Papers by Author: Liu Jie Xu

Abstract: The corrosion property of high chromium cast iron was test under different phosphoric acid medium concentration. On the base of experimental data, the binary equation model of corrosion weight loss (W) versus phosphoric acid concentration and corrosion time (c, t) was built using multiple regression analysis, which can predict corrosion property of high chromium cast iron effectively. The prediction results show that the corrosion weight loss rises lineally with increasing corrosion time, and the corrosion rate rises quadratically with increasing phosphoric acid concentration. The corrosion failure mechanism is that chromium composite carbides (M7C3) stand out of matrixes surface after the matrixes composed of martensite and austenite are corroded firstly, then the M7C3 carbides drop out of matrixes when the matrixes can not wrap M7C3 carbides, resulting gradual corrosion of high chromium cast iron. The prediction values have sufficiently mined the basic domain knowledge of corrosion process of high chromium cast iron under phosphoric acid medium. Therefore, a new way of predicting corrosion property according to corrosion conditions was provided by the authors.

Abstract: Using the steel containing 0.45 percent of carbon as matrix, high carbon ferrochrome as cast-penetrated agent, the steel-based surface composites were fabricated by conventional cast-penetrating process combined with the thermite reaction. The influence of thermite reaction on the microstructures and properties of cast-infiltration layer was researched. The results show that the interfacial bonding is metallurgical fusion between cast-infiltration layer and the matrix under the suitable technological parameters, the thermite reaction during the process of cast-penetrated realizes thermal compensation for liquid metal and improves the mobility of liquid steel by reducing oxidation film of liquid steel surface, consequently increase the thickness of cast-infiltration layer; The ceramic phase of Al2O3 which is generated during the thermite process improves the microhardness of cast-infiltration in a certain extent.

Abstract: Al₂O₃ reinforced iron based composite were prepared via in-situ synthesis with aluminum nitrate, citric acid and iron powder as raw materials, a little C and Mo as additive. The influences of the contents of Al₂O₃, C and Mo on the microstructure and micro-hardness of the Fe based composites were characterized by XRD, SEM, TEM and micro-hardness tester. The results showed that the Fe-based composite materials with high bonding strength between matrix and Al₂O₃ can be prepared by in situ synthesis method. The best ratio of the nine Al2O3 particles reinforced Fe-based composite materials in three groups is 3vol. % C, 5vol. % or 7vol. % Al₂O₃, sintering temperature is 1300°C and quenching temperature is 900°C. The microstructure of the matrix without C addition is ferrite before and after quenching; the microstructure of the matrix with C addition is pearlite before quenching, and the microstructure become to martensite after quenching, the α-Al2O3 and FeC₃ are reinforced phases. The microstructure of the matrix with Mo addition is ferrite and FeAl₂O₄ before and after quenching.

Abstract: Mo-based composites with Al₂O₃ particles were developed in order to enhance the wear resistance of molybdenum alloys. Using Al₂O₃ power and pure Mo power as raw materials, the Molybdenum powders mixed with Al₂O₃ particles were prepared using planetary ball mill. And then the Mo-based composites with 3-10vol.% Alumina were prepared by compaction and sintering at 1840°C. The morphology of the Molybdenum powder and microstructure of the composites were analyzed by SEM and XRD. The micro-hardness, density and wear property of composites were researched. The results show that the microstructure of composites is composed of α-Al₂O₃ particles and Molybdenum matrix. With the increase of Alumina content, the microhardness of Molybdenum matrix increases, and the density first increases and then decreases. The friction coefficient of composite is scarcely affected by the alumina content. While the wear resistance of the composites rises with the increase of Alumina content. The wear failure is caused by abrasive wear characterized by obvious plow furrow and abrasive dust on the worn surface.

Abstract: The wettability between ceramic particles and metal play an important role in fabrication of ceramic particles reinforced metal matrix composites(PRMMCs). In present paper, Al₂O₃ particles were coated with nickel by chemical plating to modify the preparation and properties of Al₂O₃ particles reinforced steel matrix composites. Using the Al₂O₃ particles treated by chemical nickel-plating, Al₂O₃ particles reinforced steel matrix composites were fabricated by powder metallurgy process(PM). And the wear resistance of the composites was investigated. The results show that: the nickel coating can fully and tightly cover on the surface of Al₂O₃ particles, and the nickel coating thickness is uniform about 2~3 micron; The nickel coating can effectively improve the uniform distribution of Al₂O₃ particles in the composites. And the treated Al₂O₃ particles can be tightly bonded with steel matrix,which improve the wear resistance of composites. The wear resistance of composites reinforced treated and untreated Al₂O₃ particles each is 2.5 and 1.6 times of Hadfield steel.

