Authors: G. Deniz, Şaduman Şen, Uğur Şen
Abstract: In this work, some surface properties of AISI M2 steel were improved by a thermoreactive
deposition process. Gas nitriding was realized on AISI M2 steel at 550°C for 2 h in an
ammoniac atmosphere and then, titanizing treatment performed on pre-nitrided steel in the powder
mixture consisting of ferro-titanium, ammonium chloride and alumina at 1000°C for 1-4 h.
Structural characterization of titanium nitride layer formed on the surface of AISI M2 steel was
carried out by using optical microscopy, scanning electron microscopy, electron microprobe and Xray
diffraction (XRD) analysis. The hardness measurements of titanium nitride layer were
conducted under 10 g loads by using Vickers microhardness indenter. Structural analysis studies
showed that titanium nitride layers formed on the AISI M2 steel samples were smooth, compact and
homogeneous. XRD analysis show that the coating layer formed on the steel samples includes TiN,
Fe6Mo7N2, C0.7N0.3Ti, C0.3N0.7Ti and V2N phases. The hardness of titanium nitride layers formed on
the steel samples is between 2040±186 and 2418±291 HV0.01. The thickness of titanium nitride
layer formed on the steel samples ranged from 3.86±0.43 9m to 6.13±0.47 9m, depending on
treatment time.
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Authors: Antonio Forn, Isabel Espinosa, Maite T. Baile, Elisa Rupérez
Abstract: Semi solid processing reduces porosity and amount of trapped gas and it allows heat
treatment T6 that improves a hard anodized oxide layer. The aim of this work is to show the
anodizing possibility of A356 T6 components conformed by Sub-liquidus Casting (SLC) to improve
wear and corrosion resistance. This work compares the anodizing effect on tribological properties
and corrosion resistance between components obtained by A6061 T6 extruded alloys and from
A356 T6 produced by SLC. The effect of rounded silicon crystals on the coating formation and the
fracture produced during the coating growth are described.
755
Abstract: A multi-layer coating SiC/ Si - MoSi2 /MoSi2 with good oxidation resistance has been developed by using the slurry-sintering method on the surface of graphite to improve the oxidation resistance performance at 1700 °C for more than 200 h. Microstructure and anti-oxidation property of the as-received coating were investigated. It was found that functionally gradient SiC/ Si - MoSi2 /MoSi2 coating was formed on the surface of the graphite substrate. The coating characterized by excellent thermal shock resistance can effectively protect the graphite from oxidation at 1700 °C for 200 h. The mechanism of the oxidation resistance of the coated graphite is also dicussed, and a dense SiO2 layer was formed on the surface of coating at 1700°C during the isotheral oxidation, which can protect graphite from oxidation at longer time.
1
Authors: Hong Fei Sun, Zhan Rui Niu, Can Ming Wang, Bo Yuan
Abstract: A bronze mirror dating of Han-dynasty was studied in this paper. The in-depth structure and the composition of the natural patina and substrate alloy were determined by Electron probe micro-analyzer (EPMA) observation and EDS cartographies on a cross-section, the mineral composition of patinas were analyzed using XRD. The results show the layer structure of the patina has two obvious layers, and the inner layer ranges from 90µm to 260µm. This bronze mirror is a typical ancient Chinese black mirror Heiqigu, and the formation of high tin layer is due to special surface treatment by the ancients. Tthe composition of the patinas on the mirror and that of substrate alloy were found to be highly heterogeneous, the thin black patina on the mirror containing is cassiterite.
743
Authors: Feng Zhao, Ling Yong Cao, Yu Jing Lang, Hua Cui, Lin Zhong Zhuang, Ji Shan Zhang
Abstract: The diversities and relations of microstructures and properties between the center and surface layer in thick-plate 7150 alloy were investigated by means of OM, TEM, SEM and tensile tests. The results indicated that the average width of elongated grains with fewer substructures in the center of hot-rolling thick plate is about 2 times larger than that in the surface layer. The coarser second phases are massed up at the grain boundaries of the center layer while those are crushed into smaller particles in the surface layer. By aging, the strengthening precipitates in the center are mainly GP zone and η' phase, while in the surface layer η' and η phases play the main roles. Consequently, the strength is about 80Mpa (15%) higher in the center than in the surface, with lower elongations (26% lower).
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