Surface Oxides in P/M Aluminum Alloys

Kim, Young‐Won; Griffith, WM; Froes, F. H.

doi:10.1007/bf03257675

Cited by 66 publications

(67 citation statements)

References 2 publications

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“…Reduction of the gas content in Al alloy powders prior to compaction is, therefore, critically important. [3][4][5][6] Thermodynamic calculations reveal that it is practically impossible to produce oxide-free powder because in the Al-O system, the partial pressure of O 2 in equilibrium with Al 2 O 3 is far below the range attainable under protective gases or in vacuum systems (Al oxide requires an oxygen partial pressure of 10 À144 atm at 100°C and 10 À64 atm at 500°C [7] ). Consequently, oxidation always takes place on the fresh surface of Al powders.…”

Section: Ultrafine-grained (Ufg) and Nanostruc-mentioning

confidence: 99%

“…[9] Accordingly, Al alloy powder is in general covered with an oxide layer bonded with chemisorbed water (Al 2 O 3 AE 3H 2 O) and physisorbed water (H 2 O). [3,9] For gas-atomized powders, high-temperature degassing has been investigated in Al alloys such as Al-Zn-Mg-Cu-Co (Al 7091), [3,10,11] Al-Si-Cu-Mg-Fe, [12,13] Al-Fe-Mo-Zr, [12] and Al-Fe-Mg alloys. [14] Although there is wide variation in alloy composition and production conditions, the reaction that occurs as the degassing temperature increases shows two typical peaks: at temperatures up to~350°C, decomposed water vapor is the predominant species outgassed, whereas hydrogen generation becomes dominant at higher temperatures (~350°C to 450°C), as illustrated schematically in Figure 1.…”

Section: Ultrafine-grained (Ufg) and Nanostruc-mentioning

confidence: 99%

“…[7] Accordingly, MgO is also encountered in the surface oxides. [3,14] The TGA curve of a stearic acid/ MgO mixture is shown in Figure 5 shows the presence of water, which may evolve according to the following reaction, to form magnesium stearate:…”

Section: A Stearic Acid Desorption From Mixtures With Al and Its Oxidesmentioning

confidence: 99%

“…The peak in stage (b) agreed well with the temperature range provided in the literature for the release of chemisorbed water. [3,13,20] For comparison, the pressure-vs-time curve for the atomized Al-7.5Mg was also plotted in Figure 8(a). Note that the atomized Al-7.5Mg powder showed a much stronger release of both physisorbed and chemisorbed water when compared to the cryomilled Al-7.5Mg powder.…”

Section: Degassing Of Cryomilled Powdermentioning

confidence: 99%

“…Dispersion of hydroxides into the Al matrix led to changes in the outgassing process for the chemisorbed water. The chemical reactions involved in the outgassing process are [3] Figure 11 shows the Gibbs free energy for Eqs. [3] through [6] as a function of temperature and pressure.…”

Section: A Effect Of Cryomillingmentioning

confidence: 99%

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Degassing Behavior of Nanostructured Al and Its Composites

Zhang

Dallek

Vogt

et al. 2009

Metall Mater Trans A

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The synthesis of bulk ultrafine-grained (UFG) and nanostructured Al via cryomilling can frequently require a degassing step prior to consolidation, partly due to the large surface area of the as-milled powders. The objective of this study is to investigate the effects associated with cryomilling with stearic acid additions (as a process-control agent) on the degassing behavior of Al powders. This objective was accomplished by completing select experiments with Al-7.5Mg, Al-6.4 wt pct Al 85 Ni 10 La 5 , and Al-14.3 wt pct B 4 C. The interaction between Al and stearic acid was determined using thermal analysis combined with Fourier transform infrared spectroscopy (FTIR). The degassing experiments were carried out under high vacuum (10 À4 to~10 À6 torr) in a range from room temperature to 400°C, with the pressure of the released gases monitored using a digital vacuum gage. The results showed that the liberation of chemisorbed water was suppressed in cryomilled Al powders and both the chemisorbed water and stearic acid were primarily released in the form of hydrogen. It was also demonstrated that under certain conditions, a nanostructure (grain size~100 nm) can be retained following the hot vacuum degassing of cryomilled Al.

