Degradação a baixa temperatura da Y-TZP odontológica: análise microestrutural e avaliação das propriedades mecânicas

Arata, Anelyse

doi:10.11606/t.85.2017.tde-23012017-085618

Cited by 4 publications

(11 citation statements)

References 49 publications

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“…This is similar to the arguments of Hü gel et al 39 When the distance between the beams is intermediate to these two cases, Xie 54 argued that the second beam creates a second keyhole in the weld pool behind the keyhole created by the leading beam. This is similar to the results of Arata et al 48 which showed that the speed at which humping occurred in EBW welding could be increased up to 50% by using a tandem dual beam EBW system. They attributed the suppression of undercutting and humping to the change in momentum of the backward flow of the molten weld metal as it was forced to flow around the second beam cavity.…”

Section: Techniques and Processes For Higher Welding Speedssupporting

confidence: 91%

“…This high velocity, rearward directed flow of molten weld metal in the weld pool is consistent with numerical simulations by Beck et al 47 and observations in tandem EBW by Arata and Nabegata. 48 Backfilling of the front portion of the weld pool as described by Bradstreet 5 does not occur because the recirculated molten weld metal fails to keep up with the forward moving welding arc and is pushed or held back by the high velocity and momentum of the backward directed fluid flow within the wall jet. At the tail of the weld pool, the molten weld metal accumulates to form a swelling that is drawn into a spherical bead shape by surface tension as molten metal is fed into the swelling from the front of the weld pool through the wall jet.…”

Section: Curved Wall Jet Modelmentioning

confidence: 99%

“…They suggested that the smaller arc gap and therefore lower arc forces, the larger filler metal droplet impingement area, the less focused and more lateral flow of molten filler metal droplets and the extra opposing viscous drag force from the large fusion boundary all reduced the depression of the weld pool surface and the overall momentum of the backward flow of molten weld metal in the weld pool thereby allowing significantly higher welding speeds without humping. 8,9 The tandem arrangement of GTAW torches, 18,19 GMAW torches, 50,51,52 laser beams 53,54 and electron beams 15,48 have also been shown to be very effective in delaying the onset of humping and undercuts to higher welding speeds. In recent developments, two GMAW electrodes, arranged in line with the welding direction, were reported to provide between two and three times higher welding speeds and filler metal deposition rates without the occurrence of defects such as undercut and humping.…”

Section: Techniques and Processes For Higher Welding Speedsmentioning

confidence: 99%

“…51,52 The process parameters of the trailing electrode are set to produce less severe welding conditions. In fact, there appears to be an optimal ratio between the power levels of the two GTAW electrodes, 18 the two GMAW electrodes [50][51][52] or between the two beams in the dual beam EBW 48 and dual beam LBW 27,28 welding processes.…”

Section: Techniques and Processes For Higher Welding Speedsmentioning

confidence: 99%

See 3 more Smart Citations

High speed fusion weld bead defects

Nguyen¹,

Weckman²,

Johnson³

et al. 2006

Science and Technology of Welding and Joining

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A comprehensive survey of high speed weld bead defects is presented with strong emphasis on the formation of humping and undercutting in autogenous and non-autogenous fusion welding processes. Blowhole and overlap weld defects are also discussed. Although experimental results from previous studies are informative, they do not always reveal the physical mechanisms responsible for the formation of these high speed weld bead defects. In addition, these experimental results do not reveal the complex relationships between welding process parameters and the onset of high speed weld bead defects. Various phenomenological models of humping and undercutting have been proposed that were based on observations of events in different regions within the weld pool or the final weld bead profile. The ability of these models to predict the onset of humping or undercutting has not been satisfactorily demonstrated. Furthermore, the proposed formation mechanisms of these high speed weld bead defects are still being questioned. Recent welding techniques and processes have, however, been shown to be very effective in suppressing humping and undercutting by slowing the backward flow of molten metal in the weld pool. This backward flow of molten weld metal may be the principal physical phenomenon responsible for the formation of humping and undercutting during high speed fusion welding.

