No abstract

Cr 3 C 2 -NiCr coating was deposited on SAE-347H boiler steel by high velocity oxy fuel (HVOF) spray process. Subsequently, high-temperature corrosion behavior of the bare and coated boiler steel was investigated at 700°C for 50 cycles in Na 2 SO 4 -82Fe 2 (SO 4 ) 3 molten salt, as well as air environments. Weight-change measurements after each cycle were made to establish the kinetics of corrosion. X-ray diffraction, field emission-scanning electron microscopy/energy dispersive spectroscopy, and x-ray mapping analyses were performed on the exposed samples to analyze the oxidation products. The bare 347H steel suffered accelerated oxidation during exposure at 700°C in the air as well as the molten salt environment in comparison with its respective coated counterparts. The HVOF-spray Cr 3 C 2 -NiCr coating was found to be successful in maintaining its adherence in both the environments. The surface oxide scales were also found to be intact. The formation of chromium rich oxide scale might have contributed for the better hot corrosion/oxidation resistance in the coated steel.

During hot forging/forming operations, the die surface and near surface region is subjected to severe wear. The failure of dies originates from the surface region. In this research work, plasma nitriding was done on two hot forming tool steels namely AISI H11 and AISI H13. The aim is to develop a hard and wear resistance surface required for hot forming operations. The mechanical and microstructural properties of the developed nitrided layer were critically examined. Thereafter the tribological characteristics of the untreated and plasma-nitrided specimens were studied on high-temperature pin-on-disc tribometer under the constant load of 25 N, sliding speed 0.5 m s −1 , sliding distance of 1500 m at different temperatures ranging from room temperature to 600°C. The results showed that the main wear mechanisms is predominantly adhesive at room temperatures and 200°C and a combination of adhesive and abrasive at elevated temperatures (400°C and 600°C).

The aim of the current investigation was to study the high-temperature tribological performance of the high-velocity Oxyfuel sprayed 65% (NiCrSiFeBC)−35%(WC-Co) coating at the temperatures ranging from room temperatures to 800°C. The coating was produced on the hot forming die steels namely AISI H11 and AISI H13. The microstructural characteristics, surface roughness, microhardness, porosity and bond strength of the as-sprayed coatings were determined. Tribology study was done on the pin-on-disc tribometer at 0.5 m s −1 sliding velocity under the loads of 25N and 50N. The results have shown that the developed coating exhibited lower porosity, higher microhardness and performed much better than the uncoated specimens. The wear mechanisms of the coated specimens were mainly abrasive at room temperatures. Adhesive and oxidative wear were observed as the dominant mechanisms at the elevated temperatures.

No abstract