Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings

Micro-mechanical properties of Ti(C,N) and Zr(C,N) coatings deposited by chemical vapor deposition on a WC-Co cemented carbide substrate were examined by micro-compression testing using a nanoindenter equipped with a flat punch. Scanning Electron Microscopy, Focused Ion Beam, Electron Backscattered Diffraction and Finite Element Modeling were combined to analyze the deformation mechanisms of the carbonitride layers at room temperature. The results revealed that Ti(C,N) undergoes a pure intergranular crack propagation and grain decohesion under uniaxial compression; whereas the fracture mode of Zr(C,N) was observed to be inter/transgranular failure with unexpected plastic deformation at room temperature.Peer ReviewedPostprint (author's final draft

Atom Probe Tomography investigations on grain boundary segregation in polycrystalline Ti(C,N) and Zr(C,N) CVD coatings

Atom Probe Tomography (APT) was used to obtain a direct evidence of chlor segregation and cobalt diffusion at the grain boundaries (GBs) of polycrystalline coatings deposited by moderate temperature chemical vapor deposition (MT-CVD) on a WC-Co cemented carbide substrate. Reasons behind segregations are discussed, and its effects are correlated to the micromechanical properties of Ti(C,N) and Zr(C,N). It is concluded that chlorine segregation is a relevant factor for explaining the low cohesive strength at the GBs of Ti(C,N) leading to intergranular failure during micro-compression testing, while its absence in Zr(C,N) along with Co diffusion contribute to grain boundary strengthening.Peer ReviewedPreprin

Micromechanical investigations of CVD coated WC-Co cemented carbide by micropillar compression

Deformation behavior of an industrial coated cemented carbide (WC-Co substrate coated with CVD multilayer of TiN/Zr(C,N)/Ti(C,N,O)/Al2O3) was investigated by means of micropillar compression method. In addition to the WC-Co substrate pillars, new composite pillar combination consisting of substrate, TiN interlayer and carbonitride hard coating were tested. The study targeted to document and analyze interactions between different phases and components (substrate, interlayer and coating) while subjected to compressive stress. It is found that deformation of the substrate depends mainly on the assemblage and the distribution of WC and Co phases within the pillar. The phase assemblage is subjected to changes after deformation which has an impact on the stiffness. Detailed analysis of plastic deformation within WC coarse grains pointed out that strain energy can be extensively dissipated in this phase by means of single and multiple slip. The composite/hybrid pillar formed by association of the substrate and the coating enhanced the ultimate strength in comparison to their respective individual components, highlighting the effective load-bearing response of coating and substrate acting as a coated system. This assessment was further supported by the excellent interfacial strength attested by the established TiN interlayer between the substrate and the coating

Design of Comb Crack Resistant Milling Inserts: A Comparison of Stresses, Crack Propagation, and Deformation Behavior between Ti(C,N)/α-Al2O3 and Zr(C,N)/α-Al2O3 CVD Coatings

Investigations on comb crack resistance of milling inserts coated with chemical vapor deposition (CVD) Ti(C,N)/α-Al2O3 and Zr(C,N)/α-Al2O3 showed a distinct wear evolution in both systems. Wear studies revealed that the appearance of comb cracks is connected to the initial CVD cooling crack network. Micropillar compression tests indicated a brittle intergranular fracture mechanism for the Ti(C,N) layer and a transgranular fracture accompanied with signs of plastic deformation for the Zr(C,N) coating. Additionally, for the Zr(C,N) based system, a compressive stress condition in the temperature range of interest (200–600 ◦C) was determined by in-situ synchrotron X-ray diffraction. The set of residual compressive stresses together with the ability of the Zr(C,N) layer to deform plastically are key features that explain the enhanced resistance to comb crack wear of the Zr(C,N) based system in milling of cast iron

Multiscale mechanical and microstrutural characterization of titanium and zirconium carbonitride hard coatings

