Papers by Author: X. Peng

Abstract: The paper is a short review of the fabrication, wet and dry corrosion, as well as plasma nitridation of novel Ni-Cr nanocomposites. The nanocomposites, fabricated by co-electrodeposition of Ni and nanometer-sized Cr particles, have the nanocrystalline Ni matrix dispersing the second phase of nanoparticles. They, compared to conventionally coarse-grained Ni-Cr alloys, exhibit dramatically increased resistance to liquid corrosion in a 3.5% NaCl solution, and to hot corrosion under molten salt of Na2SO4-Na2SO4-NaCl at 700oC. The reason for these is correlated with the unique structure of the nanocomposite, which guarantees the fast diffusion of chromium from the composite interior to the corrosion front for the formation of a continuous, protective layer of chromium oxide-rich films severing the composites from environmental corrosive species. During plasma nitridation at 560oC the Ni-Cr nanocomposite forms a thick nitriding layer which cannot be achieved on the conventional alloy counterpart with a comparable composition, due to enhanced nitridation kinetics.

Abstract: Formation of a protective scale such as chromia or alumina is a prerequisite for an excellent oxidation performance of high-temperature materials. Based on this principle, a novel concept of designing chromia- or alumina-forming nanocomposites by means of nanocomposite electrodeposition of Ni with Cr or/and Al nanoparticles were proposed. A brief review on the high temperature oxidation performance of such novel electrodeposited nanocomposites like Ni-Cr, Ni-Al and Ni-Cr-Al is presented.

Abstract: Two types of Ni-base nanocomposites were prepared by co-deposition of Ni with nano-sized particles of Cr or CeO2, respectively. Both Ni-Cr and Ni-CeO2 nanocomposites were mainly composed of nanocrystalline Ni matrix, in which certain content of nanoparticles of Cr or CeO2 randomly dispersed. The Ni-Cr nanocomposite was used as a precursor for preparing a novel hard Ni/CrN coating by plasma nitriding at 560oC. The Ni-CeO2 nanocomposite was used as a precursor to develop a novel oxidation-resistant chromia-forming coating by low temperature chromizing using a conventional pack-cementation method. The microhardness of the nitrided layer on the Ni-Cr nanocomposite and the oxidation resistance of the chromizing coating on the Ni-CeO2 nanocomposite were both greatly increased, in comparison to the corresponding counterparts, which were obtained by plasma nitriding on a conventional coarse-grained Ni-Cr alloy with similar Cr content and by chromizing on a coarse-grained Ni metal, respectively. The relationships among the microstructures of the nanocomposite precursors and the nitrided/or chromized coatings, and their properties were investigated and discussed.