The production of AlN-rich matrix composites by the reactive infiltration of Al alloys in nitrogen (original) (raw)
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Al alloys were infiltrated into Al 2 O 3 preforms in N 2 and N 2 -2% H 2 gas mixture in the temperature regime of 900-1200°C. The kinetics of nitridation during infiltration were continuously monitored by recording weight gained during infiltration of the preform. The weight gains that are attributed to the formation of AlN in the matrix were observed to increase with processing temperature. In addition, higher weight gains were recorded in N 2 -H 2 as compared to in N 2 atmosphere. Analysis of the composites indicates that controlled matrices of AlN/Al can be formed by selection of appropriate process parameters viz. temperature and atmosphere. Based on this study it has been demonstrated that net shaped metal matrix composites (MMCs), with varying amounts of AlN in the matrix can be fabricated by infiltrating alumina preforms at 900-1000°C in commercial nitrogen. By controlling the preform characteristics, it is possible to fabricate composites with significant variation in microstructural scale, and consequently matrix hardness and elastic modulus. 13], the molten Al-alloy reacts with the ambient atmosphere (air, oxygen or nitrogen) to form Al 2 O 3 /Al or AlN/Al composites with an interpenetrating microstructure. Al 2 O 3 /Al composites grown freely and into SiC, Al 2 O 3 preforms by directed melt oxidation have been well investigated and documented . However, similar studies on AlN/Al composites formed by nitridation of Al-Mg and Al-Sr based alloys are relatively fewer. Creber et al. and Aghajanian et al. initially reported the pressureless infiltration of Al-Mg alloys into particles of Al 2 O 3 , SiC, TiB 2 etc. over a range of temperature. They assessed the critical 2
Materials
Aluminium nitride (AlN) is an important technical ceramic with outstanding strength and thermal conductivity that has important applications for advanced heat sink materials and as a reinforcement for metal-based composites. In this study, we report a novel, straightforward and low-cost method to prepare AlN powder using a vacuum tube furnace for the direct nitridation of loose aluminium powder at low temperatures (down to 500 ∘C) under flowing high-purity nitrogen. Small amounts of magnesium powder (1 wt.%), combined with aluminium, promote nitridation. Here, we characterise the effects of time (up to 12 h) and temperature (490 to 560 ∘C) on nitridation with the aim to establish an effective regimen for the controlled synthesis of an aluminium nitride reinforcement powder for the production of metal matrix composites. The extent of nitridation and the morphology of the reaction products were assessed using scanning electron microscopy and X-ray diffraction analyses. AlN was detecte...
2009
Aluminum matrix composites reinforced with Al-Ni intermetallic compounds and Al 2 O 3 were obtained by hot pressing of high-energy milled powders. Using the reaction between Al and NiO and aiming to preserve part of the Al content after completing the reaction by increasing the relative amount of Al, composites containing Al 2 O 3 and Al-Ni intermetallic compounds were produced. These composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Depending on the Al/NiO molar ratio, the reaction can be activated either during milling or during subsequent hot pressing. Hence, two different processing routes can be used to produce such composites. Starting from powder mixtures with an Al/NiO molar ratio of 15/3, the reaction took place during milling, forming Al 3 Ni and Al 3 Ni 2 plus Al 2 O 3 reinforced Al composite powder, which was consolidated by hot pressing. An Al/NiO molar ratio of 20/3 prevented the reaction from occurring during milling, but enabled it to occur during subsequent hot pressing, forming the same reinforcement phases. The reactive-milled composite is harder and presents higher porosity than the reactive-sintered ones, after consolidation by hot pressing under the same parameters. In the latter route, the longer the milling time prior to hot pressing, the smaller the size of the reinforcement phases.
Feasibility of aluminium nitride formation in aluminum alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1995
The feasibility of forming aluminum nitride by in situ reactive nitrogen gas injection into molten aluminum alloys has been evaluated both analytically and experimentally over the temperature range from 700 to 1500 °C. It is shown that aluminum nitride can be melt formed in the presence of Mg and Si, with nitrogen and/or ammonia as the reactive gases at temperature above 1100 °C. In this role, magnesium serves as a catalyst. Magnesium nitride is first formed in the vapor phase by the reaction of vaporized magnesium and nitrogen gas, followed by incorporation of magnesium nitride particles into the molten aluminum. Via an in situ substitution reaction, aluminum nitride forms between magnesium nitride and aluminum. Up to 17 wt.% aluminum nitride in an aluminum alloy has been formed with an average reinforcement size of 3/am. The potential for this process permits economical liquid phase processing of aluminum nitride-aluminum metal matrix composite with nitrogen gas injection for structural, thermal and wear applications.
