Papers by Author: Zi Liang An

Abstract: The creep and rupture test were carried out on a non-standard specimen of 316L stainless steel (316L-SS) diffused bonding joint. And the θ-projection model was used to analyze the minimum creep strain rate and the remaining life at 500°C/6 MPa when the creep strain is 0.2%. According to the test results, design criterion for the diffusion bonding component at high temperature is established. The rupture experimental results show that the remaining life extrapolated by Larsen-Miller equation is relatively consistent with that calculated by the θ project concept method.

Abstract: The dynamic measurement model for the interface cavities of the diffusion welded joint, which based on the effective resistivity, is established by using the damage factor and the Derby Model of the Bridgman Law. Then the quantitative relationship, which between the direct current potential and the effective area of the joint at high temperature and high pressure, can be obtained. In addition, on the basis of the dynamic four-probe DC potential method and the fieldbus technology, the computer measuring system is established, so that the creep propagation behaviour for the interface cavities of the 316L stainless steel can be monitored in real-time.

Abstract: The diffusion bonding of 316L stainless steel with Ni interlayer in the temperature range of 850-1050°C, under a uniaxial pressure 10 MPa for 60 min is investigated. The diffusion bonds have been evaluated light microscopy, SEM, X-ray diffraction and tensile test. The main result is that the introduction of the interlayer may reduce the room temperature strength but increase the high temperature strength. This is attributed to the transformation of Fe_0.64Ni_0.36 formed in bonding process into FeNi₃ at high temperature. Kirkendall voids are formed in the Ni interlayer near the interface where the specimen fractured. Fractographic study indicates that the fracture mode of the joints is strongly affected by the bonding and testing temperature. The fracture is a mixed mode of brittle and ductile fracture in high temperature tensile test, while it is brittle fracture at room temperature.

Abstract: Direct diffusion bonding of 316L stainless steel was performed at 850-1100°C for 1-3 h under a pressure of 10MPa in this study. The effect of bonding temperature and holding time on mechanical performances of the joints was investigated. Tensile tests were conducted to evaluate strength and elongation of the joints at room temperature and elevated temperature of 550°C. The microstructure and fracture surfaces of the joints were examined by optical microscope (OM) and scanning electronic microscope (SEM). The results indicated that the elongation of the joints increased with the increase of bonding temperature and holding time. However, overlong holding time had a side effect on the strength of the joint. Moreover, the change of the mechanical properties was closely related to the variation of the microstructure of the joints. The X-ray diffraction (XRD) analysis revealed that FeCr and Fe0.64Ni0.36 were formed at the DB6 joint during bonding process. It is suggested that FeCr should be detrimental to the improvement of high temperature strength of the joint.

Abstract: Two types of joining specimens with and without Ni foil interlayer between 316L–SS bar have been prepared by diffusion bonding in a temperature range of 850- 1050°C, under a uniaxial pressure of 10MPa for 1hours. The relationship between the bonding parameters and the tensile strength of the joints at elevated temperature was studied. Optimized processing parameters were suggested based on the testing results. It was found that the introduction of the interlayer may reduce the room temperature strength but increase the high temperature strength. This was attributed to the transformation of Fe0.64Ni0.36 formed in bonding process into FeNi3 at high temperature.