| 1. |
- Calamba, Katherine, et al.
(författare)
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Dislocation structure and microstrain evolution during spinodal decomposition of reactive magnetron sputtered heteroepixatial c-(Ti-0.37,Al-0.63)N/c-TiN films grown on MgO(001) and (111) substrates
- 2019
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 125:10
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Tidskriftsartikel (refereegranskat)abstract
- Heteroepitaxial c-(Ti-0.37,Al-0.63)N thin films were grown on MgO(001) and MgO(111) substrates using reactive magnetron sputtering. High resolution high-angle annular dark-field scanning transmission electron micrographs show coherency between the film and the substrate. In the as-deposited state, x-ray diffraction reciprocal space maps show a strained epitaxial film. Corresponding geometric phase analysis (GPA) deformation maps show a high stress in the film. At elevated temperature (900 degrees C), the films decompose to form iso-structural coherent c-Al- and c-TiN-rich domains, elongated along the elastically soft amp;lt;100amp;gt; directions. GPA analysis reveals that the c-TiN domains accommodate more dislocations than the c-AlN domains. This is because of the stronger directionality of the covalent bonds in c-AlN compared with c-TiN, making it more favorable for the dislocations to accumulate in c-TiN. The defect structure and strain generation in c-(Ti,Al)N during spinodal decomposition is affected by the chemical bonding state and elastic properties of the segregated domains.
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| 2. |
- Calamba, Katherine, et al.
(författare)
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Effect of nitrogen vacancies on the growth, dislocation structure, and decomposition of single crystal epitaxial (Ti1-xAlx)N-y thin films
- 2021
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 203
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Tidskriftsartikel (refereegranskat)abstract
- The effect of varying nitrogen vacancies on the growth, microstructure, spinodal decomposition and hardness values of predominantly single crystal cubic phase c-(Ti1-xAlx)N-y films was investigated. Epitaxial c-(Ti1-xAlx)N-y films with y = 0.67, 0.79, and 0.92 were grown on MgO(001) and MgO(111) substrates by magnetron sputter deposition. High N vacancy c-(Ti1-xAlx)N-0.67 films deposited on MgO(111) contained coherently oriented w-(0001) structures while segregated conical structures were observed on the films grown on MgO(001). High resolution STEM images revealed that the N-deficient growth conditions induced segregation with small compositional fluctuations that increase with the number of N vacancies. Similarly, strain map analysis of the epitaxial c-(Ti1-xAlx)N-y (001) and (111) films show fluctuations in strain concentration that scales with the number of N vacancies and increases during annealing. The spinodal decomposition coarsening rate of the epitaxial c-(Ti1-xAlx)N-y films was observed to increase with decreasing N vacancies. Nanoindentation showed decreasing trends in hardness of the as-deposited films as the N vacancies increase. Isothermal post-anneal at 1100 degrees C in vacuum for 120 min revealed a continuation in the increase in hardness for the film with the largest number of N vacancies (y = 0.67) while the hardness decreased for the films with y = 0.79 and 0.92. These results suggest that nitrogen-deficient depositions of c-(Ti1-xAlx)N-y films help to promote a self-organized phase segregation, while higher N vacancies generally increase the coherency strain which delays the coarsening process and can influence the hardness at high temperatures.
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| 3. |
- Calamba, Katherine, et al.
(författare)
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Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage
- 2017
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 122:6
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Tidskriftsartikel (refereegranskat)abstract
- Aspects on the phase stability and mechanical properties of nitrogen deficient (Ti0.54Al0.46)N-y alloys were investigated. Solid solution alloys of (Ti,Al)N were grown by cathodic arc deposition. The kinetic energy of the impinging ions was altered by varying the substrate bias voltage from -30V to -80 V. Films deposited with a high bias value of -80V showed larger lattice parameter, finer columnar structure, and higher compressive residual stress resulting in higher hardness than films biased at -30V when comparing their as-deposited states. At elevated temperatures, the presence of nitrogen vacancies and point defects (anti-sites and self-interstitials generated by the ion-bombardment during coating deposition) in (Ti0.54Al0.46)N-0.87 influence the driving force for phase separation. Highly biased nitrogen deficient films have point defects with higher stability during annealing, which cause a delay of the release of the stored lattice strain energy and then accelerates the decomposition tendencies to thermodynamically stable c-TiN and w-AlN. Low biased nitrogen deficient films have retarded phase transformation to w-AlN, which results in the prolongment of age hardening effect up to 1100 degrees C, i.e., the highest reported temperature for Ti-Al-N material system. Our study points out the role of vacancies and point defects in engineering thin films with enhanced thermal stability and mechanical properties for high temperature hard coating applications. Published by AIP Publishing.
