Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing

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Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing C. KO¨RNER, M. RAMSPERGER, C. MEID, D. BU¨RGER, P. WOLLGRAMM, M. BARTSCH, and G. EGGELER Currently, additive manufacturing (AM) experiences signiﬁcant attention in nearly all industrial sectors. AM is already well established in ﬁelds such as medicine or spare part production. Nevertheless, processing of high-performance nickel-based superalloys and especially single crystalline alloys such as CMSX-4 is challenging due to the diﬃculty of intense crack formation. Selective electron beam melting (SEBM) takes place at high process temperatures (~ 1000 C) and under vacuum conditions. Current work has demonstrated processing of CMSX-4 without crack formation. In addition, by using appropriate AM scan strategies, even single crystals (SX SEBM CMSX-4) develop directly from the powder bed. In this contribution, we investigate the mechanical properties of SX SEBM CMSX-4 prepared by SEBM in the as-built condition and after heat treatment. The focus is on hardness, strength, low cycle fatigue, and creep properties. These properties are compared with conventional cast and heat-treated material. https://doi.org/10.1007/s11661-018-4762-5 The Author(s) 2018

I.

INTRODUCTION AND MOTIVATION

CMSX-4 is a second generation single crystalline superalloy containing 3 wt pct Re with a c’ volume content of about 70 pct.[1,2] Processing of these kinds of single crystalline alloys is usually by investment casting applying directional solidiﬁcation.[3] Typically, this class of alloys shows strong segregations during solidiﬁcation resulting in pronounced dendritic microstructures.[4] Thus, great eﬀorts with respect to the casting process as well as the successive heat treatments have been undertaken to homogenize the microstructure in order to improve high-temperature properties.[3,5] Generally, single crystalline components evolve from a starter block superimposed on a cooled copper chill plate combined with a spiral grain selector. The role of the chill plate is to generate a high number of grain nuclei. During solidiﬁcation within the starter block, favorably oriented grains with respect to the direction of C. KO¨RNER and M. RAMSPERGER are with the Department Materials Science, Friedrich-Alexander-Universita¨t ErlangenNu¨rnberg, Martensstr. 5, 91058, Erlangen, Germany. Contact e-mail: [email protected] C. MEID and M. BARTSCH are with the Institute of Materials Research, German Aerospace Center, Linder Ho¨he, 51147, Cologne, Germany. D. BU¨RGER, P. WOLLGRAMM and G. EGGELER are with the Institute for Materials, RuhrUniversita¨t Bochum, Universita¨tsstr. 150, 44801, Bochum, Germany. Manuscript submitted March 14, 2018.

METALLURGICAL AND MATERIALS TRANSACTIONS A

the temperature gradient prevail. The following helix has the task to select one of these already oriented grains. Ideally, only one grain remains after passing the spiral grain selector.[6] Additive manufacturing (AM) is an upcoming technology that is getting more an

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