Effect of palladium on diffusion processes in the system tungsten-chromium

Dzykovich, I. Ya.; Panichkina, V. V.; Скороход, В. В.; Shaiderman, L. I.

doi:10.1007/bf00793571

Cited by 15 publications

(4 citation statements)

References 1 publication

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“…The use of chromium as a possible alloying element in tungsten, studied here mainly as a possible solution to increase tungsten oxidation resistance, has been previously investigated by other authors. It has been reported that the synthesis of dense W-Cr alloys is difficult due to low interdiffusion coefficients in this system [36] and that the use of a third element such as Pd would be necessary to improve interdiffusion [36][37][38]. However, the presence of palladium dissolves rather large amounts of tungsten and chromium, making the whole system more complex [39].…”

Section: Introductionmentioning

confidence: 99%

SHS Synthesis, SPS Densification and Mechanical Properties of Nanometric Tungsten

Dine

Bernard

Herlin

et al. 2021

Metals

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Recent studies have shown that low grain sizes are favorable to improve ductility and machinability in tungsten, as well as a resistance to ablation and spallation, which are key properties for the use of this material in a thermonuclear fusion environment (Tokamaks such as ITER). However, as one of the possible incidents during Tokamak operation is the leakage of air or water from the cooling system inside the chamber, resulting in the so-called loss of vacuum accident (LOVA), extensive oxidation may arise on tungsten components, and the use of an alloy with improved oxidation resistance is therefore highly desirable. As current production routes are not suitable for the fabrication of bulk nanostructured tungsten or tungsten alloys samples, we have proposed a new methodology based on powder metallurgy, including the powder synthesis, the densification procedure, and preliminary mechanical testing, which was successfully applied to pure tungsten. A similar study is hereby presented on tungsten-chromium alloys with up to 6 wt.% Cr. Results show that full tungsten densification may be obtained by SPS at a temperature lower than 1600 °C. The resulting morphology strongly depends on the amount of the alloying element, presenting a possible second phase of chromium oxide, but always keeps a partial nanostructure inherited from the synthesized powders. Such microstructure had previously been identified as being favorable to the use of these materials in fusion environments and for improved mechanical properties, including hardness, yield strength and ductility, all of which is confirmed by the present study.

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Section: Introductionmentioning

confidence: 99%

SHS Synthesis, SPS Densification and Mechanical Properties of Nanometric Tungsten

Dine

Bernard

Herlin

et al. 2021

Metals

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“…Evans [5] suggested that a Pd rich phase containing Cr segregates at the surface in the Cr depleted layer and it inhibits inward diffusion of oxygen. Dzykovich et al [14] coated tungsten by 1μm of Pd and 50 µm of Cr. After annealing at 1250˚C they found diffusion of Cr into the tungsten to a distance larger by a factor of 5-10 relative to tungsten coated by Cr alone.…”

Section: Introductionmentioning

confidence: 99%

On the Mechanism of Oxidation Resistance of W-Cr-Pd Alloys

Kafri

Makonovitsky

Shneck

2018

DDF

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While studying activation sintering of tungsten, Evans [5] and Ito and Furusawa [6] revealed that W-Cr-Pd alloys exhibit unexpected oxidation resistance at elevated temperatures. The role of palladium in stimulating oxidation resistance in W-Cr alloys is the main aim of the present contribution. As previously observed, at 800 °C these alloys form a relatively dense protective scale that consists of an inner layer of Cr2O3, an intermediate layer of Cr2WO6 and an external layer of WO3. At 1200 °C only Cr2WO6 layer is found, since the Cr2O3 and WO3 evaporate. To determine the role of paladium, W and W-Pd alloys were coated with Cr layers and undergone diffusion experiments. An extraordinary affinity between the Cr and Pd was revealed, manifested by extremely fast inward diffusion of Cr along grain boundaries. In a second experiment the dissolution of Cr into W grains at 1300°C was followed and found to take place preferentially along grain boundaries. These observations assess that the Pd segregated at grain boundaries provides fast diffusion channels for Cr to the free surface and it imparts the significant improvement of the oxidation resistance of W alloys, as suggested by Lee and Simkovitz [10-12].

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“…Studies performed on binary alloys of W with Ti (0-5%), Nb (0-25%), Mo (0-5%), Ta (0-15% and 25-50%), Cr (0-50%) or Zr (0-15%) as alloying element have shown that these alloys exhibit oxidation resistance superior to that of pure W. 6,7 Among these alloys, the W-Cr alloys have been found to possess the highest resistance to oxidation, and the minimum concentration of Cr required for formation of protective oxide scale is 50 at-%. 6 However, sintering of the W-Cr alloys without adding low melting sintering activators such as Pd and Ni is quite difficult, [8][9][10] because interdiffusion in the W-Cr alloys is very slow at high temperatures. 8 Itagaki and Yoda 11,12 have studied sintering and oxidation behaviour of the W-(28?19-46?47) at-%Cr alloys containing (0?14-2?27) at-%Pd or Ni.…”

Section: Introductionmentioning

confidence: 99%

“…6 However, sintering of the W-Cr alloys without adding low melting sintering activators such as Pd and Ni is quite difficult, [8][9][10] because interdiffusion in the W-Cr alloys is very slow at high temperatures. 8 Itagaki and Yoda 11,12 have studied sintering and oxidation behaviour of the W-(28?19-46?47) at-%Cr alloys containing (0?14-2?27) at-%Pd or Ni. They have reported that Pd is more effective in enhancing the sinter density than Ni.…”

Section: Introductionmentioning

confidence: 99%

Densification and characterisation of W–Cr–Nb alloys prepared by sintering of mechanically alloyed nanocrystalline powders

2013

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Sintering of (W 12x Cr x ) 90 Nb 10 (x50?3, 0?5 and 0?6) alloys, prepared through mechanical alloying of elemental powder blends, has been investigated. Relative density of .98% could be achieved by sintering at 1790uC for 5 h. Characterisation by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy has shown the presence of W rich solid solution and Cr 2 Nb phases in the microstructures of the sintered alloys. The densification of the W-Cr-Nb alloys is possible at relatively lower temperature due to use of nanostructured powder raw material obtained through high energy milling and liquid phase sintering promoted by the presence of Cr 2 Nb having relatively lower melting point (1730uC). The matrix grain size of the sintered alloys is decreased, whereas hardness is increased noticeably with the amount of Cr 2 Nb in the microstructure.

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Effect of palladium on diffusion processes in the system tungsten-chromium

Cited by 15 publications

References 1 publication

SHS Synthesis, SPS Densification and Mechanical Properties of Nanometric Tungsten

SHS Synthesis, SPS Densification and Mechanical Properties of Nanometric Tungsten

On the Mechanism of Oxidation Resistance of W-Cr-Pd Alloys

Densification and characterisation of W–Cr–Nb alloys prepared by sintering of mechanically alloyed nanocrystalline powders

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