Nonlinear Lamb wave for the assessment of ratcheting behavior in IF steel

This work demonstrates the use of nonlinear Lamb wave for characterizing the ratcheting behavior in interstitial free (IF) steel. Lamb wave has been used to measure the generated second harmonic component during ratcheting fatigue. A pair of wedge transducers is used to generate and detect the fundamental and second harmonic component of Lamb wave at various interruption of damage and correlation is made with nonlinear ultrasonic parameter. It is seen that acoustic nonlinear parameter evaluated using Lamb wave is very much sensitive to plasticity that has been induced during ratcheting

Influence of axial and torsional cyclic loading on the fatigue behavior of 304LN stainless steel using solid and hollow specimens

Effect of loading path and geometry on fatigue behavior was evaluated for 304LN stainless steel using solid and thin walled hollow specimens. Hollow specimens were subjected to both axial and shear loading under strain control. Solid specimens were used only for strain controlled axial loading. Fatigue life was highest for shear loading despite the higher stress response and the least for the axial loading for hollow specimens. The cyclic deformation behavior marked by Masing behavior, cyclic stress strain curves and probability density function analysis was found to be remarkably different for shear loading. All disparities in the cyclic deformation behavior due to difference in loading path has been accounted by the dislocation dynamics and martensitic transformation investigated through TEM

Influence of multiaxial cyclic plastic loading on grain boundary misorientation profile in austenitic stainless steel

304LN stainless was subjected to multiaxial loading employing different waveforms and load paths. The grain boundary misorientation profile so obtained post deformation was compared across loading conditions. It was found that the uniaxial and proportional conditions of loading result in more of twins, contrary to non-proportional loading conditions that resulted in substantially higher low angle grain boundaries. Also, under non-proportional loading the trapezoidal load path resulted in remarkably altered distribution of the grain boundaries compared to its contemporaries. Predominant martensitic transformation was found to be dominant mechanism of deformation for trapezoidal loading that also contributed to the altered misorientation profile

Characterization of Tempering Behaviour of Modified 9Cr-1Mo Steel by Ultrasonic Lamb wave Mixing

This work demonstrates the use of mixing of ultrasonic Lamb waves to characterize the tempering behaviour in metallic plate. Lamb wave mixing has been used to measure the generated second harmonic during tempering of mod.9Cr-1Mo steel plate. As-received material is normalized at 1080°C and then tempered in the temperature range of 600 - 850°C with a step size of 50°C for 1.5hrs and followed by furnace cooling. Lamb wave mixing technique has been used to assess the tempering behaviour of this material. Nonlinear ultrasonic parameter β which is the ratio of 2nd harmonic amplitude to the multiplication of the fundamental amplitudes is determined from the mixing wave at each temperature and correlated with microstructural characteristics. It is seen that this nonlinear acoustic parameter (β) is sensitive towards coherency strain generated between precipitate and matrix during tempering

Correlating Effect of Temperature on Cyclic Plastic Deformation Behavior with Substructural Developments for Austenitic Stainless Steel

Low-cycle fatigue experiments have been carried out at elevated and sub-zero temperatures. Corresponding effect on cyclic plasticity characterizing parameters such as cyclic hardening/softening and Masing behavior is compared for different loading conditions. Disparities in the fatigue life as well as the cyclic plastic behavior have been attributed to the phase transformations that largely obstruct the dislocation motion. Further, the changes in strains in the materials matrix have been quantified through misorientation studies, wherein clear demarcation in strain distributions due to fatigue loading at different temperatures was obtained and further correlated with the substructural alterations observed through transmission electron microscopy

Creep Deformation Behavior of Inconel 617 Alloy in the Temperature Range of 650 degrees C to 800 degrees C

Creep behavior of the Inconel 617 alloy has been investigated through tests carried out in the temperature range of 650 degrees C to 800 degrees C under 95 to 350 MPa. Creep curves obtained from tests on the alloy exhibit a non-classical nature, with the primary creep rate decreasing to a minimum value, followed by a typical increase, which is either continuous at temperatures 5 has been rationalized by considering the existence of threshold stress, which like n has been found to decrease sharply with temperature beyond 700 degrees C. Investigation of the post-creep microstructures by transmission electron microscope has revealed the formation of gamma ' and M23C6 precipitates, which obstruct dislocation motion during the primary stage. Microstructures of the samples creep-tested at >= 750 degrees C have exhibited relatively smaller amounts of gamma '. The existence of threshold stress and the steady-state regime in the tertiary creep stage has been ascribed to obstruction of dislocation motion by M23C6 and gamma ' precipitates

On the importance of local equilibria in alloy design criteria for bulk nano-pearlitic steels and ensuing mechanical properties

A critical review of the dependence of yield strength of pearlite on interlamellar spacing unveils the contribution of solid solution strengthening of ferrite. In order to understand the evolution of solute content within pearlitic ferrite, importance of various local equilibria modes (assumed to persist during transformation) has been realized and revisited in present work. With this understanding, an alloy composition and corresponding two stage cooling process have been designed to have nano-pearlitic microstructure (interlamellar spacing < 100 nm). Characterization of elemental partitioning across the growing pearlite-austenite interface using scanning trans-mission electron microscopy coupled with energy dispersive x-ray spectroscopy (STEM-EDS) reveals no-partitioning growth mode of pearlite. Further, mechanical properties have been assessed for samples inter-rupted during cooling post pearlite formation (at 635 ?, S-635) and for those cooled till room temperature (S-RT). Reduction in ferrite width from-70 nm to-65 nm along with increase in post transformation enrichment of pearlitic ferrite with Si from S635 and SRT, has been shown to lead to an increase in the yield strength from-680 MPa to-775 MPa in the deigned alloy