The present dissertation is an in-depth investigation from the macro to atomic scale of industrial wear-resistant CVD hard coatings deposited on cemented carbides for cutting tool applications. Micro-compression tests at the micro-scale and contact damage induced by means of millimetric spherical indentation were deployed to study deformation mechanisms of two systems consisting of a defined cemented carbide substrate coated with two different films: Ti(C,N) and Zr(C,N). The latter system exhibited a superior tool life in comparison to the conventional Ti(C,N) one. Several characterization techniques were used: confocal microscopy, scanning electron microscopy, focused ion beam, electron back scattered diffraction, X-ray synchrotron and atom probe tomography. It was found that remnant structural integrity related to the absence of an extensive cracking network for Zr(C,N) - in the as deposited state - is one of the main reasons that could explain better performance in interrupted cutting. Adapted coefficient of thermal expansion toward the substrate, plastic deformation and better cohesive strength at the grain boundaries (which renders more toughness) are factors that contribute not only to this preserved structural integrity but also to the extended tool life during in-service interrupted cutting.En esta tesis doctoral se presenta una investigación extensa y detallada, desde la escala macroscópica hasta la atómica, de recubrimientos industriales - duros y resistentes al desgaste - depositados por CVD sobre carburos cementados para su aplicación como herramientas de corte. El estudio se realizó en dos sistemas recubiertos empleando diferentes capas cerámicas - Ti(C,N) y Zr(C,N) - pero sin variar el carburo cementado empleado como sustrato. Los mecanismos de deformación de ambos sistemas se evaluaron mediante ensayos de micro-compresión de pilares, así como de indentación esférica (con bolas de radios milimétricos), estos últimos buscando inducir daño de forma controlada a nivel superficial y subsuperficial. El sistema recubierto con la capa de Zr(C,N) exhibió una vida útil superior al más convencional - Ti(C,N). El estudio incluyó la implementación de varias técnicas de caracterización: microscopía confocal, microscopía electrónica de barrido, haz de iones focalizados, difracción de electrones retrodispersados, sincrotrón de rayos X, y tomografía con sonda atómica. Se encontró que la elevada integridad estructural remanente relacionada con la ausencia de fisuración interconectada en el caso de Zr(C,N) – justo después de ser depositado – es alguna de las principales razones para explicar el mayor rendimiento de este sistema recubierto en operaciones de mecanizado que involucran corte interrumpido. La adecuación del coeficiente de expansión térmica, relativo al que exhibe el sustrato, la capacidad de absorber deformación plástica, y la relevante resistencia cohesiva en los bordes de granos (lo que proporciona una mayor tenacidad) son factores que contribuyen no sólo a preservar la integridad estructural, sinó también a prolongar la vida útil de la herramienta durante condiciones de servicio que conlleven corte interrumpido.Die vorliegende Dissertation ist eine eingehende Untersuchung vom makrobis zu der atomaren Skala von industrieller verschleißfester CVD-Hartschichten auf Hartmetallschneidwerkzeugen abgeschieden. Mikrodruckversuche und Kontaktschädigung ausgelöst durch millimetergenaue Kugel Eindruck wurden eingesetzt, um Verformungsmechanismen von zwei Systemen, bestehend aus einem definierten Hartmetallsubstrat, das mit zwei verschiedenen Schichten beschichtet ist: Ti(C,N) und Zr(C,N). Letzteres System zeigt eine höhere Standzeit als das herkömmliche Ti(C,N). Es wurden eine Vielzahl von Charakterisierungstechniken eingesetzt: Konfokale Mikroskopie, Rasterelektronenmikroskopie, fokussierter Ionenstrahl, Elektronenrückstreubeugung, Synchrotron und Atomsonden- Tomographie. Es wurde festgestellt, dass die erhaltene strukturelle Integrität in Bezug auf das Fehlen eines ausgedehnten Rissnetzwerks für Zr(C,N) - im abgeschiedenen Zustand - einer der Hauptgründe ist, der die bessere Leistung beim unterbrochenen Schnitt Verfahren erklären könnte. Angepasste Wärmeausdehnungskoeffizienten entgegen das Substrat, plastische Verformung und bessere Korngrenzen-Kohäsion (was zu mehr Zähigkeit führt) sind Faktoren, die nicht nur zu dieser erhaltenen strukturellen Integrität beitragen, sondern auch zu einer verlängerten Standzeit beim Fräsen im Einsatz

