Papers by Author: Zhong Xu

Abstract: The alloying elements W-Mo cementation is carried out on the surfaces of low carbon steels by the technique of plasma metallurgy. Then by using the plasma-supersaturated carbonization, the composition of surface alloying layer reaches or approaches that of low-alloy HSS. In the end the surface alloying layer possesses high hardness, favorable red hardness and a significant improvement in properties after high temperature quenching and high temperature tempering. The surface cementation structure and phase structure of alloying layer were analyzed using metallographic microscope and X-ray diffraction (XRD), respectively; the distribution of surface composition and hardness of the layer were investigated by Glow Discharge Analytical Instrument (GDA) and micro hardness instrument, respectively; the resistance to wear was tested by a abrasion machine. The experimental results indicated that the layer consisted of W-Mo solid solution in Fe, the depth of the layer could reach 100µm and the content of tungsten exceeded 10% after ion W-Mo cementation. The carbon content of carburized layer was 1.3% above, which was composed of M6C carbide containing a lot of elements of W-Mo. The surface hardness of the alloying layer attained the HV1000 or so and appeared graded distribution after quenching and tempering. The application study showed that alloying elements W-Mo cementation was an appropriate technique to enhance surface resistance to wear and prolong operating life of accessories.

Abstract: Using a special impulse device, the impulse electroless Ni-P alloy plating were prepared. The microstructure、crystallization and the starting activation energy for crystallization was investigated by TEM、XRD and DTA, compared with electroless Ni-P alloys plating. The results showed that the diffractive ring was wider when using impulse, depositing temperature dropped up to 65°C,and crystallization temperature rose up to 310°C. Furthermore , the starting activation energy for crystallization and crystallization temperature of impulse electroless Ni-P alloys plating measured were more than that of electroless plating in the heating rate at 5、10、20、 40K/min, and it was also higher in the amorphous disorder degree and the starting crystallization temperature. Impulse electroless Ni-P alloys plating had better performance of thermal stability.

Abstract: The plasma surface alloying low-alloy high speed steel (HSS) is carried out in vacuum chamber where a source electrode (W-Mo) and a work piece are properly placed. By using the sputter of glow-discharge, under the common function of electric field and temperature field, the desired alloying elements (W- Mo) are sputtered from the source cathode, traveling toward the substrate. Subsequently the alloying elements deposit onto the surface of the substrate, forming alloy diffusion layer which the depth may vary from several micron to several hundreds micron. In the end a surface low-alloy HSS steel would be produced after ultra-saturation ion carbonization. The composition of the alloyed layer is equal or similar with it of low-alloy HSS. The carbonized layer, without coarse eutectic ledeburite structure, possesses high density of finely and dispersed alloy carbides with tungsten equivalent 10% above and a significant improvement in surface hardness and wear resistance. The principle of plasma surface alloying and its test results and commercial products application are introduced in this paper.

Abstract: By means of double glow plasma surface alloying process, Ti6Al4V surface was successively carbonitrided forming a layer with special physical and chemical properties. The depth profile of C and N elements showed a tendency of gradual decrease on the Ti6Al4V as well as the depth profile of its hardness. Friction and wear test indicate that the wear resistant property is increased greatly after carbonitriding the Ti6Al4V.

Abstract: Mo modified layers on Ti-6Al-4V alloy were obtained with plasma surface alloying technique. The properties of the Mo-diffusion layers were investigated in this paper. Results show that the Mo-diffusion layers obviously enhance the wear resistance of Ti alloys against a polished 2100 steel counterbody ball under ball-on-disc test condition. With a series of experimental results, a wear model of high wear resistance of modified layers is propounded. The noval wear behavior is a result of absolute elasticity characteristics on the subsurface of Mo modified layers.

Abstract: Plasma surface alloying for low alloy high speed power hack saw blades was introduced.The bulk material of the blade is made of low alloy steel, while the teeth of which possess a composition of high speed steel like as a result of surface modification by a plasma surface alloying process.It is a solid diffusion process eliminating method avoids the formation of coarse primary carbides which is a major problem encountered in the production of smelting high speed steel. As a result the carbides in the layer of high speed steel are fine and well-distributed.Therefore,it has not only well wear-resistance but also toughness. Besides, the blade also has the advantages of ease manufacturing and low cost.

Abstract: The Mo surface alloying layer was prepared on Ti6Al4V substrate using the plasma surface alloying technique. The component, structure and hardness of the Mo surface alloying layer were investigated. The impact test was used to determine the fatigue behavior of the Mo surface modified Ti6Al4V. The results showed that the Mo surface alloying layer enhanced the surface strength of Ti6Al4V substrate. The Mo surface alloying layer has a duplex structure with diffusing and coating layers. The diffusing layer in which the component and hardness change gradually could enhance load-bearing capacity to the surface coating and ensure the durability of the coating. In the impact test, the Mo modified Ti6Al4V showed excellent fatigue behavior and the cohesive failure mode was observed.

Abstract: Tungsten, molybdenum and cobalt were co-diffused into the surface of undecarburized 45 steel at 1150 °C for 6 hours by a double glow plasma surface alloying technique. A Fe-W-Mo-Co type gradient surface alloyed layer with very low carbon content was formed. Thickness of the surface alloyed layer is 225.2μm. Concentrations of alloying elements Co, W and Mo in the alloyed layer are mostly ranged from 21 to 14 wt.%, 12 to 6 wt.% and 7 to 5 wt.%, respectively. The concentrations of alloying elements basically meet the requirements of W11Mo7Co23 type age-hardened high speed steel. The alloyed samples were solution heat treated, ageing and high-temperature tempering. The results show that the surface alloyed layer formed on 45 steel exhibits very strong age-hardening property and anti-temper softening ability as the metallurgical age-hardened high speed steel, the surface age-hardened high speed steel on ingot and decarburized carbon steel.