Journal of Alloys and Compounds, 2009
Aluminum matrix composites reinforced with Al-Ni intermetallic compounds and Al 2 O 3 were obtained by hot pressing of high-energy milled powders. Using the reaction between Al and NiO and aiming to preserve part of the Al content after completing the reaction by increasing the relative amount of Al, composites containing Al 2 O 3 and Al-Ni intermetallic compounds were produced. These composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Depending on the Al/NiO molar ratio, the reaction can be activated either during milling or during subsequent hot pressing. Hence, two different processing routes can be used to produce such composites. Starting from powder mixtures with an Al/NiO molar ratio of 15/3, the reaction took place during milling, forming Al 3 Ni and Al 3 Ni 2 plus Al 2 O 3 reinforced Al composite powder, which was consolidated by hot pressing. An Al/NiO molar ratio of 20/3 prevented the reaction from occurring during milling, but enabled it to occur during subsequent hot pressing, forming the same reinforcement phases. The reactive-milled composite is harder and presents higher porosity than the reactive-sintered ones, after consolidation by hot pressing under the same parameters. In the latter route, the longer the milling time prior to hot pressing, the smaller the size of the reinforcement phases.
Properties of AlN-Based Magnesium-Matrix Composites Produced by Pressureless Infiltration
Materials Science Forum, 2006
A novel ceramic-metal composite with continuous interconnected ceramic and metal phases has been fabricated from sintered porous particulate AlN preforms infiltrated with magnesium. The 48 vol. % AlN composites are fabricated by pressureless infiltration in argon in the temperature range of 870 °C to 960 °C. An increase in the infiltration rate is observed as the temperature increases. Results on the mechanical characterization of the composites indicate an elastic modulus of 90 to 110 GPa and hardness of 70 to 80 HRB. The tensile strength calculated by the shear punch test method ranges from 260 to 390 MPa. As a general rule, it is observed that the lower the infiltration temperature, the higher the tensile strength. The linear coefficient of thermal expansion of the infiltrated composites in the temperature range of 215 to 315 °C is 7.65 x 10 -6 °C -1 . This value is lower than those found for similar Al/AlN composites reported in the literature.
Transactions of the Indian Institute of Metals, 2017
Present study concerns a reduction of nickel oxide by aluminum via mechanical alloying. Essentially, the reaction products depend on two parameters: the milling time and the molar ratio of elementary powders. This reaction between the starting NiO-Al powders, which takes place during the high-energy ball milling, makes it possible to produce nickel matrix composites reinforced by alumina particles. For the NiO/Al molar ratio of 3/2, the synthesis reaction begins after 4 h of milling time while for a ratio of 3/3, it ends after 2 h forming Ni-Al 2 O 3 composite. Furthermore, changing the NiO/Al ratio to 3/4 and 3/5, allows generation of different phases, where the excess Al reacts with Ni already produced to form Ni x Al y intermetallic matrix reinforced with Al 2 O 3 particles. Due the low apparent density of the green compact, a sintering treatment is necessary to densify the material. This process has been carried out at 800 and 1200°C under argon atmosphere. Experimental results show that the milling time and starting ratio of NiO/Al powders have an important effect on the reduction reaction of NiO by Al.
In-situ Synthesis of AlN/Mg Matrix Composites
Magnesium matrix composites with A1N reinforcements are potential engineering materials for automobile and aerospace applications. Attractive properties of A1N include high thermal conductivity and hardness. AlN-reinforced Mg composites have been synthesized by in-situ reaction using pure Al and AZ31B and SÍ3N4 powder as raw materials. Microstructures containing 15 vol.% A1N were obtained by heating the raw materials at 770°C for one hour under argon atmosphere. Composite microstructures were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy. Final microstructures consisted of A1N particles 1-5 micron in size that were distributed within the Mg alloy matrix.
Strengthening of Al/Ni-based composites by in situ growth of intermetallic particles
Materials Science and Engineering: A, 2002
Squeeze cast Al matrix composites reinforced with continuous fibers of Inconel 601 were submitted to different annealing treatments aiming at tuning the amount of reaction at the fiber/matrix interface. The reaction develops in the form of intermetallic nodules growing onto the fibers. The tensile flow stress of the composites increases with increasing nodule volume fraction at the expense of a progressive loss of ductility. This loss of ductility is due both to the low cohesion of the oxide layer separating the matrix from the nodules and to brittle cracking at the root of attachment of the nodules onto the fibers. Damage development is evaluated from the evolution of strain hardening. The nodules grow underneath the oxide barrier layer that protects the fibers from reacting with Al during squeeze casting. Their mechanism of growth involves the partial reduction of the oxide layer by Al, followed by diffusion of Al and Ni through the Cr-rich oxide layer.
International Journal of Mechanical and Materials Engineering
Preparation and characterization of aluminum metal matrix composites reinforced with aluminum nitride was carried out. A graphite crucible and a stainless steel permanent mould was used to prepare the samples. An optimum stirring speed was determined for a fixed stirring time before cast in the permanent mould. Morphology of the composite and particle distribution were investigated by optical microscopy. The reinforcing particles were clearly shown present at the edges and around grains of silicon primary, silicon needles and inter-metallic compound of FeMg 3 Si 6 Al 8. The result of hardness test was 44 Hv for Al-Si matrix and increased to 89 Hv for an Al-Si composite reinforced with 5% wt.% AlN powder. The higher values in hardness indicated that the AlN particles contributed to the increase of hardness of the matrix.