Al Binder Research Articles

Low temperature synthesis of bulk Boron Nitride Nanoplatelets with and without metallic binder

Boron Nitride Nanoplatelets (BNNP) are consolidated into a bulk form using a low energy processing route that consisted of cryogenic milling, cold isostatic pressing, and a short, mild heat treatment. X-ray diffraction analysis was performed to confirm the presence of the secondary metallic constituent and the different phases of Boron Nitride (BN). Unique features of BNNP such as platelet stacking and kinking are retained. A secondary metallic constituent is also included to improve processability and to enhance structural support in the bulk structure. Mechanical properties were evaluated using microhardness testing and nanoindentation. Relative density, elastic modulus, and hardness increased with the incorporation of Al binder contents of as low as 10 vol %. A high degree of load transfer efficiency is demonstrated in higher metallic binder content composites (50 vol % Al) by comparing theoretical and experimentally measured microhardness values. This study presents a novel template for manufacturing bulk 2D nanomaterials using simple and low energy processing.

Structure and Phase Composition of SHS Products in Powder Mixtures of Titanium, Carbon, and Aluminum

TiC + Al binder metal-matrix composites are fabricated by self-propagating high-temperature synthesis (SHS) in reaction power mixtures of titanium, carbon (ash), and aluminum. It is established that stable combustion in a steady wave mode is possible with a content up to 50 wt % aluminum powder in a reaction mixture. Crushing of synthesized loose cakes and subsequent sieve scattering gave composite powders with a cloddy shape close to equilibrium. This shape is favorable for good looseness, which is necessary when using powders for surfacing and sputtering of wear-resistant coatings. Synthesis products are investigated by scanning electron microscopy and X-ray structural (XRS) and energy-dispersive X-ray (EDX) analysis. It is established that the average size of carbide inclusions in the composite structure decreases monotonically with an increase in the content of the aluminum powder inert in the thermal aspect in reaction mixtures. The lattice parameter of titanium carbide determined by the XRS method turned out much smaller than known values for equiatomic-composition carbide. Herewith, no dependence of the lattice parameter on the aluminum content is found for composites. Carbide inclusions in the composite structure are investigated by the EDX method, and it is established that the titanium content corresponds to its concentration in equiatomic-composition carbide. In addition to titanium and carbon, carbide contains up to 2.5 wt % dissolved aluminum, which can affect the carbide lattice parameter.

Structure and phase composition of SHS products in titanium, carbon and aluminum reactive mixtures

The TiC + Al binder metal matrix composites were obtained by self-propagating high-temperature synthesis (SHS) in the reactive powder mixtures of titanium, carbon (carbon black) and aluminum. It was found that a steady-state wave combustion occurs when the aluminum powder content in reactive mixtures does not exceed 50 wt.%. Loose SHS cakes obtained during synthesis were crashed and screened to get lumpy, nearly equlaxial composite powders favorable to good flowability necessary for powder application in cladding and spraying of wear-resistant coatings. The synthesis products were studied by scanning electron microscopy, X-ray diffraction (XRD) and local energy-dispersive X-ray spectroscopy (EDX). It was found that the average size of carbide inclusions in the composite structure depends on the content of thermally inert aluminum powder in the reaction mixtures. The titanium carbide lattice parameter determined by XRD turned out to be slightly below the known values for equiatomic titanium carbide. However, no any dependence of the lattice parameter on the aluminum content in composites was found. TiC inclusions in the composite structure were investigated by EDX spectroscopy. Titanium content in the carbide was close to that in equiatomic titanium carbide. Titanium carbide contains up to 2.5 wt.% aluminum in addition to titanium and carbon. Aluminum dissolution in the carbide lattice can influence the lattice parameter.

Effect of temperature on the mechanical behavior of B4C joints bonded by Al infiltrated TiC tape

B4C ceramics has potential applications at moderately elevated temperatures (< 450 °C) for semiconductor industry and solar systems due to their high elastic modulus and stability. B4C sintered bodies were joined by Al infiltrated TiC tape at 1000 °C for 0.5 h in vacuum. The mechanical properties in the 20–600 °C temperature range were investigated. B4C joints (267 MPa) show comparable mechanical properties to B4C matrix (271 MPa) at room temperature according to Weibull analysis. The bending strength of B4C joint maintains to be about 250 MPa up to 500 °C and then decreases quickly with further increasing temperature. Microstructural observations on fracture surface suggest that the high-temperature strength is dominated by the softening of Al binder phase in the interlayer.

