Superalloys: A Technical Guide, 2nd Edition Digital Download (17) It does a good job of achieving its goal as a technical guide to superalloys and is written. Superalloys: a technical guide / M. Donachie, Jr., S. Donachie.—2nd ed This publication is being made available in PDF format as a benefit to members and. Superalloys a Technical Guide - Ebook download as PDF File .pdf), Text File .txt ) or read book online. Superalloys a Technical Guide, ASM superalloy.
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Download Citation on ResearchGate | Superalloys: A Technical Guide, 2nd Edition | This book covers virtually all technical aspects related to the selection. Download Citation on ResearchGate | Superalloys: a technical guide | The properties of superalloys and their processing and applications are presented in a. tisidelaso.ml: Superalloys: A Technical Guide (G) (): Matthew J. Get your site here, or download a FREE site Reading App.
They have resisted all efforts to reduce their importance and decrease the volume of use. To be sure, advances in alloy chemistry are not so easy to achieve any more, but it is being done. At Special Metals, a new generation of processing was dawning as vacuum melting of commercial alloys became a reality. The 60s saw the zenith of superalloy development as columnar grain alloys and single crystals were made feasible, and many polycrystalline alloys were brought to commercial reality.
Some other conferences have been initiated and prospered as well. Inconel and related alloys are the subjects of a continuing series of conference. ASM was an early leader in the presentation of books on high-temperature behavior of metals.
A Technical Guide. The continued success of superalloy technology has encouraged us to undertake a total revision of Superalloys: Virtually all technical aspects of superalloys are covered in this edition. The book is not intended to be exhaustive in every respect, but we believe that the ix. Chapter 4 in particular is probably the most complete and up-to-date presentation on alloy melting available.
Furthermore, the relation of properties and microstructure is covered in more detail than in previous books. The Guide has been reviewed for accuracy, but it is possible that errors will have occurred. The writers would appreciate receiving either corrections or suggestions or both from readers. If you are new to the use of superalloys, we would strongly suggest starting with Chapter 1. However, on completing appropriate chapters, you may wish to pursue reading from one of the references listed in Appendix B.
The writers wish to thank all those who contributed to this book, including the many contributors to other ASM books and the ASM Handbook series. We extend our special thanks to John Marcin and Joe Goebel who extensively reviewed Chapters 5 and 13 respectively. We particularly would like to thank Veronica Flint, retired from ASM International, for her encouragement to pursue this work and for her perseverance over the several years as the material made its way into electronic and now hard copy form.
The successful publication of this Second Edition is a tribute once more to the dedication of ASM International to providing the greatest access to materials information for the widest possible audience. MJD mattd monad. This publication is intended for use by persons having technical skill. In Japan Takahashi Bldg. You may download and print a copy of this publication for your personal use only. Ohio In Europe United Kingdom Telephone: All rights reserved.
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ASM assumes no liability or obligation in connection with any use of this information. ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. Other use and distribution is prohibited without the express written permission of ASM International.
Nothing contained in this publication shall be construed as a grant of any right of manufacture. USA www. Since the conditions of product or material use are outside of ASM's control. Wilbury Way. Tokyo Japan Telephone: As with any material. ASM International. No warranties. Publication title Superalloys: Online Visit www. The primer provided in this chapter supports such needs as those described previously by providing a concise overview of the major topics considered in the book.
Second Edition Matthew J. Stephen J. The stainless steels. Some History Designers have long had a need for stronger.
Some nickel-chromium alloys the Inconels and Nimonics. Theory is kept to a minimum. The ability to lay hands on enough practical information to solve problems or answer questions about the superalloys is the basis for this book.
Executives and managers. They soon were found to be limited in their strength capabilities. Although patents for aluminum and titanium additions to Nichrome-type alloys were issued in the s. If you are new to the subject. As for the book. The engineer may need more detail but still just a quick refresher about alloy types and design to start.
Of course. downloading agents or communications experts need a modest knowledge base to do their jobs more appropriately. This primer introduces the reader simply and directly to the wide variety of topics that must be considered in the application of superalloys.
Not all alloys can be mentioned. Cobalt-base and nickel-base superalloys may be wrought or cast. Appropriate compositions of superalloys can be forged. Fabricated structures can be built up by welding or brazing.
