The Seamless Stressometer® roll (Seamless STR) is used to measure the flatness of aluminum and steel strip when there is an extreme demand on the surface finish. To protect the roll and strip, the roll is coated with two layers deposited by high velocity oxygen fueled spraying (HVOF), Cr-Ni(Si,B) closest to the roll and WC-Co on top. This solution has several disadvantages; high cost and complicated logistics, corrosion sensitivity and high residual stresses creates the need for two coatings which in turn complicates the process. Cobalt is, in addition, sensitive to low pH coolants and environmentally unfriendly. These problems have given rise to the idea of switching both the method and material of the coating. In the first part of this work, high velocity air fueled spraying (HVAF) was evaluated as an alternative deposition method. Three materials, Cr3C2-NiCr, WC-Co and WC-CrC-Ni were deposited on steel coupons with varying chamber pressure, powder feed rate and distance from the nozzle, in order to evaluate if HVAF can be a valid technique for use in this application and to optimize the spraying recipe. The objectives were to get a sufficiently high thickness per sweep, to be able to make the depositions in a manageable number of sweeps, and to get low porosity, since the coatings need to be dense to be hard and possible to polish smooth. The tests showed that all three materials can be sprayed with the high settings on the parameters to obtain coatings that exceeded the set limits of the objectives. In the second part of this work, the recipe obtained from the first part was used to deposit samples for further analysis. The coatings were compared regarding cost, hardness, friction, wear and pick-up properties to evaluate if a switch in material from WC-Co was possible. The coatings showed both similarities and differences. The friction was very similar for the three materials. Cr3C2-NiCr was substantially cheaper than the other two, had lower hardness and higher porosity, but still probably acceptable values, and was satisfactory regarding wear and pick-up. WC-Co and WC-CrC-Ni were very similar to each other regarding cost, hardness and porosity but WC-Co was the best regarding wear and pick-up, where WC-CrC-Ni was the worst. The only clear advantage of WC-CrC-Ni over WC-Co is the lack of cobalt. Taking everything into consideration, including the fact that the wear and pick-up tests in this work was quite exaggerated, Cr3C2-NiCr is an interesting option for this application due to its low cost and acceptable test results, WC-Co had the best results but is expensive and contains cobalt and WC-CrC-Ni had as good results as WC-Co except for the wear and pick-up tests and does not contain cobalt.

Este estudo avaliou a microdureza de ligas de NiCr usadas em prótese fixa fundidas sob diferentes condições. As condições de fundição foram: 1- maçarico chama composta de GLP/oxigênio e centrífuga de mola sem controle de ambiente de fundição; 2- indução eletromagnética com ambiente controlado por argônio e vácuo. foram utilizadas três ligas NiCr, NiCrBe e NiCrTi. Foram realizados 18 fundições com 5 corpos-de-prova para cada anel, depois de fundidos os corpos-de-prova foram embutidos e polidos para as mensurações de microdureza vickers (VH) em equipamento Shimadzu-HMV-2 (1Kg por 10s). um total de 3 edentações foram feitas para cada corpo-de-prova.os dados de VH foram avaliados pelo teste de ANOVA e Tukey (=0,05) para contraste de média. A microdureza apresentou a seguinte ordem para maçarico e liga totalmente virgem: NiCrTi (42533,4)> NiCrBe (36215) > NiCr (25314,8), sendo diferentes entre si. Os valore obtidos nas condições de argônio e indução foram semelhantes (p>0,05). A microdureza depende da liga e do método de fundição. A liga de NiCrTi foi maior quando fundidas nas condições de maçarico oxigênio/GLP e totalmente refundida (42826,7). / This study evaluated the microhardess of NiCr alloys used in fixed prosthodontics after casting under different conditions. The casting were: 1-flame/air torch flame made of a gas/oxygen mixture and centrifugal casting machine in a non-controlled casting environment; 2-induction/argon electromagnetic induction in an environment controlled with argon. 18 castings with 5 in each ring were prepared. After casting the ring were embedded in resin and polished for Vickers microhardness (VH) measurements in a Shimadzu HMV-2 (1kgfor 10s). a total 3 indentations were for each ring, one in ring. The data was subjected to two-way ANOVA and Tukeys multiple comparison tests (=0,05). The VH values of NiCrTi NiCrTi (42533,4)> NiCrBe (36215) > NiCr (25314,8). The VH values obtained in the condition of the argon and induction were similar (p>0,05). The microdureza depends on the league and of the foundry method. The league of NiCrTi was larger when melted in the conditions of blowpipe oxygen/GLP and totally recast (42826,7).

