Oxidation of the carbon protective coating in SCS-6 fibre reinforced titanium alloys

Peters, P.W.M.; Hemptenmacher, J.

doi:10.1016/s1359-835x(02)00151-3

Cited by 12 publications

(3 citation statements)

References 10 publications

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“…4, identify the different crystalline structure of the alloys: a ‡ b phase Ti for the SP700 alloy and near-a (almost completely hcp a phase with traces of bcc b phase) for the Ti6242S alloy. SCS-6 bres (Textron System Corporation, Textron Incorporated, Wilmington, Massachusetts) with an average diameter of 142 mm, already used in a similar way for plasma-sprayed Ti6Al4V matrices [10,11], were selected as a highly compatible reinforcement: b silicon carbide is deposited by chemical vapour deposition (CVD) onto a graphite core, and a graded composition of the outer layers, in terms of Si-C atomic ratio, is designed to minimize bre-matrix chemical interaction [12,13].…”

Section: Methodsmentioning

confidence: 99%

Titanium matrix reinforced composites produced by hot pressing of plasma-sprayed preforms

Valente¹,

Picchiotti

Bartuli

et al. 2003

Proceedings of the Institution of Mechanical Engineers, Part L:

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The present work is focused on the fabrication of long bre reinforced titanium composites by hot pressing of plasma-sprayed preforms. Thermal spraying of two different metallic matrices [Ti-6Al-2Sn-4Zr-2Mo-0.08Si (Ti6242S) and Ti-4.5Al-3V-2Mo-2Fe (SP700)] onto prearranged silicon carbide long bres was performed using controlled-atmosphere plasma spraying equipment (CAPS), allowing deposition processes also in the high-pressure range. After optimization of the plasma spraying procedure, composite multilayers were fabricated by hot pressing at 1200 bar with different combinations of process parameters (temperature in the range 850-940¯C, and application time from 30 to 45 min). Consolidated samples were characterized by microstructural investigation and tensile testing at room and high temperature (up to 600¯C). Push-out and push-back tests were performed to investigate interfacial properties.

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Section: Methodsmentioning

confidence: 99%

Titanium matrix reinforced composites produced by hot pressing of plasma-sprayed preforms

Valente¹,

Picchiotti

Bartuli

et al. 2003

Proceedings of the Institution of Mechanical Engineers, Part L:

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“…Continuous SiC bre reinforced titanium matrix composites (SiC f /Ti) have been regarded as promising light-weight highstrength structural materials for a wide range of possible applications ranging from aerospace vehicles to propulsion systems, due to their high specic strength and stiffness at both room and elevated temperature. [1][2][3][4] Motivated by specic application in aerospace eld, the maximum service temperature of SiC f /Ti can reach up to 800 C for a long term or up to 1000 C for a short term, which is primarily limited by the bre/matrix interfacial stability and matrix material selection. 5,6 The SiC f / Ti has been considered as a candidate material for blades in turbojet engines, due to the corresponding high shear strength, transverse property and suitable retention of strength under 538 C. 7 Additionally, as the service temperature reaches up to 600-800 C, the compressor bling fabricated by the SiC f /Ti through corresponding structural design can reduce the weight by approximately 40-70%, as compared to the conventional titanium alloy material, thereby highly improving the thrust weight ratio of turbojet engines.…”

Section: Introductionmentioning

confidence: 99%

Temperature-dependent evolution of interfacial zones in SiC_f/C/Ti17 composites

Zhang

Huang

et al. 2017

RSC Adv.

