Abstract
Development of high-entropy alloy (HEA) films is a promising and cost-effective way to incorporate these materials of superior properties in harsh environments. In this work, a refractory high-entropy alloy (RHEA) film of equimolar CuMoTaWV was deposited on silicon and 304 stainless-steel substrates using DC-magnetron sputtering. A sputtering target was developed by partial sintering of an equimolar powder mixture of Cu, Mo, Ta, W, and V using spark plasma sintering. The target was used to sputter a nanocrystalline RHEA film with a thickness of ∼900 nm and an average grain size of 18 nm. X-ray diffraction of the film revealed a body-centered cubic solid solution with preferred orientation in the (110) directional plane. The nanocrystalline nature of the RHEA film resulted in a hardness of 19 ± 2.3 GPa and an elastic modulus of 259 ± 19.2 GPa. A high compressive strength of 10 ± 0.8 GPa was obtained in nanopillar compression due to solid solution hardening and grain boundary strengthening. The adhesion between the RHEA film and 304 stainless-steel substrates was increased on annealing. For the wear test against the E52100 alloy steel (Grade 25, 700–880 HV) at 1 N load, the RHEA film showed an average coefficient of friction (COF) and wear rate of 0.25 (RT) and 1.5 (300 °C), and 6.4 × 10–6 mm3/N m (RT) and 2.5 × 10–5 mm3/N m (300 °C), respectively. The COF was found to be 2 times lower at RT and wear rate 102 times lower at RT and 300 °C than those of 304 stainless steel. This study may lead to the processing of high-entropy alloy films for large-scale industrial applications.
Highlights
High-entropy alloys (HEAs), since their discovery by Yeh et al in 2004,1 have opened up researchers to a new alloy system that contains five or more equimolar principal elements
The X-ray diffraction (XRD) diffractogram of the CuMoTaWV refractory high-entropy alloy (RHEA) film deposited on the 304 stainless-steel substrate is shown in Figure 2, together with the simulated XRD diffractogram obtained from the Density functional theory (DFT)-optimized special quasirandom structures (SQSs)
We have shown that an HEA film can be synthesized from a single partially spark-plasma-sintered target
Summary
High-entropy alloys (HEAs), since their discovery by Yeh et al in 2004,1 have opened up researchers to a new alloy system that contains five or more equimolar principal elements. We report on the development of a new nanocrystalline CuMoTaWV RHEA film with high hardness, strength, and wear properties through magnetron sputtering using a single consolidated target comprising the principal elements. The RHEA composition has been chosen based on thermocalc simulation to obtain a mixture of a ductile FCC phase and a high-strength BCC solid solution, as reported in our previous work.[26] The addition of Cu to the refractory elements MoTaWV was done to investigate (I) the effect of lattice distortion in the films on combining Cu with refractory elements and its contribution toward the mechanical properties, and (II) the enhancement of the tribological properties of the refractory high-entropy film at RT and moderate temperatures by lowering the friction coefficient and wear rate with the formation of CuO.[31,32]. The XRD pattern for the fully relaxed SQS was simulated using Mercury Crystal Structure Visualization software[43] using a 2θ full width at half-maximum (FWHM) of 0.2°
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