Microstructure Of NiAl Research Articles

Effect of Heating on the Microstructure of NiAl + CrB2 Coatings Deposited by Mechanical Embedding in a Ball Mill

AbstractThe thickness of NiAl + CrB2 coatings, produced by the mechanical embedding of powders, is limited due to the increasing brittleness of processed materials with milling time. Only the NiAl grain growth and resultant softening of the coating matrix could overcome this problem. Therefore, the effect of heating up to 750°C on the microstructure of NiAl + CrB2 coatings deposited in a ball mill rotating at 350 rpm was investigated through in situ TEM observations. The performed observations proved that defect annihilation starts at ~400°C in large intermetallic grains, which are first attached to the substrate. The growth in NiAl nanocrystallites forming most of the coating is activated only above ~600°C. The average crystallite size was measured to be 5, 14, and 19 nm at RT, 650°C, and 750°C, respectively. The first stage of nano-crystallite growth is relatively fast and connected with the reconstruction of crystallite boundaries using up the amorphous material accumulated in between them. The second stage is slower and involves the expansion of larger crystallites at the expense of smaller ones. The performed experiment proved that heating up to 750°C allows the microstructure recovery and grain coarsening of coatings to be activated.

Effect of magnetic treatment on the microstructure of NiAl–Re alloy

The influence of the magnetic field on the dislocation structure of intermetallic NiAl–Re alloy is studied and is experimentally confirmed for the first time. Active displacement of dislocations is established. Rhenium inclusions perform stop functions in these conditions. In addition, Ni atoms move to the surface of the alloy and an Al-rich internal layer forms under the magnetic gradient. These results indicate that the new atomic configuration forms by diffusion due to jumps of Ni atoms to adjacent Ni vacancies in intermetallic NiAl compound.

Influence of non-reactive particles on the microstructure of NiAl and NiAl–ZrO 2 processed by thermal explosion

Nickel aluminide intermetallic alloy and NiAl–ZrO 2 composites were synthesized in a hot press by sintering reaction and thermal explosion (or Self-propagating High temperature Synthesis, SHS). The addition of a post-SHS heat treatment allows a control of the microstructure and an enhancement of the mechanical characteristics. Thus, NiAl properties processed by self-combustion are above those obtained by reactive sintering (RS). For all these syntheses, the role played by the non-reactive particles is determining. Indeed, the product granulometry is a function of the diluent size distribution since this latter acts as nucleation sites during the reactive processes. These particles can also enhance mechanical properties by specific reinforcement mechanisms and exercise an influence on SHS reaction parameters by controlling its reactivity and the thermal exchanges during self-combustion.

Effect of Ag alloying on the microstructure of NiAl

The effect of Ag on the microstructure of NiAl was investigated by Optical Microscopy, X-ray diffraction, Electron Probe Microanalysis and Transmission Electron Microscopy. The NiAl–Ag alloys consisted of two phases: β-NiAl and Ag-rich solid solution. The amount of the Ag-rich phase increased with increasing Ag content. Ag has very low solubility in NiAl and they form pseudo-binary monotectic systems.

The influence of hot deformation on the microstructure of Ni-Al and Ni-Al-Fe alloys with small Ti 2B addition

Results of microstructure investigation of Ni-Al and Ni-Al-Fe alloys with addition of 0.5at.% Ti 2B after hot deformation are presented. Ti partially dissolves in the matrix, promoting formation of a discontinuous phase and precipitates of γ′ phase of Ll 2 structure during hot deformation of Ni-Al and Ni-Al-4.3at.%Fe alloys. In all investigated alloys precipitates of different compositions, enriched in Ti, were noticed. A compression test proved that due to the grain boundaries strengthening, the fracture mechanism changes into a transcrystalline one, improving fracture toughness of the hot deformed alloy. Fracture occurs in the deformation induced Ll 0 martensite.