Investigating the Wear Mechanisms and Tribochemical Reactions of W-Based Coatings

Yuzhen Liu,Shusheng Xu 한국표면공학회 2023 한국표면공학회 학술발표회 초록집 Vol.2023 No.11-1

Study on Electroconductive Tribological Properties of Ag-based Composite Coating

Yuzhen Liu,Mingyu Gao,Shusheng Xu,김대은 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.8

Electrical contacts are widely utilized in numerous engineering applications that require high reliability. However, fretting wear due to repeated contact may lead to increased electrical contact resistance that can cause failure of the electrical system. Herein, an Ag-based coating was prepared by an electroless co-deposition technique in order to improve the electroconductive properties under fretting conditions. By carefully controlling the deposition time, a relatively smooth and continuous Ag coating could be obtained. The structure of the coating was analyzed using X-ray diffraction, 3D confocal microscopy, and scanning electron microscopy techniques. The electroconductive tribological properties of the coating were assessed using a custom-built fretting tester. The Ag coating possessed good crystallinity and exhibited improved electroconductive properties compared with the Ni interlayer deposited on a steel substrate. The high temperature of the contact zone generated by friction contributed to the reduced electric resistance. Furthermore, incorporation of graphene as a dopant could improve the coating wear resistance, resulting in more reliable electroconductive properties in the fretting condition. The wear mechanism of the coating was also investigated through wear track analysis. The experimental results are expected to aid in understanding the electroconductive tribological properties of Ag coatings used in electrical contact applications.

탄소 기반 코팅의 바이오트라이볼로지적 특성

류우진(Yuzhen Liu),김대은(Dae-Eun Kim) 한국트라이볼로지학회 2019 한국트라이볼로지학회 학술대회 Vol.2019 No.10

Identification of Novel Subregions of LOH in Gastric Cancer and Analysis of the HIC1 and TOB1 Tumor Suppressor Genes in These Subregions

Jingcui Yu,Songbin Fu,Peng Liu,Xiaobo Cui,Yu Sui,Guohua Ji,Rongwei Guan,Donglin Sun,Wei Ji,Fangli Liu,An Liu,Yuzhen Zhao,Yang Yu,Yan Jin,Jing Bai,Jingshu Geng,Yingwei Xue,Jiping Qi,Ki-Young Lee 한국분자세포생물학회 2011 Molecules and cells Vol.32 No.1

Previously, we identified 3 overlapping regions showing loss of heterozygosity (LOH, R_1-R_3 from 11 to 30 cM) on chromosome 17 in 45 primary gastric cancers (GCs). The data indicated the presence of tumor suppressor genes (TSGs) on chromosome 17 involved in GC. Among the putative TSGs in these regions, HIC1 (in SR_1) and TOB1 (in SR_3) remain to be examined in GC. By immunohistochemistry (IHC), methylation-specific PCR (MSP) and western blot, we evaluated the expression and regulation status for HIC1 and TOB1 protein in GC. We narrowed down the deletion intervals on chromosome 17 and defined five smaller LOH subregions, SR_1-SR_5 (0.54 to 3.42 cM), in GC. We found that HIC1 had downregulated expression in 86% (91/106) and was methylated in 87% (26/30) of primary GCs. Of the primary GCs showing downregulation of HIC1 protein, 75% (18/24) had methylated HIC1 gene. TOB1 was either absent or expressed at reduced levels in 75% (73/97) of the GC samples. In addition, a general reduction was found in total and the ratio of unphosphorylated to phosphorylated TOB1 protein levels in the differentiated GC cell lines. Further analysis revealed significant simultaneous downregulation of both HIC1 and TOB1 protein in GC tissue microarray samples (67%, 52/78) and in primary GCs (65%, 11/17). These results indicate that silencing of HIC1 and TOB1 expression is a common occurrence in GC and may contribute to the development and progression of the disease.

