Tailoring Titanium Hydride Decomposition Kinetics by Annealing in Various Atmospheres

Lehmhus, Dirk; Rausch, Gerald

doi:10.1002/adem.200300572

Cited by 62 publications

(38 citation statements)

References 25 publications

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“…Gas evolution from the precursor peaks earlier than for the loose powder although one might have expected the opposite arguing, e.g., that the entrapped hydrogen is held back by the metallic matrix or that decomposition of TiH 2 is delayed by the hydrogen surrounding the blowing agent in the metal. The effect of earlier hydrogen release has already been observed previously [9,17] and was explained by a possible partial fracture of the oxide layers on TiH 2 particles during compaction [9]. The evidence given by one of the TEM images discussed above showing such a fracured oxide layer could support this hypothesis but a definite proof is still lacking.…”

Section: Discussionmentioning

confidence: 48%

“…Lehmhus et al use DSC to study the influence of various pre-treatments under air and argon [17]. They find the same basic phenomena, namely a shift of both onset and peak temperature for pre-treatments under air but the peak positions they determine are significantly lower than the ones shown in Fig.…”

Section: Discussionmentioning

confidence: 81%

“…Refs. [7,17]. Accordingly, hydrogen starts to be released from TiH 2 at about 380-420 • C with some variations between powders of different origin.…”

Section: Discussionmentioning

confidence: 99%

“…The task therefore is to find treatments which form a sufficiently thick oxide layer while a minimum of hydrogen is lost. Some pre-treatments have been suggested in metal foam literature [11][12][13][14][15][16][17]. However, as the mechanisms leading to a retardation of gas evolution are not yet known, these parameters were found in a mostly empirical way.…”

Section: Introductionmentioning

confidence: 99%

“…For this purpose the decomposition of TiH 2 powder is characterised by thermogravimetric analysis (TGA) combined with mass spectrometry (MS) and differential scanning calorimetry (DSC). Unlike most studies in the literature [12][13][14][15]17] we rely on detecting hydrogen evolving from hydrides by a mass spectrometer. This allows us to separate gas release from other thermal effects caused by phase transformations and melting and provides an undisturbed measure for the effect which drives foaming.…”

Section: Introductionmentioning

confidence: 99%

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Modification of titanium hydride for improved aluminium foam manufacture

Matijasevic-Lux

Banhart

Fiechter³

et al. 2006

Acta Materialia

198

100

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Titanium hydride was used for foaming the aluminium casting alloy AlSi6Cu4. In order to improve foaming characteristics the TiH 2 powder was subjected to various heat treatments prior to processing to shift hydrogen release up into the melting range of the alloy. Untreated and pre-treated powders were characterised by oxygen analysis, thermal analysis in connection with mass spectrometry applying various temperature profiles, X-ray diffraction and transmission electron microscopy. In addition, foaming trials were carried out based on various TiH 2 powders. It was found that oxidation of TiH 2 particles is responsible for the observed shift in decomposition temperature since heating under argon did not produce this effect. The shift can be tailored by choosing suitable pre-treatment parameters. For an appropriate choice a beneficial effect on foam morphology was found.

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Section: Discussionmentioning

confidence: 48%

Section: Discussionmentioning

confidence: 81%

“…Refs. [7,17]. Accordingly, hydrogen starts to be released from TiH 2 at about 380-420 • C with some variations between powders of different origin.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Modification of titanium hydride for improved aluminium foam manufacture

Matijasevic-Lux

Banhart

Fiechter³

et al. 2006

Acta Materialia

198

100

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Potential New Matrix Alloys for production of PM Aluminium Foams

Lehmhus¹,

Busse

2004

Adv Eng Mater

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The powder compact melting technique for aluminium foam production as practised today accepts a certain mismatch between foaming agent decomposition and matrix alloy melting temperatures. This mismatch is believed to influence the pore structure in an unfavourable way. Adjustment of TiH2 decomposition as well as liquidus and solidus temperatures of matrix alloys can be used to counteract it. Effects of TiH2 thermal treatments are investigated using thermal analysis. TiH2 variants gained via annealing treatments were used to produce aluminium foam precursor materials. As matrix for these specimens, aluminium based alloys with low liquidus and solidus temperatures were selected. Alloy systems considered include established combinations of aluminium with Cu, Mg, Si and Zn as well as special quaternary mixtures of these elements. First examinations presented include thermal analysis of alloys as well as studies on expansion vs. time and temperature relationships of precursor material based on new alloys and foaming agent variants.

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The Role of Oxidation During Compaction on the Expansion and Stability of Al Foams Made Via a PM Route

Asavavisithchai

Kennedy

2006

Adv Eng Mater

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The production of Al foams via a powder metallurgy (PM) route is attractive due to the ability to produce near-net-shape components. [1] This method involves mixing Al or Al-alloy powder with a foaming agent, typically TiH 2 , followed by compaction. Heating the compact above its melting point results in expansion, due to gas release from the decomposing foaming agent, leading to a closed-cell foam structure. [2] One major factor for successful foaming via the PM route is to ensure that precursors have a density close to the theoretical density, [3] that is, with little or no residual porosity after compaction. Since the majority of research and commercial activity in PM foams centres around the Al-Si system, where the compressibility of Al-Si alloy powders, or Al with Si added, is low, compaction methods involving the application of heat are employed in order that a reduction in the flow stress of the powder mixture is achieved. These methods, which include hot uniaxial compaction and hot extrusion of isostatically pressed compacts, are expensive, mainly due to higher energy requirements and reduced productivity, and contribute significantly to the prohibitively high cost of the precursor material. Precursors compacted in the optimum temperature range (400-500°C) [2] do, however, result in foams which show good expansions and structures, and it is generally accepted that compaction at elevated temperatures is a prerequisite for good foaming.Cold compaction can, however, be used to produce high density foamable precursors from soft pure Al powder. [3][4][5] By using this system, this study aims to separate the effects of exposure to elevated temperature, through heat treatment of the powders, and the application of pressure, by cold compaction. By understanding what factors in the hot compaction process dominate the foaming behaviour, it may be possible to identify alternative, lower cost processing methods.Results. Foaming behaviour: Figure 1 shows expansion plots for Al precursors that were hot compacted at different temperatures. The expansion behaviour in all cases can be seen to be typical of the foaming process, which involves pore initiation and growth, expansion to a maximum followed by collapse to a steady-state level. As the hot compaction temperature increases from 400 to 450°C, the maximum expansion also increases. When compaction is performed at 500°C, the maximum expansion increases further, to 400 %, and a delay in the rate of foam collapse is observed. Hot compaction at 550°C results in a significantly reduced foam expansion. Figure 2 shows the foaming behaviour for precursors made from either as-received Al powder or Al powder, which was heat treated for 60 min between 400 and 550°C, mixed with as-received TiH 2 and then cold compacted. A progressive increase in the maximum expansion is observed for powders heat treated at temperatures up to 500°C, with the largest maximum expansion of approximately 460 %.

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Tailoring Titanium Hydride Decomposition Kinetics by Annealing in Various Atmospheres

Cited by 62 publications

References 25 publications

Modification of titanium hydride for improved aluminium foam manufacture

Modification of titanium hydride for improved aluminium foam manufacture

Potential New Matrix Alloys for production of PM Aluminium Foams

The Role of Oxidation During Compaction on the Expansion and Stability of Al Foams Made Via a PM Route

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