Papers by Author: Tian Han Xu

Abstract: The service life of material is much related with its corrosion resistance. Thus, the investigation on corrosion behavior is important for the better use of material. In this paper, the corrosion behavior of deformed chromium bronze experienced different processing was investigated in NaCl environment using electrochemical measurements and mass-loss tests. It has showed that the potentiodynamic polarization curves of cold rolled specimen coincide with that of cold worked specimen in two concentration of NaCl solution. The last cold working has little effect on the electrochemical behavior of cold rolled chromium bronze.The NaCl fog experiment showed that the corrosion resistance of cold rolled specimen is slightly better than that of cold worked specimen, and the mass-loss for two kinds of specimen are similar in the initial stage but the gap is increasing with corrosion time. The corrosion scales on the surface of specimen, accumulated in the form of island produced in the NaCl fog experiment , has little hindered effect on corrosion behavior.

Abstract: The corrosion resistance of Ultra-fine grain (UFG) chromium bronze, prepared by Equal-channel angular pressing (ECAP) processing, was investigated in HCl solution at room temperature and atmospheric pressure by electrochemistry technique and immersion experiment. The results shows that the corrosion potential of chromium bronze is decreased with ECAP processing. But the corrosion resistance is deteriorated slightly. According to the immersion tests, the weight-loss of UFG chromium bronze, compared with its counterpart, is higher in the initial stage and lower in the later stage, and the gap is in the range of 5%-15%. The corrosion mechanism on the UFG chromium bronze is deduced from the experiment data and corrosion morphology.

Abstract: The effects of the atomizing pressure on the microstructures and properties of the lead-free solder powder by the supersonic atomizer method were investigated. The microstructures of the brazed joint of solder paste were also observed. The results showed that with increasing atomizing pressures from 0.4 to 0.7 MPa, the powder particles are refined significantly and the effective atomization efficiency increases rapidly, but the oxygen content slightly rises. When the atomizing pressures increases from 0.7 to 0.9 MPa, the effective atomization efficiency only increases slightly, meanwhile both sphericity and roughness of the powder deteriorate. The atomized powder exhibits high effective atomizing efficiency, uniform size distribution, good sphericity and smooth surface when the atomizing pressure is 0.7 MPa. The diffusion layer brazed welded by Sn3Ag2.8Cu paste with Cu substrate is thicker and more irregular than that of by Sn37Pb paste.

Abstract: Microstructure and low-frequency noise test were measured for N80 steel casing drilling, through SEM analyzed their morphology. Results showed that: (1) power spectral density of 1/f noise increases two orders of magnitude after fatigue crack growth. (2) 1/f noise parameters of γ and B are significantly increased, indicating that the process of fatigue produced more cracks, defects, and combination centers, which were proved by microstructure morphology. From the mechanism of fatigue crack growth of N80, defects and cracks resulting from fatigue are the numbers of kind of fluctuations. In essence, low-frequency noise is a type of fluctuations, which can serve as a viable tool to study the defects and the characterization of defects.

Abstract: Electrical parameters and low-frequency noise test were measured for N80 steel casing drilling, through extracting low-frequency parameters and combining with conventional fatigue crack growth characterization methods and analyzing their morphology. After fatigue crack growth, the results showed that: (1) Electrical parameters of N80 increase, and power spectral density of 1/f noise increases two orders of magnitude. (2) Values of γ and B are significantly increased, indicating that the process of fatigue produced more cracks, defects, and combination centers, from the mechanism of fatigue crack growth of N80, defects and cracks resulting from fatigue are the numbers of kind of fluctuations. In essence, low-frequency noise is a type of fluctuations, which show that low-frequency noise as the characterization of non-destructive., which can serve as a viable tool to study the defects and the characterization of defects.