Robustness Analysis for Switched Multiple Equilibrium Points Systems

Zhi Liu,Xian-Fu Zhang,Yuzhen Wang 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.6

This article investigates the robustness of switched multiple equilibrium points systems (SMEPSs) withunstable subsystems. Each subsystem has a unique equilibrium point that is different from all equilibrium pointsof the other subsystems. Unlike the most commonly used Lyapunov function method, the analytical solutions andnumerical solutions are calculated to analyze the boundedness of the solutions for perturbation discrete-time andcontinuons-time SMEPSs, respectively. The given perturbation systems have good robustness if the ratio of totaldwell time of unstable subsystems and the total dwell time of stable subsystems is less than or equal to a constant. A numerical example is employed to validate the correctness of the theoretical results.

Sintering technology and properties of sponge city permeable bricks prepared from electrical porcelain was

Yue Liu,Yun Xiang,Jieguang Song,Dongliang Zhang,Hongbin Wen,Yuzhen Wang 한양대학교 청정에너지연구소 2022 Journal of Ceramic Processing Research Vol.23 No.6

The generated electric porcelain waste increases with the rapid development of the electric porcelain industry. Unreasonableutilization results in the waste of resources and environmental pollution. However, at present, many coal gangues and fly ashesare wasted and underutilized in my country. In this paper, electric porcelain waste is used as the main raw material, and itssintering temperature, holding time, and heating rate are discussed to study the performance of the permeable brick preparedfrom electric porcelain waste. Results show that with the increase in sintering temperature, the porosity and waterpermeability coefficient of permeable bricks decrease, and their volume shrinkage rate and compressive strength show anincreasing trend. Furthermore, porosity decreases with the increase in holding time. The volume shrinkage rate andcompressive strength increase, and the water permeability coefficient decreases. The volume shrinkage rate of the permeablebrick decreases, and its porosity, water permeability coefficient, and compressive strength increase with the heating rate. Combined with the comprehensive consideration of the porosity, volume shrinkage rate, water permeability coefficient, andcompressive strength of permeable bricks, the best sintering process for preparing permeable bricks from electrical porcelainwaste is presented with a sintering temperature of 1225 °C, holding time of 1 h, and heating rate of 6 °C/min. The porosityof the prepared permeable brick is 79.5%, the volume shrinkage rate is 25.79%, the water permeability coefficient is 2.82×10-2cm/s, and the compressive strength is 5.79 MPa.

Failure of circular tunnel in saturated soil subjected to internal blast loading

Han, Yuzhen,Liu, Huabei Techno-Press 2016 Geomechanics & engineering Vol.11 No.3

Explosions inside transportation tunnels might result in failure of tunnel structures. This study investigated the failure mechanisms of circular cast-iron tunnels in saturated soil subjected to medium internal blast loading. This issue is crucial to tunnel safety as many transportation tunnels run through saturated soils. At the same time blast loading on saturated soils may induce residual excess pore pressure, which may result in soil liquefaction. A series of numerical simulations were carried out using Finite Element program LS-DYNA. The effect of soil liquefaction was simulated by the Federal Highway soil model. It was found that the failure modes of tunnel lining were differed with different levels of blast loading. The damage and failure of the tunnel lining was progressive in nature and they occurred mainly during lining vibration when the main event of blast loading was over. Soil liquefaction may lead to more severe failure of tunnel lining. Soil deformation and soil liquefaction were determined by the coupling effects of lining damage, lining vibration, and blast loading. The damage of tunnel lining was a result of internal blast loading as well as dynamic interaction between tunnel lining and saturated soil, and stress concentration induced by a ventilation shaft connected to the tunnel might result in more severe lining damage.

