High-temperature lubricants for superplastic forming of metals

Friedman, Peter A.; Luckey, S. George

doi:10.1533/9780857092779.1.72

Cited by 4 publications

(6 citation statements)

References 9 publications

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“…Over the course of a production run, coating tends to transfer from workpiece to tool upon contact. The transferred material accumulates and compacts with subsequent contact events and can be detrimental to part surface finish and geometry . As such, it is suggested that a period of 900 °C exposure to ambient atmosphere may be sufficient to decompose adsorbed material and enable production runs to be prolonged.…”

Section: Discussionmentioning

confidence: 99%

“…A significant share of this market is occupied by coatings that are used as high temperature lubricants and release agents within the metal forming sector. Typical applications include the hot forming and superplastic forming of titanium alloys at around 900 °C, which are standard industrial methods for the manufacture of complex aerospace components . These operations tend to be performed under an inert atmosphere; however, this is not always possible.…”

Section: Introductionmentioning

confidence: 99%

“…Typical applications include the hot forming and superplastic forming of titanium alloys at around 900°C, which are standard industrial methods for the manufacture of complex aerospace components. [2] These operations tend to be performed under an inert atmosphere; however, this is not always possible. In spite of this, there is an absence of published research into the fate of h-BN under oxidizing conditions when present on substrates that are themselves susceptible to high temperature oxidation.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Fleming

2019

Materials & Corrosion

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In contrast to a mass of powder in air at 900 °C, the oxidation rate of hexagonal boron nitride does not tend to a plateau when present as a coating on austenitic stainless steel type 304 and type 310, and a real‐world hot forming tool alloy. As with a mass of powder, a molten boron trioxide diffusion barrier encapsulates each hexagonal boron nitride grain around the basal plane. These subsequently merge to form a dispersion of remnant grains throughout a molten matrix. Boron trioxide is semipermeable, and as such, the substrate oxidizes concurrently. As it does so, outwardly diffusing chromium (III) ions react with boron trioxide to form chromium borate, which depletes the diffusion barrier. This causes the oxidation of hexagonal boron nitride to be sustained at an enhanced rate and the overlayer ultimately undergoes complete decomposition. During this process, the scale comprises chromium borate and chromia only. While manganese chromium spinel and iron chromium spinel form readily at the oxide‐atmosphere interface of equivalently heat‐treated uncoated substrates, they do not form until after the coating has completely decomposed.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Fleming

2019

Materials & Corrosion

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“…As a consequence of a unique array of properties, hexagonal boron nitride (h‐BN) has a proliferation of applications that span from cosmetics to nanotubes . Due to excellent lubricity, stability at elevated temperatures and high thermal conductivity, prominent amongst these uses are high temperature lubricant and release agent coatings within the metal forming sector . It is therefore vital to know and understand the chemical reactions that h‐BN‐coated metals undergo under industrially relevant conditions.…”

Section: Introductionmentioning

confidence: 99%

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Ti‐6Al‐4V

Fleming

2019

Materials & Corrosion

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Hexagonal boron nitride (h‐BN) coatings on Ti‐6Al‐4V substrates undergo complete decomposition in air at 900 °C. This fate is similar to that of this ceramic material on chromia‐former alloys, and unlike that of a mass of powder treated in isolation. As the ceramic and alloy oxidize concurrently, outwardly diffusing aluminum (III) ions but not the predominant titanium (IV) ions react with the boron trioxide that forms around the h‐BN basal plane peripheries. Resultant aluminum borate is incorporated into the growing scale and the boron trioxide diffusion barrier is depleted. By this mechanism, the oxidation of h‐BN is maintained at an enhanced rate, until both this material and its oxide completely decompose. Liberated nitrogen from the oxidation of h‐BN can enter the underlying scale as a randomly distributed solute in rutile solid solution. The post‐coating oxide‐atmosphere interface comprises elongated aluminum borate crystallites protruding through at the boundaries between 3–5 at% nitrogen‐doped rutile grains. It differs significantly from that of oxidized, uncoated Ti‐6Al‐4V, which is occupied by a thin α‐alumina layer atop rutile. This interface does not change with an additional 72 h of heat‐treatment.

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“…RF of shells [10][11][12][13][14][15][16] on the first stage is carried out into the cavity of the rift along its contour, selected in such a way that the zones of the preform near the flange are deformed most intensively. At the second stage, when the gas pressure is reversed, the semi-finished product is formed into the cavity of the die with the predominant thinning of its central part.…”

Section: Introductionmentioning

confidence: 99%

Superplastic forming of shells from sheet blanks with thermally unstable coatings

et al. 2018

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The article is devoted to superplastic forming of non-uniformly heated sheet blanks from aluminum alloy AMg6M. To create an uneven temperature field over the surface of the blank, coatings made of sublimated substances were used from at temperatures 50…150°C below the superplastic forming temperature (450°C for AMg6M alloy). An aqueous solute of chloride and ammonium iodide having a sublimation temperature at normal pressure and a latent heat of conversion equal to 338 and 404°C, 330 and 355kJ/kg, respectively, was sprayed onto the central zones of the blanks. Superplastic forming of shells was carried out in two modes: 1) with simultaneous sublimation of the coating; 2) with the beginning of the sublimation of the coating upon reaching the height, which is formed by the workpiece, equal to 20-30% of the final shell height. The experiments showed a decrease in the thickness of the shells to be formed up to 4-10% on the working surface of the shells (without taking into account their flange zones) and the savings of sublimate during superplastic forming in the second mode. The optimal subliming coating for AMg6M alloy was ammonium chloride.

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High-temperature lubricants for superplastic forming of metals

Cited by 4 publications

References 9 publications

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Chromia‐formers

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Ti‐6Al‐4V

Superplastic forming of shells from sheet blanks with thermally unstable coatings

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