Welding of nickel base superalloy single crystals

David, S. A.; Vitek, J.M.; Babu, S. S.; Boatner, L. A.; Reed, R. W.

doi:10.1179/136217197789832880

Cited by 22 publications

(29 citation statements)

References 10 publications

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“…Solidification cracks have long been associated with SG formation. [6,10] This type of weld defect can effectively be prevented in SX weld passes if SGs are avoided. A thorough discussion of solidification cracking is provided in a separate article.…”

Section: Type 3: Root Sgsmentioning

confidence: 99%

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Stray Grain Formation in Welds of Single-Crystal Ni-Base Superalloy CMSX-4

Anderson

DuPont

DebRoy

2009

Metall Mater Trans A

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Autogenous welds on the single-crystal (SX) alloy CMSX-4 were prepared over a wide range of welding parameters and processes to investigate the formation and behavior of stray grains (SGs). The quantity and location of SGs in the welds were analyzed by orientation imaging microscopy (OIM). Heat-and fluid-flow modeling was conducted to understand the influence of welding parameters on the local solidification conditions and resultant SG formation tendency.The results indicate that constitutional supercooling and SG formation are generally reduced in low-power, high-travel-speed welds. Because of the complex effect of travel speed on temperature gradient and solidification velocity, the worst conditions for SG formation in alloy CMSX-4 for the conditions examined here occur at intermediate travel speeds of~6 mm/s. These findings were corroborated with heat-transfer/fluid-flow modeling simulations that were coupled with SG predictions. These calculations also indicate that SG formation will be greatest where different regions of dendrite growth intersect, due to the so-called off-axis heat flow. For a given set of welding conditions, the amount of SGs will also vary with substrate orientation. This effect is attributed to differences in the number and location of dendrite growth intersection regions within the melt pool that occur with changes in substrate orientation.

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Section: Type 3: Root Sgsmentioning

confidence: 99%

“…Vitek et al [6,7] expanded upon the work of Rappaz, and showed that all of the central features of SX solidification were present in SX Ni-base superalloy welds. The theory of constitutional supercooling was used to describe the formation of equiaxed grains as a function of solidification conditions.…”

Section: Introductionmentioning

confidence: 99%

Stray Grain Formation in Welds of Single-Crystal Ni-Base Superalloy CMSX-4

Anderson

DuPont

DebRoy

2009

Metall Mater Trans A

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“…As welding of directionally solidified (DS) precipitation-hardened nickel-base superalloys containing a large volume fraction of c¢ phase is generally found to be more difficult and complex than that of the CC alloys, [5][6][7][8] the welding problems of a DS IN738 component might become even more severe than those experienced during welding and during postweld heat treatment of a CC IN738 turbine component. [9][10][11][12] The sensitivity to weld cracking could be aggravated due to a coarse microstructure and a severe elemental segregation in DS cast IN738 because of a rather high concentration of alloying elements in it.…”

Section: Introductionmentioning

confidence: 99%

Microstructural Analysis of Laser-Beam-Welded Directionally Solidified INCONEL 738

Sidhu

Ojo

Chaturvedi

2007

Metall Mater Trans A

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The laser welding of a directionally solidified INCONEL 738 superalloy (DS IN738) was investigated. Microstructural analysis of the fusion zone (FZ) and the heat-affected zone (HAZ) revealed that cracking occurred mainly in HAZ with only some cracks being extended into the FZ. However, the frequently observed centerline cracking in FZ of DS and single crystal (SX) alloys did not occur, which was attributed to the presence of negligible volume fraction of c-c¢ eutectic in FZ. Constitutional liquation of secondary solidification constituents (MC carbides, M 3 B 2 borides, M 2 SC sulphocarbides, and c-c¢ eutectic) and c¢ precipitate particles was found to be the major cause of grain boundary liquation and the resultant intergranular microfissuring in the HAZ. The extent of HAZ microfissuring was, however, observed to be smaller in samples welded along the transverse direction (perpendicular to solidification direction) than when welding was done along the longitudinal direction (solidification direction). Nonetheless, more severe HAZ cracking occurred in samples of similarly welded conventionally cast (CC) alloy, and the present results indicate that the severity of HAZ liquation cracking in IN738 superalloy can be reduced by using a DS version of the alloy.

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“…When one of the easy growth directions coincides with the heat flow direction, growth conditions are optimum [26]. For this reason, among the randomly oriented grains, those grains that have one of their <100> crystallographic axis mostly aligned with the heat flow direction will be favored [27]. Furthermore, SLM is a multi-line based technology in every CAD slice layer, the moving heat resource controlled by a complex scan path can easily induce a very complicated heat diffusion process, thereby a varied heat transfer direction.…”

Section: Scan Directionmentioning

confidence: 99%

The key metallurgical features of selective laser melting of stainless steel powder for building metallic part

Shi

Wang

et al. 2011

Powder Metall Met Ceram

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UDC 621.762 316L stainless steel parts are manufactured via selective laser melting. The investigation into the main characteristics and metallurgical mechanisms of selective laser melting process are highlighted in this work. The morphologies, microstructures and elemental compositions of as received scan tracks and samples are detected through optical microscope, SEM and energy dispersive X-ray spectroscopy respectively. The morphology of melted track exhibits scaly figures from top view, which is similar to welding process. The central zone of melted track shows a cellular microstructure while the edge zone of molten pool represents a columnar structure, which is caused by the heat transfer process. The surface morphology of SLM part in low magnification can show multi-lined feature, and the surface morphology in high magnification can reflect the solidification and crystallization process. Moreover, a little amount of oxide and splash with balling effect can also be found on the SLM part surface. The microstructure of SLM part is extremely fine coupled with multiple crystal directions. The very fine crystal structure is caused by the extraordinarily rapid cooling and the multiple crystal directions are due to the variable heat transfer direction. The element distribution is homogeneous and no elemental aggregations can be found. The metallurgical mechanisms for the above characteristics are also addressed.

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Welding of nickel base superalloy single crystals

Cited by 22 publications

References 10 publications

Stray Grain Formation in Welds of Single-Crystal Ni-Base Superalloy CMSX-4

Stray Grain Formation in Welds of Single-Crystal Ni-Base Superalloy CMSX-4

Microstructural Analysis of Laser-Beam-Welded Directionally Solidified INCONEL 738

The key metallurgical features of selective laser melting of stainless steel powder for building metallic part

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