Suchergebnisse

This thesis focuses on understanding the process-structure-property relation-ships for several refractory-metal-based high-entropy alloys and nitrides synthesized by magnetron sputtering. The thesis begins with the growth of TiZrNbTaNx understoichiometric nitrides by controlling substrate temperature and nitrogen flow ratio fN. Their effects on microstructure and mechanical, electric, and electrochemical properties were investigated. TiZrNbTaN0.46 deposited at 400 ºC shows a NaCl-type structure with (001) preferred orientation and exhibits the highest corrosion resistance in 0.1 M H2SO4 aqueous solution. A stable passive region up to 3.0 V vs. Ag/AgCl could be achieved when x< 0.64. The densification effects were explored by ion energy for (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films and by high-power impulse magnetron sputtering technique for TiNbCrAl films. The local chemical distortions in the TiZrTaNb-based system with different nitrogen content were investigated by X-ray absorption fine structure spectros-copy. The influence of crystallinity on superconducting transition behavior was studied in (TiZrHf)x(TaNb)1-x, (TiZrNbTa)1-xWx, and (TiZrNbTa)1-xVx systems. The highest superconducting transition temperature (Tc) reaches 8.05 K for the TiZrNbTa film (x=0). The superconducting transition temperature Tc of these films deposited at the fixed temperature decreases monotonically as a function of x, and Tc can be increased by elevating the deposition temperature. Furthermore, the structural stability and elemental segregation under Xe-ion irradiation of TiZrNbTaV-based HEA and HEN films, and high-entropy TiZrN-bTa/CrFeCoNi metallic and nitride multilayer coatings were investigated. The microstructure of TiZrNbTaVN film remain stable after irradiation at room temperature and 500 °C. The as-deposited TiZrNbTaV film exhibited an amorphous structure and became a bcc phase structure after irradiation at 500 °C. Thermal-induced and irradiation-induced grain growth resulted in a grain-size distribution. For the multilayer coatings, the microstructure of metallic multilayers was not stable and the interdiffusion or mixing of the constituent elements is prominent under ion irradiation and/or heat treatment. no diffusion and phase trans-formation were observed for the nitride multilayers after irradiation at 500 °C. ; Funding agencies: VINNOVA for financial support to work on synchrotron based facilities and CeNano (the Linköping Center for Nanoscience) for financially supporting my collaboration with the electronic and photonic materials division at IFM. For Papers IV and VI, the MAX IV Laboratory is acknowledged for time on Beamline BALDER under Proposal 20200219. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under Contract No. 2018-07152, the Swedish Governmental Agency for Innovation Systems under Contract No. 2018-04969, and Formas under Contract No. 2019-02496.

The Cantor alloy CrFeCoMnNi is generally fcc structured, but moderate changes in the composition can have a large influence on the phase formation. The aim of this study was to understand the changes brought on in lownitrogen-containing (CrFeCo)1-yNy thin films with y = 0.19 on the addition of copper, an interesting metal in terms of atomic size and nitride formation enthalpy. (CrFeCoCux)1-yNy films were grown by reactive magnetron sputtering. The amount of copper in the films was increased from x = 0 to x = 0.15 to study competitive phase formation. Without Cu, two-phase fcc + bcc films were obtained. The addition of Cu was found to stabilize the bcc structure despite the fact that Cu as a pure metal is fcc. Nanoindentation tests showed slight increase in hardness with initial Cu addition from 11 GPa to 13.7 +/- 0.2 GPa. The occurrence of pile up as opposed to cracking is an indication of the films ductility. ; Funding Agencies|VINNOVA Competence Centre FunMat-II [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [2020.0196]; Knut and Alice Wallenberg Foundation through Electron Microscopy Laboratory at Linkoping University; Swedish Research Council via VR-RFI contract [C0514401]; Swedish Foundation for Strategic Research via SSF contract [RIF140053]

A variety of bulk high-entropy alloy superconductors have been recently discovered; however, for thin films, only the TaNbHfZrTi highentropy alloy system has been investigated for its superconducting properties. Here, (TiZrNbTa)1-xWx and (TiZrNbTa)1-xVx superconducting films have been produced by DC magnetron sputtering at different growth temperatures. The phase formation and superconducting behavior of these films depend on the content of alloying x and deposition temperature. A single body-centered cubic (bcc) phase can be formed in the low x range with enough driving energy for crystallinity, but phase transition between amorphous or two bcc structures is observed when increasing x. The highest superconducting transition temperature Tc reaches 8.0 K for the TiZrNbTa film. The superconducting transition temperature Tc of these films deposited at the same temperature decreases monotonically as a function of x. Increasing deposition temperature to 400 °C can enhance Tc for these films while retaining nearly equivalent compositions. Our experimental observations suggest that Tc of superconducting high entropy alloys relate to the atomic radii difference and electronegativity difference of involved elements beyond the valence electron number. ; Funding: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; VINNOVA Competence Centre FunMat-II [2016-05156]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW-2020.0196]; Swedish Research Council [2021-03826]

