Papers by Author: Yan Ping Liu

Abstract: A carburized layer is fabricated in the surface of TiAl alloy using plasma carburization at 975 °C. Fretting wear test at ambient temperature was carried out to evaluate wear resistance of carburized TiAl. Glow discharge spectrum, X-ray diffraction and scanning electron microscopy equipped with energy dispersive spectrometry were used to characterize the microstructure of carburized TiAl and its property capability. The experimental results show that the carburized layer with about 5 μm in thickness is mainly composed of Ti₂AlC and possesses better fretting wear resistances at ambient temperature. Precipitation of carbides in surface layer leads to a higher surface hardness and compressive stress, causing a surface strengthening of TiAl. Strengthening mechanism of carburized TiAl is also considered in this investigation.

Abstract: A new process technique that TiN permeation layer consisted of diffusion and deposition layer was synthesized on the surface of mild carbon steel has been firstly introduced, mainly according to plasma point discharge, hollow cathode effect and reactive vapor deposition technique. The surface appearance of this layer formed was uniform, compact and fine TiN cellular structure, a diffusion transitional region existing between the deposition layer and substrate. The surface texture was TiN deposition layer + TiN + Ti solid solution diffusion layer. From surface to inner Ti and N elements appeared graded distribution. This paper also mainly investigated the electrochemical corrosion behaviors of this multilayer. The polarization curves of specimens in 10% H2SO4 corrosive media were measured. The eroded surface morphologies were also surveyed by SEM. The results indicated that the erosion resistance of multi-permeation layer was increased many times than PVDTiN and a mild steel substrate, and almost equaled to that of compound process TiN layers.

Abstract: High quality TiN/Ti multi-layers have been successfully obtained on a carbon steel substrate by double glow plasma surface alloying technique (DGP). The TiN/Ti multi-layers consists of deposition layer and diffusion layer, and then on its surface TiN film (PVD) is deposited to form TiN/TiN/Ti compound multi-layers. In addition, studies were carried to compare TiN/Ti multi-layers, TiN/TiN/Ti compound multi-layers and TiN film (PVD) directly deposited on the surface of the carbon steel and their microhardness and dry friction-abrasion properties were also investigated. The results show that the thickness of TiN/Ti multi-permeated layers is above 10*m; Ti and N concentrations change gradually along the depth of alloying layer. TiN/Ti multi-layers and substrates are metallurgically bonded. Preferred orientation of TiN/Ti multi-layers is crystal surface (200). The hardness of the TiN/Ti multi-permeated layers ranges up 2200HV, its average friction coefficient is lower, abrasion crack is shallower and wear resistance better.

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: 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: Tb-doped silicon carbide (SiC:Tb) films were deposited on porous silicon (PS) substrates by rf co-sputtering. The prepared films were annealed in N2 atmosphere at different temperature from 500-1000 °C. The effects of annealing on the structure and photoluminescence (PL) characters of the films were investigated by Atomic force microscopy (AFM), Raman, Fourier transform infrared spectroscope (FTIR) and fluorescence spectrometer. The SiOx layer at the SiC:Tb/PS interface was destroyed as the annealing temperature increasing, and the oxygen-deficiency centers (ODCs) increased. The SiOx layer was restructured at higher annealing temperature and the ODCs decreased. This is the reason of origin and changing of UV band in PL spectra. The visible band origins from Tb3+, and is stable with annealing temperature.

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.