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Environmental protection of titanium alloys in centrifugal compressors at 500°C in saline atmosphere
Get PDFThe use of the titanium alloy Ti-6246 (Ti–6Al–2Sn–4Zr–6Mo, wt-%) for gas turbine compressors allows an increase in working temperature and stress level. Under severe service conditions, the material experiences combined high temperature and high mechanical stress and, in saline atmospheres, stress corrosion cracking (SCC) can occur, leading to catastrophic mechanical failure. The present study was performed to evaluate the potential of several surface treatments to protect Ti-6246 alloy, after salt deposit, from hot salt SCC at temperatures ?500°C and 500 MPa static mechanical stress conditions. Shot peening, thermal oxidation and metal–ceramic coatings were investigated. Experimental results confirm the existence of brittle stress corrosion phenomena marked by a low residual elongation of test samples and the presence of oxides on the fracture surfaces. Both shot peening and metal–ceramic coatings increase the hot salt SCC resistance of the alloy. Times to rupture were improved by a factor of 3 for shot peening and by a factor of 10 for metal–ceramic coatings. Inversely, the time to rupture of preoxidised alloys has been halved compared with uncoated alloys. As well as these interesting quantitative results, structural studies of metal–ceramic coatings showed that they are mechanically and chemically compatible with the titanium alloy substructure and should work under severe thermomechanical stresses and aggressive atmospheres
Drillability of Titanium Alloy 6246 from Surface Quality Perspective
No full textDrillablity derived from term of machinability, which is applied in drilling. In this study, drillability of titanium alloy 6246 has been investigated through observation of two responses of drilled holes quality, i.e. surface roughness and holes roundness. Taguchi L18 Design Experiment-based approach was used to gain an optimum setting of five drilling parameters: coolant, heat treatment variation, depth of drilling, cutting speed and feed rate. The tool used was TiAlN coated carbide drill insert. Minitab 17 was employed for processing the data; analysis of S/N ratio to find effect of each parameter and ANOVA were employed for analysing the significant of each parameter to the surface quality respectively. ANOVA shows that depth of drilling contributes 55% to the roughness, followed by heat treatment (25%), while coolant only affects the roughness quality by 2%. All the 5 parameters chosen in this research has no statistically significant effect to the roundness. The predicted optimum value of surface roughness of between 0.591 µm to 0.803 µm would be achieved when drilling Ti-6246 at a maximum depth of 10 mm, without coolant, cutting speed of 35 m/min and feed rate of 0.08 mm/min on the as received block
Drillability of titanium alloy 6246
No full textTitanium alloys are relatively new materials that have been used extensively, especially in aerospace applications. The main properties are: a high strength to weight ratio (three times that of steel), an ability to maintain strength at elevated temperatures, excellent corrosion resistance and biocompatibility. The latter makes these alloys suitable to be used for body implants, such as for teeth and bones. However, titanium alloys are not easy to machine. They tend to behave in a springy manner due to a low modulus (Young) ratio. Their low heat conductivity makes the heat that emerges from machining mostly absorbed by the tool. Consequently, the tool loses its ability to cut further. One titanium alloy, named as Ti-6Al-2Sn-4Zr-6Mo (or Ti-6246), which has better corrosion resistance than the most widely used Ti-6Al-4V, faces the same problem when coming into the machining workshop. Meanwhile, only limited research has been conducted on the Ti-6246 alloy relating to its machinability, such as turning, milling and slab milling. Some non-conventional machining processes have been tried, such as Electrical Discharge Drilling, and Wire-EDM. There are more advantages in attempting hybrid machining by using Ultrasonic Assisted Turning (UAT) though. However, to my knowledge, no paper has been published on drilling the Ti-6246 alloy.
Drilling is a fairly simple process. However, the geometry of the drill bit or drill insert is very complicated. During drilling, a drill insert employs a different cutting speed from zero in the centre of the chisel to the maximum at the outer side (the rubbing side). This research will concentrate on the drillability of the Ti-6246 alloy. Drillability is derived from the machinability of the drilling process. It means an attempt to find the best parameters which result in the minimum force employed for drilling, with the longest tool life, whereby the minimum surface roughness and excellent roundness can be achieved. To reach the goals an extensive and systematic set of experiments will be carried out, while simultaneously the phenomena behind the process must be understood. Therefore, an understanding of microstructure and mechanical properties during the process will be studied in depth by utilising a comprehensive analysis of tools, forces, material and chips all together.