Alloy use is a function of industry gas turbines. A representative list of superalloys and compositions. Figure 1. This time-dependent extension is called creep and. The iron-nickel-base superalloys such as the popular alloy IN are an extension of stainless steel technology and generally are wrought.
Properties can be controlled by adjustments in composition and by processing including heat treatment. In superalloys based on iron and cobalt.
Basic Metallurgy of Superalloys Iron. A Technical Guide metal alloys available for the insatiable thirst of the designer for more high-temperature strength capability. Both iron and cobalt undergo transformations and become fcc at high temperatures or in the presence of other elements alloyed with iron and cobalt.
The upper limit of use for superalloys is not restricted by the occurrence of any allotropic phase transformation reactions but is a function of incipient melting temperatures of alloys and dissolution of strengthening A Short Review of the HighTemperature Strength of Metals At ordinary temperatures. A large number of alloys have been invented and studied. Related mechanical properties such as dynamic modulus. The more highly alloyed compositions normally are processed as castings.
It continues yet! Superalloys are nickel-. Thus the creep strength of a metal or its rupture strength technically called creep-rupture strength but more commonly called stress-rupture strength or both are necessary components of understanding its mechanical behavior just as much as are the customary yield and ultimate strengths. Incipient lowest melting temperatures and melting ranges of superalloys are functions of composition and prior processing.
Advanced nickel-base single-crystal superalloys having limited amounts of. All alloys have a melting range. Pure iron has a density of 0. Working mechanical deformation. Some tendency toward transformation of the fcc phase to stable lower-temperature phases occasionally occurs in cobalt-base superalloys. Incipient melting is the melting that occurs in some part of the alloy that.
The corrosion resistance of superalloys depends primarily on the alloying elements added. The melting temperatures of the pure elements are as follows: Superalloys are strengthened not only by the basic nature of the fcc matrix and its chemistry but also by the presence of special strengthening phases.
The austenitic fcc matrices of superalloys have extended solubility for some alloying additions. Iron-nickel-base superalloys have densities of about 0. Table A Technical Guide Also contains 0. Nickel-base continued 7. Cobalt-base 62 64 63 Steels also may suffer from enhanced corrosion attack.
Refractory metals have higher melting points than superalloys but do not have the same desirable characteristics as superalloys and are much less widely used. In the cast alloys, chromium was high to start but was significantly reduced over the years in order to accommodate other alloy elements that increased the elevated temperature strength of superalloys.
In the superalloys based on nickel, the aluminum content of the alloys increased as chromium decreased. Thus, the oxidation resistance of nickel superal-. However, resistance to other types of corrosion attack decreased. Superalloys have great oxidation resistance, in many instances, but not enough corrosion resistance. Coating technology is an integral part of superalloy development and application.
Lack of a coating means much less ability to use superalloys for extended times at elevated temperatures. Many alloy elements are added to superalloys in minuscule to major amounts, particularly in the nickel-base alloys. Controlled alloy elements could be as many as 14 or so in some alloys. Nickel and cobalt as well as chromium, tungsten, molybdenum, rhenium, hafnium, and other elements used in superalloys are often expensive and strategic elements that may vary considerably in price and availability over time.
Applications The high-temperature applications of superalloys are extensive, including components for aircraft, chemical plant equipment, and petrochemical equipment. Cooling techniques reduce the actual component metal temperatures to lower levels, and superalloys that can operate at these temperatures are the major components of the hot sections of such engines.
Table 1. It will be noted, however, that not all applications re-. Bolts Blades Stack-gas reheaters Selected automotive components, such as: Turbochargers Exhaust valves Metal processing, such as in: Hot work tools and dies Casting dies Medical components, such as in: Dentistry Prosthetic devices Space vehicle components, such as: Aerodynamically heated skins Rocket-engine parts Heat treating equipment: Trays Fixtures Conveyor belts Nuclear power systems: Control-rod drive mechanisms Valve stems Springs Ducting Chemical and petrochemical industries: A Technical Guide, 1st ed.
Their high strength coupled with corrosion resistance have made certain superalloys standard materials for biomedical devices. What to Look for in This Book The text provides those who desire it a very complete understanding of superalloys.
