Papers by Author: Jing Liu

Abstract: The established cellular automata model of dynamic recrystallization for 316LN simulated microstructure evolution of recrystallization nucleation and grain growth under different conditions. And on the basis of cellular automata model, the influence of strain, strain rate, deformation temperature on dynamic recrystallization behavior was analyzed. Though the hot compress experiment done on the Gleeble-3500 thermo mechanical simulator, combined with metallographic experiment, the microstructure at deformation temperature of 950 oC, 1050 oC and 1150 oC with strain rate of 0.001 s^-1, 0.01 s^-1, 0.1 s^-1 and 1 s^-1 was obtained. Simulation results are compared with metallographic microstructure, the error is small.

Abstract: Complex equipment is mainly used in important areas of national defense, health care, banking, etc. Consequences of failure are relatively severe, while the hidden failures are contained in the most complex devices as the process is running. Hidden failures in the normal operation of the device is difficult to find, and only under certain conditions will be triggered, while other faults may be led. The stability of the running system will be undermined. In order to monitor the occurrence and development of hidden failure of complex equipment, a hidden failure warning model based on data mining has been put forward, and the theory of the model has been analyzed, the selection gist of the model parameters has been given. The result shows that the accuracy of hidden failure impact value forecast by the model is 93.33%, the impact degree of the hidden failure effect on the dominant failure can be effectively monitored, and the model makes a good preventative effect against the sudden failure caused by the hidden failure.

Abstract: A certain amount of Ti was added into high boron alloyed stainless steel with content 2.25%B, and then high boron alloyed stainless steel composite casting slab with three layers was fabricated , in which central layer is high boron alloyed stainless steel containing Ti and cladding is plain 304 stainless steel without Ti. The microstructure of core and interface and the mechanical property of the composite plate were studied after hot forged, hot rolled and solution treated process respectively. The results show that the boride in as-cast microstructure of core are (Fe,Cr)₂B phase with long strip and TiB₂ phase with petal shape, moreover the formation of TiB₂ phase decreases the amount of (Fe,Cr)₂B phase. Two kinds of boride are fully broken after hot rolling and distributed in the form of block uniformly in matrix, and TiB₂ phase is more fine uniform. The mechanical property especially plastic performance of high boron alloyed stainless steel composite plate containing Ti after solution treatment is improved significantly, it has reached and surpassed the United States ASTM A887-89 delivery standards.

Abstract: Turbine Air Powered Engine (TAPE) is a new type engine which has the character of zero emission, no pollution. Mathematical models of TAPE were established by the method of exergy analysis, the overall exergy and the exergy loss after reduced pressure with throttling were simulated in this paper. The results show that the maximum exergy loss of system is 60% during the process of reduced pressure with throttling, so the type of throttling decompression is not suitable for the system of TAPE which has bigger pressure reducing ratio. The results of bench test indicate that output power increases with the increase of inlet pressure within the scope of less pressure, and the regulation is similar to the simulating result. In the hybrid system of pneumatic internal-combustion engine, the measure which the air powered system is used in low-speed stage and the internal combustion engine powered system is adopted in high-speed stage can effectively solve the problem which the fuel consumption of the internal combustion engine is too bigger at low speed.

Abstract: High conductive Niobium-Titanium alloy has the advantages of good corrosion resistance, high specific strength, good thermal stability, etc. The rotary forging technology of Nb-Ti alloy ingot with type prepared by vacuum smelting method was studied. The results show that coarse and homogeneous casting-microstructure becomes strip deformation microstructure after rotary forging. With the increase of deformation degree and deformation velocity, the space of strip deformation microstructure decreases and yield strength of alloy increases. Nb-Ti alloy bar after deformation is still type alloy with a thermal stability.

Abstract: Modern composite armor is generally composed of faceplate with high hardness and backplate with good toughness. The 45steel/60Si₂CrA multi-layer composite armor plate with eleven layers in which 60Si2CrA steel was used as faceplate and 45 steel as backplate was fabricated by composite casting+forming process. In order to achieve good bulletproof effects, the heating treatment processes of multi-layer composite plate were researched. The results show that the yield strength and tensile strength of the composite plate reaches 956MPa and 1018MPa and the hardness of 45 steel layer and 60Si2CrA layer is 448HV and 536HV respectively under the condition of 860°C water quenching+high temperature tempering. The mechanical properties meet standard requirements of armor plate.

Abstract: Brazing of commercially pure titanium to low carbon steel by using the Ag72Cu28 interlayer at different conditions was carried out in the present work in order to investigate the tensile-shear strength, microstructure and the fracture morphology of brazed joint. The results show that different intermetallic compounds such as CuTi,CuTi₂,Cu₄Ti₃ and FeTi were formed at the bonding area. It was observed that the microstructure of joint has a considerable effect on tensile-shear strength of the brazed samples and the maximum tensile-shear strength was achieved at “750°C-10min→850°C-5min”.All the fracture paths after tensile-shear tests occurred in the interface between titanium and silver-based interlayer in spite of the different fracture morphology.

Abstract: Hard and brittle (Fe,Cr)₂B phase caused by excess boron in high boron alloyed stainless steel has adverse effects on the hot working performance and mechanical properties of material. Adding Ti into high boron alloyed stainless steel can improve the type, morphology and distribution of boride phase. The results show that TiB₂ phase with petals or small block shape forms after adding Ti into high boron alloyed stainless steel, and as the increase of Ti content, TiB₂ phase replaces (Fe, Cr)₂B gradually. Moreover, the petal-like TiB₂ phase becomes smaller and more granular after high temperature deformation, and the segregation of matrix composition is significantly weakened by the formation of TiB₂ phase.

Abstract: With deepening of roll forming technology and the proficiency of computer aided design and finite element Analysis (FEA) technology, it is widely noted that using the technology of FEA to simulate the roll forming process. In this paper, the current status of finite element simulation for roll forming process at home and abroad is summarized. And the finite element theories of deformation zone in roll forming process are analyzed. The new issues on roll forming process faced by finite element simulation, including advanced high strength steel (AHSS), multipass heterosexual cross section and coupling thermo-mechanical-metallurgical (TMM) coupling etc. are discussed. Moreover, the future trends of numerical simulation about the roll forming process are forecasted.

Abstract: The main methods for manufacturing titanium clad steel are described, also the mechanisms of cold roll bonding and explosive welding are specifically analyzed. It is showed that two opposing brittle surface layers produced by scratch brushing break up and underlying base metal is extruded through cracks of the broken layers and creates an atom-to-atom bond for cold roll bonding, however, a lot of parameters affect the bonding for explosive welding. Some new ideas for manufacturing titanium clad steel is discussed herein.