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Eckhard Nembach - One of the best experts on this subject based on the ideXlab platform.

  • the high temperature decrease of the yield strength of the γ strengthened superalloys Nimonic pe16 and Nimonic 105
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003
    Co-Authors: Eckhard Nembach, Josef Pesicka, Eckhard Langmaack
    Abstract:

    Abstract Above Tmax≈1050 K, the yield strength σt of the commercial γ′-strengthened nickel-base superalloys Nimonic PE16, Nimonic 105, and of many similar superalloys decreases drastically. In order to elucidate the physical reasons for this softening effect, σt has been measured as a function of the deformation temperature and of the plastic strain rate. Moreover, the configurations of dislocations in deformed specimens have been studied by transmission electron microscopy (TEM). The results are as follows: in Nimonic 105, the relevant dislocation processes change at Tmax: below Tmax pairs of dislocations with Burgers vectors of the type 1 2 〈1 1 0〉 shear the strengthening γ′-precipitates athermally whereas above Tmax single 1 2 〈1 1 0〉 -dislocations overcome them thermally activated. The effects of changes of the γ′-precipitate dispersion with temperature are negligible. In Nimonic PE16, however, both mechanisms—changes of the γ′-dispersion and thermally activated dislocation processes—strongly affect σt above Tmax.

  • three alternative experimental methods to determine the antiphase boundary energies of the γ precipitates in superalloys
    Philosophical Magazine, 2002
    Co-Authors: Dietmar Baither, H P Karnthaler, C Rentenberger, Eckhard Nembach
    Abstract:

    Abstract The {111} antiphase-boundary (APB) energies Γ of the L12 long-range-ordered γ′ phases that precipitation strengthen the commercial nickel-based superalloys Nimonic PE16 and Nimonic 105 were measured by three independent methods. Γ was derived, firstly, from the dependence of the critical resolved shear stress on the dispersion of the γ′ precipitates in these superalloys, secondly, from the minimum size of Orowan dislocation loops which can be sustained by γ′ precipitates and, thirdly, from the separations of the superpartial dislocations bounding APB faults in the single-phase γ′ alloys. The latter method is based on state-of-the-art transmission electron microscopy investigations and is considered as the most direct. The results determined by the three different methods show (with one exception) satisfactory agreement. This proves the validity of all three experimental approaches and thus supports the theoretical models on which the first two methods are based. Since Γ governs the strength of su...

  • crss anisotropy and tension compression asymmetry of a commercial superalloy
    Acta Materialia, 1998
    Co-Authors: A Nitz, Ulrike Lagerpusch, Eckhard Nembach
    Abstract:

    The critical resolved shear stresses (CRSS) of the {gamma}-strengthened nickel-based superalloy NIMO-NIC 105 and of its two constituent phases--disordered f.c.c. {gamma}-matrix and L1{sub 2}-long-range ordered {gamma}-phase--have been measured in tension and compression. The single crystals had the following orientations: [001], [011], [{bar 1}11], and [{bar 1}23]; the deformation temperatures T ranged from 283 to 1150 K. The dislocation processes in Nimonic 105 have been studied by transmission electron microscopy and slip trace analyses. The CRSS {tau}{sub o} of single-phase {gamma}-crystals showed the abnormalities which have been observed for many other L1{sub 2}-long-range ordered materials: (1) positive slope {partial_derivative}{tau}{sub o}/{partial_derivative}T, (2) anisotropy, (3) tension/compression (t/c) asymmetry, {tau}{sub o} of two-phase Nimonic 105 has anisotropies and (t/c) asymmetries which are similar to those of single-phase {gamma}{prime}, but they are less pronounced, {tau}{sub o} of Nimonic 105 is, however, nearly independent of T for 400 K {le} T {le} 1,000 K. Copley and Kear`s dynamic model has been adapted to relate {tau}{sub o} of two-phase Nimonic 105 to {tau}{sub o} of its constituent single-phase {gamma}- and {gamma}{prime}-phase.