Microstructure evolution of WC grains in WC–Co–Ni–Al alloys: Effect of binder phase composition

Abstract In the present work, the microstructure evolution of WC grains in WC–Co–Ni–Al alloys with different Co–Ni–Al binder phase composition, have been investigated. By combination of thermodynamic calculations and decisive experiments, a series of WC–24 wt.% (Co–Ni–Al) alloys were designed and prepared by liquid phase sintering at 1450 °C for 1 h, 8 h and 20 h, respectively. The influence of Ni3Al content in Co–Ni–Al binder on the WC morphology was investigated by scanning electron microscopy (SEM). The results show that, with the increase of Ni3Al content, the increasing interface energy raises both the energy barrier for two-dimensional (2-D) nucleation and the energy barrier for W migration. Under the influence of these two factors, the micro-faceted and stepped planes on the WC grains become more and more obvious and the WC grains become finer and blunter simultaneously. Combining the thermodynamic calculation with the experiment, the mechanism for WC morphology evolution has been revealed. The mechanical properties of the alloys were also discussed.

High temperature oxidation behaviors of Ni3Al-bonded cermets

Abstract High temperature oxidation behaviors of Ni 3 Al/Ni-bonded cermets were studied in this paper and results revealed that mass gain of Ni 3 Al-bonded cermet is less than that of Ni-bonded cermet at different oxidation temperatures and the mass gain is in accord with oxidation equation (Δm/S) = k n ·t 0.6 , in which oxidation rate constant, k n , at 800 °C, 900 °C and 1000 °C is 0.157, 0.912 and 2.27 respectively. High temperature oxidation kinetic of Ni 3 Al-bonded cermet belongs to quasi-parabolic kinetic behavior. Moreover, oxidation mechanisms and oxidation morphology of Ni 3 Al-bonded cermet were also investigated. During high-temperature oxidation, Ni 3 Al binder would be oxidized, forming double oxide, NiAl 2 O 4 , which can restrain the diffusion of oxygen in oxide, resulting in an improvement of oxidation resistance of cermet. The cross section morphology of oxidized Ni 3 Al-bonded cermet is comprised of oxide layer (OL), transformed layer (TL), and substrate. Obviously, some pores can be observed in OL and also slight pores exist in TL. Thickness of OL of Ni 3 Al-bonded cermet increased with temperature increasing and keeping time prolonging. In oxidation process, Al, Ti etc. would diffuse outwards to OL from inside of cermet and O 2 would diffuse inwards into cermet forming oxygen permeable zone, namely transitional layer.

Comparative analysis of the effect of mechanical activation in an attritor on the structure and behavior of β-RuAl and β-NiAl alloy powder mixtures during reactive sintering

The structure of Ni + Al (two ductile fcc metals) and Al + Ru (ductile aluminum and hard-to-deform hcp ruthenium) powder mixtures subjected to short-term (≤16 h) mechanical activation (MA) is studied. During MA of a 50Ni + 50Al mixture, the powder particles undergo multiple compressive and shear deformation, and large layered granules form due to contact welding and flattening of the layers of both metals. The related increase in the internal stresses, the increase in the dislocation density in particles of both metals, and the decrease in the coherent domain size (CDS) lead to the fracture and fragmentation of the powder particles. In a 49Ru + 48Al + 3Re mixture, aluminum particles are deformed and “spread” over “rigid” ruthenium particles. The formed granules consist of disperse undeformable ruthenium particles connected by an Al binder. The work hardening of ruthenium occurs due to a decrease in CDS. An increase in the contact area between metal particles and a decrease in the diffusion path lengths (aluminum in nickel and ruthenium) cause a decrease in the temperature of the onset of interaction with the participation of liquid aluminum, the activation of solid-phase interaction, and the formation of aluminum-rich nickel (ruthenium) aluminide NiAl (RuAl). Nevertheless, unreacted nickel (ruthenium) particles are retained. A microhomogeneous distribution of the basic and alloying elements and phases in a compacted material is achieved Annealing at temperatures ≥0.8T m is required to complete reactive alloy formation.

