1,753,154 research outputs found
TEM Study of High-Temperature Precipitation of Delta Phase in Inconel 718 Alloy
No full textInconel 718 is widely used because of its ability to retain strength at up to 650◦C for long periods of time through coherent metastable γ” Ni3Nb precipitation associated with a smaller volume fraction of γ’ Ni3Al precipitates. At very long ageing times at service temperature, γ” decomposes to the stable Ni3Nb δ phase. This latter phase is also present above the γ” solvus and is used for grain control during forging of alloy 718.While most works available on δ precipitation have been performed at temperatures below the γ” solvus, it appeared of interest to also investigate the case where δ phase precipitates directly fromthe fccmatrix free of γ’’precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains in δ plates, and some unexpected contrast could be explained by double diffraction due to overlapping phases
Some features of anisothermal solid-state transformations in alloy 718
No full textThis paper presents an attempt to use differential thermal analysis to study anisothermal precipitation of both the stable delta and the metastable gamma-second phases during cooling of alloy Inconel 718. Observation of the samples by scanning and transmission electron microscopy was carried out to identify the thermal arrests observed upon cooling. When the upper temperature of the cycle is above the solvus of the delta phase, a clear peak is observed that could be related to precipitation of gamma-second for all the cooling rates used in the present work. When this temperature is below the delta solvus, no thermal arrest can be observed, while when it is close to it two faint peaks were noted and associated with stable and metastable precipitation. The most striking result was that dissolution of the metastable gamma-second phase during the heating stage was found to proceed heterogeneously in the material, and this affected reprecipitation of the phases upon subsequent cooling
Tool-life and wear mechanisms of CBN tools in machining of Inconel 718
No full textThe demand for increasing productivity when machining heat resistant alloys has resulted in the use of new tool materials such as cubic boron nitride (CBN) or ceramics. However, CBN tools are mostly used by the automotive industry in hard turning, and the wear of those tools is not sufficiently known in aerospace materials. In addition, the grade of these tools is not optimized for superalloys due to these being a small part of the market, although expanding (at 20% a year). So this investigation has been conducted to show which grade is optimal and what the wear mechanisms are during finishing operations of Inconel 718. It is shown that a low CBN content with a ceramic binder and small grains gives the best results. The wear mechanisms on the rake and flank faces were investigated. Through SEM observations and chemical analysis of the tested inserts, it is shown that the dominant wear mechanisms are adhesion and diffusion due to chemical affinity between elements from workpiece and insert
Resolución UNRN Nº 718/2011. Aprobar el reglamento electoral
No full textFil: Universidad Nacional de Río Negro (U). Universidad Nacional de Río Negro. Río Negro, ArgentinaResolución UNRN Nº 718/2011. Aprobar el reglamento electoral para las elecciones de autoridades de la Universidad Nacional de Río Negrofals
Effect of Tool Materials and Lubrication on the Machining Performance of Inconel 718 in Aerospace Applications
No full textreservedLe superleghe a base nichel, in particolare l’Inconel 718, sono materiali particolarmente adatti per la produzione di componenti sottoposti ad un elevato carico meccanico e che operano ad elevata temperatura. Per questo motivo, l’Inconel 718 viene spesso impiegato per la produzione di componenti utilizzati nei motori a turbogetto, ad esempio quelli che comprendono parte della camera di combustione e della gestione dei gas di scarico. Tra le proprietà meccaniche dell’Inconel 718 spiccano la sua tenacità e tensione di snervamento mantenuta anche ad alte temperature, oltre che una buona resistenza allo scorrimento viscoso e alta resistenza all’ossidazione. Tuttavia, presenta alcune proprietà che lo rendono un materiale tra i più difficili da lavorare per asportazione: come una scarsa conducibilità termica e un’elevata durezza.
In questa tesi sono state analizzate le performance in tornitura longitudinale su Inconel 718 ottenute con inserti in WC, CBN e con inserti ceramici in Al2O3+SiCw texturizzati Le condizioni di lubro-refrigerazione sono state variate al fine di investigare la possibilità di sostituire la lubrificazione tradizionale ad olio con tecniche più sostenibili come l’uso di gas criogenico (LN2) o l’assenza di lubrificazione.
L’indagine sulle performance ha portato a tracciare le curve di usura degli inserti e a valutare la finitura e l’integrità superficiale del pezzo lavorato. La profondità del labbro d’usura è stata quantificata con microscopio ottico, mentre un microscopio elettronico a scansione ha permesso di studiare i meccanismi di usura presenti.
L’uso di gas criogenico ha portato ad un miglioramento nella finitura superficiale sia nel caso di inserti WC che CBN e, nel primo caso, anche ad una vita utensile comparabile. La tornitura a secco invece è risultata vantaggiosa nel caso di inserti in CBN garantendo una vita utile simile al caso convenzionale.