  • anisotropy of the critical resolved shear stress of a γ 47 vol hardened nickel base superalloy and its constituent γ and γ single phases
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1997
    Co-Authors: Astrid Nitz, Eckhard Nembach
    Abstract:

    Abstract Single crystals of the commercial nickel-base superalloy Nimonic 105 with four different orientations have been compression tested in the temperature range 600–1150 K. Nimonic 105 is strengthened by fine, coherent, shearable, homogeneously distributed precipitates of the L12-long-range ordered γ′-phase (47 vol.%). The same investigations were undertaken for single crystals of the two constituent phases: L12-ordered, intermetallic single-phase γ′ and disordered single-phase f.c.c. γ-matrix. Their compositions were those of the two equilibrium phases of Nimonic 105. The CRSS of Nimonic 105 and of the γ'-phase were anisotropic in the whole temperature range. The CRSS of the γ-matrix was isotropie. The interpretation of the anisotropy of Nimonic 105 follows that of single-phase L12-ordered γ′.

Eckhard Langmaack - One of the best experts on this subject based on the ideXlab platform.

  • the high temperature decrease of the yield strength of the γ strengthened superalloys Nimonic pe16 and Nimonic 105
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003
    Co-Authors: Eckhard Nembach, Josef Pesicka, Eckhard Langmaack
    Abstract:

    Abstract Above Tmax≈1050 K, the yield strength σt of the commercial γ′-strengthened nickel-base superalloys Nimonic PE16, Nimonic 105, and of many similar superalloys decreases drastically. In order to elucidate the physical reasons for this softening effect, σt has been measured as a function of the deformation temperature and of the plastic strain rate. Moreover, the configurations of dislocations in deformed specimens have been studied by transmission electron microscopy (TEM). The results are as follows: in Nimonic 105, the relevant dislocation processes change at Tmax: below Tmax pairs of dislocations with Burgers vectors of the type 1 2 〈1 1 0〉 shear the strengthening γ′-precipitates athermally whereas above Tmax single 1 2 〈1 1 0〉 -dislocations overcome them thermally activated. The effects of changes of the γ′-precipitate dispersion with temperature are negligible. In Nimonic PE16, however, both mechanisms—changes of the γ′-dispersion and thermally activated dislocation processes—strongly affect σt above Tmax.

  • on the temperature dependence of the critical resolved shear stress of the γ strengthened superalloy Nimonic pe16
    Scripta Materialia, 2002
    Co-Authors: Angelika Vennemann, Eckhard Langmaack, E Nembach
    Abstract:

    Abstract The temperature dependence of γ ′ -strengthening of the commercial nickel-base superalloy Nimonic PE16 has been investigated by measuring the critical resolved shear stress in the temperature range 373–1173 K and observing the resulting slip line patterns.

Gobbi, Vagner João - One of the best experts on this subject based on the ideXlab platform.

  • Comportamento em fluência e caracterização microestrutural das superligas VAT 36, VAT 32 e Nimonic 80A
    2014
    Co-Authors: Gobbi, Vagner João
    Abstract:

    Materiais com comportamento adequado em temperaturas elevadas tornaram-se uma necessidade nos dias atuais. Superligas são conhecidas desde a década de 1930 e utilizadas, principalmente, em aplicações aeroespaciais e automobilísticas. Com as novas regulamentações para redução das emissões atmosféricas e aumento da eficiência, surgiram projetos que submetem certos componentes de motores como válvulas, a temperaturas e pressões mais elevadas. Assim, exige-se que as ligas utilizadas na fabricação desses componentes possuam maior resistência à alta temperatura, a exemplo da Nimonic 80A. Esta é uma liga de custo elevado devido à alta quantidade de níquel (70 a 80% em peso) além de possuir tratamento térmico extenso. Uma alternativa é a utilização de ligas com menor teor de níquel (30 a 40% em peso) e tratamento térmico reduzido. Neste contexto a Villares Metals desenvolveu duas novas superligas, as VATS 32 e 36. Essas ligas são concebidas para válvulas de motores de combustão interna, porém podem ser utilizadas nos casos que necessitem de resistência mecânica a quente, resistência à fluência, corrosão a quente, especialmente por gases sulfurosos, e resistência a fadiga substituindo às ligas Nimonic 80A em diversas aplicações. A Empresa Villares Metals fez algumas caracterizações à quente das ligas VAT 32 e VAT 36 porém, não foram realizados ensaios por fluência medindo a deformação com o tempo. Portanto, este trabalho tem como objetivo fazer um estudo do comportamento em fluência, em termos de taxa de deformação secundária e tempo de fratura, das superligas VAT 36, VAT 32 e Nimonic 80A. As ligas são submetidas a ensaios de fluência na modalidade de carga constante, na faixa de temperatura de 675 a 750 ºC e na faixa de tensão de 500 a 600 MPa definidas de acordo com suas aplicações. Os ensaios de fluência são realizados conforme a norma ASTM E139. Obtem-se um conjunto de curvas de deformação verdadeira pelo tempo como função das tensões e temperaturas aplicadas. Foi avaliado a ductilidade, a taxa de fluência estacionária e o tempo de vida. Complementou-se o trabalho com caracterização microestrutural das superligas através das técnicas de microscopia ótica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X, refinamento de Rietveld e ensaios de dureza. Os resultados mostram que a liga VAT 32 apresenta maior resistência à fluência (menor taxa de deformação secundária e maior tempo de fratura) em relação à VAT 36 e Nimonic 80A. Isto se deve além do efeito benéfico dos compostos intermetálicos γ' (Ni 3(Al,Ti)), ao maior tamanho de grão e a maior fração de carbonetos ligados MC encontrado na VAT 32. Estes precipitados ricos em titânio e nióbio são estáveis a temperaturas elevadas, aumentam a resistência ao movimento de discordâncias e retardam processos difusionais associados à deformação por fluência. Ancoram os contornos de grãos dificultando o deslizamento relativo entre eles afetando a facilidade com que as vacâncias possam ser geradas nestas mesmas regiões. Por meio da análise dos expoentes de tensão, energias de ativação e imagens obtidas por microscopia eletrônica de transmissão após fluência o mecanismo de deformação dominante no estado secundário de fluência das ligas VAT 32, VAT 36 e Nimonic 80A é movimento de discordâncias envolvendo provavelmente processo de Orowan loops e cisalhamento de precipitados pelas discordâncias, além da presença de deformação por twinning para as ligas VATS e escorregamento e escalagem de discordâncias para a Nimonic 80A. ______________________________________________________________________________ ABSTRACTMaterials with appropriate behavior at elevated temperatures have become a necessity nowadays. Superalloys have been known since the 1930 and used primarily in automotive and aerospace applications. With the new regulations to reduce air emissions and increased efficiency projects emerged that submit certain engine components such as valves, temperatures and higher pressures. Thus, it is required that the alloys which are used in manufacturing these components have high temperature resistance, such as the Nimonic 80A. This alloy has high cost due to the high amount of nickel (70 to 80% wt) and extensive heat treatment. An alternative is to use alloys with lower nickel content (30 to 40% wt) and reduced heat treatment. In this context, Villares Metals has developed two new superalloys, the VATS 32 and 36. These alloys are designed for valves internal combustion engines, but can be used in cases requiring mechanical strength hot, strength creep and corrosion, substitute alloy Nimonic 80A in various applications. Villares Metals Company made some characterizations of the hot alloy VAT 32 and VAT 36 however, no tests were performed measuring creep deformation with time. The objective of this paper is to make a study of the behavior in creep in terms of secondary strain rate and rupture time of the superalloys VAT 36, VAT 32 and Nimonic 80A. The alloys are subjected for creep tests in constant load mode, of the temperature range 675-750°C and stress range 500-600 MPa defined according to their applications. The creep tests are performed according to ASTM E139. Is obtained a set of curves of deformation real by the time in function of the applied stress and temperatures. Are evaluated ductility, the stationary creep rate and life time. Work is complemented with icrostructural characterization of superalloys through the techniques of optical microscopy, SEM, TEM, X-ray diffraction, Rietveld refinement and hardness tests. The results show that the alloy VAT 32 has a higher creep resistance (lower strain rate secondary and higher fracture time) from the VAT 36 and Nimonic 80A. This is due to the beneficial effect of the intermetallic compounds γ' (Ni3 (Al, Ti)), the largest grain size and the largest fraction of MC carbides found in the VAT 32. These precipitates rich in titanium and niobium are stable at elevated temperatures, increased resistance to movement of dislocations and retard diffusional processes associated with creep deformation. Anchor the grain boundaries impairing the relative sliding between them affect the ease with which the vacancies may be generated in these same regions. Through analyzing the stress exponents, activation energies and images obtained by transmission electron microscopy after the creep deformation mechanism dominant in state secondary creep alloys VAT 32, VAT 36 and Nimonic 80A is movement of dislocations probably involving process Orowan loops and shearing of precipitates by dislocations and the presence of deformation twinning for alloys VATS and slip of dislocations and climb for Nimonic 80A