Selective release of less defective graphene during sliding of an incompletely reduced graphene oxide coating on steel

Xu, Shusheng,Liu, Yuzhen,Gao, Mingyu,Kang, Kyeong-Hee,Kim, Chang-Lae,Kim, Dae-Eun Elsevier 2018 Carbon Vol.134 No.-

<P><B>Abstract</B></P> <P>Recently, graphene has been gaining a lot of attention as a coating material that can be effectively utilized in reducing friction and wear of sliding components. In order to fully exploit the lubricious properties of graphene, the variation in the structure of the coating as sliding proceeds against a counter surface needs to be understood clearly. In this study, the structural evolution during sliding of an incompletely reduced graphene oxide (rGO) coating deposited on the 304 stainless steel by an electrodynamic spraying process was investigated. Experimental results showed that this coating possessed a low friction coefficient, below 0.05, under either low humidity air or dry N<SUB>2</SUB> gas condition. The micro-Raman and XPS analyses systematically revealed that less defective graphene structure was selectively released at the center region of the wear track. It was determined that the redistribution of graphene with different structures within the wear track was induced by frictional interaction at the sliding interface. Furthermore, it was determined that the degree of release of less defective graphene structure was proportional to both the applied normal force and sliding cycles.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of sintering temperature and alkaline elements excess on the structure and electrical properties of (K_0.462Na_0.48Li_0.058)_(1+x)NbO_3 lead-free piezoelectric ceramics

Rongxia Huang,Yuzhen Zhao,Yongjie Zhao,Rongzheng Liu,Heping Zhou 한국물리학회 2011 Current Applied Physics Vol.11 No.5

Lead-free (K_0.462Na_0.48Li_0.058)_(1+x)NbO_3(0 ≤ x ≤ 0.03) ceramics with excessive alkaline elements were synthesized by conventional ceramics processes as functions of sintering temperatures and quantities of excess alkaline elements. X-ray diffraction results reveal a transformation from tetragonal phase to orthorhombic phase with increasing the contents of excessive alkaline elements. The grain size and the piezoelectric properties were enhanced when a certain amount of excessive alkaline elements were added. Further elevation in the amount of alkaline elements added resulted in excessive liquid phase in the ceramics and deteriorated the piezoelectric properties. With x = 0.01, the ceramics sintered at 1050 ℃ show better properties of planar electromechanical coupling factor k_p = 43.4%, piezoelectric constant d_33 = 204 pC/N, dielectric constant ε^T_33/ε_0 = 704.4, and loss tangent tan δ = 2.8%.

Superior lubrication of dense/porous-coupled nanoscale C/WS₂ multilayer coating on ductile substrate

Xu, Shusheng,Liu, Yuzhen,Gao, Mingyu,Kang, Kyeong-Hee,Shin, Dong-Gap,Kim, Dae-Eun Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.476 No.-

<P><B>Abstract</B></P> <P>Sputtered carbon material has been receiving much attention as a solid lubricant coating owing to its high hardness and low coefficient of friction. However, its relatively low wear resistance performance when applied on a ductile substrate has limited its use in certain applications. In this work, a porous WS<SUB>2</SUB> sublayer was introduced to the sputtered carbon-based nanoscale multilayer coating to improve its tribological properties. The microstructural, mechanical and tribological properties of the nanoscale C/WS<SUB>2</SUB> multilayer coating were systematically investigated using various analytical techniques. Through structural optimization, a durable coating with excellent wear resistance and low frictional performances could be attained for a ductile steel substrate. The excellent toughness allowed the coating to deform with the ductile substrate without fracturing during contact sliding process. Furthermore, the first self-destruction and then recombination behaviors of dense/porous-coupled nanoscale multilayer coating as well as the selective release of carbon component to the contact interface driven by the frictional interaction aided in maintaining low friction. As a result, the nanoscale multilayer coating showed approximately 100-fold greater wear resistance than that of pure hard carbon coating on a ductile steel substrate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A hard/soft-coupled nanoscale C/WS<SUB>2</SUB> multilayer coating was constructed by sputtering. </LI> <LI> The multilayer coating exhibited excellent synchronized deformation with the ductile steel substrate. </LI> <LI> Multilayer coating on ductile steel showed 100-fold longer wear life than that of a stiff C coating. </LI> <LI> The rearranged coating on the formed deep wear track resulted in improved lubrication performance. </LI> <LI> That provided a novel way to develop lubricant protection layer on ductile material surface </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>