Ukrainets M. Structure Formation Features and Operational Properties of NiAl-MeB2 System Composites for High-Temperature Wear-Resistant Coatings

The thesis is devoted to a development of new NiAl-based composite materials armored by chromium diboride particles for obtaining of wear resistant coatings aimed to work under high temperature sliding (T<=800 °C). Reinforcement selection was made according to wetting kinetics and contact interaction determined in “NiAl-ZrB2”, “NiAl-TiB2” and “NiAl-CrB2” systems. Chromium diboride was selected as an optimal reinforcement additive due to both its good wettability with intermetallic melt and Ni-Cr-B system phase formation. Ni-Cr-B phase is an additional armoring phase. Using High-temperature Differential Thermal Analysis was determined that processes of phase formation appears at T>=1200 °C. Hereby intermetallic-based composites armored by chromium diboride are suitable for work under high temperatures (up to 800 °C). Obtained composites NiAl – 15% (30%, 45%) CrB2 have heterogeneous microstructure with chromium diboride particles uniformly distributed in the intermetallic matrix. CrB2 addition both leads to decreasing of NiAl plasticity and changes oxidation- and wear mechanisms of intermetallic. Composites of «NiAl-CrB2» systems have lower plasticity, higher strength and wear resistance comparing to initial nickel aluminum at 20-800 °C. The highest wear resistances under sliding at T<=800 °C have NiAl-15% CrB2 coatings.