Metallurgical Investigation on the Effect of BZL Welding of LPTR Blase Shrouded Tips of Aero Engines

BZL welding and assembly procedure could be an area of concern for failure of LPTR blades of acro engines that might have caused number of accidents of aircrafts. So the present investigation is aimed to understand the effect of number of times BZL welding performed on microstructure and properties of the LPTR blades shrouded tips.Hence four numbers of LPTR blades of R-29 aero engine with different number of times BZL welding carried out were investigated and the results were presented. The increase in grain size of the LPTR blade tip was observed with number of times BZL welding was carried out. Rounding of y' (gamma prime) phase is occurring with BZL weldings. The dissolution of y' (gamma prime) phase near interface between base metal and weld metal is observed. However, there is not much appreciable change in hardness of the blade tips with number of times BZL weldings performed were observed. Moreover all the BZL welded blade tips have compressive residual stress

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

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

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

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