Development of particle-reinforced nanostructured iron-based composite alloys for thermal spraying

In the field of thermal spraying, cermets are known to have excellent wear-protecting properties. However, the high price of the spraying materials and the environmental aspects of nickel and cobalt utilization are often the limitations to their wider application. Within the frame of a multi-institutional cooperation of various German research centres, the AiF/DFG research cluster “Thermal Spraying” was organised, one of the main research goals of which is the development of economically attractive alternative spray materials with new property profiles. This paper presents some results of the project that deals with the development and thermal spraying of particle-reinforced iron-based composite alloys. High-alloyed steels serve as matrix materials into which hard CrB2 particles are incorporated by means of a high-energy milling (HEM) process. The microstructure of the powder and the level of its amorphisation can be strongly influenced by appropriate milling parameters that allow the adjustment of the desired nanocrystalline structure. By using the high-velocity oxygen fuel thermal spraying process (HVOF), the microstructure of the particles can be transferred to the coatings. The deposited coatings exhibit low porosity and high microhardness values of more than 1000 HV0.3. The high abrasion wear resistance of newly developed coatings evaluated by means of the Miller test (ASTM G75-01) makes them promising for application for example in paper industry as an alternative to hard chromium coatings.