Papers by Author: Shi Zhong Wei

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: 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: The forging of crusher main shaft, with diameter of φ1540mm and weight of 47780Kg, requires 90 tons of steel ingot, and have a higher demand for grain size. In order to meet the demand of ultrasonic examination, some effective measures, including LF refining, VCD treatment and ingot casting in vacuum, were taken in process in smelting and ingot casting. In this paper, two main shafts were manufactured, and two technologies were adopted respectively to control grain size. One was without modification, relying on subsequent heat treatment to refine grain. The other was modification, adding a trace amount of Nb to refine grain. Both of methods finally make grain size to reach 7-8 degree, higher than the standards, achieving very good results.

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: In recent years, high chromium cast irons have been widely applied in many fields because they have high hardness and abrasion resistance. However, high chromium cast irons are also expensive because much alloying elements, such as chromium, molybdenum and nickel, are added into them. In order to resolve above question, a new abrasion-resistant steel with high boron content was developed in this paper. The new high boron steel, with 0.6%~0.8%B and 0.65% C, was prepared using sand casting method. The microstructure and mechanical properties were researched. The results show that the solidification microstructure of as-cast high boron steel consists of boride (FeB) and matrix composed of pearlite, ferrite, and bainite. And the borides distributes along grain boundary in the form of network. After quenching at 980°C and tempering at 250°C, the FeB transforms to Fe₂B, and the matrix transforms lath martensite. The hardness of as-cast high boron steel is 43HRC, and its impact toughness is 5J/cm². After heat treatment, they increase to 56 HRC and 7J/cm², respectively, approximating that of high chromium cast irons. The new high boron cast steel have a potential in stead of high chromium cast irons

Abstract: To enhance the wear resistance of molybdenum alloys, Mo-based composites reinforced by Al2O3 ceramic particles were developed. Using Al(NO3)3 aqueous solution and MoO3 as raw materials, the Molybdenum powders mixed with Al2O3 particles were prepared by liquid-solid incorporation, drying, pyrolysis of Al(NO3)3 and deoxidation of MoO3 by H2. 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 showed that α-Al2O3 ceramic particles and Molybdenum matrix compose the composites. With the increase of Alumina content, the molybdenum powders become fine and rule, the grains of composites become fine, 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 weight of the composite decrease with the increase of Alumina content. There are obvious plow furrow and abrasive dust on the worn surface, showing the abrasive wear characterization.

Abstract: Brazing with active filler alloys containing some active elements, which promotes wetting of ceramics surfaces, is one of the most widely methods for joining ceramics to metals. The joints formed by brazing A12O3 to metal by using copper-titanium-nickel (Cu-Ti-Ni) as brazing filler were investigated. The metals/ceramics joints were produced at a vacuum level of 10-2-10-3 Pa at 1273K, using a constant holding time of 10 min. The surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). In the brazing process, copper and titanium in the braze alloy form a series of reaction products. The formation of Ti3Cu3O and Ti2Ni at the interface is characteristic of these joints. The estimated free energies of formation of the Ti3Cu3O and Ti2Ni are -119kcal/mol and -245.92 kJ ~-263.78kJ/mol at 1200~1288K respectively. The highly negative values for the free energies of formation suggest that these compounds are thermodynamically stable.