Microstructure and Mechanical Properties of Al Based Composite Coatings Produced by the Cold Gas Dynamic Spraying Process

In this study, microstructures and mechanical properties of Al matrix B₄C reinforced composite coatings deposited on a structural steel by cold spraying were investigated. Feedstocks were prepared as the mixtures of Al and B₄C powders, where the B₄C content varied between 0 to 60 vol. %. The average sizes of the Al and B₄C powders were ~10 μm and ~60 μm, respectively. Air at room temperature was used as a propellant gas under a pressure of 6 bar. Hardness measurements and wear tests were performed to characterize the mechanical performances of the coatings. Hardness measurements were made by using Vickers micro hardness tester. Wear tests were conducted under dry sliding conditions on a reciprocating wear tester by rubbing alumina and stainless steel balls to the coatings. Presence of B4C improved the hardness and the wear resistance when compared to those of B4C free Al coating. Hardness of the coatings increased with increasing B₄C content; while the wear resistances did not show any significant change with the volume fraction of the B4C powders. In this respect, the optimum composition of the feedstock was determined as 80 vol. % Al + 20 vol. % B₄C.