  • Comportamento em fluência e caracterização microestrutural das superligas VAT 36, VAT 32 e Nimonic 80A
    2013
    Co-Authors: Gobbi, Vagner João
    Abstract:

    Tese (doutorado)-Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2013.Materiais com comportamento adequado em temperaturas elevadas tornaram-se uma necessidade nos dias atuais. Superligas são conhecidas desde a década de 1930 e utilizadas, principalmente, em aplicações aeroespaciais e automobilísticas. Com as novas regulamentações para redução das emissões atmosféricas e aumento da eficiência, surgiram projetos que submetem certos componentes de motores como válvulas, a temperaturas e pressões mais elevadas. Assim, exige-se que as ligas utilizadas na fabricação desses componentes possuam maior resistência à alta temperatura, a exemplo da Nimonic 80A. Esta é uma liga de custo elevado devido à alta quantidade de níquel (70 a 80% em peso) além de possuir tratamento térmico extenso. Uma alternativa é a utilização de ligas com menor teor de níquel (30 a 40% em peso) e tratamento térmico reduzido. Neste contexto a Villares Metals desenvolveu duas novas superligas, as VATS 32 e 36. Essas ligas são concebidas para válvulas de motores de combustão interna, porém podem ser utilizadas nos casos que necessitem de resistência mecânica a quente, resistência à fluência, corrosão a quente, especialmente por gases sulfurosos, e resistência a fadiga substituindo às ligas Nimonic 80A em diversas aplicações. A Empresa Villares Metals fez algumas caracterizações à quente das ligas VAT 32 e VAT 36 porém, não foram realizados ensaios por fluência medindo a deformação com o tempo. Portanto, este trabalho tem como objetivo fazer um estudo do comportamento em fluência, em termos de taxa de deformação secundária e tempo de fratura, das superligas VAT 36, VAT 32 e Nimonic 80A. As ligas são submetidas a ensaios de fluência na modalidade de carga constante, na faixa de temperatura de 675 a 750 ºC e na faixa de tensão de 500 a 600 MPa definidas de acordo com suas aplicações. Os ensaios de fluência são realizados conforme a norma ASTM E139. Obtem-se um conjunto de curvas de deformação verdadeira pelo tempo como função das tensões e temperaturas aplicadas. Foi avaliado a ductilidade, a taxa de fluência estacionária e o tempo de vida. Complementou-se o trabalho com caracterização microestrutural das superligas através das técnicas de microscopia ótica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X, refinamento de Rietveld e ensaios de dureza. Os resultados mostram que a liga VAT 32 apresenta maior resistência à fluência (menor taxa de deformação secundária e maior tempo de fratura) em relação à VAT 36 e Nimonic 80A. Isto se deve além do efeito benéfico dos compostos intermetálicos γ' (Ni 3(Al,Ti)), ao maior tamanho de grão e a maior fração de carbonetos ligados MC encontrado na VAT 32. Estes precipitados ricos em titânio e nióbio são estáveis a temperaturas elevadas, aumentam a resistência ao movimento de discordâncias e retardam processos difusionais associados à deformação por fluência. Ancoram os contornos de grãos dificultando o deslizamento relativo entre eles afetando a facilidade com que as vacâncias possam ser geradas nestas mesmas regiões. Por meio da análise dos expoentes de tensão, energias de ativação e imagens obtidas por microscopia eletrônica de transmissão após fluência o mecanismo de deformação dominante no estado secundário de fluência das ligas VAT 32, VAT 36 e Nimonic 80A é movimento de discordâncias envolvendo provavelmente processo de Orowan loops e cisalhamento de precipitados pelas discordâncias, além da presença de deformação por twinning para as ligas VATS e escorregamento e escalagem de discordâncias para a Nimonic 80A. ______________________________________________________________________________ ABSTRACTMaterials with appropriate behavior at elevated temperatures have become a necessity nowadays. Superalloys have been known since the 1930 and used primarily in automotive and aerospace applications. With the new regulations to reduce air emissions and increased efficiency projects emerged that submit certain engine components such as valves, temperatures and higher pressures. Thus, it is required that the alloys which are used in manufacturing these components have high temperature resistance, such as the Nimonic 80A. This alloy has high cost due to the high amount of nickel (70 to 80% wt) and extensive heat treatment. An alternative is to use alloys with lower nickel content (30 to 40% wt) and reduced heat treatment. In this context, Villares Metals has developed two new superalloys, the VATS 32 and 36. These alloys are designed for valves internal combustion engines, but can be used in cases requiring mechanical strength hot, strength creep and corrosion, substitute alloy Nimonic 80A in various applications. Villares Metals Company made some characterizations of the hot alloy VAT 32 and VAT 36 however, no tests were performed measuring creep deformation with time. The objective of this paper is to make a study of the behavior in creep in terms of secondary strain rate and rupture time of the superalloys VAT 36, VAT 32 and Nimonic 80A. The alloys are subjected for creep tests in constant load mode, of the temperature range 675-750°C and stress range 500-600 MPa defined according to their applications. The creep tests are performed according to ASTM E139. Is obtained a set of curves of deformation real by the time in function of the applied stress and temperatures. Are evaluated ductility, the stationary creep rate and life time. Work is complemented with icrostructural characterization of superalloys through the techniques of optical microscopy, SEM, TEM, X-ray diffraction, Rietveld refinement and hardness tests. The results show that the alloy VAT 32 has a higher creep resistance (lower strain rate secondary and higher fracture time) from the VAT 36 and Nimonic 80A. This is due to the beneficial effect of the intermetallic compounds γ' (Ni3 (Al, Ti)), the largest grain size and the largest fraction of MC carbides found in the VAT 32. These precipitates rich in titanium and niobium are stable at elevated temperatures, increased resistance to movement of dislocations and retard diffusional processes associated with creep deformation. Anchor the grain boundaries impairing the relative sliding between them affect the ease with which the vacancies may be generated in these same regions. Through analyzing the stress exponents, activation energies and images obtained by transmission electron microscopy after the creep deformation mechanism dominant in state secondary creep alloys VAT 32, VAT 36 and Nimonic 80A is movement of dislocations probably involving process Orowan loops and shearing of precipitates by dislocations and the presence of deformation twinning for alloys VATS and slip of dislocations and climb for Nimonic 80A

