Effect of ZrB2, CrB2 and TiB2 Additives on the Tribological Characteristics of NiAl-Based Gas-Thermal Coatings

In this study the influence of the TiB2, ZrB2, and CrB2 additives into NiAl-intermetallics on their wear behavior under friction conditions at the high temperature in the pair with steel has been investigated. It was shown, that the borides additives have influenced on the wear mechanism, significantly increasing the wear resistance of composite coatings pointed out. Among the coatings studied the NiAl-15 wt. % CrB2 coating showed the best result.

Effect of Milling Time on the Formation of NiAl Nanostructure Intermetallic Produced by the Mechanical Alloying Process

In the present study, NiAl nanostructure intermetallic produced by mechanical alloying process was investigated. Pure Al and Ni powders with the ratio of 50 at.% were mixed and milled in a planetary ball mill for different milling times in the range of 8 to 128 hours. The milled powder particles were investigated by XRD technique and scanning electron microscope. Williamson-Hall equation was employed to calculate lattice strains and crystallite sizes. The results showed that NiAl intermetallic formed after some milling times. The observation of flame or explosion in the vial just after the uncovering of it, in some cases, showed intense interaction between Al and Ni atoms after homogenization during milling. After longer milling time no flame and explosion was observed while NiAl intermetallics had been formed. Therefore, NiAl intermetallics were formed under different conditions with different structures and properties. The crystal sizes of obtained NiAl particles were less than 10 nm. The hardness changes in particles and also their internal strains were affected by milling operation at early stages of milling but they were mainly affected by transformation process of (Ni,Al) solid solution into intermetallic NiAl at longer milling times.