Abstract
A duplex, nano-scale Co-free High Entropy Alloy (HEA) based on AlCrFe2Ni2 was processed by means of Laser Metal Deposition (LMD). Process parameters in various beam diameter configurations as well as deposition strategies were developed while the alloy microstructure was investigated in as-built and heat treated condition. Interlayer regions present a duplex microstructure composed of ultra-fine FCC-platelets nucleated in nano-scale structured BCC phase. Rapid cooling during LMD induces the decomposition of the BCC phase into ordered and disordered nano-scaled structures. The hard and brittle BCC phase yields a high crack susceptibility during rapid cooling in the LMD-process. A suitable processing strategy paired with a post-processing heat treatment was developed to solve this challenge. After heat treatment at 900°C and 6 hours annealing time with subsequent furnace cooling, the material presented a homogeneous duplex ultra-fine FCC/BCC microstructure and high flexural strength values (2310 MPa) compared to a heat treated cast duplex-steel (1720 MPa), while maintaining excellent ductility (no failure at 14% bending).
Highlights
The concept of “high-entropy alloys (HEAs)” has been a breakthrough in the field of alloy development (Yeh et al, 2004)
After heat treatment, a homogenization of the microstructure throughout the samples was observed in both 0.6 and 1.8 mm samples resulting in a duplex microstructure with a phase content of 46% vs. 53% for FCC/BCC-phases, respectively
The novel Al9Cr17Fe36Ni38 HEA produced my means of LMD presents, in heat-treated condition, an over 50% increase in strength compared to a DIN-St.1.4517 duplex steel, while maintaining similar ductility
Summary
The concept of “high-entropy alloys (HEAs)” has been a breakthrough in the field of alloy development (Yeh et al, 2004). Various HEA-materials reportedly exhibit both high-strength and ductility as well as good corrosion and wear resistance in cast parts (Chuang et al, 2011; Shi et al, 2017; Chen et al, 2018; Niu et al, 2019) These materials hold great potential for the fabrication of parts, such as pump impeller blades, subject to complex stresses (Ma et al, 2016; Yan-dong et al, 2017; Yin et al, 2017). The presence of an intra-granular (spinoidal) decomposition of the BCC-Matrix into BCC/B2 was found for x = 0.2 and 0 Another Co-free HEA, namely AlCrFe2Ni2 was proposed by Dong et al (2016), which presents a microstructure consisting of spinoidally decomposed B2/BCCphase and an FCC-phase (Shang and Wang, 2017). A near- AlCrFe2Ni2 alloy with a chemical composition of Al9Cr17Fe36Ni38 (wt.%) was selected for fabrication with LMD to examine the microstructure and material behavior in the as-built and heat-treated condition
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