Donachie, Stephen J. Donachie, p DOI: Selection of Superalloys Overview General Considerations. Selection implies data. Some archival collections of tabulated data on superalloys have been made. Computer-based data collections have been produced. Unfortunately, there is little likelihood that these collections can serve as much more than a starting point.
The subject of design allowables and validated property data is much too large to cover in this book. Tables 2. Except for mill products such as sheet and bar, it is almost never true that the same nominal composition when tested at various laboratories is ever in exactly the same condition. Varying microstructures can mean varying test results. Needless to say, even with identical microstructures, nominal test conditions, and nominal chemistries, there is a random statistical nature to results.
The tracking of data on any one alloy is a laborious task. Consequently, most data compilations consist of an uncritical presentation of data derived from manufacturers and the literature.
Caveat emptor! Superalloy Forms. Superalloys are available in cast usually heat treated or otherwise processed or wrought often heat treated or otherwise processed forms. Cast products may include ingot for subsequent remelting or wrought processing e. Wrought products often are in an intermediate approximation of the shape desired or are mill products, including bar, sheet, wire, plate, and so on.
One of the major thrusts of superalloy metallurgy at the end of the 20th century was the production of net shape or near-net shape wrought products.
Cast net shapes have been available via investment casting processes for decades. Table 2. Nickel-base 96 continued 91 71 94 81 84 86 98 Nickel-base continued Effect of temperature on h stress-rupture strengths of selected wrought superalloys Rupture strength at: Bar Bar Sheet Cast alloys are found in the hot section areas of gas turbines.
For example. Wrought alloys are more homogenous than cast alloys. In the intermediate-temperature application areas of gas turbines. Wrought versus Cast Superalloys Wrought Superalloys. Most castings are polycrystalline PC equiaxed. Not all alloy compositions can be made in wrought form.
Wrought alloys generally are considered more ductile than cast alloys. Forgings obviously are also wrought products and take advantage of the superior ductility of wrought material to produce certain larger shapes.
The same composition. The superalloys. Superalloys usually are processed to optimize one property in preference to others. Cast Superalloys. The PC castings contain many grains that may vary in size from one component to another. Some alloys can only be fabricated and used in cast form. Service Temperatures for Superalloys. The bulk of this text presumes that the application will be at elevated temperature.
Even when a superalloy is used in the same product form. By adjustment of processing conditions. Wrought nickel. The majority of superalloys are strengthened by the production of secondary phases precipitates. Cast alloys are used across the temperature range but particularly at the highest temperatures.
Cryogenic applications are covered in Chapter Above that temperature. Costs of actually producing certain net shape wrought products have gone up. Chapter 3 provides detailed information about the metallurgy of all superalloy types. Metals Handbook Effect of temperature on the short-time mechanical properties of selected cast superalloys Ultimate tensile strength at: A Technical Guide Nickel-base Nickel Development Institute The Properties of Superalloys General Comments.
The coarse grain size of PC castings. Strengthening in superalloys is by solid-solution hardening substituted atoms interfere with deformation.. On the other hand For example Castings are intrinsically stronger than forgings at elevated temperature In addition.
A Technical Guide Table Carbide production a favorable distribution of secondary phases interferes with deformation also produces strength. Strength is a relative term. A visual picture also can be obtained for rupture behavior of a few alloys. Because of a melting-point advantage. The deterioration rate of some alloys with time is less than that for other alloys. Cast cobalt-base alloys. For those interested in property comparisons.
This is not an absolute fact. Modern Superalloys. Wrought cobalt-base alloys have found use as combustor parts in gas turbines. Mechanical Properties and the Application of Superalloys.
The highest hardener-content nickel-base superalloys became available as cast alloys. Astroloy no longer dominate the high intermediate-temperature range. Early iron-nickelbase superalloys.
Because strength is a function of time. Subsequent iron-nickeland nickel-base superalloys. Hot deformation is the preferred forming pro-. The superalloys are relatively ductile.
Figure 2. For more on the properties of superalloys. Many designs are concerned with the creep behavior of an alloy. Some concern themselves with creep rate. An alloy that may have a longer rupture life and. If alloys are to be used for turbine airfoils. Cost is a very important factor. As noted in Chapter 1. Selection of alloys is a preliminary step that must be expanded upon to get data and components in a reasonable time frame at acceptable costs.