Infine, l’utilizzo di una texture radiale ha permesso un miglioramento delle condizioni di lubrificazione del petto nel caso di inserti ceramici.Nickel-based superalloys, particularly Inconel 718, are suitable materials for the production of components that are subject to high mechanical loading and operate at high temperatures. For this reason, Inconel 718 is commonly used in turbojet engines components, such as those comprising part of the combustion chamber and exhaust gas management. Among the mechanical properties of Inconel 718 are its toughness and yield strength maintained even at high temperatures, as well as good creep resistance and high resistance to oxidation. However, Inconel 718 also has characteristics that make it one of the most challenging materials to machine, such as poor thermal conductivity and high hardness. This thesis analyzes the turning performance on Inconel 718 using WC, CBN and ceramic inserts in Al2O3+SiCw with textured surfaces. The lubrication conditions were varied to investigate the possibility of replacing traditional oil lubrication with more sustainable techniques, such as the use of cryogenic gas (LN2) or even the absence of lubrication.
The performance investigation resulted in the development of wear curves for the inserts, as well as an assessment of the surface finish and integrity of the machined part. The wear depth was measured using an optical microscope, while a scanning electron microscope was employed to analyze the underlying wear mechanisms.
The use of cryogenic gas led to an improvement in the surface finish for both WC and CBN inserts and, in the case of WC, also to a comparable tool life. Dry turning, on the other hand, proved beneficial for CBN inserts, providing a tool life comparable to the conventional case. Finally, the use of a texture improved the lubrication conditions in the case of ceramic inserts
SOLIDIFICATION OF ALLOY 718, ATI 718PLUS (R) AND WASPALOY
No full textAlloy 718, ATI 718Plus (R) and Waspaloy have been investigated in terms of what their respective solidification process reveals. Differential thermal analysis was used to approach the task together with secondary electron and back scattered electron detectors equipped with an energy dispersive X-ray spectroscopy detector. These experimental methods were used to construct pseudo binary phase diagrams that could aid in explaining solidification as well as liquation mechanisms in processes such as welding and casting. Furthermore, it was seen that Waspaloy has the smallest solidification range, followed by Alloy 718, and finally ATI 718Plus (R) possessing the largest solidification interval in comparison.</p
Impact of hydrogen on the high cycle fatigue behaviour of Inconel 718 in asymmetric push–pull mode at room temperature
No full textThe influence of hydrogen on the high cycle fatigue (HCF) behaviour of Inconel 718 has been studied at room temperature in asymmetric push–pull mode using an ultrasonic HCF test rig. Fatigue tests have been carried out in gaseous hydrogen (GH2) and in Ar at a pressure of 30 MPa. Oscillating stresses with amplitudes (σa) up to 450 MPa and mean stresses (σm) up to 600 MPa have been applied. For a given σa and σm, the lifetime in Ar is generally longer than in GH2, which is explained by a hydrogen-induced embrittlement of the material. For a constant σa of 218 MPa, the lifetime in Ar and in GH2 is very similar for high σm, but the difference in lifetime increases as the mean stress decreases. An approach is presented to describe the number of cycles to failure Nf as a function of σa and σm.
Microstructural analysis has been performed on the specimens tested at View the MathML source and two values of σm (300 MPa and 600 MPa). SEM analyses of the fracture surfaces of these samples indicate embrittlement of the material when tested in hydrogen atmosphere
Solidification of alloy 718, ati 718Plus® and waspaloy
No full textAlloy 718, ATI 718Plus® and Waspaloy have been investigated in terms of what their respective solidification process reveals. Differential thermal analysis was used to approach the task together with secondary electron and back scattered electron detectors equipped with an energy dispersive X-ray spectroscopy detector. These experimental methods were used to construct pseudo binary phase diagrams that could aid in explaining solidification as well as liquation mechanisms in processes such as welding and casting. Furthermore, it was seen that Waspaloy has the smallest solidification range, followed by Alloy 718, and finally ATI 718Plus® possessing the largest solidification interval in comparison
Machinability improvement of Inconel 718 superalloy using micro-textured tools and solid lubrication
No full textreservedL’Inconel 718 è una superlega a base di Nichel caratterizzata da eccellenti proprietà meccaniche, fisiche e chimiche che ne fanno un materiale strategico in numerosi settori ad alte prestazioni, in particolare in ambito aerospaziale. Questo materiale è caratterizzato da elevata resistenza termica, meccanica e capacità di resistenza alla corrosione in ambienti sfavorevoli. Nonostante i suoi importanti vantaggi applicativi, l’Inconel 718 presenta una bassa lavorabilità alle macchine utensili per via della sua elevata tenacità, spiccata tendenza all’incrudimento e bassa conducibilità termica. La rapida usura degli inserti da taglio e la qualità della superficie lavorata sono aspetti critici per queste operazioni. In questo lavoro di tesi sono state analizzate le performance in tornitura longitudinale dell’Inconel 718 con inserti ceramici tondi texturizzati. La tessitura dell’inserto è stata fatta con tre geometrie differenti: solchi radiali, solchi circonferenziali e dimples. È stato inoltre studiato il comportamento al variare della condizione di lubrificazione. In particolare, sono state confrontate due