abstract: The passivity of metals is a phenomenon of vast importance as it prevents many materials in important applications from rapid deterioration by corrosion. Alloying with a sufficient quantity of passivating elements (Cr, Al, Si), typically in the range of 10% - 20%, is commonly employed to improve the corrosion resistance of elemental metals. However, the compositional criteria for enhanced corrosion resistance have been a long-standing unanswered question for alloys design. With the emerging interest in multi-principal element alloy design, a percolation model is developed herein for the initial stage of passive film formation, termed primary passivation. The successful validation of the assumptions and predictions of the model in three corrosion-resistant binary alloys, Fe-Cr, Ni-Cr, and Cu-Rh supports that the model which can be used to provide a quantitative design strategy for designing corrosion-resistant alloys. To date, this is the only model that can provide such criteria for alloy design.The model relates alloy passivation to site percolation of the passivating elements in the alloy matrix. In the initial passivation stage, Fe (Ni in Ni-Cr or Cu in Cu-Rh) is selectively dissolved, destroying the passive network built up by Cr (or Rh) oxides and undercutting isolated incipient Cr (Rh) oxide nuclei. The only way to prevent undercutting and form a stable protective passive film is if the concentration of Cr (Rh) is high enough to realize site percolation within the thickness of the passive film or the dissolution depth. This 2D-3D percolation cross-over transition explains the compositional dependent passivation of these alloys. The theoretical description of the transition and its assumptions is examined via experiments and kinetic Monte Carlo simulations. The initial passivation scenario of the dissolution selectivity is validated by the inductively coupled plasma mass spectrum (ICP-MS). The electronic effect not considered in the kinetic Monte Carlo simulations is addressed by density functional theory (DFT). Additionally, the impact of the atomic configuration parameter on alloy passivation is experimentally measured, which turns out to agree well with the model predictions developed using Monte Carlo renormalization group (MC-RNG) methods. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

Ligas metálicas não nobres são amplamente utilizadas em odontologia desde a segunda metade do século XX. Várias ligas metálicas para utilização em próteses sobre o implante dentário têm sido propostas nos últimos anos, visando uma melhor interação metal-cerâmica e maior resistência eletroquímica ao ambiente bucal. O objetivo deste trabalho é avaliar e comparar o comportamento eletroquímico in vitro de ligas à base de cobalto-cromo e níquel-cromo, utilizadas em supra estruturas de implantes dentários. Estas ligas foram estudadas em meios de solução aquosa de NaCl 0,15 mol L-1, saliva artificial e NaCl 0,15 mol L-1 com adição de caseína, fluoreto de sódio ou ácido acético, a partir de técnicas eletroquímicas e não eletroquímicas. Como técnicas eletroquímicas foram empregadas: medidas de potencial de circuito aberto, curvas de polarização anódica, cronoamperometria, voltametria cíclica e espectroscopia de impedância eletroquímica. As técnicas não eletroquímicas utilizadas foram: espectroscopia de absorção atômica com atomização eletrotérmica (EAA-FG), espectroscopia de fotoelétrons excitados por raios-X (XPS), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS). Foram realizados testes de citotoxicidade utilizando a metodologia de incorporação do vermelho neutro. Uma boa correlação foi estabelecida entre os resultados obtidos pelas diferentes técnicas. Em solução de NaCl e saliva artificial as ligas apresentaram a seguinte ordem de resistência à oxidação: CoCrW < NiCrMo < CoCrMo. O filme formado em meio de saliva artificial se mostrou mais protetor do que o formado em meio de NaCl para todas as ligas, indicando que componentes presentes na saliva ao se adsorverem na superfície conferem uma maior proteção à mesma. As análises por XPS confirmaram a existência de um filme rico em Cr(III) com pequena concentração de cobalto e de níquel no filme passivo. As análises por EAA-FG a potenciais mais positivos mostraram que nesta região há oxidação generalizada, com a total dissolução do filme passivo e formação de Cr(VI), Ni(IV) e Co(II). As análises por MEV-EDS, para a superfície das ligas CoCrW e NiCrMo, apresentaram uma superfície quase homogênea e composições semelhantes antes e após 8h de imersão em meio de NaCl e em saliva artificial. A caseína atuou inibindo os processos de oxidação sobre a liga CoCrW e NiCrMo e sua atuação se tornou mais intensa com o