Solutal partition coefficients in nickel-based superalloy PWA-1480

Abstract

Solutal profiles in dendritic single-crystal specimens of PWA-1480 nickel-base superalloy, which were directionally solidified and quenched, were examined on several transverse cross-sections to obtain the partition coefficients. Similar to their nickel-base binaries, the partition coefficients of tantalum, titanium, and aluminum were found to be less than unity; those of tungsten and cobalt were greater than unity. The partition coefficients were temperature independent in the range 1584-1608 K. The contribution of solid-state diffusion to microsegregation was observed to be negligible.

Solute Redistribution during Planar and Dendritic Growth of Directionally Solidified Ni-Base Superalloy CMSX-10

“…shown that the back-diffusion of Nb significantly decreased to be neglected when the cooling rate increases to 10 K/min. Tewari et al [17] have reported a similar result, that the contribution of back-diffusion to microsegregation is negligible for the elements Ta, Al, Ti, Co, and W, when the cooling rate is about 7.3 K/min in the Ni-base superalloy PWA-1480. In contrast to these studies, Thirumalai et al [14] have reported that their microsegregation results cannot be rationalized without acknowledging the occurrence of back-diffusion during directional solidification of the experimental Ni-base superalloy RR2100 at a cooling rate of 10 K/min ( G = 10 K/mm and R = 1.0 mm/min).…”

“…As shown in Table II, the solute elements with i < 1 are Cr, Mo, and γ′ forming elements such as Al, Ta, Ti, and Nb, Therefore, as the solidification proceeds, these elements are continually accumulated in liquid, and if the composition of solid at the S/L interface exceeds the solubility limit of primary γ, the eutectic reaction of L → γ + γ′ would occur. Generally, it has been known that the solidification of the advanced Ni-base superalloys completes with the formation of γ/γ′ eutectic [4,7,17,29,30].…”

“…f Another potential technique involves directional solidification of the alloy followed by quenching (DSQ) [16][17][18]. In this technique, the partition coefficient of each solute element at the solid/liquid (S/L) interface is measured by microprobe analysis and hence the extent of segregation can be estimated.…”

Microstructure of the Nickel-Base Superalloy CMSX-4 Fabricated by Selective Electron Beam Melting

“…Maximum build size of this system can be up to 200 9 200 9 350 mm 3 . We used a target operating temperature above 1223 K (950°C) and a constant layer thickness of 50 lm.…”

“…Typically, c stabilizers like the refractory metals W, Co, and Re segregate within dendrite core areas, whereas c¢ stabilizers like Al, Ti, and Ta accumulate within interdendritic areas. [3,4] Thus, the cubic c¢ precipitates are smaller within the dendritic core regions and become coarser near the interdendritic areas (eutectic regions) (Figure 1(c)) due to the increased amount of c¢ stabilizers. [5] Due to the inhomogeneous c¢-distribution and remaining c/c¢-eutectic, great efforts with respect to time-consuming heat treatments have been undertaken to homogenize the microstructure in order to improve the high-temperature properties.…”