Mechanical properties of cBN–Al composite materials

The relationship between microstructure and mechanical properties for a wide range of composite materials based on polycrystalline cubic boron nitride and aluminium as a binder phase (PcBN–Al) has been examined. The PcBN–Al composites were made using high-pressure, high-temperature (HPHT) sintering methods, yielding materials with grain sizes of cBN between 2 and 20 μm and an initial amount of Al binder between 15 and 25 vol.%. Hardness ranged between 15 and 40 GPa, while fracture toughness and strength were between 6.4–8.0 MPa m 1/2 and 355–454 MPa, respectively. Fractography was employed to investigate the large scatter in fracture strengths and correlate fracture strength with fracture toughness through the size of the fracture origins.

Pulsed electric current sintered Fe3Al bonded WC composites

Abstract WC based composites with 5, 10 and 20 vol.% Fe 3 Al binder were consolidated via pulsed electric current sintering (PECS) in the solid state for 4 min at 1200 °C under a pressure of 90 MPa. Microstructural analysis revealed a homogeneous Fe 3 Al binder distribution, ultrafine WC grains and dispersed Al 2 O 3 particle clusters. The WC-5 vol.% Fe 3 Al composite combines an excellent Vickers hardness of 25.6 GPa with very high Young’s modulus of 693 GPa, a fracture toughness of 7.6 MPa m 1/2 and flexural strength of 1000 MPa. With increasing Fe 3 Al binder content, the hardness and stiffness decreased linearly to 19.9 and 539 GPa, respectively with increasing binder content up to 20 vol.%, while the fracture toughness and flexural strength were hardly influenced by the binder content. Compared to WC–Co cemented carbides processed under exactly the same conditions, the WC–Fe 3 Al composites exhibit a substantially higher hardness and Young’s modulus.

Interactions of Al(III) with phosphorylated amino acids

In order to assess the Al(III)-binding abilities of phosphorylated proteins and peptides, the interactions of Al(III) with the building blocks O-phosphoserine (PSer) and O-phosphotyrosine (PTyr) were studied. pH-metric and 31P NMR measurements were carried out to determine the stoichiometries and stability constants of the complexes formed, and to establish the most probable binding sites of the metal ion. PSer was found to bind Al(III) in a monodentate manner at the phosphate moiety, and in a tridentate manner with the simultaneous coordination of all donor groups. PTyr binds Al(III) only at the separate phosphate function. Citric acid (Cit) proved to be a stronger Al(III) binder at the physiological pH, though, it was able to displace PSer only in a rather slow process through formation of the trinuclear species Al 3(Cit) 3(OH). The results were used to evaluate the potential role of Al(III) in inducing the formation of neurofilamentous aggregates in neurological disorders.

Interactions of Aluminum(III) with Phosphates.

In order to obtain information about aluminum(III)-phosphate interactions, potentiometric measurements were carried out to characterize the complex forming properties of Al(III) with organic phosphates, phosphonates, and nucleoside-5'-monophosphates. The aluminum(III)-orthophosphate system is difficult to study due to AlPO(4) precipitation. To overcome this problem, the stability constant logarithms of the 1:1 Al(III) complexes of ligands with the same donor groups (log K(1:1)) were plotted against the basicities of the ligands (log K(PO)3(H)). The resulting linear free energy relation (LFER) indicates that organic phosphates, phosphonates, and uridine-, thymidine-, and guanosine 5'-monophosphates similarly bind Al(III). Adenosine and cytidine 5'-monophosphate fall above the LFER owing to the presence of a second microform with the nucleic base protonated and a hydroxide bound to the Al(III). From the LFER the log stability constant for Al(III) binding to HPO(4)(2-) is estimated as 6.13 +/- 0.05. From the weakness of any soluble orthophosphate complexes of Al(III) we confirm the importance of citrate as the main small molecule Al(3+) binder in the blood serum. The study includes investigation of Al(III) binding to di- and triphosphates, which bind metal ion differently than monophosphates. Structures of the complexes were supported by (31)P NMR measurements.

Ternary complex formation between Al(III)-adenosine-5′-phosphates and carboxylic acid derivatives

The possibility of ternary complex formation has been studied in the Al(III)-adenosine-5′-phosphate (AMP, ADP, and ATP)-ligand B (oxalic acid, lactic acid, and malic acid) systems by pH-potentiometric and 31P NMR methods. Formation of ternary complexes AlABH and AlAB is favored in all systems in the acidic pH range. Under physiological conditions at μmolar Al 3+ concentrations and at high ligand excess, Al(III) is bound mainly to the nucleotides: almost exclusively in the presence of the relatively weak bidentate Al(III) binder oxalic acid and lactic acid, and about 30% in the presence of the much stronger tridentate-coordinating molecule, malic acid.