Samuel Bogner

Comparative Investigation of the Downward and Upward Directionally Solidified Single-Crystal Blades of Superalloy CMSX-4

Single-crystal blades of Ni-base superalloys CMSX-4 have been directionally solidified using the downward directional solidification (DWDS) process. The possible benefits of the process were comparatively evaluated with respect to the Bridgman process’ results. The DWDS process exhibits good capabilities for casting the single-crystal components. The thermal gradients of this process are approximately seven times higher than those of the Bridgman process. It provides more advantages for solidifying the single-crystal superalloy blades by reducing the casting defects, refining the microstructure, decreasing the size of the γ/γ′ eutectic pools, refining the γ′ precipitates, alleviating the degree of the microsegregation, and minimizing the size and volume fraction of the micropores.

Microstructure of a eutectic NiAl—Mo alloy directionally solidified using an industrial scale and a laboratory scale Bridgman furnace

Abstract The eutectic NiAl-9Mo (at.%) alloy was directionally solidified using an industrial scale Bridgman furnace and using a liquid metal cooling Bridgman furnace to produce in-situ composites of aligned Mo fibers in an NiAl matrix. In the first part of the experiment, an investment casting shell mold system, produced for NiAl alloys, was used and investigated for the NiAl-9Mo alloy in the industrial scale furnace. Due to the lower temperature gradient of ∼2.8 K mm−1, the microstructure of the samples was dendritic. In the second part of the experiment, samples with well aligned Mo fibers were produced in the laboratory Bridgman furnace using a temperature gradient of ∼11 K mm−1 and growth rates of 0.33–0.66 mm min−1.

Microstructural evolution of aluminium-copper alloys during the downward directional solidification process

Abstract The microstructural evolution of Al–Cu alloys during the downward directional solidification process was investigated. At the planar-to-cellular transformation point, the planar liquid/solid (L/S) interface broke down at the centre. This was contrasted with the behaviour in the liquid metal cooling process, where the interface broke down at the periphery. The critical withdrawal rate at this point was higher than the theoretical value. In addition to this, the variation in the primary dendrite arm spacing (λ1) as a function of the withdrawal rate (V) at constant GL for the Al-2.0 wt.% Cu alloy agreed with the conventional processes. The comparison of λ1 in our experiment to the calculated value λ1 using the Kurz–Fisher, Ma and Trivedi models showed that λ1, calculated by these models, overvalued our experimental results. However, the λ1 calculated from the Hunt model agreed well with the experimental values of λ1. When we reduced the diameter of the sample from 13 mm to 9 mm and maintained the other parameters constant, the L/S interface retained a planar shape. This indicated that the L/S interface was more stable in the smaller sample than that in the larger. This result contrasted with the result in the liquid metal cooling process.