Impact of scratch depth on vacuum tightness of diffusion bonded parts

Gietzelt, Thomas; Hull, Andrew J.; Toth, V.; Messerschmidt, Florian; Thelen, Richard

doi:10.1002/mawe.201700154

Cited by 4 publications

(3 citation statements)

References 5 publications

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“…Differences may appear when material is removed out of the surface or burrs form at the rim. Investigations of depths of scratches were performed in [11]. It was found that a temporary increase of bearing pressure that activates creep of material helps to close scratches.…”

Section: Figure 12mentioning

confidence: 99%

Impacts of layout, surface condition and alloying elements on diffusion welding of micro process devices

Gietzelt

Toth

Weingaertner

2019

Materialwissenschaft Werkst

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The formation of a monolithic part during diffusion bonding is accompanied by the diffusion of atoms across the bonding planes. At sufficient low roughness, it mainly depends on the temperature and dwell time. At the same time, the diffusion process competes against grain growth. By adjusting an appropriate level of bearing pressure, it is possible to control deformation taking into account additional parameters resulting from mechanical microstructures and the design and aspect ratio of the part. Furthermore, material properties, such as the content of alloying elements, the degree of cold work hardening and the grain size, have an impact on diffusion and deformation behavior. Also the surface condition of mating surfaces is important to diffusion kinetics and the quality of the joint. Especially passivation layers of corrosion‐resistant alloys, such as stainless steels and nickel‐based alloys, impair diffusion. In contrast to this, cold work hardening at low depth below the surface, e. g. by means of a blasting processes, may facilitate formation of a good bond and help to limit grain size. For oxide dispersion‐strengthened materials, additional impacts on diffusion bonding behavior applies.

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Section: Figure 12mentioning

confidence: 99%

Impacts of layout, surface condition and alloying elements on diffusion welding of micro process devices

Gietzelt

Toth

Weingaertner

2019

Materialwissenschaft Werkst

Self Cite

View full text Add to dashboard Cite

show abstract

“…However, unfortunately, different roughness values were not investigated and compared. In [5], we investigated the depth of singular scratches on vacuum tightness and compared the impact of a constant contact pressure to a contact pressure superimposed by short peak loads. However, the influence of the absolute width of joining cross sections on the deformation behavior has not yet been investigated systematically.…”

Section: Introductionmentioning

confidence: 99%

Influence of Cross Section Thickness and Aspect Ratio on Deformation during Diffusion Bonding and Impact of Metal Diffusion and Evaporation on Temperature Measurement Accuracy

Gietzelt¹,

Toth²,

Kraut³

et al. 2020

Preprint

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Diffusion bonding is often used on pre-machined parts to generate internal cavities, e.g. for cooling injection molding tools close to the mold cavity. Only then, the workpieces are finished to their final dimensions. In the case of micro-process devices, however, it is essential to precisely control the deformation, as otherwise uncontrollable pressure losses will occur with channel cross-sections in the sub-millimeter range. Post-processing is not possible. The most important process parameters for diffusion bonding are temperature, dwell time and contact pressure, with the bonding temperature and contact pressure acting in opposite directions and showing a strong non-linear dependence on deformation. In addition, the deformation is influenced by a number of other factors such as the absolute size of the cross-section and the aspect ratio of the parts, the dimensions and distribution of the internal cross sections and the overall percentage of the cross-section to be bonded. In micro process engineering, small material cross-sections in the range of the materials microstructure can facilitate additional deformation mechanisms such as grain boundary sliding, which are not relevant at all for larger structures. For parts consisting of multiple layers, tolerances in thickness and roughness of multiple surfaces must be levelled, contributing to the percentaged deformation. This makes it difficult, especially in micro process engineering and in single or small series production, to determine suitable joining parameters in advance, which on the one hand do not cause unforeseen large deformations, but on the other hand reliably produce highly vacuum-tight components. Hence, a definition of a fixed percentaged deformation does not work for all kinds of components. This makes it difficult to specify parameters for surely obtain high-vacuum tight parts. For successful diffusion bonding, atoms must diffuse over the bonding planes, forming a monolithic part in which the original layers are no longer visible. Only then, mechanical properties identical to those of the base material, which has been subjected to identical heat treatment, can be achieved. In this paper, the impacts of different material cross section widths as well as of the aspect ratio on deformation were investigated. By accident, it was found that also accuracy of the temperature measurement may have a serious impact in terms of deformation.

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“…However, different roughness values were not investigated and compared. In [12], the authors investigated the depth of singular scratches on vacuum tightness and compared the impact of constant contact pressure to a contact pressure superimposed by short peak loads. However, the impact of the absolute width of joining cross-sections on the deformation behavior was not yet investigated systematically.…”

Section: Introductionmentioning

confidence: 99%

Comprehensive Study of the Deformation Behavior during Diffusion Bonding of 1.4301 (AISI 304) as a Function of Material Width and Aspect Ratio

Gietzelt¹,

Toth²,

Kraut³

et al. 2020

Metals

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In this paper, the impact of material width as well as aspect ratio on deformation during diffusion bonding of layered samples were investigated. For this, six annular samples with a constant cross-sectional area but an increasing diameter and thus decreasing material width were designed. In a first set of experiments, specimens of a constant height of h = 20 mm were examined. Each sample consisted of 10 sheets, 2 mm in thickness each. Diffusion bonding was performed at T = 1075 °C, t = 4 h and p = 15 MPa. Subsequently, additional samples with a constant aspect ratio of about three but different material width were diffusion bonded. For this, additional layers were added. It was expected that the deformation should be nearly constant for a constant aspect ratio. However, comparing the deformation to a sample possessing an aspect ratio of about three from the first batch, a much higher deformation was obtained now. Bonding a third sample, a deformation in the same range as for the other two samples of the second batch was obtained. It was found that due to the evaporation of metals, the thermocouples were subjected to aging, which was proven indirectly by the evaluation of heating power. Since the diffusion coefficient of the metals follows an exponential law, deformation changes considerably with temperature. This emphasizes that exact temperature measurement is very important, especially for bonding microprocessor devices at constant contact pressure. The experiments showed that the deformation depends strongly on geometry. Bonding parameters cannot be generalized. For layered setups, the contribution that thickness tolerances from manufacturing and leveling of surface roughnesses of sheets add to the overall deformation cannot be reliably separated. After diffusion bonding, thickness tolerances increase with a lateral dimension. Obviously, the stiffness of the pressure dies is crucial.

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Impact of scratch depth on vacuum tightness of diffusion bonded parts

Cited by 4 publications

References 5 publications

Impacts of layout, surface condition and alloying elements on diffusion welding of micro process devices

Impacts of layout, surface condition and alloying elements on diffusion welding of micro process devices

Influence of Cross Section Thickness and Aspect Ratio on Deformation during Diffusion Bonding and Impact of Metal Diffusion and Evaporation on Temperature Measurement Accuracy

Comprehensive Study of the Deformation Behavior during Diffusion Bonding of 1.4301 (AISI 304) as a Function of Material Width and Aspect Ratio

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