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Section: Techniques and Processes For Higher Welding Speedssupporting

confidence: 91%

Section: Curved Wall Jet Modelmentioning

confidence: 99%

Section: Techniques and Processes For Higher Welding Speedsmentioning

confidence: 99%

Section: Techniques and Processes For Higher Welding Speedsmentioning

confidence: 99%

See 2 more Smart Citations

High speed fusion weld bead defects

Nguyen¹,

Weckman²,

Johnson³

et al. 2006

Science and Technology of Welding and Joining

View full text Add to dashboard Cite

show abstract

“…This high velocity, rearward directed flow of molten weld metal in the weld pool is consistent with numerical simulations by Beck et al 19 and observations in tandem EBW by Arata and Nabegata. 20 As indicated by the height of the swelling in Fig. 5, the molten weld metal must have a high surface tension to contain a large amount of metal within the swelling.…”

Section: Resultsmentioning

confidence: 99%

The humping phenomenon during high speed gas metal arc welding

Nguyen¹,

Weckman²,

Johnson³

et al. 2005

Science and Technology of Welding and Joining

121

118

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A commonly observed welding defect that characteristically occurs at high welding speeds is the periodic undulation of the weld bead profile, also known as humping. The occurrence of humping limits the range of usable welding speeds in most fusion welding processes and prevents further increases in productivity in a welding operation. At the present time, the physical mechanisms responsible for humping are not well understood. Thus, it is difficult to know how to suppress humping in order to achieve higher welding speeds. The objectives of this study were to identify and experimentally validate the physical mechanisms responsible for the humping phenomenon during high speed gas metal arc (GMA) welding of plain carbon steel. A LaserStrobe video imaging system was used to obtain video images of typical sequences of events during the formation of a hump. Based on these recorded video images, the strong momentum of the backward flow of molten metal in the weld pool that typically occurred during high speed welding was identified as the major factor responsible for the initiation of humping. Experiments with different process variables affecting the backward flow of molten weld metal were used to validate this hypothesis. These process variables included welding speed, welding position and shielding gas composition. The use of downhill welding positions and reactive shielding gases was found to suppress humping and to allow higher welding speeds by reducing the momentum of the backward flow of molten metal in the weld pool. This would suggest that any process variables or welding techniques that can dissipate or reduce the momentum of the backward flow of molten metal in the weld pool will facilitate higher welding speeds and productivity.

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Comparison of a laboratorial scale synthesized and a commercial yttria‐tetragonal zirconia polycrystals ceramics submitted to microwave sintering

Ribeiro

Arata

Lima

et al. 2019

Int J Applied Ceramic Tech

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Conventional sintering techniques of yttria‐tetragonal zirconia polycrystals (Y‐TZP) ceramics have presented limitations regarding the sintering time and temperature, increasing the cost of the final dental and biomedical products. Herein, microwave sintering comes to be an interesting alternative by providing fast heating, high densification, and grain‐size control. The aim of this study was to compare the effect of microwave sintering of Y‐TZP dental ceramics prepared from a pre‐sintered commercial block and produced from powders synthesized in a laboratorial scale by the precipitation route. The synthetized and commercial discs were submitted to microwave sintering at 1450°C and 1350°C for 15, 30, and 60 minutes. Densification, fracture toughness, grain size, and crystalline phase quantification of the sintered groups were evaluated. Both synthetized and commercial groups sintered at 1450°C for 15 and 30 minutes showed the higher densification results (98% TD). XRD quantitative phase analysis indicates that samples present 89% tetragonal and 11% cubic phases, except for the group prepared from coprecipitated powders sintered at 1450°C for 30 minutes, that presented 79% and 21% of tetragonal and cubic phases. The microwave sintering at 1450°C allows hardness and fracture toughness values comparable to conventional sintering.

show abstract

Degradação a baixa temperatura da Y-TZP odontológica: análise microestrutural e avaliação das propriedades mecânicas

Cited by 4 publications

References 49 publications

High speed fusion weld bead defects

High speed fusion weld bead defects

The humping phenomenon during high speed gas metal arc welding

Comparison of a laboratorial scale synthesized and a commercial yttria‐tetragonal zirconia polycrystals ceramics submitted to microwave sintering

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