Zhi Yong He

Study on Tribological Performance of the TiNi Modified Layer on the Surface of the Ti6Al4V Alloy

TiNi alloyed layer was prepared on surface of Ti6Al4V substrate by plasma surface alloying process. Micro-structure, composition distribution, phase structure and hardness distributing of TiNi modified layer were analyzed. Tribological performance of TiNi alloyed layer and Ti6Al4V substrate was observed by Pin-on-disc test. The results indicated that surface microhardness of TiNi alloyed layer was about 620HV. Coefficient of friction (CoF) and relative wear rate (RWR) of TiNi alloyed layer were lower than Ti6Al4V substrate, and wear resistance of TiNi alloyed layer was improved obviously. The wear mechanism of Ti6Al4V alloy is abrasion and adhesion wearing, while TiNi alloyed layer shows abrasion wearing.

Influence of Temperature on Characteristics of TiAl Plasma Surface Niobiumizing

In this study, plasma niobium alloying of the TiAl based alloys has been carried out at 1050, 1100 and 1150°C. The effect of the alloying temperature on the characteristic of the alloyed layer was investigated by optical microscopy, scanning electronic microscopy (SEM), glow discharge spectrum (GDS) and energy dispersive spectrum (EDS). The results show that the surface roughness, chemical composition and thickness of the alloyed layer increased with the alloying temperature which is dependent on the sheath potential. A deposition layer formed on the TiAl surface at 1150 °C was resulted from the larger sheath potential or the stronger sputtering of source electrode.

Surface Plasma Molybdenized Burn-Resistant Titanium Alloy

Conventional titanium alloy may be ignited and burnt under high temperature, high pressure and high gas flow velocity condition. In order to avoid this problem, a new kind of burn-resistant titanium alloy-double glow plasma surface alloying burn-resistant titanium alloy has been developed. Alloying element Mo is induced into the Ti-6Al-4V substrate according to double glow discharge phenomenon, Ti-Mo binary burn-resistant alloy layer is formed on the surface of Ti-6Al-4V alloy. The depth of the surface burn-resistant alloy layer can reach about 100 microns and alloying element concentration can reach 59%. High energy laser ignition experiments reveal that the ignition temperature of alloyed layer with Mo concentration about 10% is about 200°C higher than ignition temperature of Ti-6Al-4V.

Oxidation Resistance of Ti-6Al-4V by Plasma Niobium Surface Alloying

A niobium modified layer on Ti-6Al-4V surface was obtained by means of the plasma surface alloying technique. The oxidation behavior of the modified layer was investigated and compared with Ti-6Al-4V at 700°C~900°C for 100h. Composition and microstructure of Ti-6Al-4V and the modified layer after oxidation at 900°C for 100h were analyzed using XRD and SEM respectively. The experimental results showed the oxidation behavior of Ti-6Al-4V at 900°C for 100h was obviously improved after the niobium alloying process.

Tribological Performance of Ti6Al4V Alloy Treated by Plasma Surface Ni Alloying

Plasma surface alloying technology was applied to introduce Ni element into Ti6Al4V to improve its tribological property. The microstructure, composition, phase constituent and hardness of the alloyed layer were examined. Wear mechanisms were discussed on the basis of wear scar observations. The tribological performance of the alloyed layer was investigated by ball-on-disk sliding tests in different environments. The results showed that the Ti-Ni alloyed layer was about 12μm in thickness and the content of Ni element reached to 28% on the surface. The surface hardness of the layer was 677HV, nearly twice as the untreated Ti6Al4V. The wear resistance of the modified Ti6Al4V substrate was improved obviously in different environments.

Fretting Wear and Microstructure of Plasma Carburized TiAl Alloy

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.

Tribological Performance of TiAl Based Alloy Treated with Plasma Surface Chromizing Process

TiAl-Cr alloy was prepared on surface of TiAl based alloy by plasma surface alloying technique. The wear resistance of the surface alloy was examined under various wear condition. During the room temperature ball-on-dic sliding test, the TiAl-Cr surface alloy showed reduced friction and improved wear resistance. For the 500°C sliding and room temperature fretting tests, the friction coefficient of TiAl-Cr surface alloy was a little higher than that of TiAl-based alloy, but the wear volume showed significant reducing, the wear resistance was improved obviously. The addition of chromium increases the strength and hardness of the TiAl-based alloy, and therefore the load bearing and anti-adhesion capacity of the surface were also enhanced, these were the main mechanisms for the improvement of wear resistance.

Nb-C Alloyed Layer Prepared on TiAl Alloys by Plasma Treatments and its First-Principles Investigation

A Nb-C alloyed layer formed on TiAl by plasma Nb alloying followed by carburization was investigated. The alloyed layer was characterized using SEM, TEM, XRD and GDS. Effects of Nb alloying and the carburizing atmosphere on microstructure of Nb-C alloyed layers were analyzed. The forming mechanism of the Nb-C alloyed layer was verified using first-principle calculation. The results reveal that the Nb-C alloyed layer is composed of NbC and Nb2C. An addition of niobium in TiAl accelerates the diffusion of carbon atoms in the Nb-alloyed layer, leading to a thicker alloyed layer with higher carbon content. The carbon concentration and diffusing depth increase with methane gas. First-principle calculation shows that the forming energy of Nb-C duplex-treated TiAl is lower than those of single carburized TiAl and Nb-alloyed TiAl.

Study on temperature distribution in double glow discharge zone

This paper deals with the temperature measuring of the glow discharge zone in double glow plasma surface alloying process. CCD technique was employed to get the temperature distribution profile. The results show that CCD method is a simple and effective non-contact temperature measuring technique, applicable in fields of low temperature and high temperature plasma processes.

Electrochemical Corrosion Behaviors of Ti2AlNb with Double Glow Plasma Surface Molybdenized

Ti2AlNb orthorhombic alloy is an attractive high temperature structural material for aero-industries, but insufficient wear-resistance is a major drawback which restricts the actual uses of this alloy in many circumstances. A double glow plasma surface molybdenizing on Ti2AlNb alloy had been carried out to resolve this problem. This paper investigated the electrochemical corrosion behaviors of the alloy after molybdenizing. The polarization curves of specimens in three corrosive media, 5% H2SO4, 5% HCl and 3.5% NaCl, were measured. The eroded surface morphologies were surveyed by SEM. The results indicate that surface molybdenizing decreased the alloy’s corrosion resistance slightly, but still exhibit good performance.