White spots are defects that occur in VAR melted ingots which appear as non-etched bright areas especially in the superalloy macro-structure. In the present study. '
Fattiigue and ttensiille properttiies of speciimens cutt from palllletts made from wastte pllasttiics by usiing of newlly develloped recyclliing apparattus are presentted.. Testted matteriialls are pollypropyllene fiillm,, pollypropyllene pelllletts,, pollyetthyllene,, pollyetthyllene-20wtt%flly ash composiitte and pollyetthyllene -20wtt% callciium carbonatte composiitte.. Itt can be conclluded tthatt tthe newlly develloped recyclliing apparattus make possiiblle tto proviide palllletts made from wastte pollypropyllene and pollyetthyllene wiitth ullttiimatte ttensiille sttrengtths of more tthan niinetty percentt of tthose made from fresh pollypropyllene and pollyetthyllene.. Itt has become cllear tthatt carefull ttreattmentt of composiitte process for wastte pllasttiics enablle tto iimprove fattiigue sttrengtth of pollyetthyllene composiittes by sttrengttheniing tthe iintterface bettween an addiittiive and base matteriiall..
Fine grains are required for Alloy 718 to obtain its high strength. Since grain size is strongly affected by forging conditions, many trial forgings are generally needed. On the other hand. grain size predictions by several simulations have been tried to reduce trial forgings. The purpose of this study is to predict grain size of Alloy 718 by combining a numerical simulation and a physical simulation. Firstly the transitions of temperature and strain of the forged material during hot forging were calculated by the 3-dimensional FEM. Secondly multi-stage plane strain compression tests using small test pieces were carried out by means of the Gleeble system according to the temperature and strain programs obtained by the numerical simulation, then the grain size was observed. These simulations were applied for predicting and refining the grain size of Alloy 718 billet forged by hydraulic 4-ram radial forging machine. Introduction Fine grains are required for Alloy 718 disks mainly used for gas turbines to obtain its high strength. To obtain the fine grain disks, it is necessary to refine the grains of the billets of which the disks are made by means of die forging. But it is difficult to refine the grains of large section size billets, especially at center position (1,2).Alloy 718 billets have been generally forged by 2-ram press or 4-ram mechanical radial forging machine (GFM) (1-8). In this study, 4-ram hydraulic radial forging machine, called SMX (by SMS EUMUCO Inc.), was used to forge Alloy 718 billets. SMX has advantages over the 2-ram press; its forging speed is higher and straighter and more truly round billet can be obtained. SMX also has advantages over GFM. The maximum load can be added throughout the full stroke by SMX whereas it can be added near the only bottom dead point by GFM. So the reduction in pass of SMX can be controlled, although that of GFM must be set a small value. Therefore SMX can easily control the forging conditions. These advantages are effective to obtain fine grains of all the regions of large section size billets.On the other hand, since grain size is strongly affected by the forging conditions, many trial forgings, which are very expensive especially for the high price materials such as Ni base superalloys and take much time, are generally needed to control the microstructure. Therefore grain size predictions by several simulations have been tried to reduce trial forgings (1,2:4-8). FEM (Finite Element Method) has been used to predict the strain and the temperature distribution and the microstructure including the grain size of forged products. Not only 2-dimensional FEM but also 3-dimensional FEM must be used for the forging by 2-ram press and 4-ram press, because the deformation behavior of these forgings is complicated. But grain size predictions only by FEM or other equations are difficult for highly-alloyed metals, because the grain growth and recrystallization behavior is very complicated. Especially, the grain sizes of Alloy 718 are strongly affected by the precipita...
In isothermal forging, since the die is heated as well as the workpiece, high-temperature strength is essentially required for the die material. In particular, isothermal forging of superalloys is carried out at high temperature ranging 10001100°C, thus a molybdenum-base alloy, TZM, is generally used as a die material. Although TZM has good high-temperature strength, its oxidation resistance is very poor at above 600°C, therefore, forging must be done in vacuum or inert-gas atmosphere. If there is a die material having both enough strength and oxidation resistance at around 1000-1100°C, isothermal forging of superalloys in air will be possible, and the forging apparatus will be simpler. To develop such a die material, the authors directed their attention to chromium free nickel-base cast alloys, because such alloys are able to contain a large amount of heavy metals such as molybdenum and tungsten, as being soluble in r and r' instead of chromium, and are expected to have higher strength at above 1000°C. Several conventional and experimental alloys were investigated. From the results of compression, compressive creep and oxidation resistance tests, " Nimowal " (Ni-IOMo-12W-6A1-0.OJY) showed the best properties as a whole. Its short-time strength is equivalent to that of Mar-M200 at 950-1000°C, higher than that of Mar-M200 and equivalent to that of TZM at 1050-1100°C. Its compressive creep strength is higher than that of Mar-M200 at 1000-1100°C. Oxidation resistance of Nimowal is equivalent to that of Mar-M200 and enough to be used in air. Moreover, JVimowal has better machinability than Mar-M200. Simulation tests of isothermal forging of superalloys in air were made with Nimowal being used as the die material. One-tenth model disk of In-100 was successfully forged from the extruded billet without any damage or significant oxidation of the die.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.