Experimental Study of Wear Performance of Tool Steel Undergone DUPLEX Surface Treatments for Hot Forging Applications

In recent years, the DUPLEX surface treatment, consisting of vacuum gas nitride followed by physical vapor deposition (PVD) coating, has earn a lot of interest for enhance the wear performance of high temperature forming application, especially hot forging. In this work the wear performance of hot forging tool steel grade AISI H13 undergone DUPLEX treatments with different top coating have been investigated. Three types of PVD coatings, e.g. TiAlN, AlCrN and AlCrTiN, were studied. The microstructure, physical and mechanical properties and surface roughness were also investigated. The wear tests were performed using a high temperature pin-on-disc arrangement at the working temperature of the hot forging tool, i.e. 300°C. The experimental results indicate that the wear behavior is strongly influenced by the level of contact stress developed at the surface. At low contact stress, harder coating shows the better wear performance while, at high contact stress, the tougher coating serves better. Examination of worn surface suggests that this might be caused by change in failure mechanism from ductile fracture to a more brittle manner at high contact stress for hard material. The understanding of the influence of working conditions and coating properties on the wear resistance of tool steels obtained from this work can be very useful in the improvement of wear performance in hot-forging tools and also other high temperature applications

Association of mast cell-derived VEGF and proteases in dengue shock syndrome

Background: Recent in-vitro studies have suggested that mast cells are involved in Dengue virus infection. To clarify the role of mast cells in the development of clinical Dengue fever, we compared the plasma levels of several mast cell-derived mediators (vascular endothelial cell growth factor [VEGF], soluble VEGF receptors [sVEGFRs], tryptase, and chymase) and -related cytokines (IL-4, -9, and -17) between patients with differing severity of Dengue fever and healthy controls. Methodology/Principal Findings: The study was performed at Children\u27s Hospital No. 2, Ho Chi Minh City, and Vinh Long Province Hospital, Vietnam from 2002 to 2005. Study patients included 103 with Dengue fever (DF), Dengue hemorrhagic fever (DHF), and Dengue shock syndrome (DSS), as diagnosed by the World Health Organization criteria. There were 189 healthy subjects, and 19 febrile illness patients of the same Kinh ethnicity. The levels of mast cell-derived mediators and -related cytokines in plasma were measured by ELISA. VEGF and sVEGFR-1 levels were significantly increased in DHF and DSS compared with those of DF and controls, whereas sVEGFR-2 levels were significantly decreased in DHF and DSS. Significant increases in tryptase and chymase levels, which were accompanied by high IL-9 and -17 concentrations, were detected in DHF and DSS patients. By day 4 of admission, VEGF, sVEGFRs, and proteases levels had returned to similar levels as DF and controls. In-vitro VEGF production by mast cells was examined in KU812 and HMC-1 cells, and was found to be highest when the cells were inoculated with Dengue virus and human Dengue virus-immune serum in the presence of IL-9. Conclusions: As mast cells are an important source of VEGF, tryptase, and chymase, our findings suggest that mast cell activation and mast cell-derived mediators participate in the development of DHF. The two proteases, particularly chymase, might serve as good predictive markers of Dengue disease severity