Effects of withdrawal rate and starter block size on crystal orientation of a single crystal Ni-based superalloy

Rezaei, Mohammad Reza; Kermanpur, A.; Sadeghi, Fazlollah

doi:10.1016/j.jcrysgro.2017.12.040

Cited by 20 publications

(20 citation statements)

References 13 publications

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“…From the simulation and experimental results of Rezaei et al., it is evident that by increasing withdrawal rate, misorientation of columnar grains declines. A further increase in withdrawal rate results in highly misoriented grains which increases the chances of the misoriented grains entering the spiral.…”

Section: Resultsmentioning

confidence: 97%

“…The conventional view point about the spiral selector is that it only contributes to the grain selection. Its parameters do not optimize the crystal orientation, but the results of some authors reveal that a few of its parameters influence the deviation angle of the crystal. Most of the researchers find that deviation angles of 12°–15° are in the acceptable range .…”

Section: Introductionmentioning

confidence: 99%

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Grain Selection and Crystal Orientation in Single‐Crystal Casting: State of the Art

Raza

Wasim

Hussain

et al. 2019

Crystal Research and Technology

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The properties of single‐crystal superalloys depend highly upon crystallographic orientation and the selection of single crystal (SX) in directional solidification (DS) process. The assessment of SX selection and crystallographic orientation determines the mechanical properties of the casting. Generally, it is considered that the deviation from [001] orientation should be less than 10° for better mechanical properties. This article provides a quantitative literature review analyzing the experimental results of 30 papers that studied the effects of process parameters on crystal orientation and grain selection in SX‐casting process. Key parameters that control the SX casting during DS process include spiral selector parameters, starter block parameters, withdrawal rate, pouring temperature, and ceramic mold temperature. The analysis in this research provides a strong evidence to assist the standard operating range of each parameter. A lack of focus in the literature on alloys is found. A framework based on the key parameters is also proposed in this review.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Grain Selection and Crystal Orientation in Single‐Crystal Casting: State of the Art

Raza

Wasim

Hussain

et al. 2019

Crystal Research and Technology

View full text Add to dashboard Cite

show abstract

“…Third, conduction of the heat through the thickness of the shell mold led to increasing temperature of the ingot, melting it and reaching a suitable super heat. It had been stated that a heat balance was being established between the cold copper chill and hot melt above it prior to withdrawal initiation . The thermophysical properties of casting melt and mold materials are shown in Table and Figure .…”

Section: Methodsmentioning

confidence: 99%

“…Grain nucleation and growth parameters were assigned in the simulation model according to Table . These parameters were determined through extensive simulation runs under different process conditions as well as data in literature …”

Section: Methodsmentioning

confidence: 99%

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Optimizing Grain Selection Design in the Single‐Crystal Solidification of Ni‐Based Superalloys

Sadeghi

Kermanpur

Norouzi‬

2018

Crystal Research and Technology

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An attempt is made to model the design of grain selection during single‐crystal solidification of an Ni‐based superalloy by the Bridgman method. Various geometrical designs of the starter block and spiral grain selector are chosen and their effects on crystal orientation of the single‐crystal part are studied. The competitive grain selection is simulated utilizing the cellular automaton finite element module of the ProCAST software. The simulated results are validated against the experimental observation of grain structure along with the crystal orientation measured by the electron backscatter diffraction (EBSD) and rotational orientation X‐ray diffraction (RO‐XRD) techniques. The results show that in order to obtain the single crystal with a minimum deviation from longitudinal axis, the height and diameter of the starter block as well as the height and the take‐off angle of the spiral should be optimized. It is found that the diameter/height ratio of the starter block should be less than 0.6 to obtain a well‐oriented single crystal prior to entrance of solidification front into the spiral. The height of starter block is found to be more influential than its diameter in selecting the suitable single grain.

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Low Cycle Fatigue Failure Analysis of a Ni‐Based Single Crystal Superalloys at 850 °C

et al. 2018

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This paper presents a low cycle fatigue (LCF) failure analysis on [001], [011], and [111] orientations of a Ni‐based single crystal superalloys at 850 °C. Fracture mechanism and microstructure damage evolution are revealed through crystal plastic theory and fracture morphology analysis. Strain‐controlled LCF tests are conducted with the standard round bar samples; the fracture morphology and microstructure characteristics, such as the fracture mechanism and microstructure damage evolution, are observed via scanning electron microscopy (SEM), optical microscopy (OM). Crystal plastic theory is adopted to establish the crystal slip system framework, considering elastic and plastic strain rate, elastic orientation factors, and the resolved shear stress (Rss). The life prediction model is established based on Levkovitch damage theory, theoretical analysis, and test results has good consistency. The results demonstrate that fatigue life on [001] orientation is the longest, but considering the effects of stress amplitude and Young's modulus, [011] orientation exhibits the best fatigue performance. Under LCF loading, the initial crack starts to occur on surface of specimen if the internal defects are small and negligible; in contrast the initial crack starts to occur in subsurface or internal of specimen if the microstructure defects exist in material. The LCF cross‐section of SC belongs to the quasi‐cleavable type, the crack propagates in the direction of {111} plane and then extends along the vertical stress axis until the specimen fractures.

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Effects of withdrawal rate and starter block size on crystal orientation of a single crystal Ni-based superalloy

Cited by 20 publications

References 13 publications

Grain Selection and Crystal Orientation in Single‐Crystal Casting: State of the Art

Grain Selection and Crystal Orientation in Single‐Crystal Casting: State of the Art

Optimizing Grain Selection Design in the Single‐Crystal Solidification of Ni‐Based Superalloys

Low Cycle Fatigue Failure Analysis of a Ni‐Based Single Crystal Superalloys at 850 °C

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