Multiscale mechanical and microstructural characterization of titanium and zirconium carbonitride hard coatings

The present dissertation is an in-depth investigation from the macro to atomic scale of industrial wear-resistant CVD hard coatings deposited on cemented carbides for cutting tool applications. Micro-compression tests at the micro-scale and contact damage induced by means of millimetric spherical indentation were deployed to study deformation mechanisms of two systems consisting of a defined cemented carbide substrate coated with two different films: Ti(C,N) and Zr(C,N). The latter system exhibited a superior tool life in comparison to the conventional Ti(C,N) one. Several characterization techniques were used: confocal microscopy, scanning electron microscopy, focused ion beam, electron back scattered diffraction, X-ray synchrotron and atom probe tomography. It was found that remnant structural integrity related to the absence of an extensive cracking network for Zr(C,N) - in the as deposited state - is one of the main reasons that could explain better performance in interrupted cutting. Adapted coefficient of thermal expansion toward the substrate, plastic deformation and better cohesive strength at the grain boundaries (which renders more toughness) are factors that contribute not only to this preserved structural integrity but also to the extended tool life during in-service interrupted cutting.En esta tesis doctoral se presenta una investigación extensa y detallada, desde la escala macroscópica hasta la atómica, de recubrimientos industriales - duros y resistentes al desgaste - depositados por CVD sobre carburos cementados para su aplicación como herramientas de corte. El estudio se realizó en dos sistemas recubiertos empleando diferentes capas cerámicas - Ti(C,N) y Zr(C,N) - pero sin variar el carburo cementado empleado como sustrato. Los mecanismos de deformación de ambos sistemas se evaluaron mediante ensayos de micro-compresión de pilares, así como de indentación esférica (con bolas de radios milimétricos), estos últimos buscando inducir daño de forma controlada a nivel superficial y subsuperficial. El sistema recubierto con la capa de Zr(C,N) exhibió una vida útil superior al más convencional - Ti(C,N). El estudio incluyó la implementación de varias técnicas de caracterización: microscopía confocal, microscopía electrónica de barrido, haz de iones focalizados, difracción de electrones retrodispersados, sincrotrón de rayos X, y tomografía con sonda atómica. Se encontró que la elevada integridad estructural remanente relacionada con la ausencia de fisuración interconectada en el caso de Zr(C,N) – justo después de ser depositado – es alguna de las principales razones para explicar el mayor rendimiento de este sistema recubierto en operaciones de mecanizado que involucran corte interrumpido. La adecuación del coeficiente de expansión térmica, relativo al que exhibe el sustrato, la capacidad de absorber deformación plástica, y la relevante resistencia cohesiva en los bordes de granos (lo que proporciona una mayor tenacidad) son factores que contribuyen no sólo a preservar la integridad estructural, sinó también a prolongar la vida útil de la herramienta durante condiciones de servicio que conlleven corte interrumpido.Die vorliegende Dissertation ist eine eingehende Untersuchung vom makrobis zu der atomaren Skala von industrieller verschleißfester CVD-Hartschichten auf Hartmetallschneidwerkzeugen abgeschieden. Mikrodruckversuche und Kontaktschädigung ausgelöst durch millimetergenaue Kugel Eindruck wurden eingesetzt, um Verformungsmechanismen von zwei Systemen, bestehend aus einem definierten Hartmetallsubstrat, das mit zwei verschiedenen Schichten beschichtet ist: Ti(C,N) und Zr(C,N). Letzteres System zeigt eine höhere Standzeit als das herkömmliche Ti(C,N). Es wurden eine Vielzahl von Charakterisierungstechniken eingesetzt: Konfokale Mikroskopie, Rasterelektronenmikroskopie, fokussierter Ionenstrahl, Elektronenrückstreubeugung, Synchrotron und Atomsonden- Tomographie. Es wurde festgestellt, dass die erhaltene strukturelle Integrität in Bezug auf das Fehlen eines ausgedehnten Rissnetzwerks für Zr(C,N) - im abgeschiedenen Zustand - einer der Hauptgründe ist, der die bessere Leistung beim unterbrochenen Schnitt Verfahren erklären könnte. Angepasste Wärmeausdehnungskoeffizienten entgegen das Substrat, plastische Verformung und bessere Korngrenzen-Kohäsion (was zu mehr Zähigkeit führt) sind Faktoren, die nicht nur zu dieser erhaltenen strukturellen Integrität beitragen, sondern auch zu einer verlängerten Standzeit beim Fräsen im Einsatz