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“…The porosity of the oxide allowed oxygen to diffuse faster close to the oxide/metal interface and consequently to diffuse into the base alloy. The oxidation of Ti-6Al-2Sn-4Zr-2Mo in the temperature range 450-750 ºC was studied by Peters et al [74] based on weight gain measurements up to 100 hours. Moreover, the authors were focused on the mechanical behaviour of the alloy using four and three-point bending experiments and reported that premature cracking occurred due to subsurface oxygen embrittlement.…”

Section: Factors That Influence the Oxidationmentioning

confidence: 99%

Environment related surface phenomena and their influence on properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : oxidation at elevated temperature and corrosion during chemical treatment

Sefer

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This thesis covers investigation of the surface phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion during chemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored phenomena are related to manufacturing and service conditions of aero-engine components. During manufacturing and operation, the alloys are sunjected to elevated temperatures in oxygen environment. In such conditions an oxide on the surface and an oxygen enriched layer below the oxide, commonly referred as alpha-case is formed. Alpha-case is a hard and brittle layer that is detrimental to the mechanical properties and must therefore be completely eliminated. A conventional method for elimination of alpha-case is chemical processing in HF/HNO3 solutions, i.e. chemical milling. Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carried out in this thesis. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Mo exhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linear oxidation rate was observed at 700 ºC and = 200 hours for both alloys. The difference in the oxidation kinetics of the two alloys is suggested to be related with the chemical composition of the alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thickness was measured using conventional metallographic and microscopic techniques. The parabolic rate constants, the oxygen diffusion parameters and activation energies were estimated in the temperature range of 500-700 ºC for both alloys. Moreover, the oxidation for 500 hours at 700 ºC resulted in microstructural changes and element re-distribution. The bulk and alpha-case layer hardness at micro- and nano-scale were measured using microhardness and nanoindentation techniques. The alpha-case layer had higher hardness due to the solid solution strengthening effect of the diffused oxygen. The effect of chemical milling in 1:11 HF/HNO3 solution on the surface integrity, and the influence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy was investigated. Five and sixty minutes chemical processing times and three imposed total strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observed for the samples etched before LCF testing, as compared to the non-etched samples. The influence from etching was found to be most detrimental for fatigue samples tested at the lowest strain ranges. The fatigue life reduction was correlated with the number of crack initiation sites. Multiple crack initiation sites were observed for the etched samples, whereas only one crack initiation site was discerned in the non-etched samples. Inspection of the surface of the etched samples revealed selective and severely etched prior ß grain boundaries and pit formation at the triple joints of the prior ß grain boundaries. These surface defects were considered as stress raisers promoting an earlier fatigue crack initiation. The influence of two molar concentration ratios of HF and HNO3 acids (1:3 and 1:11) on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigated by electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the two alloys was a function of the concentration ratio of the acids and also of the alloys¿ chemical compositions. The AFM measurements showed faster dissolution rate of the a-phase than the ß-phase in the Widmanstätten microstructure. It was considered that the reason for this is formation of local micro-galvanic cells between the phases. Moreover, the Volta-potential was measured using scanning Kelvin probe force microscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential between the a- and the ß-laths in both alloys. This observation strengthened the likelihood for formation and operation of micro-galvanic cells between the phases. En esta tesis doctoral se estudian los fenómenos superficiales relacionados con la oxidación a alta temperatura y la corrosión producidos durante el tratamiento químico en soluciones de ácido fluorhídrico-nítrico (HF-HNO3) en las aleaciones Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo. Estos fenómenos se producen durante la fabricación y el servicio de componentes para motores aeronáuticos, pues se