Anti-oxidation characteristics of Cr-coating on surface of Ti-45Al-8.5Nb alloy by plasma surface metallurgy technique

TiAl-based alloys have received extensive attention recently due to their excellent properties. However, the weak oxidation resistance at temperatures higher than 800℃ can limit their further high-temperature structural applications.To improve the oxidation resistance of a high-Nb-content γ-TiAl alloy(Ti-45 Al-8.5 Nb, in units of at.%), a chromium(Cr)coating is prepared by using the plasma surface alloying technique, separately, at 800℃ and 1000℃. The x-ray diffraction(XRD) patterns reveal that an oxide surface layer consisting of Cr2O3, Al2O3, and TiO2 is produced on the Cr-coated Nb containing γ-TiAl substrates during the initial oxidation. However, the Cr2O3 is dominated in the oxide surface layer after being isothermally oxidized for 300 h. The oxidation kinetic curves are composed of a parabolic law stage(≤ 90 h) and a biquadratic law stage(≥ 90 h), fit by weight–gain curves. Due to diffusion in the fabrication process and oxidation process,the Cr-coated specimens have an adhesion force after being isothermally oxidized, specifically 69 N for a specimen after oxidation for 300 h. These results demonstrate that the Cr coating enhances the oxidation resistance and adhesion of a Ti-45 Al-8.5 Nb alloy, which may provide a new feasible scheme for designing oxidation protection layers.

The Diagnosis of Plasma Parameters in Surface Alloying Technique by Optical Emission Spectrometry

Electron density （Ne） in a glow discharge plasma for the surface alloying technique is diagnosed by optical emission spectrometry （OES）. With CH4 as the feeding gas, Ne is obtained by comparing the Hβ spectrum according to the Stark broadening effect. It is noticed that Ne varies with the working pressures （30 Pa to 70 Pa） and cathode voltages （500 V to 1000 V）, respectively. Due to an abnormal glow discharge, Ne is between 1. 71 × 10^15 /cm^3 to 6.64 × 10^15 /cm^3 and increases rapidly with working gas pressures and cathode voltages. The results show that OES is a useful method to measure the plasma parameters in a surface alloying glow discharge plasma.

Structure and Corrosion Behaviours of Mo Modified Titanium in Saliva

The Mo surface modified layer on titanium was obtained by the plasma surface alloying technique. The structure and composition of the Mo modified titanium were investigated by X-ray diffraction （XRD） and glow discharge optical emission spectroscopy （GDOES）. The Mo modified layer contains Mo coating on subsurface and diffusion layers between the subsurface and substrate. The Xray diffraction analysis of the Mo modified titanium reveals that the outmost surface of the Mo modified titanium is composed of pure Mo. The electrochemical corrosion performance of the Mo modified titanium in saliva was investigated and compared with that of titanium. The chemical corrosion performance of the Mo modified titanium in 37 ℃ saliva was investigated and compared with that of titanium. The experimental results indicated that self-corroding electric potentials and corrosion-rate of the Mo modified titanium were higher than that of titanium in saliva. Corrosion-rate of the Mo modified titanium was lower than that of titanium in 37 ℃ saliva.

Corrosion property of copperized layer on Zr formed by double glow plasma surface alloying technique

Zr and its alloys have excellent mechanical properties as new structural material,but in specific application environment,its corrosion resistance still needs to be further explored.In this work,double glow plasma surface alloying technique was used for copperizing on pure Zr surface.Besides,X-ray diffraction（XRD）,scanning electron microscope（SEM） and energy dispersion spectrum（EDS） were employed to characterize the samples.Furthermore,research was also conducted on the polarization curve of the samples in different solutions.Copperizing on surface can improve corrosion resistance of pure Zr in 3.5 % Na Cl and 0.5 moláL-1Na OH solutions.Especially in 0.5 moláL-1Na OH solution,the corrosion resistance can achieve significant improvement.However,copperizing has no influence on the improvement of corrosion resistance of pure Zr in 0.5 moláL-1H2SO4 solution.The results may provide new insight into way for improving the corrosion property of zirconium alloys.

Microstructure and Wear Resistance of N-Doped TiO_2 Coatings Grown on Stainless Steel by Plasma Surface Alloying Technology

N doped TiO2 （N-TiO2） coatings were obtained by oxidation of titanium nitride coatings, which were pre pared by the plasma surface alloying technique on stainless steel （SS）. The microstructure of N-TiO2 coatings was characterized by X-ray diffraction （XRD）, glow discharge optical emission spectrometry （GDOES）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）, respectively. Ball-on-disc sliding wear was applied to test and compare the tribological behaviors of the coatings and substrate. XRD patterns showed that anatase type TiO2 existed in the coatings after oxidation. GDOES showed that the resultant coatings had a layered structure, comprising of N-TiO2 layer at the top and a diffusion-type interface. Such a hybrid coatings system showed good adhesion with the substrate. According to XPS, residual N atoms partially occupied O atom sites in the TiO2 lattice. Uniform, continuous and compact coatings were observed by SEM images of coatings after oxidation. Under a load of 7.6 N, the coefficient of friction was in the range of 0.27--0.38 for the N-TiO2/Al2O3 systems and the wear rate of the coatings was only one-fourteenth of that for untreated 316L SS. N-TiO2 coatings displayed much better wear resistance and antifrietion performance than SS substrate.

Diversified manufacturing processes and multiple mineral sources:Features of Warring States bronze vessels excavated from Chutai Cemetery M1,Anhui Province

Northern Anhui was an important region for diverse bronze culture convergence and extensive metal resource circulation in the Pre-Qin Period.In this paper,metallographic microstructure analysis,chemical composition analysis,and lead isotope ratio analysis were conducted on 12 samples of 6 Warring States Period(476–221 BCE)bronze vessels excavated from Chutai Cemetery M1,Fuyang,Anhui Province,revealing the integrated application of diversified manufacturing processes,such as casting,forging,cold working,and welding and multiple metal minerals.The analytical results showed that 2 Ding vessels(鼎)were made by casting,and 2 He vessels(盒)and 2 Dui vessels(敦)were made by forging followed by cold working.These two types of bronze vessels made by different manufacturing processes have significantly distinct alloy ratios and mineral sources,among which the Cu and Sn contents of the 2 cast bronze vessels are lower and the Pb content is higher,while the Cu and Sn contents of the 4 forged bronze vessels are higher and the Pb content is lower.The lead minerals of the two types of bronze vessels might come from Western Henan and the middle and lower reaches of the Yangtze River,respectively.In addition,the 3 pieces of solder used to weld bronze vessels were all made of pure Sn,their metal minerals should come from the densely distributed area of tin ore in Southern China,and Sn solders were mainly discovered in the Chu culture area during the Eastern Zhou Period.