Shengwang Yu

Wear and corrosion properties of Mo surface-modified layer in TiNi alloy prepared by plasma surface alloying

In order to improve the wear resistance and restrain nickel release of TiNi alloys, the Mo modified layers on TiNi substrates were obtained using the double glow plasma surface alloying technique. Scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES) and X-ray diffraction (XRD) were employed to investigate the morphology, composition and structure. Microhardness test and scratch test were performed to analyze the microhardness and coating/substrate adhesion. Tribological and electrochemical behaviors of the Mo modified layers on TiNi were tested by the reciprocating wear instrument and electrochemical measurement system. The Ni concentrations in Hanks’ solution where surface electrochemical tests took place were measured by mass spectrometry. The surface-modified layer contained a Mo deposition layer and a Mo diffusion layer. The X-ray diffraction analysis revealed that the modified layers were composed of Mo, MoTi, MoNi, and Ti2Ni. The microhardnesses of the Mo modified layers treated at 900 °C and 950 °C were 832.8 HV and 762.4 HV, respectively, which was about 3 times the microhardness of the TiNi substrate. Scratch tests indicated that the modified layers possessed good adhesion with the substrate. Compared with as-received TiNi alloy, the modified alloys exhibited significant improvement of wear resistance against Si3N4 with low normal loads during the sliding tests. Mass spectrometry displayed that the Mo alloy layers had successfully inhibited the Ni release into the body.

Influence of power density on high purity 63 mm diameter polycrystalline diamond deposition inside a 2.45 GHz MPCVD reactor

63 mm diameter polycrystalline diamond (PCD) films were synthesized via a microwave plasma chemical vapor deposition (MPCVD) reactor in 99% H2–1% CH4 atmosphere. Two different conditions, i.e. the typical condition (input power of 5 kW and gas pressure of 13 kPa) and the high power density condition (input power of 10 kW and gas pressure of 18 kPa), were employed for diamond depositions. The color changes of the plasma under the two proposed conditions with and without methane were observed by photographs. Likewise, the concentrations of hydrogen atoms and carbon active chemical species in plasma were analyzed by optical emission spectroscopy (OES). The morphologies and purity of the PCD films were investigated by scanning electron microscopy (SEM) and Raman spectroscopy, respectively. Finally, the transmission spectrum of the polished PCD plates was characterized by a UV–Vis–NIR spectrometer. Experimental results showed that both the concentrations of hydrogen atoms and carbon radicals increased obviously, with the boost input power and higher pressure. The films synthesized under the high power density condition displayed higher purity and more uniform thickness. The growth rates in 10 kW and 18 kPa reached ~7.7 µm h−1, approximately 6.5 times as much as that occurred in the typical process. Moreover, the polished plates synthesized under the high power density condition possessed a relatively high optical transmittance (~69%), approaching the theoretical values of approximately 71.4% in IR. These results indicate that the purity and growth rate of big-area PCD films could be simultaneously increased with power density.

Effect of Substrate Temperature on Tantalum Carbides Interlayers Synthesized onto WC-Co Substrates for Adherent Diamond Deposition

Tantalum carbides (TaXC) interlayers have been synthesized by double glow plasma surface alloying (DG-PSA) method at different temperature for subsequent deposition of diamond coatings. The evolution of the microstructures, phase composition and adhesion of the interlayers dependent on substrate temperature has been discussed. The results show that the layers are composed of TaXC (i.e. Ta2C, TaC) with nanocrystalline microstructure and small amounts of CoTa2. The layer produced at 700∘C is formed of specific flower-shaped rings embedded in smooth structures. As the temperature increases to 800∘C, interacted rings are covered the full surface, and the surface roughness is increased. As the temperature increases further, the rings are replaced by irregular-shaped pits, caused a decreasing surface roughness. Besides the special microstructure with interactional rings and relatively high roughness, the layer prepared at 800∘C possesses higher adhesion, better wear performance and higher hardness than those of...

SURFACE Nb-ALLOYING ON 0.4C–13Cr STAINLESS STEEL: MICROSTRUCTURE AND TRIBOLOGICAL BEHAVIOR

0.4C–13Cr stainless steel was alloyed with niobium using double glow plasma surface alloying and tribological properties of Nb-alloyed steel such as hardness, friction and wear were measured. Effects of the alloying temperature on microstructure and the tribological behavior of the alloyed steel were investigated compared with untreated steel. Formation mechanisms of Nb-alloyed layers and increased wear resistance were also studied. The result shows that after surface Nb-alloying treatment, the 0.4C–13Cr steel exhibits a diffusion adhesion at the alloyed layer/substrate interface and improved tribological property. The friction coefficient of Nb-alloyed steel is decreased by about 0.3–0.45 and the wear rate after Nb-alloying is only 2–5% of untreated steel.