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        Investigation on microstructure and mechanical properties of ni-based alloy overlayer by ultrasonic impact treatment

        Xilong Zhao,Kangming Ren,Xinhong Lu,Feng He,Yuekai Jiang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.8

        Ultrasonic impact treatment (UIT) was performed on the Ni-based alloy overlayer of austenitic stainless steel pipe girth weld. The difference of microstructure, microhardness and maximum shear strength distribution of the joint before and after UIT was studied by autobiographic test and shear punch test. The electrode potential data were tested by a threeelectrode electrochemical workstation and tafel curve was drawn. The results show that a grain refinement layer of about 30 um and a transition layer of about 60 um are formed in the overlayer of nickel-based alloy after UIT. Meanwhile, the transition layer has high corrosion sensitivity to oxalic acid solution, and the main precipitates in the overlayer are austenite and M23C6. In 3.5 % NaCl solution, the self-corrosion potential is -432 mV. The average microhardness of the overlayer of nickel-based alloy is 270 HV, which is 18.9 % higher than that of the sample without UIT. In the meantime, the maximum shear strength of nickel-based alloy is 955 MPa, which is 9.6 % higher than the sample without UIT. It is found that the ferrite is mainly lath and skeleton with no obvious change under UIT or not. Meanwhile, an average microhardness is 191 HV, and shear strength is 678 MPa. The microstructure of the welded joint is mainly consisted of austenite phase and ferrite phase, and FA solidification mode has been a major influence in the welding process. At the boundary between overlayer and circumferential welded joint of 304 austenitic stainless steel, reheat cracks in this area are occurred easily. Due to the migration of carbon, local martensite bands will be formed which will lead to large heterogeneity of microhardness.

      • KCI등재

        Analytical Prediction for Tunnel-Soil-Pile Interaction Mechanics based on Kerr Foundation Model

        Zhiguo Zhang,Chengping Zhang,Kangming Jiang,Zhiwei Wang,Yunjuan Jiang,Qihua Zhao,Minghao Lu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.6

        Existing analytical method to predict tunneling-induced pile deformation is generally based on the Winkler foundation model that neglects shear effects of soil, which is not sufficient for engineering practice. A simplified solution based on Kerr foundation model is presented in this study to investigate the tunnel-soil-pile interaction. In order to improve the accuracy of the prediction for tunneling-induced free-field movements, the cavity contraction theory is utilized in the first stage which received a higher accuracy than the previous solution. In the second stage, the soil free-field displacement is imposed on the existing pile, and the simplified solution for pile deformation governed by the disturbance of passive displacement is established based on the Kerr foundation model, which can take account of the soil shear effects. The applicability and accuracy of the simplified solution are then verified by several cases including the reported analytical solution, centrifuge modeling tests and observed data in situ. Good agreements are obtained in the comparative analyses, which demonstrates that the proposed solution can serve as an alternative approach for conservatively estimating tunneling-induced pile deformation in the preliminary design in clay. Furthermore, the parametric analysis associated with the pile deformation has also been performed. As a result, it is of primarily theoretical and practical significance to investigate the influence of soil shear effects on the tunnel-soil-pile interaction mechanics.

      • KCI등재

        Influence of ultrasonic impact treatment on microstructure and mechanical properties of nickel-based alloy overlayer on austenitic stainless steel pipe butt girth joint

        Zhao Xilong,Ren Kangming,Lu Xinhong,He Feng,Jiang Yuekai 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.11

        Ultrasonic impact treatment (UIT) is carried out on the Ni-based alloy stainless steel pipe gas tungsten arc welding (GTAW) girth weld, the differences of microstructure, microhardness and shear strength distribution of the joint before and after ultrasonic shock are studied by microhardness test and shear punch test. The results show that after UIT, the plastic deformation layer is formed on the outside surface of the Ni-based alloy overlayer, single-phase austenite and g type precipitates are formed in the overlayer, and a large number of columnar crystals are formed on the bottom side of the overlayer. The average microhardness of the overlayer increased from 221 H V to 254 H V by 14.9%, the shear strength increased from 696 MPa to 882 MPa with an increase of 26.7% and the transverse average residual stress decreased from 102.71 MPa (tensile stress) to 18.33 MPa (compressive stress), the longitudinal average residual stress decreased from 114.87 MPa (tensile stress) to 84.64 MPa (compressive stress). The fracture surface has been appeared obvious shear lip marks and a few dimples. The element migrates at the fusion boundary between the Ni-based alloy overlayer and the austenitic stainless steel joint, which is leaded to form a local martensite zone and appear hot cracks. The welded joint is cooled by FA solidification mode, which is forming a large number of late and skeleton ferrite phase with an average microhardness of 190 H V and no obvious change in shear strength. The base metal is all austenitic phase with an average microhardness of 206 H V and shear strength of 696 MPa

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