Roman Gr. Maev

Reliable process monitoring and quality evaluation for resistance spot welding (RSW) have become more important now than ever. An ultrasonic probe embedded into welding electrodes has enabled the acquisition of data about molten pool formation throughout welding, but automation of high-performance ultrasonic data analyses is still necessary to fully realize a monitoring system. This work proposes a two-stage deep learning (DL) approach for automated ultrasonic data analysis for RSW processing monitoring. The first stage conducts semantic segmentation on ultrasonic M-scan welding process signatures, yielding masks for identified molten pool and stack regions from which weld penetration measurements can be directly extracted, as well as expulsion occurrences throughout welding. From input images and segmentation outputs, the second stage directly estimates resultant weld nugget diameters using an additional neural network. Both stages leveraged architectures based on TransUNet, mixing elements of both convolutional neural networks (CNN) and vision transformers, and the effect of cross-attention for stack-up sheet thickness data fusion was investigated via an ablation study. Additionally, in the diameter estimation stage, the ablation study included alternative feature extraction architectures in the network and investigated the provision of M-scans to the model alongside segmentation masks. In both cases, cross-attention was determined to improve performance, and in the case of diameter estimation, providing M-scans as input was found to be beneficial in general. With cross-attention, the segmentation approach yielded a mean intersection over union (IoU) of 0.942 on molten pool, stack, and expulsion regions in the M-scans with 13.4 ms inference time. With cross-attention, diameter estimates yielded a mean absolute error of 0.432 mm with 4.3 ms inference time, representing a significant improvement over algorithmic approaches based on ultrasonic time of flight. Additionally, the approach attained >90% probability of detection (POD) at 0.830 mm below the acceptable diameter threshold and <10% probability of false alarm (PFA) at 0.828 mm above the threshold. These results demonstrate a novel production-ready application of DL in ultrasonic nondestructive evaluation (NDE) and pave the way for zero-defect RSW manufacturing.

With the rapid growth of the lithium-ion battery (LIBs) market, recycling and re-using end-of-life LIBs to reclaim the critical Li, Co, Ni, and Mn has become an urgent task. Presently, high temperature, strong acid, and alkali conditions are required to extract blended critical metals (CM) from the typical battery cathode. Hence, there is a need for more effective recycling processes for recycling blended Li, Co, Ni, and their direct regeneration for re-use in LIBs. The goal of the offered paper is the development of recycling technology for degraded battery cathode-active materials based on the thermal decomposition of polyvinylidene fluoride (PVDF) using calcination and air-jet stripping of active materials. The proposed air-jet erosion method of calcined cathode material stripping from Al foil allows for the flexible industry-applicable separation process, which is damage-free for both particles and substrate. The CaO calcination air-jet separation process and equipment can significantly improve the PVDF decomposition and the separation efficiency of the cathode materials. It is demonstrated that low-temperature CaO calcination at 350–450 °C associated with air-jet separation of active material is characterized by low environmental impact, high purity of the recycled material, and low cost as compared to pyro- and hydrometallurgical methods.

Yttrium-stabilized zirconia thermal barrier coatings (TBCs) of combustion chambers and piston crowns are used most frequently to increase the chamber temperature and the internal combustion engine efficiency. The development of multilayer metal matrix composite coating is of great importance to diminish the ceramic thermal barrier coating’s brittleness and susceptibility to degradation providing the similar thermal insulation. Our group is developing multilayer TBCs based on intermetallic (Fe-Al) compounds combined with alternating zirconia-based layers made by low-pressure cold spraying (LPCS) and sintering. The Fe-Al intermetallic phase was synthesized during reaction sintering of stainless steel and Al particles in the powder layer previously obtained by cold spraying. A double-nozzle low-pressure cold-spraying gun was used to deposit two layers (stainless steel and Al-YSZ) per one track. The effect of the breaking of the brittle ZrO₂ particles due to impingement with the substrate results in the formation of a relatively homogeneous structure with ZrO₂ particle size of 3–10 μm. Cold-spray deposition of additional Cu-Ni-Graphene catalytic layers on the TBCs is developed to improve performance and emissions of engines. The microstructure, thermal conductivity, thermal shock behavior and microhardness of TBCs were examined and discussed.

Hydroxyapatite is a widely used material used for the bioactivation of an implant’s surface. A promising hydroxyapatite coating approach is the kinetic deposition of powder particles. The possibility of solid-state deposition improvement through the merging of Aerosol Deposition and Low Pressure Cold Spraying techniques is a promising prospect for improving the deposition efficiency and the quality of coatings. The objective of the paper is to study the possibilities of hydroxyapatite coating structure modification through changes in the coating process and post-heat treatment. The novel Aerosol Cold Spraying system joining Low Pressure Cold Spraying and Aerosol Deposition was used for the deposition of coatings. The coating’s post-processing was conducted using two techniques: Spark Plasma Sintering and Pressureless Sintering. The coating’s structure was examined using scanning, transmission, and light microscopy, and X-ray diffraction. Substrate–coating bond strength was assessed using a tensile test. Homogenous buildup using Aerosol Cold Spraying of hydroxyapatite was achieved. Various pores and microcracks were visible in the sprayed coatings. The deposition process and the thermal post-processing did not lead to significant degradation of the hydroxyapatite phase. As a result of the Spark Plasma Sintering and Pressureless Sintering at 800 °C, an increase in tensile adhesion bond strength and crystal size was obtained.