Atom Probe Tomography investigations on grain boundary segregation in polycrystalline Ti(C,N) and Zr(C,N) CVD coatings

Atom Probe Tomography (APT) was used to obtain a direct evidence of chlor segregation and cobalt diffusion at the grain boundaries (GBs) of polycrystalline coatings deposited by moderate temperature chemical vapor deposition (MT-CVD) on a WC-Co cemented carbide substrate. Reasons behind segregations are discussed, and its effects are correlated to the micromechanical properties of Ti(C,N) and Zr(C,N). It is concluded that chlorine segregation is a relevant factor for explaining the low cohesive strength at the GBs of Ti(C,N) leading to intergranular failure during micro-compression testing, while its absence in Zr(C,N) along with Co diffusion contribute to grain boundary strengthening.Peer Reviewe

Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings

Micro-mechanical properties of Ti(C,N) and Zr(C,N) coatings deposited by chemical vapor deposition on a WC-Co cemented carbide substrate were examined by micro-compression testing using a nanoindenter equipped with a flat punch. Scanning Electron Microscopy, Focused Ion Beam, Electron Backscattered Diffraction and Finite Element Modeling were combined to analyze the deformation mechanisms of the carbonitride layers at room temperature. The results revealed that Ti(C,N) undergoes a pure intergranular crack propagation and grain decohesion under uniaxial compression; whereas the fracture mode of Zr(C,N) was observed to be inter/transgranular failure with unexpected plastic deformation at room temperature.Peer Reviewe

Micromechanical investigations of CVD coated WC-Co cemented carbide by micropillar compression

Deformation behavior of an industrial coated cemented carbide (WC-Co substrate coated with CVD multilayer of TiN/Zr(C,N)/Ti(C,N,O)/Al2O3) was investigated by means of micropillar compression method. In addition to the WC-Co substrate pillars, new composite pillar combination consisting of substrate, TiN interlayer and carbonitride hard coating were tested. The study targeted to document and analyze interactions between different phases and components (substrate, interlayer and coating) while subjected to compressive stress. It is found that deformation of the substrate depends mainly on the assemblage and the distribution of WC and Co phases within the pillar. The phase assemblage is subjected to changes after deformation which has an impact on the stiffness. Detailed analysis of plastic deformation within WC coarse grains pointed out that strain energy can be extensively dissipated in this phase by means of single and multiple slip. The composite/hybrid pillar formed by association of the substrate and the coating enhanced the ultimate strength in comparison to their respective individual components, highlighting the effective load-bearing response of coating and substrate acting as a coated system. This assessment was further supported by the excellent interfacial strength attested by the established TiN interlayer between the substrate and the coating.Peer Reviewe

Impact of temperature on chlorine contamination and segregation for Ti(C,N) CVD thin hard coating studied by nano-SIMS and atom probe tomography

High resolution characterization by Atom Probe Tomography (APT) and Secondary Ion Mass Spectrometry (SIMS) imaging were combined to highlight the nature of chlorine contamination and impact of deposition temperature for chemical vapor deposited Ti(C,N) thin hard coating. It is highlighted that chlorine is spread and segregates exclusively at the grain boundaries. With increasing temperature (at 930°C), columnar grains of Ti(C,N) become coarser and chlorine segregation at the grain boundaries is reduced about 3 times in comparison to lower temperature (at 885°C). It also appears that chlorine is less homogeneously distributed with chlorine rich/free regions as it is demonstrated by the powerful combination of nano-SIMS and APT which gave a great insight of the spatial distribution of segregating elements at grain boundaries at nano- and micrometric scales.Peer ReviewedPostprint (author's final draft