Physical Properties and Density. The essence of superalloy selection for intermediate-temperature applications is that there are standard alloys of capability similar to Waspaloy and down that can be procured and forged by conventional means. Gas turbine airfoils experience temperatures in this range. High-Temperature Applications—Cast Alloys. Powder metallurgy processing enables production of forged components not otherwise processable.
A Technical Guide cess. In addition to maximizing creep-rupture strength.
If an alloy is to be used as sheet. Good tensile ductility is important. The physical properties. To maximize strength. An alloy for the most stringent turbine airfoil applications will have a high melting point.
For the higherstrength applications. Increases achieved in alloy capability can be negated if a large density increase results as well. Modern cast nickel-base superalloys tend to have densities in the high end of the density range. Density can be important in aircraft gas turbines where increased density can result in increased stress on mating components. If alloys to be used are intended for massive applications.
The lower moduli result from DS processes. Massive parts. A special type of superalloy. As section thickness is reduced. MA is another such alloy that may have enough strength for a high-pressure turbine blade in aircraft gas turbines. An HPT disk has blades attached.
For low-pressure turbine LPT airfoils. A power train in which there are: A disk is a component attached to a shaft and that turns the shaft or is turned by it.
Note that the hot sections occur near the rear of the engine. TMF problems must be minimized by using DS-produced oriented grain or crystal structures to reduce stresses. In the most demanding conditions. For turbine vanes where no centrifugal load exists. A schematic of a typical gas turbine is shown in Fig. Oxide-dispersion-strengthened alloys are not common.
MA relies on yttria dispersed in a corrosion-resistant nickel-chromium matrix to provide adequate creep-rupture capability. Typical gas turbine parts made from superalloys consist of the following components.
The disks being considered here would turn the shafts. An Example of Gas Turbine Disks. The various requirements that might have to be met in the choice of material for an HPT disk for a gas turbine engine. At the same time. IN is the alloy of choice for a majority of gas turbine disks. Steels are out of the question. On the other hand. Wrought alloys have better ductility and higher tensile properties than cast alloys. By checking the available yield and ultimate strengths.
An example is the prevalence of IN as the standard low intermediate-temperature turbine disk in aircraft gas turbine engines. When a cobalt shortage and attendant high alloy prices occurred in the latter part of the s. An additional factor in the selection of an alloy for this disk application becomes the cost and availability of material.
Cost and availability. IN had wide acceptance but not necessarily better properties overall than some competitive materials. Cast alloys are not a satisfactory choice. A disk fracture is a major event. A Technical Guide An alloy with the best ductility and uniformity of properties is indicated for the disk because of the criticality of the application.
Yield and ultimate strengths plus LCF resistance were quite satisfactory. The alloy was available. Wrought iron-nickel-base alloys are a possibility. To summarize the selection process.
Up until about This fatigue is LCF and is found at the high-stress. Cobalt-base super- alloys are not in contention here.
High yield and ultimate strengths are required to resist the high centrifugal forces caused by rapid rotation and the mass of the disk and its attached blades. Carbides may provide limited strengthening directly e. If body-centered tetragonal bct is added to the list. Crystal Structures. Secondary phases of value in controlling properties are the fcc carbides MC. The superalloys derive their strength mostly from solid-solution hardeners and precipitated phases.
As noted earlier. In addition to macrostructure. That is. In addition to grain size and morphology. Phases in Superalloys. The extent to which they contribute directly to strengthening de-.
Figure 3. When hard sphere models representing the crystal structures of most metals are constructed. Carbides are found in all three superalloy groups. Ordering is very important in the strengthening of superalloys. Metals tend to have relatively simple crystal structures. There is no special need to describe the crystal structure of all phases. Face-centered cubic fcc.
Some alloys. Alloys in this last category vary from DL stainless with slight chromium and nickel adjustments. Some carbide. Nickel atoms are always on faces. At the current time ironnickel-base superalloys invariably are used in the wrought condition.
