The effects of mechanical alloying on the physical and thermal properties of CuCrFeTiV alloy

https://doi.org/10.1016/j.mseb.2020.114805Get rights and content

Highlights

  • The powders reveal an increasing content in iron as the millings are prolonged.

  • The elemental composition of the sintered alloy confirms the increase of iron.

  • The alloy presents an electrical resistivity with a ferromagnetic behaviour.

  • The results indicate that the alloy can be used as thermal barrier.

Abstract

The present work reports the production and key properties of the CuCrFeTiV high entropy alloy synthetized by mechanical alloying and spark plasma sintering. The milled powders and the as-sintered samples were analysed through scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy and particle induced X-ray emission. Magnetic properties together with electrical resistivity, thermal conductivity, specific heat and differential thermal analysis were also evaluated on the consolidated samples. The powders reveal an increasing content in iron as the millings are prolonged up to 20 h. The elemental composition of the sintered alloy, determined through particle induced X-ray emission, confirms the final composition after mechanical alloying with an increase of iron and a decrease in the remaining elements. Furthermore, although the alloy presents an electrical resistivity typical of a high entropy alloy, a ferromagnetic behaviour was found, consistently with a major Fe content as detected in prior observations. Finally, thermal measurements show that this CuCrFeTiV high entropy alloy possesses thermal properties suitable for its potential use as thermal barriers.

Introduction

For decades, the demand to supply energy at a global scale has been escalating, requiring new, more powerful ways of energy production. Nuclear reactors can convert the energy released by controlled nuclear fusion into thermal energy for further conversion to mechanical or electrical forms. With the implementation of these machines the opportunity to produce clean energy with nearly unlimited energy reserves arises. In these reactors, the divertor has a plasma facing wall made up of tungsten (W) monoblocks, that will be exposed to high heat and radiation loads. To remove the heat from the monoblocks, these tiles are built to be in contact with CuCrZr cooling tubes where pressurized water will flow. Since the optimum operating temperature ranges of the component materials, W and CuCrZr, do not overlap, it is desirable to use an intermediate layer, a buffer layer capable of functioning as a thermal barrier, guaranteeing an adequate thermal transport between both materials while keeping their temperatures in the proper working intervals.

The concept of high entropy alloys (HEA) introduces a new path of developing advanced materials with the required properties. High entropy alloys are alloys with five or more principal elements, each with a concentration between 5 and 35 atomic percent [1], with substantially higher mixing entropies than in conventional alloys. Because of their unique composition, HEAs potentially offer special properties, such as high-temperature strength [2], outstanding wear resistance and structural stability [3], good corrosion and oxidation resistance [4]. Therefore, HEAs are attractive for use in many fields, including as thermal barriers for nuclear fusion reactors. Apart from the well-rounded compositional and microstructural properties of the HEAs, such as magnetic, electrical conductivity and thermal conductivity and heat capacity enable the assessment of a component lifetime and the evaluation of structural stability. Many studies dedicated to the evaluation of magnetic properties of HEAs, indicate that, when these alloys contain more than 50 at.% of the magnetic elements Fe, Co, and Ni, they are either paramagnetic or ferromagnetic with a saturation magnetization that depends mainly on the composition and crystal structure [5]. Furthermore, the publications have shown that as-cast high entropy alloys produced by arc melting, constituted of Fe and Cr, typically have electrical resistivities between 100 μΩ⋅cm and 220 μΩ⋅cm in the 0–300 K temperature range [6], [7]. Moreover, their thermal conductivity increases with increasing temperature, with values between 10 and 27 W⋅K−1⋅m−1 [7], in contrast to that seen in most pure metals. Despite the studies performed, insufficient data is available concerning the assessment of HEAs with appropriate properties for working under extreme conditions.

