Combustion synthesis of NiAl/Al2O3 composites by induction heating

The aim of this work was to develop a new process for the synthesis of TiC and NiAl/TiC composite in which the combustion reaction was ignited using a high frequency induction heater. High density, two-layer TiC-NiAl composites were also produced using this process. Temperature profiles during synthesis were measured with an IR thermometer and a high resolution thermal image camera was used to monitor the reaction process. Phase transformation was investigated using XRD and SEM was used to characterize the microstructure of the synthesized composites. The mechanical properties of the products were evaluated by measuring hardness. The results show that the reaction was complete and that stoichiometric products of NiAl and TiC were produced. The properties of NiAl/TiC composites were found to be functions of composition and processing parameters. The reaction mechanism was analyzed using temperature monitoring, thermodynamic analysis and microstructure investigation.

Materials Science and Technology, 2019

NiAl-TiC composites were synthesised by volume combustion (VC) method from elemental powders to improve the mechanical properties and high temperature performance of nickel aluminide. Synthesised specimens with porous nature were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. XRD results showed that NiAl was dominant phase and other phases like Al 3 Ni 2 (in NiAl + 5 wt-% TiC, NiAl + 10 wt-% TiC specimens) and AlNi 3 (in equimolar NiAl-TiC) were present in specimens. Synthesised specimens of NiAl, NiAl + 5 wt-% TiC, NiAl + 10 wt-% TiC, NiAl + 15 wt-% TiC and equimolar NiAl-TiC achieved Vickers microhardness values of 508, 590.25, 628, 724 and 838.5, respectively. Addition of TiC increased the porosity of specimens from 4.7% for single phase NiAl to 60.63% for equimolar NiAl-TiC.

Intermetallic NiAl has the potential to be used for elevated temperature applications. To date different ignition techniques have been utilized to synthesize NiAl and produce coatings. Self-propagating hightemperature synthesis (SHS) has been developed as a relatively simple route to obtain intermetallics. This paper considers using induction heating to preheat and ignite the synthesis directly and investigates the effect of processing parameters on the phase transformation, microstructures and properties of Ni/Al compacts synthesized by SHS. The results show that single phase NiAl can be produced by induction heating whilst processing parameters such as heating rates and green densities have a significant effect on the properties and structures of sintered products.

Metallurgical and Materials Transactions B, 2000

The reaction steps in the formation of NiAl/TiB 2 composites produced by reaction synthesis have been determined using differential thermal analysis (DTA). The DTA technique reveals that the formation of NiAl/TiB 2 composites occurs in a two-step reaction. NiAl forms first at approximately 550 ЊC, followed by TiB 2 , which forms at approximately 1050 ЊC. Both X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) were performed on composites produced by reaction synthesis in a hot-press facility using the same heating rate used in the DTA experiments. It was found that the formation of NiAl and TiB 2 is preceded by the formation of intermediate compounds such as Ni 3 Al, TiAl, Ti 3 A1, Ti 2 Ni, and TiB. The relative density measured in the composites with 0, 0.25, 0.50, and 0.75 volume fractions of TiB 2 was in excess of 96 pct of the theoretical density, since, during synthesis, NiAl is a transient liquid that acts as a binder phase for the TiB 2 particles.

Metals, 2021

The effect of PTFE, continuous boron, and tungsten fibers on the combustion behavior and strength of reactive Ni–Al compacts was examined in this study. The introduction of continuous fibers into Ni–Al compacts according to the developed scheme was found to increase the flexural strength from 12 to 120 MPa. Heat treatment (HT), leading to chemical interaction of the starting components, increases the strength of compacts at temperatures not exceeding 550 °C. The combination of reinforcement and HT significantly increases the strength without reducing reactivity. Experimental results showed that strength and combustion rate increase with the reduction in PTFE to 1 wt % in Ni–Al compacts. A favorable effect of the addition of PTFE from 5 to 10 wt % on the reduction of the threshold for the shock-wave initiation of reactions in Ni–Al was established. The obtained results can be used to produce reactive materials with high mechanical and energy characteristics.

Journal of Alloys and Compounds, 1998

High pressure self propagating synthesis (HPSHS) was used to synthesise the NiAl compound. In this paper, the influence of both the kinetic and the thermal effects of the reaction on propagation were studied by using Boddington's model. This analysis was based on experimental results and it shows clearly that pressure and heating rate have great importance in the nature and the stability of the reaction between nickel and aluminium. In effect, we will show clearly the existence of three domains of reaction modes: solid state diffusion, unstable SHS and stable SHS. Additionally, we tried to define the influence of experimental parameters such as grain size of the reactants and porosity of the sample.

Scripta Metallurgica et Materialia, 1994

Metallurgical and Materials Transactions B, 2009

In this work, dense NiAl/TiB 2 composites with varying amounts of TiB 2 were produced by combustion synthesis routes. The morphology of the TiB 2 phase in the composite has been modified by changing the reactants in the initial powder mixture. In the first processing route, NiAl and TiB 2 phases were obtained from Ni, Al, Ti, and B elemental powders. In the second processing route, TiB 2 was added, instead of Ti and B, along with Ni and Al to produce NiAl and TiB 2 phases. The XRD performed on the products of both processing routes confirmed that the synthesized phases were indeed TiB 2 and NiAl. The NiAl grain size is smaller for the composites obtained in the first processing route. In addition, the first processing route leads to clusters of TiB 2 submicron particles in which the matrix is either TiB 2 or NiAl depending on the starting composition. The second processing route results in less dense composites in which the matrix is the NiAl and the TiB 2 exists as dispersed platelets. The hardness (H) and Young's modulus (E) were observed to be higher for composites produced by the first processing route. This difference in the mechanical properties is caused by the difference in microstructure, as well as the difference in porosity between the two processing routes.

Combustion Science and Technology, 2002

Journal of Alloys and Compounds, 2013

Synthesis of a novel NiAl matrix composite powder reinforced with 0-40 wt.% NbB 2 by combustion synthesis in thermal explosion mode was investigated. The elemental powders of Ni, Al, Nb, and amorphous boron were used as starting material. For all compositions final products consisted of only the NiAl and NbB 2 phases. Coarser NbB 2 with a relatively uniform distribution in NiAl matrix was formed with rising NbB 2 content. Microhardness of NiAl considerably increased from 377 ± 13 HV 0.05 to 866 ± 81 HV 0.05 for NiAl with 40 wt.% NbB 2. High microhardness, proper size and distribution of NbB 2 in NiAl matrix make it a good candidate as precursor for thermal spray application.