aumento do potencial. A liga NiCrMo apresentou maior resistência à corrosão em meio de caseína quando comparada com a liga CoCrW. Os íons fluoreto atuam melhorando as características passivantes do filme, mas este efeito decresce com o aumento do potencial; a presença de ácido acético causa um aumento do efeito passivante do filme, à medida que cresce o potencial. As ligas CoCrW e NiCrMo não apresentaram efeito citotóxico, de acordo com a metodologia utilizada. / No noble metallic alloys are largely employed in odontology since the second part of the XX centrury. Different alloys have been proposed in order to be used in prosthesis on dental implants at last years, with the objective to obtain electrochemical resistance to oral environment. The aim of this work is to evaluate and to compare the electrochemical behavior \"in vitro\" of Co-Cr and Ni-Cr based alloys, used on dental implants structures. These alloys were studied in 0.15 mol L-1 NaCl aqueous in the absence and presence of casein, artificial saliva, sodium fluoride and acetic acid, using electrochemical and non-electrochemical techniques. Open circuit potencial measurements, anodic polarization curves, cronoamperometry, cyclic voltametry and electrochemical impedance spectroscopy were used as electrochemical techniques. Atomic absorption spectroscopy with graphite furnace (EAA-GF), X-ray photoelectron spectroscopy (XPS), scaning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used as non electrochemical techniques. Cytotoxicity tests using the neutral red incorporation methodology were performed. A good correlation between the different techniques it was obtained. The alloys presented the following corrosion resistance order: CoCrW < NiCrMo < CoCrMo. The film formed in artificial saliva has been showed a better protective action than the observed in NaCl medium for the three studied materials as an indicative of the adsorption of substances present on saliva and the consequent inhibitive effect. XPS analysis have confirmed the presence of a Cr2O3 film with low Co(II) and Ni(II) concentrations. EAA-GF analysis at more positive potentials have shown the presence of generalized oxidation with total dissolution of the passive film resulting in Cr(VI), Ni(IV) and Co(II) ions as soluble products. MEV and EDS analysis have shown a quasi homogeneous and similar surface before and after 8h immersion in NaCl and artificial saliva. Casein has acted as inhibitor for oxidation process of CoCrW and NiCrMo in NaCl medium and its effects increases as the potential becomes more positive. The alloy NiCrMo presented a higher corrosion resistance in NaCl solution containing casein when compared to the CoCrW alloy. Ions fluoride has promoted a better performance of the film at Ecorr but its effects decreases at more positive potentials.The presence of acetic acid increases the passivating effect as potencial becomes more positive. Cytotoxicity was not observed for the alloys studied, using the described methodology

Ligas metálicas não nobres são amplamente utilizadas em odontologia desde a segunda metade do século XX. Várias ligas metálicas para utilização em próteses sobre o implante dentário têm sido propostas nos últimos anos, visando uma melhor interação metal-cerâmica e maior resistência eletroquímica ao ambiente bucal. O objetivo deste trabalho é avaliar e comparar o comportamento eletroquímico in vitro de ligas à base de cobalto-cromo e níquel-cromo, utilizadas em supra estruturas de implantes dentários. Estas ligas foram estudadas em meios de solução aquosa de NaCl 0,15 mol L-1, saliva artificial e NaCl 0,15 mol L-1 com adição de caseína, fluoreto de sódio ou ácido acético, a partir de técnicas eletroquímicas e não eletroquímicas. Como técnicas eletroquímicas foram empregadas: medidas de potencial de circuito aberto, curvas de polarização anódica, cronoamperometria, voltametria cíclica e espectroscopia de impedância eletroquímica. As técnicas não eletroquímicas utilizadas foram: espectroscopia de absorção atômica com atomização eletrotérmica (EAA-FG), espectroscopia de fotoelétrons excitados por raios-X (XPS), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS). Foram realizados testes de citotoxicidade utilizando a metodologia de incorporação do vermelho neutro. Uma boa correlação foi estabelecida entre os resultados obtidos pelas diferentes técnicas. Em solução de NaCl e saliva artificial as ligas apresentaram a seguinte ordem de resistência à oxidação: CoCrW < NiCrMo < CoCrMo. O filme formado em meio de saliva artificial se mostrou mais protetor do que o formado em meio de NaCl para todas as ligas, indicando que componentes presentes na saliva ao se adsorverem na superfície conferem uma maior proteção à