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

Nonlinear Lamb wave mixing for assessing localized deformation during creep

Nonlinear ultrasonic is known to be a promising technique to characterize the microstructural degradation in engineering materials. This work demonstrates the use of nonlinear Lamb wave mixing technique to assess the localized deformation in modified 9Cr–1Mo steel during creep. Two Lamb wave modes of different frequencies ( ω 1 & ω 2) are allowed to mix within the material under certain resonant condition to generate third type of harmonic waves of frequencies ( ω 1 ω 2). This new generated wave carries the information of material nonline- arity from the mixing site and independent of the other extraneous nonlinear factors. Amplitude of the generated third wave depends on the third order elastic constants of the material. This study reveals that nonlinear Lamb wave mixing technique could be used to assess the localized deformation much prior to its failure

Pitting Stochastic Study in Airframe Aluminium Alloy using Non-linear Ultrasonic

Pitting corrosion is considered to be one of the principal degradation mechanisms for high-strength aluminum alloys. The aircraft airframe has been the most demanding application for aluminum alloys. The combined effects of corrosion and cyclic loading have been shown to produce cracks from corrosion pits and pits have frequently been the source of cracks on aircraft components operating in fleets. Once the pit or group of pits form, the rate of pit growth is dependent mainly on the material, environmental conditions and type and state of stress. Therefore, to estimate the total corrosion fatigue life of a component, it is of great importance to develop realistic models to establish the component life in these situations and to formulate methods by which designers and operators know likely sources of pitting early in the design and fleet operation. There are certain gaps in knowledge with regards to life prediction for pitting initiated fatigue. The need is to gauge the extent of pitting damage of a component or material non-destructively and predict the remaining life through superimposition of the pertinent operational, environmental and material parameters. However, a foolproof non-destructive means to characterize and three-dimensionally map pits is not available. The pitting phenomenon has to be analyzed statistically and the kinetics of pitting assessed through a change in the statistical distribution parameter of pits rather than deterministic equations relating pit dimensions to time. In this work we have applied high frequency ultrasonic and non-linear ultrasonic to assess the damage due to pitting and attempt has been made to establish correlations between this non-destructive tools and pit stochastic

Microstructural Characterization of Precipitation Process in a Nickel-Alloy by Non-linear Ultrasonic

The nonlinear ultrasonic technique, using the amplitude ratio of higher harmonic frequencies and fundamental frequency, has been found to be strongly sensitive to the microstructure of bulk materials. It was reported earlier that in Al 2024 alloy the nonlinearity parameter increased with the generation of coherency precipitates. Similarly, Hurley et al reported that the nonlinear parameter linearly increases as a function of inhomogeneous strain due to the generation of a precipitate in low alloy steel. In contrast to these studies, in which researchers have studied ultrasonic nonlinearity in the context of single crystals and simple metals, we would like to study structural materials for the purpose of structural health monitoring. In order to characterize the material properties in facilities and during operation, one needs to understand the relation between the material degradation of structural materials and the features of the NDE parameters. Therefore, in the present study we attempted to assess the thermal degradation in one such structural material namely: Nimonic-263, nickel based precipitation hardenable alloy using the nonlinear technique. From the present study it was found that the response of the non-linear ultrasonic parameter b is faster and larger compared to the normal velocity measurements

Evaluation of Crystallographic Texture in SS316L Steel by Ultrasonic Signal Analysis

An attempt has been made to evaluate crystallographic texture in AISI 316L austenitic stainless steel through the analysis of ultrasonic signals. Results of ultrasonic signal analysis and birefringence effect were compared with orientation distribution function (ODF) of the material (macrotexture) evaluated using conventional X-Ray diffraction. In polycrystalline aggregates, ultrasonic wave velocities were strongly affected by crystallographic texture. In this work, 70% rolled steels of AISI 316L stainless steel was annealed isothermally at temperatures 450oC to 750oC at an interval of 50oC with holding time of 30 minutes at each temperature. Ultrasonic longitudinal and transverse velocities were measured in each annealed sample. Power spectrum of the windowed ultrasonic signal as well as peak shift of the shear wave signal were analyzed and co-related with the texture data. It was seen that power spectrum analysis of windowed signal could be a potential tool for evaluation of crystallographic texture in polycrystalline materials