modalità: la lubrificazione convenzionale e una lubrificazione mista, ottenuta dall'uso simultaneo di lubrificante tradizionale a base d'olio e di nanopiastrine di grafite impiegate come lubrificante solido. A completamento dell'analisi sono state acquisiste le forze di taglio ed è stato condotto uno studio sulla morfologia dei trucioli ottenuti, col fine di ottenere ulteriori informazioni sul meccanismo di asportazione del materiale e sulle condizioni di taglio. L'indagine sulle prestazioni ha portato a tracciare le curve di usura degli inserti e dell’andamento della rugosità superficiale del pezzo lavorato. Dalle analisi effettuate si evince che la geometria della texture influenza sia il grado di usura che la forma della curva. In condizioni di lubrificazione convenzionale, l'inserto con tessitura dimples è risultato essere quello con la maggiore vita utile, mentre con l'utilizzo del lubrificante solido il miglioramento più significativo è stato osservato per l'inserto con texture circonferenziale, anche in termini di finitura superficiale.Inconel 718 is a nickel-based superalloy characterized by excellent mechanical, physical and chemical properties, making it a strategic material in numerous high-performance sectors, particularly in the aerospace industry. This material shows high thermal and mechanical resistance, as well as corrosion resistance in harsh environments. Despite its significant application advantages, Inconel 718 exhibits poor machinability due to its high toughness, pronounced work-hardening tendency and low thermal conductivity. The rapid wear of cutting inserts and the quality of the machined surface are critical issues in machining operations. This thesis investigates the longitudinal turning performance of Inconel 718 using round textured ceramic inserts. The insert texturing was carried out with three different geometries: radial grooves, circumferential grooves and dimples. Additionally, the influence of lubrication conditions was studied. In particular, two methods were compared: conventional lubrication and a hybrid lubrication, achieved through the simultaneous use of traditional oil-based lubricant and graphite nanoplatelets employed as a solid lubricant. To complete the analysis, cutting forces were measured and a chip morphology study was conducted in order to obtain further information about the material removal mechanism and cutting conditions. The performance investigation resulted in plotting the wear progression of the inserts and the surface roughness trend of the machined workpiece. The results show that the texture geometry influences both the degree of tool wear and the shape of the wear curve. Under conventional lubrication conditions, the dimples-textured insert showed the longest tool life; with the use of solid lubricant the most significant improvement was observed with the circumferential-textured insert, even in terms of surface finish
Fission-track analyses of detrutal apatites from ODP Sites 116-717 and 116-718
No full textThis paper presents fission-track ages and confined track-length measurements from detrital apatites recovered from Ocean Drilling Program Leg 116 Site 717 and 718 cores. We interpret these data in terms of the post-depositional thermal history at these two sites and the thermotectonic history of apatite source areas. Composite apatite samples were derived by combining fine-grained sand samples from Sites 717 and 718 cores over 70- to 120-m intervals over the total depth penetrated at Sites 717 (T.D. = 820 mbsf) and 718 (T.D. = 960 mbsf). Thirty apatite grains per composite sample from ten samples (at least every other sampled interval) were dated and track-length measurements (20-50 per sample) were obtained for all samples.
Mean track lengths from Site 717 samples are statistically identical, ranging from 14.4 ± 0.4 to 14.8 ± 0.3 ?m (all errors are the 95% confidence interval), and mean fission-track ages increase monotonically downhole from 4.8 ± 1.1 to 14.3 ± 2.3 Ma. For Site 718, located approximately 7 km to the south of Site 717 on an adjacent fault block, mean track lengths to 560 mbsf are equivalent to those measured from Site 717 samples. A decrease in mean track length (14.6 ± 0.3 to 13.2 ± 0.4 µm) and a corresponding decrease in mean fission-track age (21.1 ± 2.9 to 15.8 ± 2.4 Ma) with depth for samples between 560 and 960 mbsf from Site 718 indicates that post-depositional downhole shortening of fission tracks at elevated temperatures has taken place.
Track-length shortening, based on mean track lengths relative to an unannealed mean track length of 16.3 µm, is approximately 10% for all Site 717 samples and for samples from the upper 560 m of Site 718. The total amount of shortening of the lowermost sample from Site 718 is approximately 20%. Based on extrapolation of published laboratory annealing experiments, maximum isothermal time-temperature condition extremes that could produce this degree of annealing at the base of Site 718 are estimated to range from 50°C for a duration of 17 m.y. (since deposition) to 55°C for a duration of 7.5 m.y. (since the onset of deformation). These estimates argue against regional thermal conduction as the only mechanism for post-depositional heating and support seafloor heat flow and shipboard geochemical evidence for local convective heat transfer in the vicinity of Site 718.
In terms of source-area implications, dated samples have mean apatite fission-track ages that are only 0 to 10 m.y. older than depositional ages. These young ages imply rapid transport of sediment to the distal Bengal Fan and source areas characterized by high denundation rates (<300 m/m.y.). These rates suggest that source areas similar to parts of the present-day Himalayas supplied sediment to the distal Bengal Fan since at least 17 Ma
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