P K Datta - One of the best experts on this subject based on the ideXlab platform.

  • studies of high temperature sliding wear of metallic dissimilar interfaces ii incoloy ma956 versus stellite 6
    Tribology International, 2006
    Co-Authors: I A Inman, S R Rose, P K Datta
    Abstract:

    The development of wear surfaces formed during limited debris retention sliding wear of Incoloy MA956 against Stellite 6 between room temperature and 750 °C, and sliding speeds of 0.314 and 0.905 m s−1 (7 N applied load, 4522 m sliding distance) were investigated. At 0.314 m s−1, mild oxidational wear was observed at all temperatures, due to oxidation of Stellite 6-sourced debris and transfer to the Incoloy MA956; this debris separated the Incoloy MA956 and Stellite 6 wear surfaces. Between room temperature and 450 °C, the debris mainly took the form of loose particles with limited compaction, whilst between 510 °C and 750 °C the debris were compacted and sintered together to form a Co–Cr-based, wear protective ‘glaze’ layer. The behaviour was identical to that previously observed on sliding Nimonic 80A versus Stellite 6 at 0.314 m s−1. At 0.905 m s−1, mild oxidational wear was only observed at room temperature and 270 °C and dominated by Incoloy MA956-sourced debris. At 390 and 450 °C, the absence of oxide debris allowed ‘metal-to-metal’ contact and resulted in intermediate temperature severe wear; losses in the form of ejected metallic debris were almost entirely Incoloy MA956-sourced. This severe wear regime was also observed from 510 up to 630 °C, but increasingly restricted to the early stages of wear by development of a wear protective Incoloy MA956-sourced ‘glaze’ layer. This ‘glaze’ layer formed so rapidly at 690 °C and 750 °C, that severe wear was all but eliminated and wear levels were kept low. The behaviour observed for Incoloy MA956 versus Stellite 6 at 0.905 m s−1 contrasts sharply with that previously observed for Nimonic 80A versus Stellite 6, in that the Incoloy MA956-sourced high Fe–Cr debris formed a protective oxide ‘glaze’, whilst the Nimonic 80A-sourced Ni and Cr oxides formed an abrasive oxide that at high sliding speeds assisted wear. The data indicates that the tendency of oxide to form a ‘glaze’ is readily influenced by the chemistry of the oxides generated.