The Taguchi L-18 method was used for designing the experiments. This was followed by an ANOVA analysis of data using Minitab 17 software, where the optimum characteristic of drillability has been achieved. However, combinations of different machining parameters and environments have been suggested due to the different criterion of the characteristics of drillability. As displayed by the chip formation the optimum result was achieved when keeping the Ti-6246 alloy in its received condition and applying a cutting speed of 50 m/min, and a feed rate 0.15 mm/rev for drilling 30 mm with a coolant. Consequently, in accordance with tool deterioration criterion, machining with a coolant, at 30 mm deep, a cutting speed of 50 m/min and a feed rate of 0.15 mm/min simultaneously, this would result in the least tool deterioration. Further, the optimal condition for drilling forces would be achieved when drilling with a cutting speed of 27 m/min, a feed rate of 0.08 m/rev on depth of only 10 mm without coolant, while the material should be HT1 treated. Lastly, the optimum surface roughness between 0.3113 µm to 0.5235 µm was achieved when drilling with these parameters: Cltoff, HTAR, h10, Vc35, Fr0.08
[Hebard Cypress Co., Engine Drawing Card, Sketch No. 6246]
No full textThis engine drawing card was created for Hebard Cypress Company, Class 10-30E. Section N-10E. Sketch 6246. Copy Spec. C-2677
Drillability of Titanium Alloy 6246
No full textTitanium alloys are relatively new materials that have been used extensively, especially in aerospace applications. The main properties are: a high strength to weight ratio (three times that of steel), an ability to maintain strength at elevated temperatures, excellent corrosion resistance and biocompatibility. The latter makes these alloys suitable to be used for body implants, such as for teeth and bones. However, titanium alloys are not easy to machine. They tend to behave in a springy manner due to a low modulus (Young) ratio. Their low heat conductivity makes the heat that emerges from machining mostly absorbed by the tool. Consequently, the tool loses its ability to cut further. One titanium alloy, named as Ti-6Al-2Sn-4Zr-6Mo (or Ti-6246), which has better corrosion resistance than the most widely used Ti-6Al-4V, faces the same problem when coming into the machining workshop. Meanwhile, only limited research has been conducted on the Ti-6246 alloy relating to its machinability, such as turning, milling and slab milling. Some non-conventional machining processes have been tried, such as Electrical Discharge Drilling, and Wire-EDM. There are more advantages in attempting hybrid machining by using Ultrasonic Assisted Turning (UAT) though. However, to my knowledge, no paper has been published on drilling the Ti-6246 alloy.
Drilling is a fairly simple process. However, the geometry of the drill bit or drill insert is very complicated. During drilling, a drill insert employs a different cutting speed from zero in the centre of the chisel to the maximum at the outer side (the rubbing side). This research will concentrate on the drillability of the Ti-6246 alloy. Drillability is derived from the machinability of the drilling process. It means an attempt to find the best parameters which result in the minimum force employed for drilling, with the longest tool life, whereby the minimum surface roughness and excellent roundness can be achieved. To reach the goals an extensive and systematic set of experiments will be carried out, while simultaneously the phenomena behind the process must be understood. Therefore, an understanding of microstructure and mechanical properties during the process will be studied in depth by utilising a comprehensive analysis of tools, forces, material and chips all together.
The Taguchi L-18 method was used for designing the experiments. This was followed by an ANOVA analysis of data using Minitab 17 software, where the optimum characteristic of drillability has been achieved. However, combinations of different machining parameters and environments have been suggested due to the different criterion of the characteristics of drillability. As displayed by the chip formation the optimum result was achieved when keeping the Ti-6246 alloy in its received condition and applying a cutting speed of 50 m/min, and a feed rate 0.15 mm/rev for drilling 30 mm with a coolant. Consequently, in accordance with tool deterioration criterion, machining with a coolant, at 30 mm deep, a cutting speed of 50 m/min and a feed rate of 0.15 mm/min simultaneously, this would result in the least tool deterioration. Further, the optimal condition for drilling forces would be achieved when drilling with a cutting speed of 27 m/min, a feed rate of 0.08 m/rev on depth of only 10 mm without coolant, while the material should be HT1 treated. Lastly, the optimum surface roughness between 0.3113 µm to 0.5235 µm was achieved when drilling with these parameters: Cltoff, HTAR, h10, Vc35, Fr0.08
Experimental ecology of Plantago maritima
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6246.pdf (Publisher’s version ) (Open Access
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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