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| 4. |
- Calamba, Katherine, et al.
(författare)
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Growth and high temperature decomposition of epitaxial metastable wurtzite (Ti1-x,Al-x)N(0001) thin films
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 688
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Tidskriftsartikel (refereegranskat)abstract
- The structure, growth, and phase stability of (Ti1-x,Al-x)N films with high Al content were investigated. (Ti1-x,Al-x)N (x= 0.63 and 0.77) thin films were grown on MgO (111) substrates at 700 degrees C using a UHV DC magnetron sputtering system. The (Ti-0.37,Al-0.63)N film is a single crystal with a cubic NaCl (B1) structure while the (T-i0.23,Al-0.77)N film only shows epitaxial growth of the same cubic phase in the first few atomic layers. With increasing film thickness, epitaxial wurtzite (B4) forms. The thin cubic layer and the wurtzite film has an orientation relationship of c-(Ti-0.23,Al-0.77)N(111)[110]parallel to w-(Ti-0.23,Al-0.77)N(0001)[11 (2) over bar0]. Continued deposition results in a gradual break-down of the epitaxial growth. It is replaced by polycrystalline growth of wurtzite columns with a high degree of 0001 texture, separated by a Tienriched cubic phase. In the as-deposited state, c-(Ti-0.27,Al-0.63)N displays a homogeneous chemical distribution while the w-(Ti-0.23,Al-0.77)N has segregated to Al- and Ti-rich domains. Annealing at 900 degrees C resulted in the spinodal decomposition of the metastable c-(Ti-0.27,Al-0.63)N film and formation of coherent elongated c-AlN and cTi-N-rich domains with an average width of 4.5 +/- 0.2 nm while the width of the domains in the w-(Ti-0.23,Al-0.77)N film only marginally increases to 2.8 +/- 0.1 nm. The slower coarsening rate of the wurtzite structure compared to cubic is indicative of a higher thermal stability.
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| 5. |
- Calamba, Katherine M., 1988-
(författare)
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Phase stability and defect structures in (Ti,Al)N hard coatings
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study highlights the role of nitrogen vacancies and defect structures in engineering hard coatings with enhanced phase stability and mechanical properties for high temperature applications. Titanium aluminum nitride (Ti,Al)N based materials in the form of thin coatings has remained as an outstanding choice for protection of metal cutting tools due to its superior oxidation resistance and high-temperature wear resistance. High-temperature spinodal decomposition of metastable (Ti,Al)N into coherent c-TiN and c-AlN nm-sized domains results in high hardness at elevated temperatures. Even higher thermal input leads to transformation of c-AlN to w-AlN, which is detrimental to the mechanical properties of the coating. One mean to delay this transformation is to introduce nitrogen vacancies.In this thesis, I show that by combining a reduction of the overall N-content of the c-(Ti,Al)Ny (y < 1) coating with a low substrate bias voltage during cathodic arc deposition an even more pronounced delay of the c-AlN to w-AlN phase transformation is achieved. Under such condition, age hardening is retained until 1100 ˚C, which is the highest temperature reported for (Ti,Al)N films. During cutting operations, the wear mechanism of the cathodicarc-deposited c-(Ti0.52Al0.48)Ny with N-contents of y = 0.92, 0.87, and 0.75 films are influenced by the interplay of nitrogen vacancies, microstructure, and chemical reactions with the workpiece material. The y = 0.75 coating contains the highest number of macroparticles and has an inhomogeneous microstructure after machining, which lower its flank and crater wear resistance. Age hardening of the y = 0.92 sample causes its superior flank wear resistance while the dense structure of the y = 0.87 sample prevents chemical wear that results in excellent crater wear resistance.Heteroepitaxial c-(Ti1-x,Alx)Ny (y = 0.92, 0.79, and0.67) films were grown on MgO(001) and (111) substrates using magnetron putter deposition to examine the details of their defect structures during spinodal decomposition. At 900 ˚C, the films decompose to form coherent c-AlN- and c-TiN- rich domains with elongated shape along the elastically soft <001> direction. Deformation maps show that most strains occur near the interface of the segregated domains and inside the c-TiN domains. Dislocations favorably aggregate in c-TiN rather than c-AlN because the later has stronger directionality of covalent chemical bonds. At elevated temperature, the domain size of (001) and (111)- oriented c-(Ti,Al)Ny films increases with the nitrogen content. This indicates that there is a delay in coarsening due to the presence of more N vacancies in the film.The structural and functional properties (Ti1-x,Alx)Ny are also influenced by its Al content (x). TiN and (Ti1-x,Alx)Ny (y = 1, x = 0.63 and x = 0.77) thin films were grown on MgO(111) substrates using magnetron sputtering technique. Both TiN and Ti0.27Al0.63N films are single crystals with cubic structure. (Ti0.23,Al0.77)N film has epitaxial cubic structure only in the first few atomic layers then it transitions to an epitaxial wurtzite layer, with an orientation relationship of c-(Ti0.23,Al0.77)N(111)[1-10]ǀǀw-(Ti0.23,Al0.77)N(0001)[11-20]. The w-(Ti0.23,Al0.77)N shows phase separation of coherent nm-sized domains with varying chemical composition during growth. After annealing at high temperature, the domains in w-(Ti0.23,Al0.77)N have coarsened. The domains in w-(Ti0.23,Al0.77)N are smaller compared to the domains in c-(Ti0.27,Al0.63)N film that has undergone spinodal decomposition. The results that emerged from this thesis are of great importance in the cutting tool industry and also in the microelectronics industry, because the layers examined have properties that are well suited for diffusion barriers.
