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Thin-walled parts with low stiffness and poor machinability are prone to chatter during milling. Chatter can adversely affect machined surface quality and workpiece performance. Most existing chatter monitoring models require training and test data from workpieces with the same stiffness as well as large amounts of training data. In this paper, force signals from workpieces with different stiffnesses are obtained through a series of experiments as source and target domain data. Autoencoders are utilized for feature extraction and support vector machines for chatter recognition. Model-agnostic meta-learning (MAML) optimizes the global model parameters, and transfer learning reduces the demand for target domain samples. The model can monitor the chatter of two types of workpieces at the same time through one training. Compared with common transfer learning models visual geometry group network-16 (VGG-16), this paper decomposes force signals using ensemble empirical mode decomposition (EEMD) and extracts intrinsic mode function (IMF) components as features. VGG-16 model is optimized by adding fully-connected layers, dropout, L2 regularization for chatter recognition. The proposed method achieves 99% accuracy on source domain and 98% on target domain. The target domain accuracy is 6% higher than without using MAML optimization, and 8% higher than the VGG-16 method. [ABSTRACT FROM AUTHOR]

Intermetallic TiAl alloys attract much attention in advanced engineering fields due to their low density (3.9–4.2 g/cm3) and excellent high-temperature properties. After more than half a century of research and development, TiAl alloys have found applications in aerospace, automotive, and related industries. However, as a kind of semi-brittle materials, intermetallic TiAl alloys exhibit different mechanical behavior from metallic and ceramic materials. Thus, it is necessary to systematically understand their mechanical behavior to ensure further developments and safe engineering applications. In this paper, the principal mechanical behavior of TiAl alloys was reviewed comprehensively, including tension, creep, fatigue, and strengthening mechanisms. The mechanical performance and the corresponding deformation mechanisms are summarized and discussed in detail. The future directions of mechanical research on TiAl alloys are also overviewed to expedite their extensive utilization in engineering fields. [ABSTRACT FROM AUTHOR]

To clarify the correlation of single-crystalline structure with corrosion performance in high-strength TiAl alloys, electrochemical and surface characterization was performed by comparing Ti-45Al-8Nb dual-phase single crystals with their polycrystalline counterparts in NaCl solution. Polarization curves show a lower corrosion rate and a higher pitting potential of ∼280 mV for the dual-phase single crystals. Electrochemical impedance spectroscopy and potentiostatic polarization plots revealed a higher impedance of the charge transfer through the compact passive film. Surface composition analysis indicated a compact film with more content of Nb, as twice as that in the film on the polycrystals. Our results reflect that the dual-phase Ti-45Al-8Nb single crystals possess a higher corrosion resistance in NaCl solution, compared with their polycrystalline counterpart, arising from a more homogeneous microstructure and composition distribution. [ABSTRACT FROM AUTHOR]