The most important class of iron-nickel-base superalloys includes those alloys that are strengthened by intermetallic compound precipitation in an fcc matrix. Table 3. Introduction to the Alloy Groups Fig. Nickel-Base Superalloys. These minor elements are not customarily found in most cobalt-base alloys. Additional tabular information on phases is provided in Tables 3. Detrimental phases also form in the superalloys. Although there are solid-solution-hardened nickel-base su- pends on the alloy and its processing.
These phases are so-called topologically close-packed tcp phases and may not be of concern in trace amounts. A Technical Guide Fig.
Donachie mj donachie sj 2002 superalloys a technical
Borides may form in the iron-nickeland nickel-base superalloys.. Gamma prime is spherical in ironnickel-base and in some of the older nickel-base alloys. Ti Principal strengthening phase in many nickel. Form of precipitation is important. In the more recently developed nickel-base alloys. Observed in overaged Inconel Randomly distributed carbide. Found in iron-nickel-. Generally observed as a blocky intergranular shape. Nitrides are observed in alloys containing titanium.
For niobium-strengthened nickel-base superalloys. A Technical Guide Table 3. Co 7 Mo. W 6 Observed in iron-nickel. For alloys with titanium and aluminum. Zr N Ti. These three alloys IN An additional dimension of nickel-base superalloys has been the introduction of morphological grain-aspect ratio and orientation control as a means of improving properties.
Nickel-base superalloys are used in both cast and wrought forms. Alloys of this type are IN and IN In fact. Wrought alloy grain sizes tend to be smaller than grain sizes in cast alloys Nb Cr La. Properties in superalloys usually are developed for a given composiTable 3. Nb Al. Cr La. Cr Mo C.
Major Elements in Superalloys Re a Not all these effects necessarily occur in a given alloy. Grain size in castings is a direct function of the casting process and. Grain structure is developed by processing. Chemistry is very important in providing for the level of strength and corrosion properties that may be achieved. Ta Al. Microstructural changes are invariably produced by dissolving all or most of the carbides and other intermetallic precipitate phases e.
Microstructure includes not only grain size and morphology but also the type and distribution of secondary phases in the superalloy austenitic matrix. Ce La. The essential distinction in these alloys is between cast and wrought structures..
Co Al. The cobalt-base superalloys are invariably strengthened by a combination of carbides and solid-solution hardeners. Hf Cr Cr.. Wrought alloy grain sizes can be varied over a wider range.. Th Cr. Superalloys contain a variety of elements in a large number of combinations to produce desired effects..
Ni Ti Alloying Element Summary. Some elements go into solid solution to provide one or more of the following: Lanthanum has been added to some alloys to promote oxidation resistance. Chromium is the principal element needed for hot corrosion resistance. Detrimental Tramp Elements in Superalloys.
The height of the element blocks indicates the amounts that may be present. The evolution of microstructure has been much more pronounced in the iron-nickel-base and nickel-base superalloys than in cobalt-base alloys. The major alloying elements that may be present in nickel-base superalloys are illustrated in Fig.
A Technical Guide peralloys. Many elements cobalt. Some elements boron. Minor elements carbon and boron are added to form carbides and borides. Elements Causing Brittle Phase Formation. The tcp phases usually have low ductility are brittle and cause loss of mechanical and sometimes corrosion properties when present in anything more than trace amounts.
In such cases. All true superalloys contain some chromium plus other elements to promote resistance to environmental degradation. The role of chromium is to promote Cr2O3 formation on the external surface of an alloy. The most obvious microstruc-. Elements such as silicon. Elements such as magnesium tend to tie up and remove some detrimental elements such as sulfur in the form of a compound. Microstructure Introduction. Some of the elements mentioned previously produce readily discernible changes in microstructure.
Microprobe and Auger spectroscopic analyses have determined that grain boundaries can be decorated with tramp elements at high local concentrations.
A major addition to nickel-base superalloy chemistry in recent years has been the element rhenium. The precise microstructural effects produced are functions of processing and heat treatment. MC carbides tend to decompose and generate other carbides. Summary of Phases in Iron Nickel.
The major phases and form of occurrence in iron-nickel. During heat treatment and service. Other elements. These rafts may be useful for increasing creep-rupture properties.
