Lightweight epoxy-based abradable seal coating with high bonding strength

To gain high efficiency and low fuel consumption, aluminum-based abradable seal coatings had been widely used in the compressor casing of aero engines or gas turbines owing to the low elastic modulus. However, the adhesive transfer phenomenon frequently occurs when the radial rubbing generates between titanium alloy blade tips and aluminum-based coating. It tends to increase scratch force and results in blades vibration and even engine jam. To eliminate this problem, a new lightweight epoxy-based abradable seal coating with high bonding strength was developed by an effective and porosity controllable mixing process that distributes spherical pores uniformly in the continuous matrix. A lightweight coating of 63% porosity with a hardness of 33.1(HR15 Y) can be reached when the content of hollow microspheres is 31 wt.%. The coating density is 0.5 g/cm3 and the bonding strength is as high as 18 MPa.The performance of the epoxy-based coating is comprehensively better than aluminum-based coatings in five essential indices. This study is expected to provide a new technical path for obtaining high-quality abradable seal coatings to guarantee the efficient and safe operation of compressors.

Self-lubricating epoxy-based composite abradable seal coating eliminating adhesive transfer via hierarchical design

Aluminum-based composite abradable seal coatings are pivotal to improving the efficiency of aero engines or gas turbines.However,the adhesive transfer frequently occurs between metallic blade tips and aluminum-based composite coatings,resulting in engine vibration and even jam.Many past studies had tried to solve this problem by reducing coating hardness,improving lubrication,or strengthening blade tips,but all had failed.In this paper,we proposed a novel epoxy-based composite abradable seal coating,eliminating adhesive transfer by changing metal-to-metal scraping pair to metal-to-polymer scraping pair.The coating was developed via a hierarchical structure design.Large spherical pores were uniformly distributed in the continuous epoxy matrix with fine graphite dispersion.By adding 20 vol.%graphite and 50 vol.%hollow microspheres,a self-lubricating epoxy-based coating of 0.26 friction coefficient with thermal conductivity of 0.28 W/(m·K),coating HR15 Y hardness at 54.8,and bonding strength at 18.7 MPa can be reached.When the metallic blades scrape the epoxy-based composite coating,no adhesive transfer occurs.Besides,a smooth scraped surface is formed by pseudoplastic deformation.This epoxy-based composite abradable seal coating opens a new way to improve the efficiency and reliable operations of air engine compressors.

Contrast-enhanced ultrasound as a valuable imaging modality for characterizing testicular lesions

Contrast-enhanced ultrasound(CEUS)is a new form of ultrasound(US)that can dynamically display microvessels in a highly sensitive manner.The purpose of this study was to investigate the efficacy of CEUS for characterizing testicular lesions in comparison with conventional US.Forty-seven patients with testicular lesions were enrolled.The histopathology results revealed that 31 cases were neoplastic(11 cases of seminomas,8 nonseminomatous germ cell tumors,8 lymphomas,2 Leydig cell tumors,and 2 nonspecific tumors),and 16 cases were nonneoplastic(8 cases of infarctions,3 epidermoid cysts,and 5 inflammation).The indicators of shallow lobulated morphology and cystic-solid echogenicity on conventional US were suggestive of germ cell tumors.More indicators on CEUS were found to be useful for characterizing testicular lesions.All the neoplastic lesions showed hyperenhancement on CEUS.Moreover,germ cell tumors presented with heterogeneous enhancement(73.7%,14/19),a twisted blood vessel pattern,rapid wash-in and wash-out,and peripheral rim hyperenhancement signs.Lymphoma was characterized by nonbranching linear vessel patterns(87.5%,7/8),rapid wash-in and slow wash-out.In nonneoplastic lesions,infarction and epidermoid cysts showed no enhancement,and abscesses were observed with marginal irregular enhancement.The sensitivity,specificity,and accuracy of CEUS for differentiating between neoplastic and nonneoplastic lesions were 100%,93.8%,and 97.9%,respectively,and these values were higher than those for conventional US(90.3%,62.5%,and 80.9%,respectively).CEUS can sensitively reflect the microvascular perfusion in testicular lesions and offers high accuracy for characterizing them.