dan condiciones de elevada temperatura en un ambiente rico en oxígeno, las cuales favorecen la formación de óxido en la superficie y también de una capa enriquecida en oxígeno debajo del óxido, comúnmente conocida como alpha-case o capa alfa. La alpha-case es una capa dura y frágil, perjudicial para las propiedades mecánicas, por lo que debe ser minimizada o totalmente eliminada. Un método convencional para eliminar la capa alfa es el procesado químico en soluciones de ácido fluorhídrico-nítrico, conocido como chemical milling. En este estudio se han efectuado tratamientos isotérmicos en aire a 500, 593 y 700 °C, con duración máxima de 500 horas. Ambas aleaciones desarrollaron óxido tipo rutilo, en tanto que la Ti-6Al-2Sn-4Zr-2Mo mostró mejor resistencia a la oxidación que la Ti-6Al-4V. Se observó una transición de la velocidad de oxidación de parabólica a lineal a 700 °C y tiempos = 200 horas, para ambas aleaciones. Las diferencias en la cinética de oxidación entre ambas aleaciones se han relacionado con su composición química. La capa rica en oxígeno, i.e. alpha-case, fue caracterizada y su espesor medido mediante técnicas metalográficas. Se observó que la velocidad de crecimiento de la capa alfa seguía una relación parabólica con el tiempo para ambas aleaciones. La difusión del oxígeno y la energía de activación se estimaron en el rango de temperaturas de 500-700 °C. Adicionalmente, se comprobé que el tratamiento isotérmico a 700 °C durante 500 horas dio lugar a cambios microestructurales y a la redistribución de elementos. Las durezas del interior y de la capa alfa se midieron a escalas micro- y nano- mediante técnicas de microdureza y nanoindentación. La capa alfa mostró mayor dureza debido al efecto de endurecimiento por solución sólida debido al oxígeno difundido. El efecto de la solución 1:11 HF-HNO3 en la integridad superficial y en la resistencia a fatiga en el régimen de oligofatiga (LCF = Low Cycle Fatigue) de la aleación Ti-6Al-2Sn-4Zr-2Mo fue investigado. Se evaluaron tiempos de procesado químico cortos y largos (5 y 60 minutos) y tres valores de amplitud de deformación total. Se observó una significativa disminución de la vida a fatiga para las muestras atacadas antes de los ensayos LCF, en comparación con las muestras no atacadas. La influencia del ataque se mostró más perjudicial a bajos valores de deformación impuesta. La reducción en la vida a fatiga se correlacionó con el número de zonas de iniciación de grietas. Múltiples zonas se observaron para las muestras atacadas, mientras que solo un lugar de nucleación de grieta se detectó para las no atacadas. La inspección de las superficies de las muestras atacadas reveló un ataque selectivo y severo en los bordes de grano prior beta y la formación de picaduras en los puntos triples de los bordes de grano prior beta. Estos defectos superficiales fueron considerados como exaltadores de tensiones que promueven la temprana nucleación de las grietas de fatiga. Se investigó la influencia en el comportamiento a corrosión de Ti-6Al-4V y Ti-6Al-2Sn-4Zr-2Mo de dos diferentes relaciones de concentración (1:3 y 1:11) de los ácidos HF y HNO3. Se emplearon para ello técnicas electroquímicas y microscopía de fuerza atómica (AFM). La corrosión de las dos aleaciones depende de la concentración de HF-HNO3 y posiblemente también de sus composiciones químicas. Las medidas de AFM revelaron una velocidad de disolución mayor de la fase alfa que de la beta en la microestructura tipo Widmanstätten. Se considera que la razón de esta disolución selectiva es la formación de celdas micro-galvánicas.

show abstract

Oxidation of the carbon protective coating in SCS-6 fibre reinforced titanium alloys

Cited by 12 publications

References 10 publications

Titanium matrix reinforced composites produced by hot pressing of plasma-sprayed preforms

Titanium matrix reinforced composites produced by hot pressing of plasma-sprayed preforms

Temperature-dependent evolution of interfacial zones in SiC_f/C/Ti17 composites

Environment related surface phenomena and their influence on properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : oxidation at elevated temperature and corrosion during chemical treatment

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Oxidation of the carbon protective coating in SCS-6 fibre reinforced titanium alloys

Cited by 12 publications

References 10 publications

Titanium matrix reinforced composites produced by hot pressing of plasma-sprayed preforms

Titanium matrix reinforced composites produced by hot pressing of plasma-sprayed preforms

Temperature-dependent evolution of interfacial zones in SiCf/C/Ti17 composites

Environment related surface phenomena and their influence on properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo : oxidation at elevated temperature and corrosion during chemical treatment

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Temperature-dependent evolution of interfacial zones in SiC_f/C/Ti17 composites