Thermally sprayed hardmetal coatings are often used to protect valves in steam turbines against wear. Normally the valve spindles are made of CrMo steel and their bearings are made of Stellite, a cobalt-base alloy. In this investigation, a block-on-ring wear test is used with rings and blocks made of the same materials as the spindles and bearings. The rings were coated with Cr3C2-NiCr by HVOF spraying. Wear tests showed increasing weight loss up to 400°C and a sharp decline at 600°C due to a thin surface oxide layer that begins growing at 450°C. The coatings are characterized based on SEM, EDX, and hardness measurements. Paper text in German.

In the present project, the widest possible variety of coats applied by means of high-speed flame spraying are investigated with regard to their applicability to components of hydroelectric power stations. The investigations concentrate on protective coats for the wear surfaces of turbine wheels and various guide vanes. The structural shapes and specific features of different turbine wheels, forms of wear phenomena and their causes as well as experience with different materials and coatings are described. The resulting planning and stipulation of suitable testing conditions for the targeted investigations with high-speed flame- sprayed coats are also described. Paper text in German.