence of dislocation debris.

Effects of hot isostatic pressing treatment on the microstructure and tensile properties of Ni-based superalloy CM247LC manufactured by selective laser melting

Abstract: This study manufactured CM247LC Ni-based superalloy, which has outstanding mechanical properties, using the laser powder bed fusion (L-PBF) method and selective laser melting (SLM). Furthermore, the effect of hot isostatic pressing (HIP) post treatment on the microstructure and mechanical properties of SLM-built CM247LC was investigated. The defect characteristics of SLM-built superalloy changed significantly according to scan speed and hatch space, and it achieved the optimal microstructure at an intermediate scan speed (600 mm/s). SEM, EBSD, and ECCI analyses of the as-built alloy identified grains that developed in the build direction, sub-grains consisting of dislocation networks and MC carbides. In addition, γ’ phase formed evenly throughout the sample after HIP post treatment. The as-built CM247LC showed a yield strength of 933.5 MPa and tensile strength of 1144.0 MPa. In the case of the HIP alloy, the yield strength remained at a similar level, but tensile strength increased significantly up to 1457.1 MPa, and tensile elongation increased four times compared to the as-built alloy. Based on the above findings, this study discussed the correlations between microstructure, improved tensile properties and deformation mechanism.

Effect of Warm Laser Shock Peening on the Low-Cycle Fatigue Behavior of DD6 Nickel-Based Single-Crystal Superalloy

Abstract: By conducting tension–tension low-cycle fatigue tests on three groups of specimens, this paper determined the mechanism and effect of warm laser shock peening (WLSP) on the fatigue performance of DD6 nickel-based single-crystal superalloy. The WLSP treatment induced ripples at the specimen surface, residual stress fields, and dislocation structures in the near-surface layers. The induced ripples increased the surface roughness of the specimens, and the residual stress fields and dislocation structures improved their surface microhardness. Moreover, both the surface roughness and surface microhardness exhibited a tendency to increase with the increase in the WLSP treatment number. During the low-cycle fatigue tests, the specimens underwent plastic deformation, and the $$a/2\left\langle {110} \right\rangle \left\{ {111} \right\}$$ slip system was activated. In addition, the WLSP-induced dislocation structures developed during the low-cycle fatigue tests produced dislocation networks and superlattice intrinsic stacking faults, both of which had a positive effect on prolonging the fatigue life of the material. Furthermore, the fatigue life of the material tended to increase with the increasing number of WLSP impacts.