The Cantor alloy (CoCrFeMnNi) and its variants, in bulk as well as thin films, have been extensively studied. They are known to exhibit cubic crystal structures and thermodynamic stability regardless of their complex chemical composition. Therefore, they may find use as hard, wear-resistant, corrosion and oxidation-resistant coatings. The addition of light elements, such as nitrogen, is known to help improve these properties further through processes such as amorphization and nitride compound formation. Here, we investigate the ternary CrFeCo system to study the effects of nitrogen addition. (CrFeCo)Ny multicomponent thin films are grown on silicon substrates by DC magnetron sputtering. Changes in crystal structure, morphology, mechanical and electrical properties with gradual increases of nitrogen in the film are described and discussed. Increased addition of nitrogen from 14 at.% to 28 at.% in the film leads to a transformation from an fcc to a bcc crystal structure, affects both the mechanical and electrical properties. XPS analysis shows the tendency of nitrogen to bond with Cr over other metals. The films display hardness values between 7 and 11 GPa with resistivities values ranging between 28 and 165 μΩ cm. ; Funding: VINNOVA Competence Centre FunMat-II [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Knut and Alice Wallenberg Foundation through the Electron Microscopy Laboratory at Linkoping University; Swedish Research Council via VR-RFI [C0514401]; Swedish Foundation for Strategic Research via SSF [RIF14-0053]

Mg3Sb2-based thermoelectric materials attract attention for applications near room temperature. Here, Mg-Bi films were synthesized using magnetron sputtering at deposition temperatures from room temperature to 400 °C. Single-phase Mg3Bi2 thin films were grown on c-plane-oriented sapphire and Si(100) substrates at a low deposition temperature of 200 °C. The Mg3Bi2 films grew epitaxially on c-sapphire and fiber-textured on Si(100). The orientation relationships for the Mg3Bi2 film with respect to the c-sapphire substrate are (0001) Mg3Bi2‖(0001) Al2O3 and [112⎯⎯2¯0] Mg3Bi2‖[112⎯⎯2¯0] Al2O3. The observed epitaxy is consistent with the relatively high work of separation, calculated by the density functional theory, of 6.92 J m−2 for the Mg3Bi2 (0001)/Al2O3 (0001) interface. Mg3Bi2 films exhibited an in-plane electrical resistivity of 34 μΩ m and a Seebeck coefficient of +82.5 μV K−1, yielding a thermoelectric power factor of 200 μW m−1 K−2 near room temperature.This work was supported financially by the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971), the Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program (No. KAW-2020.0196), the Swedish Research Council (VR) under Project Nos. 2016-03365 and 2021-03826, the National Key Research and Development Program of China under Grant No. 2018YFB0703600, the National Natural Science Foundation of China under Grant No. 51872133, the Guangdong Innovative and Entrepreneurial Research Team Program under Grant No. 2016ZT06G587, and the Tencent Foundation through the XPLORER PRIZE, Guangdong Provincial Key Laboratory Program (No. 2021B1212040001) from the Department of Science and Technology of Guangdong Province. The computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at National Supercomputer Centre (NSC) partially funded by the Swedish Research Council through Grant Agreement No. 2018-05973.

Mg3Sb2-based thermoelectric materials attract attention for applications near room temperature. Here, Mg-Bi films were synthesized using magnetron sputtering at deposition temperatures from room temperature to 400 & DEG;C. Single-phase Mg3Bi2 thin films were grown on c-plane-oriented sapphire and Si(100) substrates at a low deposition temperature of 200 & DEG;C. The Mg3Bi2 films grew epitaxially on c-sapphire and fiber-textured on Si(100). The orientation relationships for the Mg3Bi2 film with respect to the c-sapphire substrate are (0001) Mg3Bi2||(0001) Al2O3 and [11 2 over bar 0] Mg3Bi2||[11 2 over bar 0] Al2O3. The observed epitaxy is consistent with the relatively high work of separation, calculated by the density functional theory, of 6.92 J m(-2) for the Mg3Bi2 (0001)/Al2O3 (0001) interface. Mg3Bi2 films exhibited an in-plane electrical resistivity of 34 mu omega m and a Seebeck coefficient of +82.5 mu V K-1, yielding a thermoelectric power factor of 200 mu W m(-1) K-2 near room temperature. ; Funding Agencies|Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW-2020.0196]; Swedish Research Council (VR)Swedish Research Council [2016-03365, 2021-03826, 2018-05973]; National Key Research and Development Program of China [2018YFB0703600]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [51872133]; Guangdong Innovative and Entrepreneurial Research Team Program [2016ZT06G587]; Tencent Foundation through XPLORER PRIZE [2021B1212040001]

Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr, 0.12 ≤ x ≤ 0.30) films were deposited on Si(100) substrates at 400 °C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from ∼10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 ≤ x ≤ 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1–x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached ∼3.1 GPa in Hf- and Cr-containing films deposited at −130 V. The hardness reached a maximum value of 28.0 ± 1.0 GPa at a negative bias ≥100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1–x films can thus guide the design of protective high-entropy nitride films. ; Funding Agencies|VINNOVA Competence Centre FunMat-II [2016-05156]; VINNOVA research infrastructure grantVinnova [2020-00825]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; M-ERA.net [2013-02355]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [2020.0196]; Electron Microscopy Laboratory at Linkoping University; Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR 2018-04139]; VR-RFI [2017-00646_9]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [RIF14-0053]

