Effect of Microstructure on Electrical Conductivity of Nickel-Base Superalloys
- PDF / 5,127,052 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 91 Downloads / 230 Views
RODUCTION
MOST of the aerospace components undergo mechanical surface treatments (MST) such as shot peening, laser shock peening, or deep rolling for fatigue life improvement through induced cold work and compressive residual stress.[1] One of the biggest challenges regarding the process control of MST has been the evaluation of residual stress over the surface and subsurface of the components. The existing measurement techniques such as center hole drilling (CHD) and X-ray diffraction (XRD) are either destructive or semi-destructive for evaluating residual stress over the subsurface-treated depth. Efforts in developing a non-destructive system for the residual stress measurement have been ongoing for decades.[2–4] A promising non-destructive method for residual stress depth profiling of subsurface components, which is suitable for BALASUBRAMANIAN NAGARAJAN and SWAMINATHAN ANNAMALAI are with the Rolls-Royce@NTU Corporate Laboratory, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. SYLVIE CASTAGNE, ZHENG FAN, and WAI LUEN CHAN are with the School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. Contact e-mail: [email protected] Manuscript submitted November 16, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
nickel-base superalloys, has been proposed by Blodgett and Nagy[5] using eddy current (EC) spectroscopy. The principle behind the eddy current method is the piezoresistivity relationship between electrical conductivity and elastic stress in the material. Different methodologies to calculate the residual stress from coil impedances have been developed by various researchers.[6–9] However, the residual stress evaluation from the eddy current conductivity profile is affected by the cold work and microstructure of the surface-treated components.[10] Different microstructure variables including grain size, chemical composition, presence of short-range orders, dislocations, fraction and size of the precipitates could influence electrical conductivity.[11–14] For a reliable characterization of the near-surface residual stress of surface-treated components using the eddy current technique, it is important to understand the effect of material microstructure on electrical conductivity profiles. Zergoug et al.[15] observed a change in coil impedance for different heat treatment conditions on both ferrous and non-ferrous materials, where a correlation between the grain size, microstructure types, and hardness was demonstrated. Hillman et al.[16] reported a change in the electrical conductivity of IN718 with and without precipitation hardening, mainly due to the grain size and the precipitates. Bassam et al.[17] systematically
studied the microstructure effect of IN718 on the eddy current conductivity using various heat treatment cycles. For an increasing time and temperature of aging, a significant increase in the hardness and bulk conductivity (measured as AECC, apparent eddy current conductivity) of the material was observe
Data Loading...
