Manufacturing Of High-Entropy Alloys Research Articles

Additive manufacturing of Fe28.2Mn32.9Ni18.8Cr6Al14.1 high-entropy alloy by applying consumable fillers of metal powders and polyvinyl alcohol

Simultaneous application of welding methods and metal additive manufacturing facilitates the production of various 3D physical samples from metals and alloys. One of the technical impediments, especially for additive manufacturing of high entropy alloys, is the variety of elements in their chemical composition that makes the fabrication of fillers in welding methods very challenging. In the present research, the additive manufacturing of Fe28.2Mn32.9Ni18.8Cr6Al14.1 high entropy alloy with the use of consumable fillers, including metal powders and polyvinyl alcohol binder through gas tungsten arc welding process has been investigated. To perform the gas tungsten arc welding process, the experiments were designed using the Taguchi method. The parameters of current, torch angle, torch speed, and substrate temperature were selected as the input parameters. Then, through Grey analysis, the optimum width and height of the weld bead were determined to deposit thin layers with high height and low width. The results of the experiments confirmed that the proposed method for fabricating consumable fillers successfully performed layer-by-layer deposition of the sample using the gas tungsten arc welding process. Moreover, the elemental mapping images proved the presence of all elements in the Fe28.2Mn32.9Ni18.8Cr6Al14.1 sample. Furthermore, no internal voids were detected upon inspection of the fabricated sample using a micro-computed tomography scanner.

High-strength Fe32Cr33Ni29Al3Ti3 fabricated by selective laser melting

Additive manufacturing of high entropy alloys (HEAs) has attracted increasing interest. A high-strength Co-free HEA with eutectic structure was developed using selective laser melting (SLM) technology in this work. This material shows excellent mechanical properties over a wide temperature range, from 25 °C to 500 °C, owing to its ultra-fine eutectic cellular structure with BCC phase wrapped by FCC phase. Specifically, the Co-free HEA exhibits a room temperature tensile strength exceeding 1200 MPa, and a yield strength of more than 880 MPa. The strength results of this Co-free HEA represent a significant improvement compared to other Co-free HEAs or middle entropy alloys (MEAs) manufactured using SLM. Given their low cost, Co-free HEAs are highly promising for commercial large-scale applications, and this research suggests that this high-strength Co-free HEA with eutectic structure may have particular value in SLM manufacturing mold applications.

Additive Manufacturing of High Entropy Alloys: Trends, Challenges and Future Perspectives

Additive Manufacturing of High Entropy Alloys: Trends, Challenges and Future Perspectives

Recent Advances in Additive Manufacturing of High Entropy Alloys and Their Nuclear and Wear-Resistant Applications

Alloying has been very common practice in materials engineering to fabricate metals of desirable properties for specific applications. Traditionally, a small amount of the desired material is added to the principal metal. However, a new alloying technique emerged in 2004 with the concept of adding several principal elements in or near equi-atomic concentrations. These are popularly known as high entropy alloys (HEAs) which can have a wide composition range. A vast area of this composition range is still unexplored. The HEAs research community is still trying to identify and characterize the behaviors of these alloys under different scenarios to develop high-performance materials with desired properties and make the next class of advanced materials. Over the years, understanding of the thermodynamics theories, phase stability and manufacturing methods of HEAs has improved. Moreover, HEAs have also shown retention of strength and relevant properties under extreme tribological conditions and radiation. Recent progresses in these fields are surveyed and discussed in this review with a focus on HEAs for use under extreme environments (i.e., wear and irradiation) and their fabrication using additive manufacturing.

Tribo-corrosion response of additively manufactured high-entropy alloy

High-entropy alloys (HEAs) with multiple principal elements represent a paradigm shift in structural alloy design and show excellent surface degradation resistance in corrosive environment. Here, the tribo-corrosion response of laser-engineered net-shaped CoCrFeMnNi HEA was evaluated in 3.5 wt% NaCl solution at room temperature. The additively manufactured (AM-ed) CoCrFeMnNi showed five times lower wear rate, regenerative passivation, and nobler corrosion potential during tribo-corrosion test compared to its arc-melted counterpart. A significant anisotropy was seen in the tribo-corrosion response with 45° to the build direction showing better performance compared to tests along the build direction and perpendicular to it. The open circuit potential curves were characterized by a sharp drop to more negative values as wear began, followed by continuous change for the active tribo-corrosion duration and finally a jump to nobler value at the end of the test indicating excellent surface re-passivation for the AM-ed alloy. The superior tribo-corrosion resistance of AM-ed CoCrFeMnNi was attributed to the refined microstructure and highly protective surface passivation layer promoted by the sub-grain cellular structure formed during additive manufacturing. These results highlight the potential of utilizing additive manufacturing of HEAs for use in extreme environments that require a combination of tribo-corrosion resistance, mechanical durability, extended service life, and net shaping with low dimensional tolerance.

On the development of pseudo-eutectic AlCoCrFeNi2.1 high entropy alloy using Powder-bed Arc Additive Manufacturing (PAAM) process

A new Powder-bed Arc Additive Manufacturing (PAAM) processing which includes on-line remelting of deposited material has been developed for the manufacturing of high entropy alloys (HEAs) based on an existing AlCoCrFeNi2.1 pseudo-eutectic system. The remelting process is typically applied in the arc melting process to improve the homogeneity of prepared material. We investigated the microstructure and mechanical properties of produced AlCoCrFeNi2.1 HEA after applying a remelting process (1, 3, and 6 times) on each deposited layer. The results show the formation of the pseudo-eutectic microstructure, which consists of relatively large columnar grains of the dominant FCC phase (~90 wt%) and fine dendritic grains of the minor BCC phase (~10 wt%). The applied layer-remelting process shows negligible effects on the phase fractions and their compositions, however, it significantly degraded the tensile strength and ductility of prepared alloys. Particularly, the ductility of the alloy reduced dramatically from about 27% after one time layer-remelting to only about 3% after 3 times layer-remelting. This is rationalised by the significant localisation of thermally induced plasticity caused by repeated remelting of deposited material. We also show that this thermally induced plasticity leads to an increased amount of local misorientation in both constitute phases, which suggests an increased amount of stored dislocations in the microstructure. Despite the potentially strain hardening due to this accumulation of the thermally induced plasticity, the appreciable growth and constrained dendritic morphology of BCC grains that developed after remelting play a prevailing role on the materials strength, which limit the interfacial strengthening of the eutectic microstructure and consequently result in the loss of the tensile strength. The obtained results will assist in the further development and microstructure optimisation of novel HEAs using powder-based additive manufacturing processes.

Additive Manufacturing of High Entropy Alloys

Additive Manufacturing of High Entropy Alloys

Manufacturing of High Entropy Alloys

High entropy alloys (HEAs) have generated interest in recent years due to their unique positioning within the alloy world. By incorporating a number of elements in high proportion they have high configurational entropy, and thus they hold the promise of interesting and useful properties such as enhanced strength and phase stability. The present study investigates the microstructure of two single-phase face-centered cubic (FCC) HEAs, CoCrFeNi and CoCrFeNiMn, with special attention given to melting, homogenization and thermo-mechanical processing. Large-scale ingots were made by vacuum induction melting to avoid the extrinsic factors inherent in small-scale laboratory button samples. A computationally based homogenization heat treatment was applied to both alloys in order to eliminate segregation due to normal ingot solidification. The alloys fabricated well, with typical thermo-mechanical processing parameters being employed.