Microstructural Investigations of Ni-Based Superalloys by Directional Solidification Quenching Technique

Abstract

The improvement of the mechanical properties of Ni-based superalloys is achieved in most cases by modifying the chemical composition. Besides that, the processing can be modified to optimize the as-cast microstructure with regard to the mechanical properties. In this context, the present study highlights the solidification mechanism of several Ni-based superalloys by conducting experiments using a modified, laboratory-scale Bridgman-Stockbarger furnace. In that context, the single-crystal rods are partially melted, directionally solidified and quenched sequentially. Several characterization methods are applied to further analyze the influence of the alloying elements and the variation of the withdrawal rate on the as-cast microstructure. Four stages of solidification are distinguished whereby the morphology observed in the different stages mainly depends on the cooling rate and the local concentration of the carbide forming elements. The effect of carbide precipitation and the effect on the as-cast microstructure is investigated by employing energy dispersive X-ray spectrometry (EDX) and electron backscatter diffraction (EBSD) analysis techniques. A local polycrystalline structure is observed in the single-crystal system as consequence of the influence of the carbon content and the cooling rate. The present work aims to develop strategies to suppress the formation of the polycrystalline structure to maintain the single-crystal microstructure.

Prediction of creep deformation based on the Zc parameter method

“…in wt.%) have better mechanical properties due to eliminated transverse grain boundaries and are widely used in the manufacture of advanced aeroengine blade components. [24][25][26] The constant load creep tests are carried out using the RSW-500 creep test machine, and the temperature difference in the furnace does not exceed ±2 C. The creep specimen size is Φ5 Â 25 mm. Creep tests were conducted at temperatures ranging from 900 C to 980 C and stresses ranging from 130 to 300 MPa, as shown in Figure 1.…”

“…Directionally solidified nickel‐based alloys (composition of Cr: 13.4–14.1, Co: 9.0–10.0, Ti: 4.7–5.1, Al: 2.8–3.3, W: 4.1–4.3, Mo: 1.3–1.7, Ta: 2.5–3.3, Ni: Bal. in wt.%) have better mechanical properties due to eliminated transverse grain boundaries and are widely used in the manufacture of advanced aeroengine blade components 24–26 …”

Influence of Process Parameter and Alloy Composition on Misoriented Eutectics in Single-Crystal Nickel-Based Superalloys

“…Up to three single-crystal cylindrical samples produced from the industrial Bridgman furnace (withdrawal rate 4 mm/min) were partially remelted and directionally solidified in the Bridgman–Stockbarger furnace from Linn High Therm GmbH (Hirschbach, Germany). The single-crystal structure was reproduced using the seeding technique, whose exact method has already been described in [ 18 ]. This process enabled investigations at higher temperature gradients and lower withdrawal rates compared with the industrial system.…”

The Effect of CoAl2O4 as a Nucleating Agent and Pouring Temperature on the Microstructure and Properties of Inconel 713C® Nickel-Based Superalloy Castings

“…To address this issue, castings generally are modified by adding refiners, which contain highly stable particles, or by introducing an inoculant to the prime coat of the ceramic mold [ 15 , 16 ]. Grain refinement in the primary microstructure is directly related to increased heterogeneous nucleation sites during solidification [ 17 ]. Introducing inoculants can make the microstructure more uniform.…”