Carbides in nominal solid-solution alloys may form after extended service exposures. All nickel-base alloys contain this phase as the matrix. This phase provides very high strength at low-to-intermediate temperatures. This is the principal high-temperature strengthening phase. There are several carbide phases. It appears as spheres or cuboids when properly formed. This precipitate is found in only a few nickel nickel-iron- base alloys. They are mentioned again in Chapter Typical operating microstructures of representative superalloys are shown in Fig.
When cast nickel-base superalloys became available in the mids and became necessary for design applications after It is possible to pack more precipitate in the matrix gamma phase this way.
Some principal hardening precipitate characteristics that act to obstruct deformation are: Initial microstructures of all superalloys contained some amount of carbide. As alloy development proceeded. The ordered precipitates possess an energy antiphase domain boundary or APB rep-. The product in early alloys was. The introduction of preferred positions ordering for individual atoms increases the amount of energy required to pass deformation elements dislocations through a precipitate.
The likelihood of their presence increases as the solute segregation of the ingot increases. Microstructural phase morphology can vary widely. A Technical Guide ron segregates to grain boundaries. How Microstructures Evolved. In the iron-nickel-base and nickel-base precipitation-hardened superalloys which appeared after the development of solutionhardened superalloys. Precipitates strengthen an alloy by impeding the deformation process that takes place under load. Typical Microstructures.
Some additional microstructures are shown in Appendix B. These phases can cause lowered rupture strength and ductility. Superalloy Strengthening Precipitates and Strength. The optimal situation is for matrix and precipitate to have the same crystal structure and almost the same size of crystal lattice.
There are several boride phases. Macrostructures are shown for a polycrystalline PC cast cobalt and a PC cast nickel superalloy and indicate the carbide phases that are usually seen. Note script carbides in a and b as well as eutectic carbide-cobalt grain-boundary structures in a. IN right. The change in morphology is related to a matrix-precipitate mismatch. Optimal size is a function of the property being measured.
It is stable over a relatively narrow range of compositions but possesses remarkable properties that enable it to provide high-temperature strength to ironnickel. Gamma double prime is a coherent precipitate of composi-. Gamma Prime. It precipitated as spheroidal particles in early nickelbase alloys. Gamma prime is an intermetallic compound of nominal composition Ni3Al with titanium and other elements dissolved in it.
Gamma Double Prime. For wrought superalloys. In creep rupture. Higher APB energies require correspondingly more force for deformation to occur. When size is too large. When the size is too low. Other types of intermetallic phases. In cast alloys. The carbides are particularly essential in the grain boundaries of PC cast alloys for production of desired strength and ductility characteristics.
MC carbides form from the melt and are created either by that reaction or the precipitation from supersaturated solid solutions at high temperatures. Carbide levels in wrought alloys always have been below those in cast alloys. As noted previously. MC is a high-temperature carbide.
M6C carbides gen- Fig. As cleanliness of superalloys has increased. Carbides may provide some degree of matrix strengthening. Various types of carbides are possible. Carbides are also an important constituent of superalloys.
M6C is intermediate in temperature of formation. The latter is invariably incoherent and does not confer strength when present in large quantities. In many cases. In the absence of iron. Some carbides are virtually unaffected by heat treatment while others require such a step in order to be present. Carbides in microstructures of nickel-base superalloys. The carbide M23C6 is found primarily at grain boundaries Fig. The carbides encountered in superalloys serve three principal functions.
The MC carbide usually exhibits a coarse. MC carbides are a major source of carbon for subsequent phase reactions during processing. Because M6C carbides are stable at higher temperature levels than are M23C6 carbides.
Magnesium assists as well. The M7C3 Carbides. Although M7C3 is not widely observed in superalloys. MC carbides.
Although limited information has been generated on MxZry compounds. Although usually seen at grain boundaries Fig. MB12 is also known but has been little investigated. Additions of such elements as cobalt. TiC and HfC. They are distributed heterogeneously through the alloy. M atoms can readily substitute for each other. Little or no orientation relation with the alloy matrix has been noted.
Small additions of minor elements. The boride commonly found in superalloys is of the form M3B2.
