Microstructure investigation on the fusion zone of steel/nickel-alloy dissimilar weld joint for nozzle buttering in nuclear power industry

Microstructure of the fusion zone of steel/nickel-alloy dissimilar metal welds (DMWs) for nozzle buttering was investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron back-scattered microscopy (EBSD). The results showed that the dissimilar joint was complete, without welding defects. The structures of the fusion zone included the beach structure along the fusion boundary, the peninsula structures connected with the fusion boundary, and the island structures in the weld. The distribution of these three types of structures near the fusion boundary was uneven. The beach structure was formed because of the insufficient mixing and solidification of the molten liquid base material and the filler metal, with the width ranging between 0 and 150 μm. The peninsula and island structures were formed by the undercooling of the insufficiently mixed liquid base material and filler metal that entered the weld because of the convection and scouring of the weld pool. The composition of the three structures depended on the degree of mixing of the liquid base material and the filler metal, with a dilution ratio between 40 and 60%. The degree of dilution for the beach, peninsula, and island structures decreased in turn. With an increase in the dilution ratio, the initial solidification temperature of the corresponding composition increased significantly. When the dilution ratio exceeded 94.5%, the initial solidification phase transformed from the face-centered cubic γ-austenite into a body-centered cubic ferrite, with island structures solidified in the form of ferrites in the weld near the fusion boundary. The austenite grain orientations at weld side are dispersed with 75% large (> 15°) misorientation in frequency and the overall texture orientation distributes dispersedly with deviating from the < 100 > direction.

Восстановление изображения отражателей на границе основного металла и сварного соединения с использованием ультразвуковых антенных решеток

The article suggests an effective method of replacing zonal focusing with an antenna array, traditionally used for automated ultrasonic inspection of welded joints with a narrow cutting to detect defects at the fusion boundary. This method, based on the use of multi-circuit digital focusing antenna technology (DFA), allows you to obtain and analyze high-quality images of reflectors. The proposed method, in comparison with zonal focusing made using phased array technology, is less sensitive to the accuracy of positioning the antenna array relative to the seam axis and to changes in the thickness of the control object, allows you to estimate the height of defects not by the amplitude attribute, but by the size of the glare reflectors.

The Relationship Between Tinnitus Pitch, Audiogram Edge Frequency, and Auditory Stream Segregation Abilities in Individuals With Tinnitus

Purpose Around 80%–93% of the individuals with tinnitus have hearing loss. Researchers have found that tinnitus pitch was related to the frequencies of hearing loss, but unclear about the relationship between tinnitus pitch and audiometry edge frequency. The comorbidity of tinnitus and speech perception in noise problems had also been reported, but the relationship between tinnitus pitch and speech perception in noise had seldom been investigated. This study was designed to estimate the relationship between tinnitus pitch, audiogram edge frequency, and speech perception in noise. The speech perception in noise was measured using auditory stream segregation paradigm. Method Thirteen individuals with bilateral mild-to-severe tonal tinnitus and minimal-to-mild cochlear hearing loss were selected. Thirteen individuals with hearing loss without tinnitus were also selected. The audiogram of each participant with tinnitus was matched with that of the participant without tinnitus. Tinnitus pitch of the participants with tinnitus was measured and compared with audiogram edge frequency. The stream segregation thresholds were calculated at the participants' admitted tinnitus pitch and one octave below the tinnitus pitch. The stream segregation thresholds were estimated at fission and fusion boundary using pure-tone stimuli in ABA paradigm. Results High correlation between tinnitus pitch and audiogram edge frequency was noted. Overall stream segregation thresholds were higher for individuals with tinnitus. Higher thresholds indicated poorer stream segregation abilities. Within tinnitus participants, the thresholds were significantly lesser at frequency corresponding to admitted tinnitus pitch than at one octave below the tinnitus pitch. Conclusions The information from this study may be helpful in educating the patients about the relationship between hearing loss and tinnitus. The findings may also account for speech-perception-in-noise difficulties often reported by the individuals with tinnitus.

To Calculation of Fillet Welds

When making welded joints, it is not always possible to press tightly elements to be joined before surfacing the weld. In normative documents on welded joints, the allowable gap between the elements to be connected can reach 3 mm when welding with a covered electrode and 2 mm when welding in shielded gases. At the same time the presence of a gap is not taken into account in the standards for calculation of welded joints. Experimental studies have been carried out to determine effect of the gap on the bearing capacity of the weld. Specimens have been made with welded joints of two types: for work in shear and pull-out. For the purpose of comparison, half of the specimens have been made without gaps, and the other half with gaps between the elements to be joined. The specimens have been made at the Minsk plant of technological metal structures, and their tests have been carried out in a research laboratory of the Belarusian National Technical University. Based on the results of the experiments, it has been concluded that the gaps between the elements to be joined significantly reduce the bearing capacity of the welded joints. In addition, inspection of fracture surfaces have shown that, in the presence of a gap, the cut surfaces of the weld pass along the fusion boundary of the base and deposited metals. It has been experimenttally established that the existing gap leads to a slight increase in the penetration depth. However, the latter factor does not compensate for the decrease in the bearing capacity of the welded joint due to the presence of a gap between the elements to be joined.