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| 6. |
- Calamba, Katherine, et al.
(författare)
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The effect of nitrogen vacancies on initial wear in arc deposited (Ti-0.52,Ti- Al-0.48)N-y, (y < 1) coatings during machining
- 2019
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 358, s. 452-460
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen deficient c-(Ti0.52Al0.48)Ny, y = 0.92, y = 0.87, and y = 0.75 coatings were prepared in different N-2/Ar discharges on WC-Co inserts by reactive cathodic arc deposition. The microstructure of the y = 0.92 coating show that spinodal decomposition has occurred resulting in the formation of coherent c-TiN- and c-AIN rich domains during cutting. The y = 0.87 and y = 0.75 coatings have exhibited a delay in decomposition due to the presence of nitrogen vacancies that lowers the free energy of the system. In the decomposed structure, grain boundaries and misfit dislocations enhance the diffusion of elements from the workpiece and the substrate (e.g. Fe, Cr, and Co) into the coatings and it becomes more susceptible to crater wear. The y = 0.87 sample displays the highest crater wear resistance because of its dense grain boundaries that prevent chemical wear. The y = 0.92 sample has the best flank wear resistance because the decomposition results in age hardening. The y = 0.75 sample contains the MAX-phase Ti(2)AIN after cutting. The chemical alteration within the y = 0.75 sample and its high amount of macroparticles cause its low wear resistance. The different microstructure evolution caused by different amount of N-vacancies result in distinctive interactions between chip and coating, which also causes difference in the initial wear mechanism of the (Ti,Al)/N-y coatings.
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| 7. |
- Harsani, M., et al.
(författare)
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Adhesive-deformation relationships and mechanical properties of nc-AlCrN/a-SiNx hard coatings deposited at different bias voltages
- 2018
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 650, s. 11-19
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Tidskriftsartikel (refereegranskat)abstract
- A series of Al-Cr-Si-N hard coatings were deposited on WC-Co substrates with a negative substrate bias voltage ranging from -50 to -200 V using cathodic arc evaporation system. A Rockwell-C adhesion test demonstrated that excellent adhesion was observed at lower bias voltages of -50 V and -80 V, while further increases in bias voltage up to -200 V led to severe delamination and worsening of the overall adhesion strength. X-ray diffraction and transmission electron microscopy analysis revealed a single phase cubic B1-structure identified as an AlCrN solid solution with a nanocomposite microstructure where cubic AlCrN nanocrystals were embedded in a thin continuous amorphous SiNx matrix. Coatings exhibited a 002-texture evolution that was more pronounced at higher bias voltages (amp;gt;=-120 V). Stress-induced cracks were observed inside the coatings at high bias voltages (amp;gt;=-150 V), which resulted in stress relaxation and a decline in the overall residual stresses.
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| 8. |
- Salamania, Janella, 1992-, et al.
(författare)
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High-resolution STEM investigation of the role of dislocations during decomposition of Ti1-xAlxNy
- 2023
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Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- The defect structures forming during high-temperature decomposition of Ti1-xAlxNy films were investigated through high-resolution scanning transmission electron microscopy. After annealing to 950 °C, misfit edge dislocations a/6〈112〉{111} partial dislocations permeate the interface between TiN-rich and AlN-rich domains to accommodate lattice misfits during spinodal decomposition. The stacking fault energy associated with the partial dislocations decreases with increasing Al content, which facilitates the coherent cubic to wurtzite structure transition of AlN-rich domains. The wurtzite AlN-rich structure is recovered when every third cubic {111} plane is shifted by along the [211] direction. After annealing to 1100 °C, a temperature where coarsening dominates the microstructure evolution, we observe intersections of stacking faults, which form sessile locks at the interface of the TiN- and AlN-rich domains. These observed defect structures facilitate the formation of semicoherent interfaces and contribute to hardening in Ti1-xAlxNy.
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