Introducing porosity is attractive for tailoring electronic, thermal, and mechanical properties of inorganic materials. Nanoporosity is typically either inherent in crystallographic channels in the structure or obtained by external templating during synthesis and sintering. However, controllably engineering porosity in materials with laminated crystal structures without channels remains a challenge. Here, we demonstrate the realization of faceted and oriented nanopores in textured Ca3Co4O9-a laminated ceramic with a misfit-layered structure of importance for thermoelectric applications-from chemical reactions in CaO/Co3O4 multilayers. We show that CaO conversion to Ca(OH)(2) and the cobalt oxide stoichiometry are key determinants of nanoporosity. Adjusting the unreacted CaO fraction alters the nanopore size and fraction and the thermoelectric properties of Ca3Co4O9. The preferred orientation of Ca3Co4O9 is underpinned by the texture of the reactant multilayers and reactant-product crystallographic relationships and density difference. Oriented pore formation is attributed to basal plane removal driven by local densification of textured Ca3Co4O9 nuclei through growth and impingement. These findings point to possibilities for controllably engineering nanoporosity and properties in a variety of inorganic materials with laminated crystal structures. ; Funding Agencies|Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW 2020.0196]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Energy AgencySwedish Energy AgencyMaterials & Energy Research Center (MERC) [46519-1]; China Scholarship CouncilChina Scholarship Council

Multicomponent TixNbCrAl nitride films were deposited on Si(100) substrates by reactive direct current magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) in the absence of substrate heating and bias. Three single Ti, Nb, and Cr50Al50 targets were either driven by three de or three HiPIMS power supplies. The Ti content in the films was varied by tuning the power applied to the Ti target. The composition was determined by ion beam analysis. The nitrogen content is nearly stoichiometric (48-50 at.%) in the HiPIMS series, while the dcMS are understoichiometric (39-45 at.%). The crystal structure, stress and density of the studied film were investigated by X-ray techniques and the microstructure was examined by scanning electron microscopy. All the Ti-containing films for both series exhibit an fcc NaCl-type phase structure. In particular, the dcMS series shows a (111) preferred orientation, resulting in a faceted surface morphology compared to a dense and smooth microstructure of the HiPIMS films. The compressive stress of the HiPIMS series (> 2.0 GPa) is significantly larger than the values of the dcMS series (<0.5 GPa). Nanoindentation measurements show a maximum hardness of 29.9 GPa and Youngs modulus of 304 GPa were obtained in the HiPIMS series. The results may promote HiPIMS techniques for the synthesis of complex multicomponent films for the application aspect to protective and hard coatings. ; Funding Agencies|VINNOVA Competence Centre FunMat-II [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; M - ERA. net (project MC2) [2013-02355]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [2020.0196, KAW 2015.0043]; Electron Microscopy Laboratory at Linkoping University; Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR 2018-04139]; Swedish Research Council VR-RFISwedish Research Council [2019-00191]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [RIF14-0053]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [51805102]; Guizhou Provincial Natural Science Foundation [[2020]1Y228]; China Scholarship Council (CSC)China Scholarship Council

A series of (TiNbZrTa)Nx coatings with a thickness of similar to 1.1 mu m were deposited using reactive magnetron sputtering with segmented targets. The deposition temperature was varied from room temperature to 700 degrees C resulting in coatings with different microstructures. The coatings were characterized by electron microscopy, atomic force microscopy, compositional analysis, and X-ray diffraction. Effects of the deposition temperature on the electrical, mechanical and corrosion properties were studied with four-point probe, nanoindentation and potentiodynamic polarization measurements, respectively. X-ray photoelectron spectroscopy (XPS) analyses reveal a gradual change in the chemical state of all elements with increasing growth temperature from nitridic at room temperature to metallic at 700 degrees C. A NaCl-type structure with (001) preferred orientation was observed in the coating deposited at 400 degrees C, while an hcp structure was found for the coatings deposited above 400 degrees C. The resistivities of the TiNbZrTa nitride coatings were found to be around 200 mu Ocm. In 0.1 M H2SO4 aqueous solution, a corrosion current density of 2.8 x 10(-8) A/cm(2) and a passive behaviour up to 1.5 V vs. Ag/AgCl were found for the most corrosion resistant coating. The latter corrosion current is about two orders of magnitude lower than that found for a reference hyper-duplex stainless steel. ; Funding Agencies|VINNOVA Competence Center FunMat-II [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; M -ERA.net (project MC2) [2013-02355]; Electron Microscopy Laboratory at Linkoping University; Swedish Research Council VRSwedish Research Council [201803957]; VINNOVAVinnova [2018-04290]; Aforsk Foundation [16-359]; Carl Tryggers Stiftelse for Vetenskaplig Forskning [CTS 17:166]; Wallenberg Academy Fellows program at Linkoping University