Jingchuan Zhu

Fabrication of ZrO2–NiCr functionally graded material by powder metallurgy

Abstract ZrO2–NiCr functionally graded material (FGM) was developed by powder metallurgical process. After investigating the preforming and sintering process of mixed powders with different compositions, the suitable fabrication procedure of FGM was determined. Microscopic observations demonstrate that the chemical composition and microstructure of ZrO2–NiCr FGM distribute gradually in stepwise way, eliminating the macroscopic ceramic/metal interface such as that in traditional ceramic/metal joint. The mechanical properties of ZrO2–NiCr system strongly depend on constitutional variation, and display various graded distributions as well.

Increasing sp3 hybridized carbon atoms in germanium carbide films by increasing the argon ion energy and germanium content

We have prepared germanium carbide (Ge1−xCx) films on Si(0 0 1) by radio frequency (RF) reactive sputtering a pure Ge(1 1 1) target in a CH4/Ar mixture discharge, and found that the sp3 hybridized carbon atoms in the Ge1−xCx film can be significantly increased in two ways. One is by increasing the Ge content via increasing the RF power during the film deposition, which can lead to a transition from sp2 C–C to sp3 C–Ge bonding in the film. Another is by increasing the Ar ion energy in a discharge Ar/CH4 gas by applying the negative bias voltage, which plays an important role in inducing the compressive stress in film. We find that when the compressive stress increases above a critical value of 2.2 GPa, an abrupt transition from sp2 C–C to sp3 C–C bonding occurs in the Ge1−xCx film, which is a consequence of energy minimization.

Inhibition of liquid Si infiltration into carbon-carbon composites by the addition of Al to the Si slurry pre-coating: mechanism analysis

Abstract The mechanism of the inhibition of liquid Si infiltration (LSI) into a two-dimensional carbon–carbon composite (2D-C/C) by the addition of Al to the Si slurry pre-coating was investigated. It was shown by means of a vapor treatment experiment designed intentionally that the surface composition of the inner pores beneath the Si slurry pre-coating before the occurrence of LSI was pure carbon and SiC, while before the occurrence of the LSI with the Si–6 wt.%Al slurry pre-coating, the surface composition of the inner pores was Al 4 C 3 , SiC and a small amount of pure carbon. The formation of the SiC and the Al 4 C 3 was the result of the evaporation of almost all the Al additive and a little Si during the heating. For reactive infiltrations, reactions at the vapor–liquid–solid triple line are believed to affect the final infiltration depth. Faster reactions at the triple line lead to faster infiltration velocity and hence deeper reactive infiltration. The reaction at the triple line for the LSI with the Si–6 wt.%Al slurry pre-coating was mainly between liquid Si and the surface Al 4 C 3 , which was probably slower than the reaction of liquid Si with the pure carbon at the triple line corresponding to the LSI with the Si slurry pre-coating. Therefore, the extent of the penetration of liquid Si during the LSI with Si–6 wt.%Al slurry pre-coating was lower than that with the Si slurry pre-coating.

Effect of Al additive in Si slurry coating on liquid Si infiltration into carbon-carbon composites

Abstract Two-dimensional carbon–carbon composites (2D-C/C) applied with a pure Si pre-coating or a Si–6 wt.%Al pre-coating by dipping slurry method were heated above Si melting point to perform liquid Si infiltration. For pure Si slurry pre-coating, liquid Si excessively infiltrated into the C/C composite and many cracks were formed inside resulting in serious degradation of the flexural strength of the C/C composite. For Si–6 wt.%Al pre-coating, only a little amount of liquid Si infiltrated into the C/C composite and the flexural strength was mostly retained after performing liquid Si infiltration. No deleterious effect of the Al additive on the formation of SiC conversion layer was found.