Effective mechanical properties of multilayer nano-heterostructures

Two-dimensional and quasi-two-dimensional materials are important nanostructures because of their exciting electronic, optical, thermal, chemical and mechanical properties. However, a single-layer nanomaterial may not possess a particular property adequately, or multiple desired properties simultaneously. Recently a new trend has emerged to develop nano-heterostructures by assembling multiple monolayers of different nanostructures to achieve various tunable desired properties simultaneously. For example, transition metal dichalcogenides such as MoS2 show promising electronic and piezoelectric properties, but their low mechanical strength is a constraint for practical applications. This barrier can be mitigated by considering graphene-MoS2 heterostructure, as graphene possesses strong mechanical properties. We have developed efficient closed-form expressions for the equivalent elastic properties of such multi-layer hexagonal nano-hetrostructures. Based on these physics-based analytical formulae, mechanical properties are investigated for different heterostructures such as graphene-MoS2, graphene-hBN, graphene-stanene and stanene-MoS2. The proposed formulae will enable efficient characterization of mechanical properties in developing a wide range of application-specific nano-heterostructures

Application of Ultrasonic Technique for Materials property evaluation

The modulus of a material is defined by the ratio of stress component field to the strain component field. For an isotopic elastic material, two modulus values are sufficient to characterize the linear elastic behaviour but in case of anisotropic material more than two elastic moduli are needed to characterize the elastic behaviour

Evaluation of Equiaxed zone in Continuously Cast (CC) Billets using Ultrasonic C-Scan Imaging

The continuous cast billets has a heterogeneous structures consist of dendritic, columnar, equiaxed etc. Due to the fine grain structure, the core is harder compared to the columnar zone that causes breakage while drawing the rods. Moreover the carbon segregation takes place at the inter-columnar areas. Hence a large equiaxed zone is a desirable structure for the cast billets for drawing rods. Using Electromagnetic stirring (EMS), a well established high efficiency technique, is possible to achieve effective and reliable stirring of the molten steel in the continuous casting process, which can meet the metallurgical objective of improving the quality and productivity of cast products. This project attempts to establish the effect of EMS current on percentage equiaxed zone, central porosity and segregation of continuous cast HC billet for achieving acceptable high C billet quality

Determination of modulus of Aluminium alloy by ultrasonic technique

The determination of elastic moduli by ultrasonic wave technique relies on the relationships between the acoustic wave velocities in a material and the density and elastic properties of the material. Moreover ultrasonic wave propagations measurements afford a non-destructive means for determining elastic constants. This can be done by introducing longitudinal and transverse waves in the test objects and measuring corresponding velocities. Under this project, 2 and 5 MHz ultrasonic longitudinal and shear wave probes were used to measure the longitudinal and shear velocities of the supplied Aluminium alloy samples. Modulus of the samples was determined from the measured velocity using the software “ Ultrasoft” developed at NML. Measurements were carried on the supplied samples and report of each measurement was submitted within 10 days of receiving the samples

Effect of microstructure on non-linear behavior of ultrasound during low cycle fatigue of pearlitic steels

Influence of microstructural changes on the second harmonics of sinusoidal ultrasonic wave during low cycle fatigue (LCF) deformation in pearlitic steel was studied. Fatigue tests were interrupted and at every interruption, non-linear ultrasonic (NW) parameter (beta) was determined. Microstructures of cyclically deformed specimens at various cycles were examined by transmission electron microscopy (TEM). The variation of beta with fatigue cycles was correlated with the microstructural changes and the results were explained through the variation in dislocation morphology and carbon content of the steel. (C) 2010 Elsevier B.V. All rights reserved