mesma. As análises por XPS confirmaram a existência de um filme rico em Cr(III) com pequena concentração de cobalto e de níquel no filme passivo. As análises por EAA-FG a potenciais mais positivos mostraram que nesta região há oxidação generalizada, com a total dissolução do filme passivo e formação de Cr(VI), Ni(IV) e Co(II). As análises por MEV-EDS, para a superfície das ligas CoCrW e NiCrMo, apresentaram uma superfície quase homogênea e composições semelhantes antes e após 8h de imersão em meio de NaCl e em saliva artificial. A caseína atuou inibindo os processos de oxidação sobre a liga CoCrW e NiCrMo e sua atuação se tornou mais intensa com o aumento do potencial. A liga NiCrMo apresentou maior resistência à corrosão em meio de caseína quando comparada com a liga CoCrW. Os íons fluoreto atuam melhorando as características passivantes do filme, mas este efeito decresce com o aumento do potencial; a presença de ácido acético causa um aumento do efeito passivante do filme, à medida que cresce o potencial. As ligas CoCrW e NiCrMo não apresentaram efeito citotóxico, de acordo com a metodologia utilizada. / No noble metallic alloys are largely employed in odontology since the second part of the XX centrury. Different alloys have been proposed in order to be used in prosthesis on dental implants at last years, with the objective to obtain electrochemical resistance to oral environment. The aim of this work is to evaluate and to compare the electrochemical behavior \"in vitro\" of Co-Cr and Ni-Cr based alloys, used on dental implants structures. These alloys were studied in 0.15 mol L-1 NaCl aqueous in the absence and presence of casein, artificial saliva, sodium fluoride and acetic acid, using electrochemical and non-electrochemical techniques. Open circuit potencial measurements, anodic polarization curves, cronoamperometry, cyclic voltametry and electrochemical impedance spectroscopy were used as electrochemical techniques. Atomic absorption spectroscopy with graphite furnace (EAA-GF), X-ray photoelectron spectroscopy (XPS), scaning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used as non electrochemical techniques. Cytotoxicity tests using the neutral red incorporation methodology were performed. A good correlation between the different techniques it was obtained. The alloys presented the following corrosion resistance order: CoCrW < NiCrMo < CoCrMo. The film formed in artificial saliva has been showed a better protective action than the observed in NaCl medium for the three studied materials as an indicative of the adsorption of substances present on saliva and the consequent inhibitive effect. XPS analysis have confirmed the presence of a Cr2O3 film with low Co(II) and Ni(II) concentrations. EAA-GF analysis at more positive potentials have shown the presence of generalized oxidation with total dissolution of the passive film resulting in Cr(VI), Ni(IV) and Co(II) ions as soluble products. MEV and EDS analysis have shown a quasi homogeneous and similar surface before and after 8h immersion in NaCl and artificial saliva. Casein has acted as inhibitor for oxidation process of CoCrW and NiCrMo in NaCl medium and its effects increases as the potential becomes more positive. The alloy NiCrMo presented a higher corrosion resistance in NaCl solution containing casein when compared to the CoCrW alloy. Ions fluoride has promoted a better performance of the film at Ecorr but its effects decreases at more positive potentials.The presence of acetic acid increases the passivating effect as potencial becomes more positive. Cytotoxicity was not observed for the alloys studied, using the described methodology

O desgaste é um dos fatores que causam a maior parte das falhas e redução na vida útil de ferramentas, além de resultar em produtos com condições superficiais inadequadas. A crescente demanda da indústria por menores custos, maior produtividade e melhor qualidade estão entre as justificativas para que se busquem maneiras de incrementar o desempenho dessas ferramentas. Neste contexto, o trabalho tem como objetivo avaliar e caracterizar superfícies projetadas para resistência ao desgaste utilizando o processo de aspersão térmica oxicombustível de alta velocidade (HVOF). Fez-se um estudo comparativo de caracterização e comportamento tribológico de um aço ferramenta com deposição por aspersão térmica de dois diferentes revestimentos. O estudo abrange o aço ABNT H13, utilizando o tratamento superficial de aspersão térmica HVOF com revestimentos de Cr3C2-25(NiCr) e WC-10Co-4Cr. A avaliação da superfície e do comportamento tribológico envolveu perfis de microdureza, análise de fases por difração de raios X, metalografias, obtenção da composição química, caracterização