They form during lower-temperature heat treatment and service. The M6C carbides have a complex cubic structure. Rene In these carbides. Mo C is found in U M6C is the carbide more commercially important as a grain-boundary precipitate for controlling grain size during the processing of wrought alloys.
The preferred order of formation in order of decreasing stability in superalloys for these carbides is HfC. Borides are hard particles. Heat treatment is the most commonly known of the process steps. Microstructures are not only a function of chemistry but also a function of melting. The general microstructural changes brought about by processing result from the overall alloy composition plus the processing sequence.
Processing and alloying elements are interdependent. References for additional reading in the area and in other aspects of superalloys are given in Appendix C. Processing and Microstructure. The effects of processing are discussed in more detail in the appropriate chapters. Special processing—for example. The SCDS blade shows no grain boundaries.
As previously indicated. Laves phases and carbides are hard particles. Freckled structures must be avoided in any superalloy that is intended for service where fatigue life is an important design criterion. Figure 4. The effect of the phase diagram on solute rejection in IN is shown in Fig.
Composition of freckle vs. Freckle Formation. The primary dendrites reject solute into the interdendritic liquid and. For IN A Technical Guide pendicular to the primary dendrite axis is shown as Fig. Several theories have been proposed to explain the self-perpetuating nature of a freckle.
The use of LST measurement and mushy zone thickness calculation cannot yet be used to predict freckle formation. With regard to changes in alloy content. High-density freckle formation favors the formation of radial freckles.
Also evident from Fig. Alloys forming high-density interdendritic liquids also may form vertical freckles. The channel remelts some of the primary dendrites and becomes several dendrites in diameter. Cutting the Ingots for Obtaining the Different Samples The ingots were cut to obtain different samples.
The samples for the oxidation tests were ground with grit SiC papers with smoothing of their edges and corners. The objective was to explore how their microstructures may evolve at high temperature. The samples destined to the oxidation tests were exposed to a 1.
The weight versus time files were plotted to visualize the type and rate of mass gain kinetic. The oxidized samples were coated by cathodic pulverization of gold and then by an electrolytic nickel deposition in order to protect the scales during cutting. The coated samples were then cut in two parts to prepare cross-sections for the metallographic observations. The samples devoted to the creep tests were placed in a TMA Placed on two bottom supports separated from one another by 12 mm, a central top support applied the constant load.
This one was preliminarily calculated, taking into account the exact values of sample thickness and width, to induce a tensile stress of 20 MPa in the middle of the bottom face of the sample. The creep deformation curves were plotted as displacement of the central point versus time. Preparation of the Metallographic Samples For each alloy, the as-cast part, the two halves of the aged part, and the two halves of the oxidized sample were embedded in a cold resin mixture ESCIL, France.
They were ground with SiC papers from grit up to grit. Results 3. In addition the chromium carbides have obviously disappeared. Carbides are not so elongated as in the as-cast state and they are replaced by alignments of small blocky round carbides. Here too, the chromium carbides existing initially have disappeared. Due to these two phenomena the ZrC carbides became very coarse and round.
They are thus morphologically very different from the initial fine script-like ZrC carbides. One can anticipate a long lasting quality of this reinforcing carbides network at high temperature. All the other alloys, maybe except the TiC-reinforced one, encounter more or less severe but always significant carbide fragmentation phenomena.
The curves illustrating the deformation kinetic are plotted together in Figure 9. After completed cooling the sample looks like the second macrograph presented in Figure 10 b. The previous comment is confirmed by the mass gain kinetic which is faster for the Hf-containing alloy after 50 hours, almost twice gain in mass.
However, as for the reference Ta-containing alloy, the external oxide scale was continuous and adherent to the substrate, as suggested by the really parabolic shape of both of them.
After cross-section preparation, the surface states and subsurface states were observed using the SEM in BSE mode Figure 12 , and the EDS device for measuring the individual chemical compositions of the oxides. The HfC carbides close to the oxidation front were oxidized on place and converted into oxides without release in Hf in the neighbour parts of matrix which remained totally free in Hf. In addition, a real carbide-free zone developed from the oxidation front inwards the bulk, in this Ta-containing alloy.
