This thesis explores nanostructuring in TiSiCN, ZrAlN, and TiAlN thin films deposited by cathodic arc evaporation onto cemented carbide substrates, with intended applications for cutting tools. The three systems were found to exhibit age hardening upon annealing, by different mechanisms, into the superhard regime (≥30 GPa), as determined by a combination of electron microscopy, X-ray diffraction, atom probe tomography, erda, and nanoindentation tech- niques. TiSiCN forms nanocomposite films during growth by virtue of Si segregation to the surface of TiCN nanocrystallites while simultaneously pro- moting renucleation. Thus, the common columnar microstructure of TiCN and low-Si-content (≤5 at. %) TiSiN-films is replaced by a “feather-like” nanos- tructure in high-Si-content (≥10 at. %) TiSiCN films. The presence of C promotes the formation of this structure, and results in an accelerated age hardening beginning at temperatures as low as 700 °C. The thermal stability of the TiSiCN films is, however, decreased compared to the TiSiN system by the loss of Si and interdiffusion of substrate species; C was found to ex- acerbate these processes, which became active at 900 °C. The ZrAlN system forms a two-phase nanostructure during growth consisting of cubic ZrAlN and wurtzite ZrAlN. Upon annealing to 1100 °C, the c-Zr(Al)N portion of the films recovers and semicoherent brick-like w-(Zr)AlN structures are formed. Age hardening by 36 % was obtained before overageing sets in at 1200 °C. As-deposited and annealed solid solution Ti0.33Al0.67N thin films were characterized for the first time by atom probe tomography. The as-deposited film was found to be at the very initial stage of spinodal decomposition, which continued during annealing of the film at 900 °C for 2 h. N preferentially segregates to Al-rich domains in the annealed sample, causing a compositional variation between Ti-rich and Al-rich domains, to maintain the stoichiometry for the developing AlN phase. That effect also compensates for some of the coherency strain formed between cubic domains of TiN and AlN. Finally, a possible Kirkendall effect caused by an imbalance in the metal interdiffusion during the spinodal decomposition was discovered.

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Increasing productivity is a constant demand for the manufacturing industry. Low-carbon-steel is one of the most commonly used ferrous materials in the part manufacturing market. Improving productivity as well as making the process eco-friendly by implementing a dry machining condition is the essential goal of this study. Built-up-edge (BUE) is often formed in the low-carbon-steel machining process, which, results in poor surface finish and short tool life. The high-speed-machining technique can be used to reduce the BUE formation and realize an increase in productivity. Cubic boron nitride (CBN) tools are most commonly used in hard turning and cast-iron machining at high cutting speeds. There are a limited number of studies regarding low-carbon-steel machining with CBN under a high-speed and with a dry machining condition. In this study, the investigation shows the preferable type of CBN tool and the wear mechanisms involved during finish turning operations of AISI 1018 under high speed and dry machining conditions. Test results show that a low CBN content with a TiCN binder and smaller grain size offers the best tool life and surface integrity of the final part. Currently manufacturers use coated carbide tools with a recommended cutting speed of 200-300m/min with coolant to complete the finishing process for turning low carbon steel parts. In this study, by implementing CBN tools under the dry condition at 500 m/min cutting speed (speed was selected from the preliminary test performed using the uncoated CBN from 500 to 1200 m/min), the buildup edge formation has been reduced, tool life was measured to increase by 307% compared to the benchmark tool (Coated Carbide), and surface finish was measured in the range of 0.8-1.6μm Ra. / Thesis / Master of Applied Science (MASc)

TiAlN and TiAlN-based coatings that are used of relevance as protection of cutting tool inserts used in metal machining have been studied. All coatings were deposited by reactive cathodic arc evaporation using industrial scale deposition systems. The metal content of the coatings was varied by using different combinations of compound cathodes. The as-deposited coatings were temperature annealed at ambient pressure and in some cases also at high pressure. The resulting microstructure was first evaluated through a combination of x-ray diffraction and transmission electron microscopy. In addition, mechanical properties such as hardness by nanoindentation were also reported. TiAlN coatings with two different compositions were deposited on polycrystalline boron nitride substrates and then high pressure high temperature treated in a BELT press at constant 5.35 GPa and at 1050 and 1300 °C for different times. For high pressure high temperature treated TiAlN it has been shown that the decomposition is slower at higher pressure compared to ambeint pressure and that no chemical interaction takes place between TiAlN and polycrystalline cubic boron nitride during the experiments. It is concluded that this film has the potential to protect a polycrystalline cubic boron nitride substrate during metal machining due to a high chemical integrity. TiZrAlN coatings with different predicted driving forces for spinodal decomposition were furthermore annealed at different temperatures. For this material system it has been shown that for Zr-poor compositions the tendency for phase separation between ZrN and AlN is strong at elevated temperatures and that after spinodal decomposition stable TiZrN is formed.