da rugosidade, ensaio de abrasão e adesão, pino-disco e ensaio do anel. O objetivo de conseguir aumentar a resistência ao desgaste utilizando um aço ferramenta com deposição via processo de HVOF, bem como o de caracterizar este processo foi alcançado. A utilização do aço ABNT H13 com deposição via aspersão térmica HVOF e revestimentos à base de carboneto de cromo e tungstênio demonstrou-se recomendável para proteção de substratos, fornecendo alta dureza e boa resistência ao desgaste. O revestimento de WC-10Co-4Cr obteve o melhor desempenho geral, apresentando uma microdureza 192% maior frente ao aço sem revestimento, uma redução de 315% do coeficiente de atrito, além de uma adesão maior ao substrato quando comparado com o revestimento Cr3C2-25(NiCr). / Wear is one of the factors that cause most of the failures and reduction of lifespan for tools, it also results in products with no quality in the surface conditions. The increasing demand of the industry for lower costs, higher productivity and better quality are among the justifications for finding ways to increase the performance of these tools. In this context, the objective of this work is to evaluate and characterize surfaces designed for wear resistance using the high velocity oxyfuel (HVOF) thermal spray process. A comparative study of characterization and tribological behavior of a tool steel with thermal spray deposition was performed for two different coatings. The study covers the ABNT H13 steel, using the surface treatment of HVOF thermal spray with coatings of Cr3C2-25(NiCr) and WC-10Co-4Cr. The surface and the tribological behavior evaluation involved microhardness profiles, phase analysis by x-ray diffraction, metallography, chemical composition, roughness characterization, abrasion and adhesion test, pin-on-disk and ring test. The objective of increasing the wear resistance using a tool steel with deposition through HVOF process, as well as to characterize this process was achieved. The use of ABNT H13 steel with chrome and tungsten carbide coatings deposited by thermal spray HVOF has proved to be recommended for substrates protection, providing high hardness and good wear resistance. The WC-10Co-4Crcoating had the best overall performance, presenting a microhardness 192% higher than the steel with no coating, a reduction of 315% of the coefficient of friction, and a higher adhesion to the substrate compared to the Cr3C2-25(NiCr) coating.

O desgaste é um dos fatores que causam a maior parte das falhas e redução na vida útil de ferramentas, além de resultar em produtos com condições superficiais inadequadas. A crescente demanda da indústria por menores custos, maior produtividade e melhor qualidade estão entre as justificativas para que se busquem maneiras de incrementar o desempenho dessas ferramentas. Neste contexto, o trabalho tem como objetivo avaliar e caracterizar superfícies projetadas para resistência ao desgaste utilizando o processo de aspersão térmica oxicombustível de alta velocidade (HVOF). Fez-se um estudo comparativo de caracterização e comportamento tribológico de um aço ferramenta com deposição por aspersão térmica de dois diferentes revestimentos. O estudo abrange o aço ABNT H13, utilizando o tratamento superficial de aspersão térmica HVOF com revestimentos de Cr3C2-25(NiCr) e WC-10Co-4Cr. A avaliação da superfície e do comportamento tribológico envolveu perfis de microdureza, análise de fases por difração de raios X, metalografias, obtenção da composição química, caracterização da rugosidade, ensaio de abrasão e adesão, pino-disco e ensaio do anel. O objetivo de conseguir aumentar a resistência ao desgaste utilizando um aço ferramenta com deposição via processo de HVOF, bem como o de caracterizar este processo foi alcançado. A utilização do aço ABNT H13 com deposição via aspersão térmica HVOF e revestimentos à base de carboneto de cromo e tungstênio demonstrou-se recomendável para proteção de substratos, fornecendo alta dureza e boa resistência ao desgaste. O revestimento de WC-10Co-4Cr obteve o melhor desempenho geral, apresentando uma microdureza 192% maior frente ao aço sem revestimento, uma redução de 315% do coeficiente de atrito, além de uma adesão maior ao substrato quando comparado com o revestimento Cr3C2-25(NiCr). / Wear is one of the factors that cause most of the failures and reduction of lifespan for tools, it also results in products with no quality in the surface conditions. The increasing demand of the industry for lower costs, higher productivity and better quality are among the justifications for finding ways to increase the performance of these tools. In this context, the objective of this work is to evaluate and characterize surfaces designed for wear resistance