Discussion Five CoCr This is a rather unusual role for these elements in the chemical compositions of superalloys since their addition is generally done by aiming other objectives. For instance, Hf is a key element in the DSHf directionally solidified superalloy [ 12 ]. It is recognized that its addition may influence the microstructure [ 13 ] and the properties [ 14 ] of superalloys. Niobium, which is considered for superalloys from several decades [ 15 ], can be found in substitution into Al in the gamma prime particles reinforcing the nickel-based single crystalline alloys but it may be chosen as a base element [ 16 ].
Tantalum is used in the MarM cobalt-based superalloy to form TaC carbides besides chromium carbides [ 1 , 2 ]. Titanium, which is a -former element too, as Al and Nb, may be a base element as in the well-known TA6V alloy [ 17 ]. It is involved in different types of aluminides for high temperatures [ 18 ].
Zirconium, which can be present in the chemical compositions of superalloys based on cobalt [ 19 ] or on nickel [ 20 ], is also the main element of the famous Zircaloy-4 [ 21 ]. After their elaboration by foundry, the microstructures of the alloys were all of the same type: dendritic matrix and interdendritic script-like MC carbides whatever the M element. This means that, in a cobalt-chromium base, TiC, TaC, NbC, HfC, and ZrC are carbides more stable than chromium carbides, this confirming what can be expected by considering their free enthalpies of formation.
However, the script-like shape inherited from the mechanisms of crystallization at the end of the solidification of the alloys is not stable in all cases.
Only the HfC carbides demonstrated a high stability at high temperature. The observed performance is particularly remarkable since this alloy is a simple equiaxed polycrystalline alloy, as is to say of a type which is usually not considered for applications under stress at so high temperature.
Obviously, the interdendritic cohesion brought by the mix of the periphery of dendrites with the script-like HfC carbides was really efficient for delaying much later the beginning of the third stage of creep the one concerned by the coalescence of the cavities resulting of the accumulation of the dislocation in the interdendritic boundaries. This is questionable and need further investigations to understand such difference of secondary creep deformation rate between the two alloys.
Indeed, this torque, accompanied by particularly intense shear, favours a local rotation which cannot be obstructed by TaC rounded carbides which move instead of resisting, but to which morphologically not affected HfC elongated script-like carbides may more efficiently resist. This is probably here the key of the folding resistance of the HfC-strengthened sample.
An explanation for that is the nature of the oxide scales formed on surface, which is more a spinel oxide than really chromia as for the Ta-containing alloy. Obviously, the presence of high quantity of Hf, more precisely of great fraction of interdendritic HfC carbides, was deleterious in this field, possibly by obstructing chromium diffusion along the interdendritic boundaries since HfC carbides remained as carbides or as oxides in these locations, even close to the oxidation front.
For the Ta-containing alloy, for which a TaC-free zone developed from the oxidation front, the chromium diffusion was not obstructed along the interdendritic boundaries over several tens first hours or hundreds hours and later of micrometres in depth.
Conclusion The HfC strengthening of equiaxed polycrystalline cobalt-chromium alloys studied in this work appeared very promising for their creep resistance. As demonstrated here by letting competing different MC carbides in the same base, this systems emerged above the others, with additionally the explanation of this superiority: high stability of HfC allowing them resisting both volume fraction decrease and fragmentation.
This CoCr The creep resistance may be improved again by hardening matrix and its high temperature oxidation resistance, currently at a level not high enough, must be itself significantly improved to expect profiting of this major creep resistance at elevated temperature.
Conflicts of Interest The author declares that they have no conflicts of interest. References C. Sims and W. Donachie and S. Nembach and G. Cui, D. Ping, Y. Gu, and H. Mishra, M. Ionescu, and T. View at Google Scholar M. Klauke, D. Mukherji, B. Gorr, V.This book covers virtually all technical aspects related to the selection, processing, use, and analysis of superalloys.
At that point. We extend our special thanks to John Marcin and Joe Goebel who extensively reviewed Chapters 5 and 13 respectively.
Customer Service. Aerodynamically heated skins Rocket-engine parts Heat treating equipment: Add to Basket. It does a good job of achieving its goal as a technical guide to superalloys and is written at a level that is both educational to those who desire to become more familiar with superalloys as well as a good reference book for those working in the field who are well acquainted with the subject.
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