Tailoring a Refractory High Entropy Alloy by Powder Metallurgy Process Optimization

Abstract

This paper reports the microstructural evolution and mechanical properties of a low-density Al0.3NbTa0.8Ti1.5V0.2Zr refractory high-entropy alloy (RHEA) prepared by means of a combination of mechanical alloying and spark plasma sintering (SPS). Prior to sintering, the morphology, chemical homogeneity and crystal structures of the powders were thoroughly investigated by varying the milling times to find optimal conditions for densification. The sintered bulk RHEAs were produced with diverse feedstock powder conditions. The microstructural development of the materials was analyzed in terms of phase composition and constitution, chemical homogeneity, and crystallographic properties. Hardness and elastic constants also were measured. The calculation of phase diagrams (CALPHAD) was performed to predict the phase changes in the alloy, and the results were compared with the experiments. Milling time seems to play a significant role in the contamination level of the sintered materials. Even though a protective atmosphere was used in the entire manufacturing process, carbide formation was detected in the sintered bulks as early as after 3 h of powder milling. Oxides were observed after 30 h due to wear of the high-carbon steel milling media and SPS consolidation. Ten hours of milling seems sufficient for achieving an optimal equilibrium between microstructural homogeneity and refinement, high hardness and minimal contamination.

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs)

“…The fracture toughness property goal necessitates the new materials to show some degree of metallic behaviour to distinguish them from ceramic UHTMs [ 3 ]. Research and development work is in progress to find metallic UHTMs that can be used in structural engineering applications [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ].…”

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

“…At present, bulk RHEAs are commonly produced by liquid metallurgy (arc melting, induction melting, and laser melting), [65,223,234] field-assisted PM (SPS, high-pressure consolidation, and hot isostatic pressing), [67,69,227,[235][236][237][238][239][240][241][242][243][244] and deposition techniques for thin films. Due to the high melting temperatures of refractory metals, the differences in their atomic size and chemistry, and sensitivity to trace oxygen impurity, mixing all elements uniformly by melting and casting is quite challenging.…”

An Overview of High-Entropy Alloys Prepared by Mechanical Alloying Followed by the Characterization of Their Microstructure and Various Properties

“…As such, the concept of HEAs was not successfully realized for many years. However, contemporary metallurgists have realized the importance of these alloys and developed new grades of HEAs using arc melting, induction melting [8], sputtering, molecular beam epitaxy [9], thermal spray, laser cladding, electrodeposition [10], and mechanical alloying using a high-energy ball mill [11,12]. Overall, mechanical alloying is proven to be one of the best methods for preparing HEAs, which can reduce the burdens of time, energy, and cost as compared with other conventional metallurgical methods.…”

“…If any alloy contains two or three elements, it is possible to explain intermetallic compounds and intermediate phases in terms of binary-or ternary-phase diagrams. However, recent reports have proven that the use of CALPHAD and a database of thermodynamic data could explain phase diagrams, even for HEAs [12,13]. In the late 18th century, a German metallurgist, named Franz Karl Archard, studied multicomponent To collect the publication data, the author performed a selective search of the Scopus database and tried different combinations of keywords, such as 'high-entropy alloys', and 'mechanical alloying'.…”