CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Synthesis and Characterization of High Entropy Alloy and Coating
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Lulea University of Technology. (Engineering Materials)
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

High entropy alloys (HEAs) are a new class of alloys that contains five or more principal elements in equiatomic or near-equiatomic proportional ratio. The configuration entropy in the HEAs tends to stabilize the solid solution formation, such as body-centered-cubic (BCC), face-centered-cubic (FCC) and/or hexagonal-closed-pack (HCP) solid solution. The high number of principal elements present in HEAs results in severe lattice distortion, which in return gives superior mechanical properties compared to the conventional alloys. HEAs are considered as a paradigm shift for the next generation high temperature alloys in extreme environments, such as aerospace, cutting tools, and bearings applications.

The project is based on the development of refractory high entropy alloy and film. The first part of the project involves designing high entropy alloy of CuMoTaWV using spark plasma sintering (SPS) at 1400 oC. The sintered alloy showed the formation of a composite of BCC solid solution (HEA) and V rich zones with a microhardness of 600 HV and 900 HV, respectively. High temperature ball-on-disc tribological studies were carried out from room temperature (RT) to 600 oC against Si3N4 counter ball. Sliding wear characterization of the high entropy alloy composite showed increasing coefficient of friction (COF) of 0.45-0.67 from RT to 400 oC and then it decreased to 0.54 at 600 oC. The wear rates were found to be low at RT (4 × 10⁠−3 mm⁠3/Nm) and 400 oC (5 × 10⁠−3 mm⁠3/Nm) and slightly high at 200 oC (2.3 × 10⁠−2 mm⁠3/Nm) and 600 oC (4.5 × 10⁠−2 mm⁠3/Nm). The tribology tests showed adaptive behavior with lower wear rate and COF at 400 oC and 600 oC, respectively. The adaptive wear behavior at 400 oC was due to the formation of CuO that protected against wear, and at 600 oC, the V-rich zones converted to elongated magneli phases of V2O5 and helped in reducing the friction coefficient.

The second part of the project consists of sintering of novel CuMoTaWV target material using SPS and depositing CuMoTaWV refractory high entropy films (RHEF) using DC-magnetron sputtering on silicon and 304 stainless steel substrate. The deposited films showed the formation of nanocrystalline BCC solid solution. The X-ray diffraction (XRD) studies showed a strong (110) preferred orientation with a lattice constant and grain size of 3.18 Å and 18 nm, respectively. The lattice parameter were found to be in good agreement with the one from the DFT optimized SQS (3.16 Å). The nanoindentation hardness measurement at 3 mN load revealed an average hardness of 19 ± 2.3 GPa and an average Young’s modulus of 259.3 ± 19.2 GPa. The Rutherford backscattered (RBS) measurement showed a gradient composition in the cross-section of the film with W, Ta and Mo rich at the surface, while V and Cu were found to be rich at the substrate-film interface. AFM measurements showed an average surface roughness (Sa) of 3 nm. Nano-pillars of 440 nm diameter from CuMoTaWV RHEFs were prepared by ion-milling in a focused-ion-beam (FIB) instrument, followed by its compression. The compressional yield strength and Young’s modulus was calculated to be 10.7 ± 0.8 GPa and 196 ± 10 GPa, respectively. Room temperature ball-on-disc tribological test on the CuMoTaWV RHEF, after annealing at 300 oC, against E52100 alloy steel (Grade 25, 700-880 HV) showed a steady state COF of 0.25 and a low average wear rate of 6.4 x 10-6 mm3/Nm.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2019.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Metallurgy and Metallic Materials Other Materials Engineering
Research subject
Engineering Materials
Identifiers
URN: urn:nbn:se:ltu:diva-73882ISBN: 978-91-7790-394-9 (print)ISBN: 978-91-7790-395-6 (electronic)OAI: oai:DiVA.org:ltu-73882DiVA, id: diva2:1314477
Presentation
2019-06-13, E231, Lulea University of Technology, lulea, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , 228220Available from: 2019-05-09 Created: 2019-05-08 Last updated: 2019-06-14Bibliographically approved
List of papers
1. High temperature tribology of CuMoTaWV high entropy alloy
Open this publication in new window or tab >>High temperature tribology of CuMoTaWV high entropy alloy
2019 (English)In: Wear of Materials, 2019, Vol. 426-427, p. 412-419Conference paper, Published paper (Refereed)
Abstract [en]

An equiatomic high entropy alloy (HEA) CuMoTaWV was designed for room temperature to high temperature wear applications using spark plasma sintering of elemental powder mixture at 1400 °C. The sintered solid solution showed uniform distribution of elements in a BCC high entropy alloy phase along with V rich solid solution phase with an average hardness of 600 Hv and 900 Hv, respectively. Room temperature (RT) dry sliding wear tests, against alloy steel (700–880 Hv) for 200 m sliding distance at 5 N normal load, showed negligible wear of 5 × 10−7 mm/N m and a coefficient of friction (COF) of 0.5. Sliding wear characterization of sintered CuMoTaWV alloy against Si3N4 (1550 Hv) counter body from RT to 600 °C showed an increasing average COF of 0.45–0.67 from RT to 400 °C and then reducing to 0.54 at 600 °C. The wear rate was found to be lower at RT (4 × 10−3 mm3/N m) and 400 °C (5 × 10−3 mm3/N m), and slightly higher at 200 °C (2.3 × 10−2 mm3/N m) and 600 °C (4.5 × 10−2 mm3/N m). The CuMoTaWV alloy showed wear mechanisms specific to the test temperatures. The wear of CuMoTaWV alloy was governed by adhesive wear at RT and 200 °C and oxidative wear at 400 °C and 600 °C. The analyses of wear surfaces showed that the low wear rate at RT was due to the high hardness of the HEA, presence of V rich zones and formation of W and Ta tribofilm. At 400 °C, the formation of CuO tribolayer reduced the wear and hindered oxidation of wear track. At 600 °C, the wear rate increased due to oxidation of Cu, Ta and W. Moreover, the formation of lubricating elongated magneli phase V2O5 in V rich regions of CuMoTaWV alloy reduced the COF to 0.54.

Keywords
Sliding wear, High temperature wear, Adaptive wear, High, Entropy alloy (HEA, ) Refractory, Tribology, Spark plasma sintering (SPS)
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73687 (URN)10.1016/j.wear.2018.12.085 (DOI)000464583700044 ()
Conference
22nd International Conference on Wear of Materials, April 14-18 2019, Miami, USA
Available from: 2019-04-17 Created: 2019-04-17 Last updated: 2019-06-14Bibliographically approved

Open Access in DiVA

fulltext(3045 kB)53 downloads
File information
File name FULLTEXT01.pdfFile size 3045 kBChecksum SHA-512
569bac20127d53fe57eb7c88c1cd62528383dd96bf065e640a6ff470b07df5698c9f211a6e702480fd803e90523c136068d5c168af267b14abd95be3b1e403b9
Type fulltextMimetype application/pdf

Authority records BETA

Alvi, Sajid

Search in DiVA

By author/editor
Alvi, Sajid
By organisation
Material Science
Metallurgy and Metallic MaterialsOther Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 53 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 518 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf