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When dealing in ultrasonic testing with
inhomogeneous material structure data interpretation can be
rather difficult. This is especially the case when using anisotropic
dissimilar welds made from austenitic steel or nickel based alloys,
which are currently used for modern power plant concepts. In
this work we present an electrodynamic technique to visualize
sound waves with frequencies up to 3 MHz in steel components
providing a simple use and a high signal-to-noise ratio. By
detecting the grazing beam with an electrodynamic probe, we
measured the particle displacement as a function of time with a
spatial resolution in the order of 1 mm. Adapting the
electrodynamic probe and its coil alignment allows for measuring
the displacement components in all three dimensions. This
comprises the detection of the horizontal and vertical particle
displacement with respect to the surface and thus also the
transformation from longitudinal waves into transversal waves
and vice versa. We report on measurements of the sound field in
a complex narrow-gap weld, joining a nickel alloy with a chrome
steel with a substantial anisotropy of the weld structure. The test
system enables us to visualize the wave propagation within the
weld and indicates the reflection scenario and the energy losses
due to both the anisotropic structure and material defects.
A x-ray radioscopy technique for measuring in situ chemical diffusion coefficients in metallic melts
is presented. The long-capillary diffusion measurement method is combined with imaging
techniques using microfocus tubes and flat panel detectors in order to visualize and quantitatively
analyze diffusive mixing of two melts of different chemical composition. The interdiffusion
coefficient as function of temperature and time is obtained by applying Ficks diffusion laws.
Tracking the time dependence of the mean square penetration depth of the mixing process allows to
detect changes in the mass transport caused by convective flow. The possibility to sort out
convective mass transport contributions from analysis enhances significantly the accuracy compared
to the conventional long-capillary diffusion measurement method with postmortem analysis. The
performance of this novel diffusion measurement method with x-ray radiography technique is
demonstrated by a diffusion experiment in an Al-Ni melt.
Dissimilar metal weld overlays of nickel base alloys on low alloy steel components are commonly used in the oil and gas, petro-chemical, and power generation industries to provide corrosion and oxidation resistance in a wide range of service environments and temperatures. Traditionally, weld overlays are produced using cold or hot wire gas tungsten arc welding (GTAW). Potential advantages of cold metal Transfer (CMT) welding, a low heat input gas metal arc welding process, over the conventional GTAW in production of weld overlays were evaluated. Metallurgical characterization was performed on CMT overlays of Alloy 625 filler metal on Grade 11 and Grade 22 steels. Significant grain refinement was found in the high temperature HAZ compared to the traditional coarse-grained HAZ in arc welding. Evidences of incomplete carbide dissolution, limited carbon diffusion, and incomplete transformation to austenite were also found. These phenomena were related to high heating and cooling rates and short dwell times of the high-temperature HAZ in austenitic state. Tempering effects in the steel HAZ were identified, showing a potential for development of CMT temperbead procedures. Based on the results of this study, the steel HAZ regions in CMT overlays were classified as high-temperature HAZ and intercritical HAZ.
Dissimilar metal weld overlays of nickel-base alloys on low-alloy steel components are commonly used in the oil and gas, petrochemical, and power generation industries to provide corrosion and oxidation resistance in a wide range of service Environments and temperatures. Traditionally, dissimilar weld overlays are produced using cold or hot wire gas tungsten arc welding.
This study aims to identify and evaluate potential advantages of low heat input gas metal arc welding processes over the conventional gas tungsten arc welding in the production of such overlays. Parts I and II of this publication series described characteristics of the heat-affected zone and the transition zone region of alloy 625 on grade 22 steel overlays. These results indicate a good resistance against hydrogen-assisted cracking, which is being verified within this third part of the publication series. To determine the hydrogen-assisted cracking susceptibility, welded samples are tested using the delayed hydrogen-assisted cracking test. Fractography is performed using scanning electron microscopy along with energy dispersive spectroscopy. The results confirm the suitability and efficiency of low heat input gas metal arc welding for dissimilar weld overlays. Variation of the postweld heat treatment procedure bears potential for improvement in this respect.
Dissimilar metal weld overlays of nickel-base alloys on low-alloy steel components are commonly used in the oil and gas, petrochemical, and power generation industries to provide corrosion and oxidation resistance in a wide range of service Environments and temperatures. Traditionally, dissimilar weld overlays are produced using cold or hot wire gas tungsten arc welding.
This study aims to identify and evaluate potential advantages of low heat input gas metal arc welding processes over the conventional gas tungsten arc welding in the production of such overlays. Parts I and II of this publication series described characteristics of the heat-affected zone and the transition zone region of alloy 625 on grade 22 steel overlays. These results indicate a good resistance against hydrogen-assisted cracking, which is being verified within this third part of the publication series. To determine the hydrogen-assisted cracking susceptibility, welded samples are tested using the delayed hydrogen-assisted cracking test. Fractography is performed using scanning electron microscopy along with energy dispersive spectroscopy. The results confirm the suitability and efficiency of low heat input gas metal arc welding for dissimilar weld overlays. Variation of the postweld heat treatment procedure bears potential for improvement in this respect.
A new technique for investigation of interfacial dislocations in nickel-base superalloys by scanning electron microscopy is presented. At high temperatures the pressure of interfacial dislocations against the γ/γ'-interface causes grooves. This 'fingerprint of the dislocation network' is visualized by deep selective etching, which removes the γ'-phase down to the γ/γ'-interface. Compared with transmission electron microscopy, the proposed method has important advantages: observation of large sample areas, no superposition of dislocations lying in different specimen depths, possibility of three-dimensional view of dislocation configurations, information about the dislocation mobility, reduced time for preparation and visualization. The method can be applied for multiphase materials where the interface is grooved by interfacial dislocations.
The influence of small rhenium additions on the lattice spacing of a nickel solid solution was investigated using a nickelrhenium single crystal with an axial macrosegregation of rhenium. The effect of rhenium on the lattice spacing of the nickel solid solution was found to be similar to that of tungsten.
A new technique for investigation of interfacial dislocations in nickel-base superalloys by scanning electron microscopy is presented. At high temperatures the pressure of interfacial dislocations against the gamma/gamma'-interface causes grooves. This 'fingerprint of the dislocation network' is visualized by deep selective etching, which removes the gamma'-phase down to the gamma/gamma'-interface. Compared with transmission electron microscopy, the proposed method has important advantages: observation of large sample areas, no superposition of dislocations lying in different specimen depths, possibility of three-dimensional view of dislocation configurations, information about the dislocation mobility, reduced time for preparation and visualization. The method can be applied for multiphase materials where the interface is grooved by interfacial dislocations.