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The applications of carbon allotrope-reinforced Ti-based composites have witnessed enormous expansion in recent times owing to their light weight and competitive properties. However, a consistent controversy still exists on the process of in-situ TiC formation (during powder preparation, reinforcement dispersion and synthesis), its site within the composite and particularly the role it plays on the properties of the bulk composite. Although some authors have opined that the presence of TiC in the bulk composite enhances its overall properties, others hold a contrary opinion. Hence, this current study is aimed at reviewing the positions of the previous studies on this seemingly controversial subject up to date; with a view to broadening the available knowledge base on this crucial area of interest. [ABSTRACT FROM AUTHOR]

The densification process and grain analysis of consolidated NiAl-CNT composites at 1000 °C, and at varied heating rates from 50 °C/min to 150 °C/min was investigated. The results revealed the effect of heating rate on the densification behaviour of the samples. The displacement of the composites decreased from 3.39 mm to 2.63 mm with increasing heating rate, while the porosity increased by 69% at rapid heating rate. The grain analysis of the sintered samples through the electron backscattered (EBSD) technique indicates the evolution of bigger grains as the heating rate proceeds higher. Furthermore, the mean grain size of the consolidated composites increased from 3.93 μm, to 8.05 μm due to the concentration of defects. Interestingly, there was no texture or predominance of any color evolution in the sintered materials.

Various electrochemical techniques were used to study the corrosion behaviour of the CNT-reinforced NiAl alloys under NaCl and Na2SO4 environments. The potentiodynamic polarization curves revealed activation Tafel behaviour when the NiAl alloy specimens were immersed in NaCl solution while passivation followed by slight development of transpassivation resulted under Na2SO4 environment. The reinforcement of pure NiAl alloy with up to 1.0 wt.% CNT increased the corrosion rate from 0.10 to 0.63 mm/yr under NaCl environment, while under Na2SO4 environment, the corrosion rate increased from 0.04 to 0.12 mm/yr. The observed increase in corrosion rate with an increase in CNT reinforcement (under both NaCl and Na2SO4 environments) suggested that the reinforcement of NiAl alloys with CNT reduced the corrosion resistance of NiAl. The X-ray diffraction analysis revealed that the corrosion products consisted of oxides including Al2O3 under NaCl environment, while scanning electron microscope analysis showed a porous passive layer on the surface of the alloy specimens immersed in Na2SO4 solution. [ABSTRACT FROM AUTHOR]

The novelty of incorporating carbon nanotubes (CNTs) in various matrices is becoming increasingly significant for the development of various composites to match the rising technological demands in industry. However, for the potentials of CNTs to be fully realized, the mandatory requirement to uniformly disperse them must be achieved. To effectively disperse these nanotubes in metallic matrices, ball milling has emerged as an effective method, but concerns still persist as to the ability of this method to achieve uniform dispersion without significant damage to the CNTs. In this work, multi-walled carbon nanotubes (MWCNTs) were dispersed in a nickel aluminide matrix via three different milling methods, using both low and high energy milling regimes. The admixed powders were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry and transmission electron microscopy techniques. Results show that a two-stage milling, comprised of a 6-h low energy milling with a short-term follow-up of a low speed 2-h high energy milling achieved the best MWCNTs dispersion and retained their structural integrity. [ABSTRACT FROM AUTHOR]