Abstract: This paper dealt with how the aging time and temperature affected the hardness of beryllium bronze layer in the explosive welded beryllium-bronze/carbon-steel composite plate. The properties of shearing, bonding, cold bending and microhardness were studied in term of the composite plate, including the aging and nonaging. The optimum aging treatment process of the composite plate is aging temperature at 320°C for 3 hours. And the results show that: aging treatment has no obvious effects on the shear strength but sharply decreases bond strength of the composite plate. And aging treatment to a certain extent reduce the cold bending prroperty. After aging treatment, the microhardness value and distribution of carbon steel was no obvious change, and the microhardness of beryllium bronze sharply raised and smoothly distributed.

Abstract: High-alloy materials such as high chromium cast iron and high speed steel have excellent wear resistance under extreme wear conditions. But they consume much expensive chromium, molybdenum, tungsten and other alloying elements too. The hypereutectic high boron alloy has good wear resistance because it contains many high hardness primary borides. But the dimension of primary borides is big. In this paper, the hypereutectic high boron alloy was prepared using sand casting method, and the primary borides were modified by different amount of K / Na modificator. The results show that the primary boride of hypereutectic high boron alloy is Fe₂B. K/Na modificator has a significant influence on primary Fe₂B. The best grain refinement effect of primary Fe₂B is obtained when the amount of K/Na modificator is 0.3%. The refining mechanism of primary Fe₂B is that K/Na modificators can not only increase the supercooling degree to improve nucleation rate but attach to the crystal face of fastest growth direction to prevent grain from growing

Abstract: To increase the wear resistance of components in slurry pump suffering from serious corrosive abrasion, new super high chromium cast iron (SHCCI) which contains 37wt.% chromium approximately and different carbon content were developed based on the high chromium cast iron with 26wt.% Cr (Cr26). The microstructure of SHCCI was investigated by SEM and XRD. The hardness and impact toughness of SHCCI was tested, and the corrosive wear property of SHCCI was also researched using MCF-30 type erosion abrasion tester under H3PO4 medium condition. The results show that the microstructure of SHCCI is composed of carbide of M7C3+M23C6, martensite and retained austenite. With the increase of carbon content, the hardness of SHCCI first increases and then decreases, the toughness increases, and the corrosive wear property decreases. The relative wear resistance of SHCCI is obviously superior to that of Cr26 cast iron, and the maximal relative wear resistance of SHCCI is three times higher than that of Cr26 cast iron.

Abstract: In this study, beryllium bronze/steel composite plates were fabricated through explosive welding process using different ratios of explosive. Microstructures of the joint were examined, and then shearing strength, peeling strength, Bending tests and hardness measurements were carried out on the bonded specimens. Experimental studies show that, beryllium bronze and steel could be bonded with a good quality. The interface is wavy texture changing in turns from flat - wavelet - large wave - stable large wave beginning with initiation point. Grains near the interface are elongated parallel to the explosion direction. As the ratio of explosive increase, the amplitude and wavelength of wave are increased, which leads to the increasing of shearing strength and bonging strength. No shearing in the interface is seen from the tensile-shear tests and fracture take place in the low strength material. The bended specimens show that defects such as separation and tearing were not observed. Hardness is increased with increasing explosive ratio and the highest hardness values are obtained near the bonding interface.

Abstract: The components in slurry pump suffer serious corrosion abrasion under H3PO4 medium. Presently, High chromium cast irons are often used to produce the components in slurry pump. New high vanadium high speed steel(HVHSS) has been proved to be a more excellent wear resistance material than high chromium cast irons under abrasive wear and rolling wear. In order to apply HVHSS in slurry pump to replace high chromium cast irons, the corrosion properties of HVHSS were tested under different H3PO4 medium concentration conditions. Using back-propagation (BP) neural network, the non-linear relationship between the corrosion weight losses (W) and H3PO4 concentration, corrosion time (C, t) is established on the base of the dealing with experimental data. The results show that the well-trained BP neural network can predict the wear weight loss precisely according to H3PO4 concentration and corrosion time. The prediction results reveal that the corrosion time and H3PO4 concentration have obvious effect on corrosion weight loss of HVHSS. And corrosion weight loss takes on linear relationship with corrosion time and H3PO4 concentration, respectively.