Tracking pores during solidification of a Ni-based superalloy using 4D synchrotron microtomography

Abstract

Time-resolved in situ microtomography is employed to track the nucleation and growth of individual pores during solidification of a commercial nickel-based superalloy. Three cooling rates (0.1, 0.5 and 1°C/s) are investigated to evaluate the effect of this key processing parameter on the formation of porosity. Phase contrast obtained with a coherent X-ray beam is used to visualize the evolution of dendritic structures in absence of a sufficient absorption contrast. Two mechanisms leading to shrinkage pores have been identified. The first mechanism (mechanism A) is associated with the coalescence of secondary dendrite arms at temperature during the early stages of solidification. The second mechanism (mechanism B) is related to insufficient liquid feeding in the interdendritic region during the last stages of solidification, at lower temperatures. A variation of cooling rate by a factor 2 does not affect the nucleation rate of pores generated through mechanism B. However, it seems to affect the nucleation rate of small pores obtained through the mechanism A. The kinetics of growth for the majority of individual pores can be described using an exponential-like function. This kinetics is faster for mechanism B compared to mechanism A.

Very high cycle fatigue durability of an additively manufactured single-crystal Ni-based superalloy

“…pores having a ≈ 1.7 µm average diameter size [24,25], which contrasts with the Bridgman method that results in solidification pores of up to 200 µm after the complete solution heat treatment (SHT) for this alloy [28]. processed by PBF-E after standard heat treatment and (g) after HIP treatment.…”

Duplex Nucleation and Its Effect on the Grain Size and Properties of Near Eutectic Al-Si Alloys

“…For the sake of studying the effect of Al-2Ti-0.5B-0.5C master alloy on the near-eutectic Al-Si alloy, the three-dimensional structure of B1 and B4 alloy was tested by microscopic CT, as shown in Figure 10 . Meanwhile, software was used to calculate the characteristic values of the three-dimensional structure constructed by the alloy phase and eutectic silicon [ 30 , 31 , 32 ], the calculation results were shown in Table 2 . Compared with 12.24% of the original alloy, the connectivity rate is increased by 58.3%, which indicates that the alloy phase and eutectic silicon are connected more closely after the addition of Al-2Ti-0.5B-0.5C master alloy.…”

X‐ray Tomography and Tomoscopy on Metals: A Review

“…[316,317] For this purpose, digital volume correlation [318][319][320] and particle tracking methods have been developed in the past decade. [321,322] Nevertheless, the actual trend focuses on machine learning tools. Strohmann et al used a convolutional neural network for the segmentation of phases in AlSi alloys.…”