This thesis is a theoretical study of configurational and magnetic interactions in multicomponent solids. These interactions are the projections onto the configurational and magnetic degrees of freedom of the underlying electronic quantum mechanical system, and can be used to model, explain and predict the properties of materials. For example, the interactions govern temperature induced configurational and magnetic order-disorder transitions in Heusler alloys and ternary nitrides. In particular three perspectives are studied. The first is how the interactions can be derived from first-principles calculations at relevant physical conditions. The second is their consequences, like the critical temperatures for disordering, obtained with e.g. Monte Carlo simulations. The third is their origin in terms of the underlying electronic structure of the materials. Intrinsic defects in the half-Heusler system NiMnSb are studied and it is found that low-energy defects do not destroy the important half-metallic property at low concentrations. Deliberate doping of NiMnSb with 3d-metals is considered and it is found that replacing some Ni with extra Mn or Cr creates new strong magnetic interactions which could be beneficial for applications at elevated temperature. A self-consistent scheme to include the effects of thermal expansion and one-electron excitations in the calculation of the magnetic critical temperature is introduced and applied to a study of Ni1−xCuxMnSb. A supercell implementation of the disordered local moments approach is suggested and benchmarked for the treatment of paramagnetic CrN as a disordered magnetic phase. It is found that the orthorhombic-to-cubic phase transition in this nitride can be understood as a first-order magnetic order-disorder transition. The ferromagnetism in Ti1−xCrxN solid solutions, an unusual property in nitrides, is explained in terms of a charge transfer induced change in the Cr-Cr magnetic interactions. Cubic Ti1−xAlxN solid solutions displays a complex and concentration dependent phase separation tendency. A unified cluster expansion method is presented that can be used to simulate the configurational thermodynamics of this system. It is shown that short range clustering do influence the free energy of mixing but only slightly change the isostructural phase diagram as compared to mean-field estimates.

With the amalgamation of hard coating in cutting tools industries for three decades now, a stage with proven performance has been reached. Today, nearly 40% of all cutting tools used in machining applications are sheltered with coatings. Coatings have proven to dramatically improve wear resistance, increase tool life and enable use at higher speed. Over the years TiN, TiAlN and TiC have emerged as potential materials to coat machining tools. Chemical vapor deposition was the first technology to be used to deposit these coatings followed by physical vapor deposition. Currently, extensive use is being made of cathodic arc evaporation and sputtering for coatings components. The principal limiting factor in the performance of these cutting tools lies in their failure due to the brittleness of these coatings. These hard coatings, usually coated on soft steel substrates, are subjected to contact damage during service. This contact damage is driven by mismatch strain between the elastically deforming film on a plastically deforming substrate. Understanding of the contact damage is the key parameter for improvement in the coating design. Contact damage involves initiation of cracks and subsequent propagation within coating. Multiple cracking modes are seen in nitride coatings on soft substrate and mutual interaction of cracks may lead to spallation of the coating, exposing the substrate to extreme service conditions. Hence visualization of subsurface crack trajectories facilitates the classification of benign and catastrophic modes of failure, which consequently allows us to tailor the coating architecture to eliminate catastrophic failure. Multilayers have shown to perform better then monolayer coatings. In multilayer coatings, application specific particular properties can be engineered by alternately stack-ing suitable layers. The multilayer utilizes benefits of interfaces by crack deflection, crack blunting and desirable transition in residual stress across the interface. Hence, designing interfaces is the key parameter in the multilayer coating. However, very few studies exist that describe experimental visualization of deformation modes in multilayer coatings with different types of interfaces, e.g. nitride/nitride and nitride/metal. Thus the prime objective of the present study is to comprehend the influence of different interface structures as well as its architecture on the various contact damage modes in these coatings. TiAlN/TiN has shown better tribological properties compared to its constituent monolayers. There is an order of magnitude augmentation in loads for cracking without any hardness enhancement relative to monolayers of constituents, with the additional feature that both constituents exhibit similar hardness and modulus. The resistance to cracking is seen to increase with increase in number of interfaces. Hence this uniqueness in toughening without drastic reduction in mechanical properties provides the motivation for understanding the fundamental mechanisms of toughening provided by the interfaces in these hard/hard coatings. Another combination for the present study is with interfaces between hard-soft phases ZrN/Zr, a composite that seeks to compromise hardness in order to achieve greater toughness. The selected combination has potential of providing a model system without any substoichiometric nitrides influencing the interfacial structure. There is a great need to optimize the metal fraction/thickness for exploiting the benefits of toughening without much compromise on hardness and stiffness, since the principal applications of these coatings lies in preventing erosive and corrosive wear. As all the deformation