On the origin of sliver defects in single crystal investment castings

Aveson, J.W.; Tennant, P.A.; Foss, Benjamin; Shollock, Barbara A.; Stone, H.J.; D’Souza, N.

doi:10.1016/j.actamat.2013.04.071

Cited by 74 publications

(42 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is arguably the mechanism underlying the similar misorientation patterns measured by EBSD by Newell et al [7,8]. Furthermore, it has recently been concluded elsewhere that sliver defects are a result of bending moments arising on dendrites from differential thermal contraction between mould and metal [4]. The direct observation of dendrite showing cantilever behaviour in the same alloy under similar processing conditions supports this conclusion.…”

Section: Discussionsupporting

confidence: 74%

“…By applying a rotation about the cross product of the primary axes of the seed and the measurement, such that they are brought to co-incidence, the secondary angle -the torsion angle -can be calculated. The detailed mathematics of the operation are given in Reference [4]. Figure 4 shows the results of the DIC analysis performed on a sequence of radiographs taken during solidification.…”

Section: Methodsmentioning

confidence: 99%

“…a Corresponding author: j.aveson@fnc.co.uk They found that sliver grains emanated from constricted channels that were designed to act as simplified grain selectors [3]. Investigations using finite element modelling and electron microscopy identified that the sliver defects formed at regions of high stress during solidification, and that the oxide defects found played no role [4].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Origins of misorientation defects in single crystal castings: A time resolved in situ synchrotron X-ray radiography study

Aveson

Reinhart

Nguyen-Thi

et al. 2014

MATEC Web of Conferences

Self Cite

View full text Add to dashboard Cite

Abstract. The presence of grain boundaries in single crystal castings is intolerable owing to the detrimental impact on creep and fatigue behaviour. Whilst the origins of many defects such as freckles have been understood since the 1970s, other defects such as slivers, or indeed the small mosaicity observed in many castings have eluded comprehensive treatments. In the present work, in situ X-ray imaging has been used to examine the origin of misorientation defects that arise during solidification. Dendrite deformation was observed, which impacted growth characteristics and led to a permanent misoriention. Digital image correlation analysis showed the dendrites becoming increasingly bent as solidification progressed. In order to probe the deformation modes further, a method was devised to convert standard EBSD data into measurements of bending and torsion angle. It was demonstrated that such defects form as the result of bending moments arising from differential thermal contraction and gravity.

show abstract

Section: Discussionsupporting

confidence: 74%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Origins of misorientation defects in single crystal castings: A time resolved in situ synchrotron X-ray radiography study

Aveson

Reinhart

Nguyen-Thi

et al. 2014

MATEC Web of Conferences

Self Cite

View full text Add to dashboard Cite

show abstract

“…Figure 3 shows SEM images of the boundary layers detected in several different surface defect grains which formed during solidification of turbine blades. [9,[18][19][20][21] The layer was also visible at the boundary of the matrix grain and a stray grain found on a shroud region ( Figure 3 . It should be emphasized that the layer is also found even in grain boundaries with low angles of mismatch ( Figure 3(d)) where the mis-orientation angle between the adjacent grains was measured using a reflected Laue X-ray system at 6.1 deg.…”

Section: Methodsmentioning

confidence: 99%

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

Kim

Withey

2017

Metall Mater Trans A

View full text Add to dashboard Cite

The boundary region formed on the surface of nickel-based single-crystal turbine blades was investigated by high-resolution microscopy observation. There was a distinguishable intermediate layer with the size of about 2 to 5 lm between the matrix and surface defect grains such as stray grains, multiple grains, freckle grains, and even low-angle grain boundaries which were formed during the solidification of turbine blades. The intermediate layer was composed of many elongated c¢ as well as c phases. In addition, only one side of the intermediate layer was coherent to the matrix grain or defect grain due to good orientation match. At the coherent interface, the c¢ (as well as c) phase started to extend from the parent grain and coincidently, rhenium-rich particles were detected. Furthermore, the particles existed within both elongated gamma prime and gamma phases, and even at their boundary. Based on experimental observations, the formation mechanism of this intermediate layer was discussed.

show abstract

“…It is well known that the freckle chains are caused by double diffusive convection of solute-enriched interdendritic liquid in the mushy zone during solidi cation 42) , and the resultant defect arises from dendrite fragmentation through remelting which is driven by convection in the interdendritic channels 43) . In addition, it is also known that there is a strong correlation between the level of refractory alloying additions, such as Mo, Hf, Ta, W and Re in CMSX-10 in this study, and the occurrence of the freckle chains 44) .…”

Section: Detection Of Re-rich Particles At Freckle Chainsmentioning

confidence: 99%

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Kim

Withey

2016

Mater. Trans.

View full text Add to dashboard Cite

Ni-base single crystal superalloy turbine blades containing defect grains were investigated by high resolution electron microscopy. Several different types of defects, such as, stray grains, equiax grains and freckle chains which formed during casting, and recrystallized grains which formed during subsequent heat treatment, were selected. Regardless of the region of the turbine blade, many particles with large amounts of rhenium were detected at the boundary of the stray grain and matrix. The Re-rich particles were also detected at the boundary of the matrix and other defect grains, such as, equiax grains and freckle chain grains, and even at a low angle grain boundary. However, the boundary of the recrystallised grain and matrix which was formed after solution heat treatment showed just one Re-rich particle. Also, the composition of these Re-rich particles is different from any topologically close packed phases which have been reported in Ni-base superalloys. The results suggest that during solidi cation, the particles are formed from the melt and pushed ahead of each solidi cation front of the defect grain and the matrix, and piled up at the boundary of the matrix/defect grain.

show abstract

On the origin of sliver defects in single crystal investment castings

Cited by 74 publications

References 39 publications

Origins of misorientation defects in single crystal castings: A time resolved in situ synchrotron X-ray radiography study

Origins of misorientation defects in single crystal castings: A time resolved in situ synchrotron X-ray radiography study

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Contact Info

Product

Resources

About