using the high velocity oxyfuel (HVOF) thermal spray process. A comparative study of characterization and tribological behavior of a tool steel with thermal spray deposition was performed for two different coatings. The study covers the ABNT H13 steel, using the surface treatment of HVOF thermal spray with coatings of Cr3C2-25(NiCr) and WC-10Co-4Cr. The surface and the tribological behavior evaluation involved microhardness profiles, phase analysis by x-ray diffraction, metallography, chemical composition, roughness characterization, abrasion and adhesion test, pin-on-disk and ring test. The objective of increasing the wear resistance using a tool steel with deposition through HVOF process, as well as to characterize this process was achieved. The use of ABNT H13 steel with chrome and tungsten carbide coatings deposited by thermal spray HVOF has proved to be recommended for substrates protection, providing high hardness and good wear resistance. The WC-10Co-4Crcoating had the best overall performance, presenting a microhardness 192% higher than the steel with no coating, a reduction of 315% of the coefficient of friction, and a higher adhesion to the substrate compared to the Cr3C2-25(NiCr) coating.

O desgaste é um dos fatores que causam a maior parte das falhas e redução na vida útil de ferramentas, além de resultar em produtos com condições superficiais inadequadas. A crescente demanda da indústria por menores custos, maior produtividade e melhor qualidade estão entre as justificativas para que se busquem maneiras de incrementar o desempenho dessas ferramentas. Neste contexto, o trabalho tem como objetivo avaliar e caracterizar superfícies projetadas para resistência ao desgaste utilizando o processo de aspersão térmica oxicombustível de alta velocidade (HVOF). Fez-se um estudo comparativo de caracterização e comportamento tribológico de um aço ferramenta com deposição por aspersão térmica de dois diferentes revestimentos. O estudo abrange o aço ABNT H13, utilizando o tratamento superficial de aspersão térmica HVOF com revestimentos de Cr3C2-25(NiCr) e WC-10Co-4Cr. A avaliação da superfície e do comportamento tribológico envolveu perfis de microdureza, análise de fases por difração de raios X, metalografias, obtenção da composição química, caracterização da rugosidade, ensaio de abrasão e adesão, pino-disco e ensaio do anel. O objetivo de conseguir aumentar a resistência ao desgaste utilizando um aço ferramenta com deposição via processo de HVOF, bem como o de caracterizar este processo foi alcançado. A utilização do aço ABNT H13 com deposição via aspersão térmica HVOF e revestimentos à base de carboneto de cromo e tungstênio demonstrou-se recomendável para proteção de substratos, fornecendo alta dureza e boa resistência ao desgaste. O revestimento de WC-10Co-4Cr obteve o melhor desempenho geral, apresentando uma microdureza 192% maior frente ao aço sem revestimento, uma redução de 315% do coeficiente de atrito, além de uma adesão maior ao substrato quando comparado com o revestimento Cr3C2-25(NiCr). / Wear is one of the factors that cause most of the failures and reduction of lifespan for tools, it also results in products with no quality in the surface conditions. The increasing demand of the industry for lower costs, higher productivity and better quality are among the justifications for finding ways to increase the performance of these tools. In this context, the objective of this work is to evaluate and characterize surfaces designed for wear resistance using the high velocity oxyfuel (HVOF) thermal spray process. A comparative study of characterization and tribological behavior of a tool steel with thermal spray deposition was performed for two different coatings. The study covers the ABNT H13 steel, using the surface treatment of HVOF thermal spray with coatings of Cr3C2-25(NiCr) and WC-10Co-4Cr. The surface and the tribological behavior evaluation involved microhardness profiles, phase analysis by x-ray diffraction, metallography, chemical composition, roughness characterization, abrasion and adhesion test, pin-on-disk and ring test. The objective of increasing the wear resistance using a tool steel with deposition through HVOF process, as well as to characterize this process was achieved. The use of ABNT H13 steel with chrome and tungsten carbide coatings deposited by thermal spray HVOF has proved to be recommended for substrates protection, providing high hardness and good wear resistance. The WC-10Co-4Crcoating had the best overall performance, presenting a microhardness 192% higher than the steel with no coating, a reduction of 315% of the coefficient of friction, and a higher adhesion to the substrate compared to the Cr3C2-25(NiCr) coating.