  • microscopy of wear affected surface produced during sliding of Nimonic 80a against stellite 6 at 20 c
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003
    Co-Authors: P K Datta, I Inman, R Geurts, Christian Kubel
    Abstract:

    Abstract The microstructures of a wear induced surface glazed layer formed during sliding wear of Nimonic 80A against Stellite 6 at 20 °C using a speed of 0.314 ms −1 under a load of 7 N have been investigated using X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy in combination with electron energy loss spectroscopy (EELS) and energy dispersive X-ray (EDX) analysis. The results indicate the formation of a wear resistant nano-structured glazed layer. The mechanisms responsible for the formation of the nano-polycrystalline glazed layer are discussed.

  • use of pvd deposited tin coating in retarding high temperature sulphidation
    Surface & Coatings Technology, 1996
    Co-Authors: H L Du, A S James, P K Datta, J S Burnellgray, A Matthews
    Abstract:

    Abstract TiN coated Inconel 600 and Nimonic PE11 alloys were exposed to an atmosphere comprising a high sulphur potential (pS 2 ∼ 10 −1 Pa) and a low oxygen potential (pO 2 ∼ 10 −18 Pa) at 750 °C for periods up to 72 h. The sulphidation kinetics, determined by a discontinuous gravimetric method, demonstrated that the TiN coating greatly enhanced the sulphidation resistance of the substrates, particularly during the early stages of exposure. For TiN coated Inconel 600 the post-exposure analysis by scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction and glancing angle X-ray diffraction, showed the formation of an outer layer containing Ni 3 S 2 on the surface of the TiN coating while an inner layer consisting of Cr 2 S 3 developed at the coating/substrate interface. The double layered scale formed on uncoated Inconel 600 consisted of Ni 3 S 2 and Cr 2 S 3 . For the TiN coated Nimonic PE11, sulphide nodules consisting of three layers — (Fe,Ni) 9 S 8 (outmost) Cr 2 S 3 MoS 2 (innermost) were observed to develop and the TiN coating was sandwiched between (Fe,Ni) 9 S 8 and Cr 2 S 3 . The portion of the TiN coating which was enveloped by those sulphide nodules became unstable after long-term exposure and subsequently dissociated thereby causing the loss of environmental protection. Moreover, the coating was damaged mechanically by the growth of the sulphide nodules. The scale formed on the uncoated Nimonic PE11 showed the formation of a similar structure in a similar sequence.

  • influence of plasma sprayed mo coating on sulphidation behaviour of inconel 600 and Nimonic pe11 alloys
    Surface & Coatings Technology, 1995
    Co-Authors: H L Du, P K Datta, J S Burnellgray
    Abstract:

    Abstract Sulphidation is a serious problem in many energy conversion systems. Sulphidation attack is particularly severe in environments of low oxygen ( p O2 ~10 −18 Pa) and high sulphur ( p S2 ~ 10 −1_10−3 Pa) potentials at temperatures above 700°C. Recognizing that refractory metals have a high resistance to sulphidation in reducing environments, their use as overlay coatings in sulphur-containing environments deserves serious consideration. In the adoption of such an approach, Mo has been recognized as a highly sulphidation-resistant metal with a Kp value of 10 −12 g 2 cm −4 s −1 in an atmosphere of p S2 ~ 10 −1 Pa at 750°C. In this study, Mo was deposited on two superalloys, Inconel 600 and Nimonic PE11, using air plasma spraying. The coated specimens were tested at 750°C for up to 168 h in an environment comprising p S2 ~ 10 −1 Pa and p O2 ~ 10 −18 Pa. The sulphidation kinetics (this is not real through-layer kinetics, since the specimens had open edges) were determined by a discontinuous gravimetric method. The exposed samples were characterized and analysed using SEM, EDX and XRD techniques. For uncoated Inconel 600, a duplex scale was formed which consisted of an outer Ni 3 S 2 layer and an inner Cr 2 S 3 layer. The scale developed on uncoated Nimonic PE11 comprised three sub-scale layers—an outer (Fe, Ni) 9 S 8 layer, a mid Cr 2 S 3 layer and an inner MoS 2 layer. However, after prolonged exposure, the outer layer contained both (Fe, Ni) 9 S 8 and Ni 3 S 2 on the surface of the uncoated Nimonic PE11. The kinetics results demonstrated that Mo coating enhanced the corrosion resistance of both alloys, and particularly so for Nimonic PE11. For both substrates, Mo coating led to the development of two sub-scale layers at the early stages of exposure (e.g. up to 5 h). The outer layer consisted of Ni 3 S 2 for Inconel 600 and (Fe, Ni) 9 S 8 for Nimonic PE11. A MoS 2 layer constituted the inner layer for both materials. After prolonged sulphidation, a Cr 2 S 3 layer gradually developed between the outer layer and the inner MoS 2 layer. It is apparent that the use of Mo coating hindered the formation of the Cr 2 S 3 layer.

Mehmet Erdi Korkmaz - One of the best experts on this subject based on the ideXlab platform.

  • characteristics high temperature wear and oxidation behavior of boride layer grown on Nimonic 80a ni based superalloy
    Surface & Coatings Technology, 2021
    Co-Authors: Ali Gunen, Mehmet Erdi Korkmaz, Kadir Mert Doleker, Mustafa Sabri Gok, Azmi Erdogan
    Abstract:

    Abstract Nickel-based superalloy Nimonic 80A was pack-borided in a solid medium at temperatures of 850 °C and 950 °C for 2 h and 4 h using silicon-free boriding powders. To investigate the effects of the boriding treatments on mechanical properties (hardness, modulus of elasticity, fracture toughness) and high temperature oxidation resistance, the layers grown on the surfaces were characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, and evaluated using microhardness, nanoindentation, wear and oxidation tests. Wear tests were performed on untreated and borided Nimonic 80A alloys using a ball-on-disc tribometer at room temperature and at 500 °C under dry sliding conditions. Oxidation tests were carried out in air at 1000 °C for 5 h, 25 h and 75 h. Characterization studies revealed a smooth, 22 to 86 μm thick crack-free boride layer consisting mainly of Ni2B and minor quantities of CrB, Cr2B and Cr5B3 in the borided samples. The hardness and elastic modulus of the boride layer was measured as 15.57–18.95 GPa and 142–217 GPa, respectively. Increasing the boriding temperature and time increased the concentrations of chromium in the boride layer. The hardness and elastic modulus of the boride layer increased with chromium content while its fracture toughness decreased. The boriding treatments improved the dry sliding wear resistance. Increasing boriding time and temperature generally led to a higher wear resistance values. However, the treatments had no significant effect on oxidation resistance. The results of this study show that boriding can significantly improve the wear resistance of Nimonic 80A without compromising its oxidation resistance.

  • performance analysis of coated carbide tool in turning of Nimonic 80a superalloy under different cutting environments
    Journal of Manufacturing Processes, 2020
    Co-Authors: Mustafa Gunay, Mehmet Erdi Korkmaz, Nafiz Yasar
    Abstract:

    Abstract Nimonic 80A is a difficult-to-machine nickel-based superalloy thanks to its superior tensile strength in high temperatures and oxidation resistance. However, cutting fluids applied to improve machinability performance during the processing of such materials increase tool life, while at the same time increasing machining costs and causing health and environmental problems. Thus, the present research has been focused on cutting tool life and wear characteristics and analysis of machined surface in turning of Nimonic 80A superalloy under different cutting environments namely dry, air-cooling and oil-spraying method. The performance of the coated tool has been characterized by using optical microscope, SEM and EDS analysis. The results of the tool life and microscopic analysis showed that the oil-spraying method has longer tool life than dry and air-cooling method in turning of Nimonic 80A alloy. Moreover, the volume of material removed has been modeled by response surface method for predicting tool performance under various machining conditions. Lastly, the microstructural and microhardness variations of the machined surface have been evaluated when the cutting tool reaching the wear criterion. The best performance in terms of tool life and surface integrity was obtained at cutting speed of 60 m/min in oil-spraying environment.