modes in theses coatings are stress driven, the influence of different variables on stress field would dictate the emerging damage. To understand the role of stress fields on contact damage, finite element method and an analytical model was used to predict the stress field within the coating. The TiAlN/TiN coatings were deposited by cathodic arc evaporation, while sputtering was employed to procure the ZrN/Zr multilayer coatings with much finer layer spacing. Microstructural characterization of the as received coatings was done by XRD, scanning electron microscopy, focused ion beam cross section machining and transmission electron microscopy. Mechanical properties like hardness and modulus were evaluated by nanoindentation with restricted penetration depths to allow measurements that were not influenced by the substrate. Contact damage was induced by micro indentation at high loads. Indentations were examined from plan view as well as cross section for getting details of crack nucleation as well as propagation trajectories. Focused ion beam was used to examine cross sections of indents as well as to prepare electron transparent thin foils for transmission electron microscopy examination of subsurface damage induced by indentation. To emphasize specific issues in detail, the present work is divided into four sections: 1 Microstructure and mechanical characterization of the as deposited coatings of ZrN/Zr multilayer (while that of TiAlN/TiN has been reported elsewhere) 2 Details of contact damage in ZrN/Zr coating 3 Resolution of micro mechanistic issues in TiAlN/TiN coating utilizing detailed microscopy 4 The effect of change in architecture through heat-treatment of ZrN/Zr multilayer coatings on the mechanical behavior and contact damage Detailed microstructural, compositional and mechanical characterization was done on ZrN/Zr as received multilayer coatings. Thickness of metal layer was seen to influence the texture in the nitride, thick metal acquiring basal texture in turn inducing (111) texture in the nitride to reduce interfacial energy. Microstructure revealed that the nitride grows with interrupted columnar grains, renucleating at each metal/nitride interface. Presence of both phases was confirmed at even very low bilayer spacing, with slight changes in multilayers architecture, from planar interfaces to curved interfaces. The chosen system proved to be an ideal system for multilayer study without formation of secondary nitrides. Residual stress and hardness reduced with increase in metal layer thickness, whereas modulus was seen to follow the rule of mixture value. Detailed contact damage study of ZrN/Zr is reported in section two with influence of volume fraction and metal layer thickness. All the experimental results were corroborated with finite element methods. A comparative study of contact damage of multilayer with monolayer was carried out with cross section as well as plan view of indents. Metal plasticity was able to distribute damage laterally as well as vertically, hence reducing the stress concentration. There lies an optimum thickness of the metal providing maximum toughening by increasing the threshold load required for edge cracking. The sliding of columns is resisted by the metal. However, thick metal layers promote microcracking in individual nitride layers. Cracking is restricted to within individual nitride layers, eliminating through thickness cracking. The intermediate metal thickness was able to provide a mechanism of laterally distributing sliding and hence a higher tolerance level of the indentation strain that can be accommodated without cracking. Thin metal multilayers were seen to show delamination, strongly influenced by the multilayer architecture. We use the finite element method to understand the influence of stress fields in driving these various modes of damage for varying volume fraction and metal layer thicknesses. It is demonstrated how metal plasticity results in stress enhancement in the nitride layer compared to a monolayer and reduces the shear stress, which is the driving force for columnar sliding. The micro cracking to columnar shearing transition with metal thickness was explained with the help of average shear and normal stress across the multilayer which could explain the transition from cracking and sliding to interfacial delamination in thin metal layer multilayers with enhancement in interfacial shear stress. TiAlN/TiN multilayer allowed to exploit a form of compositional contrast to measure the strain with respect to depth. Layers acting as strain markers quantify the amount of sliding in terms of the offset in layers with respect to depth within the coating. We illustrate with transmission electron micrographs, the flaw generation that occurs as a result of sliding of misaligned column boundaries. These boundary kinks,upon further loading, may lead to cracks running at an angle to the indentation axis in an otherwise dense, defect free, as deposited coating. A previous study illustrates the increase in resistance of multilayers to multiple modes of cracking that are seen in the monolayer nitride coatings on steel substrates. We provide evidence of the enhanced plasticity, seen as macroscopic bending, which in reality is column sliding in a series of distributed small steps. We discuss the role of misfit dislocations in spreading the material laterally to accommodate the constraints during indentation and lattice bending. Interfacial sliding is seen to reduce the stress concentration by distributing the vertical column sliding and accommodating the flaws generated by the sliding of misaligned column boundaries. Some preferred boundaries with special orientation relations do slide, while near the substrate, the sliding is facilitated by the relaxation in intrinsic residual stresses. An analytical model which was formulated earlier is used to support our experimental findings. Investigations of the plausible reasons for the naturally occurring multilayer mollusc sea shells to reach stiffnesses equal to