The Control of Solidification of Ni‐Based Superalloy Single‐Crystal Blade by Mold Design Modification using Inner Radiation Baffle

Abstract

This work is focused on an investigation of the directional solidification process of CMSX‐4 single‐crystal blades in the mold modified by application of inner radiation baffle (IRB). Micro‐ and macrostructure examination is carried out along the height of single‐crystal blades which are manufactured using standard and modified mold, at the withdrawal rates of 3 and 5 mm min−1. It is established that application of modified mold allows better control over liquidus isotherm and leads to increase in temperature gradient, as compared to the manufacturing of blades using standard mold. The average value of temperature gradient in airfoil increases from 14 up to approx. 30 K cm−1 and from 16 up to approx. 40 K cm−1, for withdrawal rate of 5 and 3 mm min−1, respectively. The curvature of liquidus isotherm diminishes and attains near‐flat profile along the airfoil for both values of withdrawal rate. The application of proposed technique results in reduction of primary dendrites arm spacing (PDAS) particularly in the inner and middle part of the blade. PDAS reaches average value of approx. 360 μm for withdrawal rate of 5 mm min−1 and is lower as compared to the standard mold casting withdrawn at the rate of 3 (433 μm) and 5 mm min−1 (468 μm).

Application of Inner Radiation Baffles in the Bridgman Process for Flattening the Temperature Profile and Controlling the Columnar Grain Structure of Directionally Solidified Ni-Based Superalloys

“…The measured cooling curves were then compared with the predicted ones (Figure 3a). In that way, the values of thermophysical properties of the materials and boundary conditions used in numerical simulations were verified in the investigations, as well as in the previously conducted studies [9,13,31]. Good agreement of the predicted and measured temperature distribution versus time was found at points from one to five of the casting manufactured using AERB (Figure 3a).…”

“…In the following section of the article, this part is called the adjusted external radiation baffle (AERB). The schematic image of the furnace with AERB was shown in earlier works [13,31], and, in the present study, is shown in Figure 2a,d. The mold was preheated to the temperature of 1520 °C, and then the molten CMSX-4 Ni-based superalloy of the same temperature was poured into the cavity.…”

“…The temperature of the mold and that of the molten alloy, as well as the withdrawal rate, were assumed the same as in the experiments. The boundary condition (interface heat transfer coefficient h) and thermophysical properties of CMSX-4 Ni-based superalloy, ceramic mold, thermal insulation, radiation baffle, as well as their emissivity ε , were chosen based on the research conducted by Szeliga et al [13,31] (Figure 2). These values have been carefully verified in the previous studies by comparing a large number of experimental cooling curves with the predicted ones [13,31].…”

“…Another approach to control the solidification of single crystal platform and whole blades with the use of so-called inner radiation baffles (IRBs) have been recently developed by the authors [31,32]. It was found that the modification of the mold design by placing the IRBs between the blades and the central rod significantly reduced the curvature of liquidus isotherm and increased the temperature gradient along the single crystal component compared with the standard Bridgman process [31,32]. Due to the promising results previously obtained and lack of information in the literature about this technique, an attempt was made to control the directional solidification of casting with columnar grain structure using the IRBs.…”

The Effect of Withdrawal Rate on Crystal Structure Perfection, Microstructure and Creep Resistance of Single Crystal Castings Made of CMSX-4 Nickel-Based Superalloy

“…In most cases, it is the [001] direction, in order to provide high creep resistance. Therefore, creep behavior of a single crystal is determined by its structure perfection [1,2,3,4,5,6].…”