  • numerical and experimental investigation of cutting forces in turning of Nimonic 80a superalloy
    Engineering Science and Technology an International Journal, 2020
    Co-Authors: Mehmet Erdi Korkmaz, Nafiz Yasar, Mustafa Gunay
    Abstract:

    Abstract The study presents the machinability of Nimonic 80A superalloys depending on the cutting forces in both the turning experiments and simulations by finite element method (FEM) in order to approve the precision of the predetermined Johnson-Cook (JC) parameters from our previous study. In the first part of the paper, the turning experiments have been performed on Nimonic 80A superalloy with coated carbide tools to determine the cutting forces namely main cutting force, feed force and radial force. Three different cutting parameters namely depth of cut, cutting speed and feed rate have been used with three levels. The effect levels of the cutting parameters on cutting forces have been also determined with the analysis of variance (ANOVA) at 95% confidence level. Secondly, predetermined JC material model parameters have been inputted into the software running by FEM. Thereafter, the turning simulations have been performed by FEM with the same cutting conditions as experimental ones. According to ANOVA results, depth of cut is the most important parameter on Fc and Ff while feed rate is the most important factor on the Fr. Through the closer results (the mean of 6.45% deviation) of cutting forces between the experiments and simulations, the JC parameters of the material and the boundary conditions of the simulations have been approved with high accuracy.

  • Investigation of tensile Johnson-Cook model parameters for Nimonic 80A superalloy
    Journal of Alloys and Compounds, 2019
    Co-Authors: Mehmet Erdi Korkmaz, Mustafa Gunay
    Abstract:

    Abstract Developing high temperature technology increases the need for high temperature resistant materials. Nimonic 80A alloy is generally preferred due to its high creep resistance, oxidation resistance and high resistance to high temperature corrosion. The study determines the tensile constitutive equation (JC parameters) of Nimonic 80 A superalloys. Johnson Cook (JC) model is preferred amongst the various material constitutive equations (Zerille Armstrong, Bordner Partom, JC model). Three different kinds of tensile experiment were performed to identify the model parameters. These are quasi-static tensile experiments applied at room temperatures. These experiments were carried out at 0.001, 0.01 and 0.1 s−1 strain rates. Therefore, the reference strain rate for all experiments was selected to be 10−3. As a second test, tensile experiments were conducted at room temperature at high strain rates (102–103 s−1) using the Split Hopkinson pressure bar (SHPB). Lastly, tensile experiments were conducted at high temperatures (300–900 °C) at 0.001 s−1. It was observed whether all tests are compatible with each other or not, and so five Johnson-Cook (JC) parameters of Nimonic 80 A alloy were identified via the data found from the experiments. After determination of parameters, tensile test simulations by finite element method (FEM) were performed in ANSYS Workbench. As a result, the accuracy of the JC parameters is verified since there is a deviation of %2.84 between the experimental and the simulation results.

  • Identification of Constitutive Model Parameters for Nimonic 80A Superalloy
    Transactions of the Indian Institute of Metals, 2018
    Co-Authors: Mehmet Erdi Korkmaz, Mustafa Gunay
    Abstract:

    Nimonic 80A is a nickel-chrome superalloy, commonly used due to its high resistance against creep, oxidation, and temperature corrosion. This paper presents the material constitutive models of Nimonic 80A superalloy. Johnson–Cook (JC) and modified JC model is preferred among the different material constitutive equations (Zerill Armstrong, Bodner Partom, Arrhenius type) due to its accuracy in the literature. Three different types of compression tests were applied to determine the equation parameters. Firstly, quasi-static tests were performed at room temperature. These tests were conducted at 10^−3, 10^−2, and 10^−1 s^−1 strain rates. Secondly, compression tests were performed at room temperature at high strain rates (370–954 s^−1) using the Split-Hopkinson pressure bar. Finally, compression tests were performed at a temperature level from 24 to 200 °C at the reference strain rate (10^−3 s^−1). Johnson–Cook and modified JC model parameters of Nimonic 80A were determined with the data obtained from these tests, and they were finally verified statistically.