Transition metal carbides have great industrial importance with a wide area of applications. Unlike many ceramic materials which can be produced from raw materials found in nature, the refractory carbides generally do not exist in the natural state. Synthesis of these carbides is costly and exacting. Sputtered coatings of the refractory metal carbides are of great interest for applications where hard wear-resistant materials are desired. Understanding how the experimental conditions affect the microstructure and properties in reactive sputtering deposition process is still an area of intense research activity. Reactively sputtered zirconium carbide thin films were grown on (100) silicon substrate and the influence of substrate temperature on the properties of the films were investigated. The substrate temperature was varied from ambient to 500°C and partial pressures of the sputter gas and reactive gas (argon and methane) were optimised to obtain crystalline films. Structural characteristics showed that the films exhibit nanocomposite structure consisting of ZrC nanocrystallites embedded in amorphous carbon typically at lower growth temperature (TS < 300°C), and at higher growth temperatures film were highly textured. In addition, Films deposited at 325 °C showed a distinct increase in FWHM which had considerable effect on the mechanical properties of the film. Maximum hardness of 24.8 GPa was seen at 325ºC. The changes in atomic bonding structures, their relative fractions with respect to substrate temperature were discussed. We also report superhard nanocrystalline nanocomposite NbC thin film deposited on Si (100) under 500˚C growth temperature via reactive magnetron sputtering. The pronounced nano hardness and modulus value of 42 GPa and 267 GPa at 40/60 C/Nb ratio were found to be strongly dependent on the grain size and higher percentage of carbide content. HRTEM studies further confirm the formation of nanocomposite structure with nanocrystalline grains embedded in amorphous matrix. The influence of vapour incidence angle (α= 0˚ to 75˚) on optimized ZrC and NbC thin films were investigated by depositing films in Oblique angle deposition geometry (OAD). The anisotropic growth rate of crystallographic planes and the mechanism of development of micro structural features in OAD of carbide films have been investigated. XRD and pole figure measurements indicated that the films grown at higher growth temperatures (800°C) exhibited higher degree of preferred orientation coupled with larger crystallite size whereas the films deposited at room temperature displayed random polycrystalline nature. The strong increase in porosity with increase in deposition angle with distinctly separated nanometer sized columns resulted in lowering of hardness and reduced modulus value. The film with zero incidence angle exhibited a maximum hardness and reduced modulus of 28 GPa and 223 GPa respectively. On the other hand, NbC films deposited with OAD, remained to be polycrystalline in nature with less intense peaks and also exhibited loss of preferential orientation indicating lower crystal quality with increase in vapor deposition angle. It is apparent that variation in crystallographic texture coupled with sculptured nanostructures are solely material dependent properties. Nano metric modulated ZrC/NbC superlattice multilayer structure performance has been evaluated for structural stability and hardness enhancement. Multilayers present superlattice effect in XRD patterns, which are attributed to the precise periodical stacking of crystalline monolayers also confirmed by cross section FESEM. X-ray photoelectron spectroscopy depth profile analysis was performed to get information on chemical composition of modulated layers and also to get an insight on the interface region. Hardness and modulus value of 43.2 GPa and 272 GPa was observed which is higher than individual monolayers response to mechanical loading. The enhanced hardness is possibly due to the inhibition of dislocation motion along the interface and also due to strain effects at the interface.