Papers by Author: Jie Zhao

Abstract: The dissimilar weld joint of HR3C steel and T92 steel is widely used in the ultra supercritical (USC) boiler due to the different service conditions of HR3C steel and T92 steel. It is important to study how serviced influenced the HR3C/T92 dissimilar joint. The HR3C/T92 dissimilar joint had already served 51020 h under 605 °C and 26.25 MPa. The microstructure and mechanical properties of the long term serviced HR3C/T92 dissimilar joint were tested by XRD, SEM, EPMA,TEM, the impact testing machine and the creep and stress rupture testing machine. The XRD results show that the weld is mainly γ-Fe, which is similar to the HR3C base metal, while the T92 base metal is mainly α-Fe. The SEM results indicate that serviced HR3C’s precipitation behavior is complicated, cause multiple precipitated phases precipitated during the service. Chain-liked M₂₃C₆ precipitated along the grain boundary. M₂₃C₆ phase cause the chromium depletion zone along the grain boundary. T92 base metal precipitated lots of carbide particles during the service. Those carbide particles are around 1 μm. The impact fracture of HR3C base metal is brittle fracture while the impact fracture of T92 base metal is ductile fracture. Moreover, the impact fracture of weld is mixed fracture. Chain-liked M₂₃C₆ along the grain boundary is the main cause of the brittleness of serviced HR3C steel.The constant strain creep tests were proceeded under 650 °C, 700 °C and 750 °C. The high-temperature creep resistance of HR3C base metal is better than that of T92 base metal after service. The resistant to high-temperature creep of served joint is similar to that of serviced T92 base metal. With the increase of temperature, the creep resistance of the T92 base metal decreases the most. On the contrary, the creep resistance of the HR3C base metal shows the minimum reduction.

Abstract: The current paper proposes a so-called Zc method to evaluate creep strain and rupture life of heat resistant steels by considering the scattering distribution of experimental data, where the Zc value indicates the deviation of the fitted σ-P curves at different creep strains to the main curve. It is shown that the value of Zc increased rapidly at first and then became stable with increasing creep strain, meanwhile, the degree of deviation between experiment data and the corresponding fitted curves came to decrease. The current method provides a statistic method for predicting creep stain and rupture life and get good agreement with experiment result.

Abstract: P92 heat-resistant steel was used to demonstrate that creep rupture life evaluation period could be shorted by the assistant of the creep data from short-period stress relaxation test without reducing the prediction precision. Research showed that the minimum creep rate and the relaxation creep rate were exchangeable, and the stress exponent and the apparent activation energy analysis of the constant strain creep and the constant stress creep showed a similar deformation mechanism at the condition of T and . The creep rupture life predicted through the combination of these two kinds of creep data was closer to the real creep data than that evaluated by the traditional method based on the time to rupture only, and the precision of the evaluated creep strength increased at last 14.5 %.

Abstract: The current paper investigates on the creep behavior of 12Cr-Mo-W-0.25V heat resistant steel base on the long-term stress relaxation test data. It is shows that the stress relaxation curve can be divided into 2 stages: the high stress stage has higher apparent activation volume of 79~350 b³ and the low stress stage is 35~78 b³. Besides, the Helmholtz free energy at the high stress stage is 827~1034 kJ/mol which is higher than 210~252 kJ/mol of the low stress stage. Taking both apparent activation volume and activation energy into account, it is assumed that the high stress stage is mainly controlled by dislocation slip and the low stress stage is more related to diffusion.

Abstract: Multi-elements alloy with good thermal stability is expected to serve as the superheater tube material of ultra-supercritical boiler and may suffer from hot corrosion under the coal-fired atmosphere. In this study, the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 coated with alkali metal sulfates at 750°C is investigated systematically. The results showed the corrosion kinetics curves of the alloy followed a parabolic growth rate. The corrosion products, which consisted of volatile Na (CrO₄) (SO₄), (Fe,Ni) xSy, Cr/Ti oxide as well as compound oxides with spinel structure AB2O4, were found in the oxide scale and internal attack zone of the alloy. The oxide layer had good adhesion with the matrix at the beginning of corrosion. Prolonging corrosion time, the oxide layer in thickness increased and became loose as well as porous. The micro-pores generated in the interface between the oxide scale and matrix with the occurrence of the internal oxidation and internal sulfidation. In a word, the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 at 750°C can be attributed to the formation of the protective oxide layers and to the basic fluxing in molten Na₄SO₄ induced by low melting point eutectic.

Abstract: Creep rupture data plays vital role in life prediction and safety assessment of high temperature components. In order to describe the scattering of the data, a statistical analysis of creep rupture data for 4Cr25Ni35 steel was performed by Z-parameter method. With the application of Z-parameter, reliability design for allowable stress of creep rupture strength was carried out according to design life. It is found that Manson-Haferd method appears better correlation results with experimental data. Statistical analysis shows that the scattering of Z-parameter for 4Cr25Ni35 steel is supported by normal distribution. Compared with safety factor method, the method based on Z-parameter can perform reliability design for allowable stress of creep rupture strength by considering the dispersibility of the rupture data. Reliability design based on Z-parameter is more agree with experimental data.

Abstract: In this study, 304 stainless steel particles were deposited on IF steel substrates by cold dynamic spray technology. The effect of gas temperature on bonding features and deposition critical velocity were studied and compared. The results demonstrated that the successful bonding between 304SS particle and substrate could be attributed to the adiabatic shear instability mechanism, increasing gas temperature led to enhance the particle interface bonding, deduce the deposition critical velocity, and also increase both deposition efficiency and density of coatings.

Abstract: A statistical analysis of creep rupture data for 2.25Cr-1Mo steel was performed. The scattering of creep rupture data was represented by Z-parameter method based on Manson-Haferd method. With the application of Z-parameter, reliability design for allowable stress of creep rupture strength was carried out according to design life. The higher the value of confidence level, the lower the allowable stress. In comparison with safety factor method and minimum rupture strength method, it can be seen that reliability design based on Z-parameter is more agree with experimental data than other methods. Reliability design provides more precise results by considering the real distribution of creep rupture property and provides more flexible choice for design due to the need of safety and economy.

Abstract: The mollusk shell mobilizes calcium from environment for skeletal mineralization. This occurs through synthesizing solids in solution in the presence of organic molecules of specific interior regions of the conch shell. The ultrastructure of the Hemifusus tuba conch shell living in the Huang/Bo sea area is investigated in the paper. It is shown that the composition and microstructure of the mollusk shell vary in different positions. The prodissoconch shell consists only of aragonite with the crossed-lamellar microstructure. While the spiral shell and the body shell of the Hemifusus tuba conch shell are composed of one calcite layer and several aragonite layers. The calcite layer consists of cylindrical grains, but the aragonite layers are crossed-lamellar ultrastructure. The margin of shell aperture is only composed of calcite with cylindrical grains. This natural optimization of the shell microstructure is intimately due to the growth of the organic matrix. The process of growth allows a constant renewal of the material, thus enabling the functional adaptation of the shells.

Abstract: ZnO films were grown under different oxygen partial pressures by metal organic chemical vapor deposition on the substrates of Corning glass. We investigated the quality of the films by SIEMENS D8 X-ray diffractometer. The surface morphology of the films were observed by Digital Nanoscope ІІІa AFM with normal silicon nitride tip in the contact mode. The hall effect measurements were carried out with indium ohmic contact. The transmission spectrum of the films were measured. The transmission ratio is larger than 80% in the region above the wavelength of 385nm, and sharply decreased under 10% below the wavelength of 375 nm.