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Section: Ultrafine-grained (Ufg) and Nanostruc-mentioning

confidence: 99%

Section: Ultrafine-grained (Ufg) and Nanostruc-mentioning

confidence: 99%

Section: A Stearic Acid Desorption From Mixtures With Al and Its Oxidesmentioning

confidence: 99%

Section: Degassing Of Cryomilled Powdermentioning

confidence: 99%

Section: A Effect Of Cryomillingmentioning

confidence: 99%

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Degassing Behavior of Nanostructured Al and Its Composites

Zhang

Dallek

Vogt

et al. 2009

Metall Mater Trans A

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The Role of Oxidation in Blowing Particle‐Stabilised Aluminium Foams

Babcsán¹,

Leitlmeier²,

Degischer

et al. 2004

Adv Eng Mater

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Metal foams were produced by blowing gas into aluminium alloy melts. The effect of oxygen content of the blowing gas on composition and structure of the inner surface of the foam cells is studied by varying gas composition from argon, nitrogen and air to pure oxygen. Scanning Electron Microscopy, Auger Electron Spectroscopy and Transmission Electron Microscopy are used to analyse the surfaces. Initially particle‐free melts are pre‐treated by bubbling air through them after which a certain degree of foam stability is achieved. The oxidation products are characterised by microscopy on such foams.

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In Situ X‐Ray Observations and Microstructural Characterizations for Understanding Combustion Foaming and Reaction Processes to Synthesize Porous Al₃Ti Composites From Al–Ti–B₄C Powders

et al. 2021

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The combustion foaming behaviors to synthesize closed-cellular porous Al 3 Ti composites are observed in situ using X-ray radioscopy. The in situ observation of the thermal explosion (TE) mode foaming reveals that the combustion foaming process consists of six steps. The shape of the sample changes uniformly in the first three steps before the sample foams. First, the sample expands uniformly 1) gradual expansion) and maintains an almost constant volume for a fixed period 2) temporary steady state at a constant volume). During these stages, bubbles are not generated inside the sample. Subsequently, the sample shrinks uniformly 3) slight shrinkage). After these three steps, the bubbles are rapidly generated inside the sample 4) rapid foaming). Immediately after foaming, the sample shrinks drastically while bubbles are ruptured and combined 5) severe shrinkage and bubble coarsening). Finally, the sample solidifies as a porous metal 6) solidification). The sample fabricated under the self-propagating hightemperature synthesis (SHS) mode includes graded microstructures corresponding to steps (1)-(4). The microstructures of the samples foamed under the TE and SHS modes are characterized. These results are used for discussing the elementary reaction steps arising at steps (1)-(4).

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Surface Oxides in P/M Aluminum Alloys

Cited by 66 publications

References 2 publications

Degassing Behavior of Nanostructured Al and Its Composites

Degassing Behavior of Nanostructured Al and Its Composites

The Role of Oxidation in Blowing Particle‐Stabilised Aluminium Foams

In Situ X‐Ray Observations and Microstructural Characterizations for Understanding Combustion Foaming and Reaction Processes to Synthesize Porous Al₃Ti Composites From Al–Ti–B₄C Powders

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Surface Oxides in P/M Aluminum Alloys

Cited by 66 publications

References 2 publications

Degassing Behavior of Nanostructured Al and Its Composites

Degassing Behavior of Nanostructured Al and Its Composites

The Role of Oxidation in Blowing Particle‐Stabilised Aluminium Foams

In Situ X‐Ray Observations and Microstructural Characterizations for Understanding Combustion Foaming and Reaction Processes to Synthesize Porous Al3Ti Composites From Al–Ti–B4C Powders

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In Situ X‐Ray Observations and Microstructural Characterizations for Understanding Combustion Foaming and Reaction Processes to Synthesize Porous Al₃Ti Composites From Al–Ti–B₄C Powders