K. Morsi

The diversity of combustion synthesis processing: a review

The harnessing of heat emanating from powder-based exothermic reactions to produce advanced materials has been around for many decades, and is manifested in the process of combustion synthesis (CS). A plethora of work has been published on the topic covering fundamental aspects of the process for a large number of material systems. Over time, CS has been combined with other processes and effects to potentially improve on conventionally produced CS products and alleviate some of the inherent disadvantages of CS. This article discusses processing aspects of CS, and provides a review of CS-related hybrid processes with the intent to exemplify the diversity of CS processing. Approaches such as reactant microstructural design, reactive bulk deformation/compaction processes, reactive casting, laser-assisted CS, activation techniques (field/current, mechanical, microwave), and unconventional heat treatments are discussed together with other methods.

Effect of mechanical and electrical activation on the combustion synthesis of Al 3 Ti

Titanium aluminides have attracted immense interest as lightweight intermetallic compounds that possess good high-temperature mechanical and corrosion properties. In the present work, titanium aluminides (Al3Ti) have been reactively processed from elemental powder using a combined mechanical and electrical activation approach. The effect of mechanical activation and electric current intensity on the ignition and phase development is discussed. Ignition was not possible when powders were milled for a short time, while prolonged milling resulted in mechanical activation that promoted a self-propagating-type reaction. The time to engulfment of the compact with the reaction wave was found to decrease with an increase in current intensity. A secondary reaction occurred at the higher current intensity, which in turn increased the product homogeneity.

Processing, characterization, and properties of aluminum-carbon nanotube open-cell foams

This paper discusses the processing, characterization, and properties of aluminum–carbon nanotube (Al–CNT) open-cell foams. The effect of spark plasma sintering temperature on the developed internal surface macro/microstructure and local mechanical response is discussed. Grain size and amount of oxygen-rich internal scales increased with an increase in sintering temperature. Room temperature spherical indentation tests showed a general decline in load-bearing capacity of the foams with increase in sintering temperature. Cell-wall failure was found to be due to brittle fracture rather than plastic collapse. Analyses of the indentation unloading curves showed Al–CNT foams to be ~16% stiffer than Al foams processed at the same condition.

Reactive Current-Activated Tip-Based Sintering of Ni–Al Intermetallics

Current-activated tip-based sintering (CATS) is a new process that imposes local current-activated sintering conditions to consolidate selected areas of a powder compact/bed through the controlled application of a contacting tip electrode. The process has the ability of achieving very high sintering rates and obtaining complex-sintered geometries through the controlled precision motion of the electrically conductive tip. In this study, the high current densities afforded by CATS are utilized to locally activate a macroscopic combustion synthesis type reaction in compacts of reactive mixtures of nickel and aluminum to rapidly form nickel aluminides. The effect of current intensity on the ignition time, microstructure, homogeneity, and properties of the combustion synthesized products is discussed in this article. It was found that ultra-rapid formation of aluminum-rich intermetallics precedes and contributes to the major ignition event. Moreover, time to ignition was found to decrease with an increase in current intensity, also leading to less homogenous microstructures.

Piezoelectric Actuator-Based Nanoindentation

In this article we report a novel depth-sensing nanoindenter using a lead zirconium titanate (PZT) stack actuator to measure the Youngs modulus of Titanium composite. The nanoindenter uses an open-loop positioning control scheme with displacement sensors. In general, the conventional nanoindenters require closed-loop controls for precise loading of the indenter tip. The developed open-loop control scheme compensates for the hysteresis and the creep errors of PZT actuators. We have shown that the overall system structure can be simplified and a high positioning repeatability can be achieved. To verify the system performance, we conducted the indentation tests on titanium matrix composite surfaces. Besides the basic nanoindentation functions, the developed system also has the capability for surface imaging through a scanning function. The pre-indentation scanning capability proved to be a very useful method for positioning the tip in the desired indentation location. Similarly, post-indentation scanning allows for visualization of the indentation marks after the tests.

Electrically activated reactive synthesis (EARS) and electro-annealing of 3Ni–Al powder compacts

The present study investigates the electrically activated reactive synthesis (EARS) and post-reaction electro-annealing of 3Ni–Al powder compacts. The effect of initial relative green density on EARS processing and on the microstructure and phases produced was investigated. Post-reaction electro-annealing was also conducted to investigate its effects on phase transformations and consolidation. The initial reaction resulted in the formation of Ni3Al as the major phase, with 3R martensite also being formed. The investigated variation in relative green density was found to have limited effect on the product porosity and microstructure. Post-reaction electro-annealing, however, resulted in harder products with unique microstructures, particularly the formation of Ni4.22Al0.9 in very high amounts.

Mechanical vibration induced electro-spinning of polyvinylidene difluoride (PVDF)

Polyvinylidene difluoride (PVDF) is a piezoelectric polymer with a low-cost, high flexibility and biocompatibility that is suitable for various energy conversion applications between the electrical and mechanical forms of energy. One of the novel techniques to create PVDF fibers is electro-spinning. In the present work, the above technique has been applied to develop electro-spun thin-film based on PVDF with the use of high electric field and a high-frequency mechanical vibratory motion as an electro-spinning setup. The high-frequency vibratory motion is used to create effective fluid viscous forces to achieve a localized fluid spreading and thinning behavior of extremely thin polymer fiber solution.

Fabrication of TiNi shape memory alloy thin films by current activated tip-based sintering (CATS)

We report on the production of thin films of titanium nickelides (TiNi) shape memory alloy, prepared via Current- Activated Tip-based Sintering (CATS), a new localized powder sintering process. Mechanically alloyed equi-atomic TiNi powder was tip-sintered at varying currents and cycles of current exposure time. The effect of processing conditions on the developed localized microstructure and properties are discussed. The number of cycles of current exposure time and current magnitude were studied. Both number of cycles and current magnitude in general result in an increase micro-hardness and a reduction in residual porosity in the sintered thin films.