A new strategy is proposed for the accommodation of the thermal mismatch between the W tiles and the CuCrZr tubes involving the use of CuCrFeTiV high entropy alloy, this new concept is explored in the present research. Despite the numerous studies of high-entropy alloys concerning microstructure and mechanical properties, only a few recent studies have been developed regarding the processing route and its impact on thermal, magnetic and electrical properties – mainly focused on systems composed of Al, Co, Cr, Cu, Fe, Ni, and Ti [6], [8].

Therefore, this paper presents the powder metallurgy processing of CuCrFeTiV high-entropy alloy via ball milling followed by plasma sintering, together with its microstructural properties, electrical resistivity, magnetic properties, thermal conductivity, specific heat measurements and differential thermal analysis.

Section snippets

Alloys preparation and consolidation

Powders of Cr, Cu, Fe, Ti and V with purity greater than 99.5% and 45 μm particle size (Alpha Aesar) were mixed in equiatomic ratios inside a glove box, filled with argon to prevent oxidation, to obtain the CuCrFeTiV powder mixture. The powders were mechanically alloyed in a high energy planetary ball mill, PM 400 MA type, with stainless steel balls and vials. The balls were used in a ball-to-powder ratio of 10:1, and the milling occurred for effective times up to 20 h, at 380 rpm. A solution

Influence of milling time in phase evolution

The iron and chromium contents were evaluated as a function of milling time using the EDS results after milling times of 0 h, 6 h and 20 h, as presented in Fig. 1 (a). The Fe content increases from the initial 20 at.% to about 55 at.%, while the Cr content stays almost constant (from 20 at.% to approximately 17.1 at.%). In fact, after 2 h of milling, the diffraction peaks of the individual elements can still be observed, but after 6 h, these disappear and are replaced by a main broad peak, as

Conclusions

CuCrFeTiV alloy was prepared by a powder metallurgy route consisting of mechanical milling followed by sintering. With the process used, prior to 2 h of milling there is no significant alloying, instead, after 6 h, there is a significant and traceable amount of formed alloy. As the milling time increases, the XRD result showed the formation of a single BCC structure. Moreover, the microstructural evaluation showed the formation of different phases: one rich in Cu and a major one, Cr and Fe

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

IST activities received financial support from “Fundação para a Ciência e Tecnologia” through project Pest-OE/SADG/LA0010/2013. Financial support was also received from the “Fundação para a Ciência e Tecnologia” (FCT) under the PTDC/CTM/100163/2008 grant and the PEST-OE/CTM-UI0084/2011 contracts. M. Dias acknowledges the FCT grant SFRH/BPD/68663/2010.

This research had financial support from the Fundação para a Ciência e a Tecnologia through Grant UID/Multi/04046/2013 (BioISI).

References (22)

  • C. Hsu et al.

    Wear resistance and high-temperature compression strength of Fcc CuCoNiCrAl ^ s

    Metall. Mater. Transcations A

    (2004)
  • Cited by (6)

    • Charged particles: Unique tools to study irradiation resistance of concentrated solid solution alloys

      2023, Journal of Materials Science and Technology
      Citation Excerpt :

      Frequently used ion beam analysis (IBA) techniques typically include Rutherford Backscattering Spectrometry (RBS) along channeling or non-channeling directions [102–104], Nuclear Reaction Analysis (NRA), and Time-of-flight Elastic Recoil detection Analysis (ToF-ERDA). Other ion-based analytical techniques include secondary ion mass spectrometry (SIMS) for chemical and isotopic identification [105], particle induced x-ray emission (PIXE) for composition quantification, as well as possible identification of impurities or contamination [106]. In this review, we discuss the application of commonly used IBA techniques, especially RBS along channeling directions (RBS/c), for CSA studies, as they are highly sensitive and have been utilized to determine defect production, damage accumulation, gas element concentrations and profiles, as well as changes in elemental concentration.

    • High-Entropy Materials: From Basics to Applications

      2023, High-Entropy Materials: from Basics to Applications
    View full text