the upper bound of the rule of mixture value have concluded that its brick and mortar organization is responsible for its exceptional mechanical properties. Inspired by the same model, heat treatment was used to change the architecture of the soft-hard metal/nitride combination from that of the planar interface of the as deposited multilayer to a brick and mortar arrangement. Such an interconnected ZrN microstructure was successfully achieved and the stiffness and hardness were both seen to increase relative to the as received coatings. The possible reasons for this enhancement are discussed in term of this newly emerged architecture ,change in residual stress as well as changes in stoichiometry after heat treatment. The contact damage, though, was found to be more catastrophic relative to the as deposited coating with increased propensities for edge and lateral cracking. This was attributed to the interconnected nitrides formed in the brick and mortar architecture as well as residual stress changes due to the dissolution of Zr in ZrN to form off-stoichiometric nitrides. The cracks feel the presence of the metal and deviate from the otherwise smooth trajectory and take a path along the interface of the metal packet and the interconnected nitride. Summarizing, the present study clearly illustrates the fact that interfaces play an important role in damage control under contact loading. Fracture and deformation are either controlled by metal plasticity, distributing the column sliding in metal/nitride multilayers or by interfacial sliding mediated by interfacial misfit dislocations in case of the nitride/nitride multilayer coatings. The effective role of interfaces is to distribute damage laterally as well as horizontally to relieve stresses and hence enhance the damage tolerance under indentation. Optimum metal layer thickness has been proposed for maximum toughening in the metal/nitride multilayer coating and the role of interfaces in providing modes of plasticity is presented for the nitride/nitride multilayer coatings by use of extensive transmission electron microscopic investigations. A new interconnected architecture coatings provides a unique way of combining stiffness and toughness along with scope for further developing such configurations with improved mechanical properties.

High-performance materials such as stainless steels and nickel based super alloys are widely used in demanding applications where high mechanical and thermal properties are required. The applications of super alloys are mainly found in jet engines, power plants and gas turbines demanding high fatigue strength, corrosion and oxidation resistance as well as wear resistant properties. In order to use them, they go through various machining processes such as milling, turning, cutting, polishing etc. until the final product is achieved. Modern manufacturing industries employs various machining tools and technologies to improve the machining process of heat resistant super alloys. However, there are still challenges which needs to be addressed. Among them, adhesive wear of the machining tools is one of the main wear mechanism during the tribological interaction of tool and workpiece, preventing them to achieve the desired quality and surface finish of the end product. Moreover, it damages the tool reducing its lifecycle and in return, increasing the production cost. Among the cutting tools tungsten carbide (WC/Co) tools coated with TiAlN coating due to their good high temperature performance are extensively used. Nonetheless, these coatings still face issue like adhesive wear, abrasion, oxidation at higher temperature damaging the tools and subsequent machining. Therefore, it is imperative to understand the initiation mechanism of adhesive wear during the tribological interaction of super alloys and coated cutting tool material. In this research work, the tribological response of two coatings deposited by physical vapour deposition (PVD), having the composition Ti60Al40N and Ti40Al60N have been studied against two super alloys material, i.e. Inconel 718 and stainless steel 316L. A high temperature SRV (Schwingung (Oscillating), Reibung (Friction), Verschleiß (Wear)) reciprocation friction and wear test set up was employed to investigate the friction behaviour, wear rate and dominant wear mechanisms.  For Ti60Al40N coating, the experimental results revealed that generally, friction increases in case of sliding against Inconel 718 up to 400 °C and drops at 760 °C. A high wear volume at room temperature and a decrease to a minimum at 760 °C has been observed for Inconel 718. On the other side, Stainless steel 316L (SS 316L) faces a continuous rise in friction coefficient with highest value at 760 °C during sliding against Ti60Al40N coating. Wear is highest at 400 °C for SS 316L pin. The worn surfaces shows that both workpiece materials experience increase in material transfer due to adhesive wear with rise in temperature. At 400 °C, adhesion is the primary wear mechanism for both workpiece materials. A further rise in temperature to 760 °C promotes the adhesive wear through oxides formation on both material surfaces.  Similarly, Ti40Al60N coating shows the same friction behaviour with change in average steady state friction values for both material of Inconel 718 and SS 316L. Both workpiece materials responds in a similar way to wear volume loss, i.e. lowest at room temperature and highest at 760 °C. For Inconel 718, transfer of coating constituents on to the Inconel 718 pin surface was detected and associated with coating rupture and peeling, exacerbating with rise in temperature. Adhesion, abrasion, and oxidation are primary wear mechanisms at 400 °C and 760 °C. For SS 316L, coating transfer only happen at 400 °C. No damage of coating at 40 °C, a complete damage at 400 °C, and formation of dense porous oxides layers at 760 °C have been noticed. At 400 °C, adhesion, abrasion, and chipping while at 760 °C, adhesion, three body abrasion, ploughing and oxidation are the main wear mechanisms.

