A novel rate based methodology for creep fatigue life estimation of superalloys

In this present work, we present an accumulated inelastic strain rate based methodology to predict creep fatigue life of two different superalloys i.e. Haynes 282 and IN 718. The evolution of differential strain rate during creep and fatigue respectively motivated the present work. As creep is the rate controlling damage process in creep fatigue interaction, present mean strain rate based approach considers creep strain rate as a kinetic variable controlling the process. The other variable considered for this approach is accumulative cyclic strain during Creep-fatigue interaction. Our prediction method is purely based upon a relative accumulation rate of creep and fatigue strain. This method correlates the creep fatigue life with rate of interaction in strain-controlled regions successfully from the data of creep fatigue tests on those superalloys at two temperatures, 650 °C and 760 °C. We found suitable microstructure sensitive constants in a lifing model

Surface Modification of Al-7075 Alloy by SiC-Cu Ceramic Electrode in Electrical Discharge Coating

5-142023The present study aims to enhance and evaluate Electrical Discharge Coating (EDC) on Al-7075 alloy using SiC-Cu ceramic electrode. The study analyses the impact of input parameters such as current, composition and compaction load on EDC responses, including Material Deposition Rate (MDR), Tool Wear Rate (TWR) and Surface Roughness (SR). Trial tests were performed using Taguchi's L9 experimental design, and thereafter, Grey Relational Analysis (GRA) and technique for order preference by similarity to an ideal solution (TOPSIS) were implemented to optimize all the responses. The experiments were optimized to achieve a higher MDR, lower TWR and lower SR. Analysis of variance was also employed to statistically investigate the experimental data and determine the contribution of each parameter to achieve better results. Optimum condition was achieved with a compaction load of 5 ton, current 6 A and composition 50:50, using both the GRA and TOPSIS methods. At the optimum condition, there was an improvement in GRA from 0.5603 to 0.7778, while TOPSIS showed an improvement from 0.2418 to 0.7659. Further, the morphology of the coated surface was investigated using scanning electron microscopy images and X-ray diffraction analyses, which confirmed the migration of SiC-Cu from the tool materials

Influence of ageing on high temperature tensile deformation of a Ni- based superalloy, HAYNES 282

The effect of ageing time and temperature on the deformation mechanism and corresponding tensile properties are investigated in a gamma/gamma ' Ni-based superalloy, HAYNES 282. Through a systematic variation in duration (24 h and 216 h) and temperature of ageing (650 degrees C and 760 degrees C), a significant variation in strengthening microstructural features was achieved in the resulting microstructures. While in one case (650 degrees C, 24 h ageing condition), a microstructure with no gamma ' was observed, for the rest of the cases, gamma ' precipitates of varied sizes were observed. In one specific case (760 degrees C, 216 h ageing condition), very fine (4-6 nm) MC carbides were observed along with gamma ' precipitates; in which these tiny MC carbides became the deciding factor for strength over gamma ' precipitates. While common knowledge of smaller gamma ' precipitates giving higher strength could explain the higher strength at 760 degrees C, 24 h ageing condition as compared to 650 degrees C, 216 h ageing condition, the further increase in strength in case of 760 degrees C, 216 h ageing condition, even with much larger gamma ' precipitates was something quite interesting and counterintuitive. This paper elucidates this puzzling observation. The variation of tensile properties of these wide varieties of microstructures will be described in this paper in light of the underlying deformation mechanisms. A change in deformation mechanism from planar slip (microstructure with no gamma ') to twinning (microstructure with gamma ') and Orowan-looping (microstructure with gamma ' along with fine nano carbides) as a function of microstructure explains the difference in strength, ductility, and strain hardening phenomena among the varied ageing conditions.(c) 2022 Elsevier B.V. All rights reserved

Ultrasonic quantification of high temperature cyclic damage in an advanced nickel based superalloy

Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefficient and number of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly influencing attenuation coefficient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and backwall echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence

Ultrasonic quantification of high temperature cyclic damage in an advanced nickel based superalloy

Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefficient and number of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly influencing attenuation coefficient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and badman echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence. (C) 2014 Elsevier B.V. All rights reserved