<p>Proučavane su koroziona postojanost i tendencija lepljenja različitih<br />materijala u kontaktu sa tečnom Al&ndash;Si&ndash;Cu legurom. Ispitivanjem su<br />obuhvaćeni čelik za rad na toplo, plazma nitrirani čelik i dupleks<br />slojevi sa CrN, TiAlN, TiAlSiN i CrAlN prevlakama, različitog nivoa<br />površinske hrapavosti. Za ispitivanja pomenutih fenomena<br />primenjena je metoda izvlačenja, koja je unapređena kako bi se povećale<br />njena tačnost i verodostojnost simulacije procesa livenja. Korozioni<br />efekti su pojačani tako što su uzorci osim kratkog kontakta sa odlivkom<br />zadržavani i u dužim periodima u kontaktu sa tečnom legurom (5 i 20<br />min). Uprkos opštim stavovima, za ispitivane materijale je<br />ustanovljeno da su sile izvlačenja uzoraka iz Al&ndash;Si&ndash;Cu odlivaka<br />nezavisne od njihovog hemijskog sastava. Uticaj hrapavosti je izražen<br />kod uzoraka sa prevlakama kod kojih pri smanjenju hrapavosti dolazi do<br />povećanja sile izvlačenja. Sve ispitane prevlake su sklone mehaničkom<br />lepljenju Al&ndash;Si&ndash;Cu legure za svoje površine, ali sa aspekta korozije u<br />tečnom metalu značajno prevazilaze performanse čelika i plazma<br />nitriranog sloja. Duži kontakt livene legure sa površinama prevlaka<br />uzrokovao je niže vrednosti sila izvlačenja, što je posledica<br />oksidacije površina prevlaka. Ustanovljeno je da su ispitivane<br />prevlake inertne ka tečnoj leguri aluminijuma. Međutim, dolazi do<br />oksidacije i korozije materijala podloge kroz greške rasta koje su<br />prisutne u prevlakama. Stečena znanja o identifikovanim<br />mehanizmima habanja i propadanja zaštitnih slojeva prevlaka<br />poslužiće daljem razvoju dupleks slojeva namenjenih za zaštitu alata<br />za livenje pod pritiskom.</p> / <p>Corrosion resistance and soldering tendency of different materials in molten<br />Al&ndash;Si&ndash;Cu alloy were studied. Hot-working tool steel, plasma nitrided steel and<br />duplex layers with CrN, TiAlN, TiAlSiN and CrAlN top coatings, which were<br />produced to various degree of surface roughness, were covered by the study.<br />An ejection test was employed for investigation of the concerned phenomena.<br />The ejection test was improved in order to increase its accuracy and the<br />reliability of process simulation. Samples were examined in both short and<br />extended periods of contact (5 and 20 min) with liquid casting. Casting<br />solidification was extended in order to intensify the corrosion effects. Contrary<br />to common findings, it was found that the ejection force of the investigated<br />materials does not depend on their chemical composition. For the coated<br />samples, a pronounced dependence of the ejection force on the surface<br />roughness was found. The ejection force increases with decrease in surface<br />roughness. All investigated coatings are prone to mechanical soldering by Al&ndash;<br />Si&ndash;Cu alloy. Still, their corrosion resistance substantially exceeds the corrosion<br />resistance of steel and plasma nitrided layer. Longer exposure of coated<br />samples to cast alloy induced lower ejection forces, which is a consequence<br />of coatings oxidation. It was found that the investigated coatings are inert to<br />liquid aluminium. However, the underlying material undergoes oxidation and<br />corrosion through coating growth defects. The findings concerning the wear<br />mechanisms of protective layers support further development of duplex layers<br />intended for die casting tools protection.</p>