Precipitation Hardening

10 Key excerpts on "Precipitation Hardening"

• 

  eBook - ePub

  Creep-Resistant Steels

  • Fujio Abe, Torsten-Ulf Kern, R Viswanathan(Authors)
  • 2008(Publication Date)
  • Woodhead Publishing

    (Publisher)

  10

  Precipitation during heat treatment and service: characterization, simulation and strength contribution

  E. Kozeschnik; I. Holzer    Graz University of Technology, Austria

  10.1 Introduction

  Precipitation Hardening is one of the most prominent ways of strengthening materials. Precipitates can effectively hinder dislocation and subgrain movement and thus increase the resistance of the material microstructure against plastic deformation. In industrial processes, size and number density of precipitates are controlled by the chemical composition of the alloy as well as the thermomechanical processing route. Owing to the significant influence of precipitates on the mechanical properties of the material, efficient characterization, modelling and simulation of precipitation processes in multi-component alloys are of considerable relevance for industry as well as for academics. The goal of these activities is to be able to produce materials with an optimized spectrum of mechanical properties based on a fundamental understanding of the complex interactions between precipitates and microstructure.

  Materials with superior creep properties are characterized by a microstructure, which exhibits a superior long-term resistance against plastic deformation. This can be achieved by strong pinning forces upon dislocations and subgrain boundaries. The two major effects of precipitates on the creep properties of a material are:

  •  

  Increase of the creep strength by direct interaction between precipitates and dislocations. Precipitates effectively hinder dislocations in their ability to move through the material as a consequence of an external load. Thus, the creep process is considerably slowed down and the creep rate is minimized.

  •  

  Stabilization of the initial microstructure by pinning of grain and sub-grain boundaries. The high strength of the materials in the as-received condition, i.e. the conditions in the delivery state before service, is conserved, because grain and sub-grain coarsening is minimized.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Modern Physical Metallurgy

  • R. E. Smallman(Author)
  • 2016(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Chapter 11 Phase transformations I Precipitation Hardening transformation 11.1 Introduction The production of a material which possesses considerable strength at both room and elevated temperatures is of great practical importance. We have already seen how alloying and cold working can give rise to an increased yield stress, but in certain alloy systems it is possible to produce an additional increase in hardness by heat treatment alone. Such a method has many advantages, since the required strength can be induced at the most convenient production stage of the heat treatment and fabrication schedule and, moreover, the component is not sent into service in a highly stressed, plastically deformed state. The basic requirement for such a special alloy is that it should undergo a phase transformation in the solid state. One type of alloy satisfying this requirement, already considered, is that which has an order-disorder reaction, and the hardening accompanying this process (similar in many ways to Precipitation Hardening) is termed order hardening. The conditions for this form of hardening are, however, quite stringent, so that the two principal hardening reactions commonly used are (a) precipitation from super-saturated solid solution, and (b) eutectoid decomposition. In this chapter we shall deal with the first of these phase transformations. 11.2 Precipitation from supersaturated solid solution The basic requirements of a precipitation-hardening alloy system is that the solid solubility limit should decrease with decreasing temperature as shown in Figure I LI for the Al-Cu system. Here an ahoy exists as a homogeneous α-solid solution at high temperatures, but on coohng becomes saturated with respect to a second phase, Θ; at lower temperatures the ö-phase separates out and lattice hardening often resuhs.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Essentials of Materials Science and Engineering, SI Edition

  • Donald Askeland, Wendelin Wright(Authors)
  • 2018(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Gayle and co-workers showed that the aluminum alloy used by the Wright brothers for making the engine of the first airplane ever flown picked up copper from the casting mold. The age hardening occurred inadvertently as the mold remained hot during the casting process. The application of age hardening started with the Wright brothers’ historic flight and, even today, aluminum alloys used for aircrafts are strengthened using this technique. Age or Precipitation Hardening is probably one of the earliest examples of nanostructured materials that have found widespread applications. Before we examine the details of the mechanisms of phase transformations that are needed for age hardening to occur, let’s examine some of the applications of this technique. A major advantage of Precipitation Hardening is that it can be used to increase the yield strength of many metallic materials via relatively simple heat treatments and without creating significant changes in density. Thus, the strength-to-density ratio of an alloy can be improved substantially using age hardening. For example, the yield strength of an aluminum alloy can be increased from about 140 to 415 MPa as a result of age hardening. Nickel-based superalloys (alloys based on Ni, Cr, Al, Ti, Mo, and C) are pre-cipitation hardened by precipitation of a Ni 3 Al-like g9 phase that is rich in Al and Ti. Similarly, titanium alloys (e.g., Ti 2 6% A1 2 4% V), stainless steels, Be-Cu, and many steels are precipitation hardened and used for a variety of applications. Figure 12-8 (a) A noncoherent precipitate has no relationship with the crystal structure of the surrounding matrix. (b) A coherent precipitate forms so that there is a definite relationship between the precipitate’s and the matrix’s crystal structures. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  The Science and Engineering of Materials, Enhanced, SI Edition

  • Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
  • 2020(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Gayle and co-workers showed that the aluminum alloy used by the Wright brothers for making the engine of the first airplane ever flown picked up copper from the casting mold. The age hardening occurred inadvertently as the mold remained hot during the casting process. The application of age hardening started with the Wright brothers’ historic flight and, even today, aluminum alloys used for aircrafts are strengthened using this technique. Age or Precipitation Hardening is probably one of the earliest examples of nanostructured materials that have found widespread applications. Before we examine the details of the mechanisms of phase transformations that are needed for age hardening to occur, let’s examine some of the applications of this technique. A major advantage of Precipitation Hardening is that it can be used to increase the yield strength of many metallic materials via relatively simple heat treatments and without creating significant changes in density. Thus, the strength-to-density ratio of an alloy can be improved substantially using age hardening. For example, the yield strength of an aluminum alloy can be increased from about 140 to 415 MPa as a result of age hardening. Nickel-based superalloys (alloys based on Ni, Cr, Al, Ti, Mo, and C) are pre- cipitation hardened by precipitation of a Ni 3 Al-like g9 phase that is rich in Al and Ti. Similarly, titanium alloys (e.g., Ti 2 6% A1 2 4% V), stainless steels, Be-Cu, and many steels are precipitation hardened and used for a variety of applications. Figure 12-8 (a) A noncoherent precipitate has no relationship with the crystal structure of the surrounding matrix. (b) A coherent precipitate forms so that there is a definite relationship between the precipitate’s and the matrix’s crystal structures. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Multiscale Materials Modeling

  Approaches to Full Multiscaling

  • Siegfried Schmauder, Immanuel Schäfer, Siegfried Schmauder, Immanuel Schäfer(Authors)
  • 2016(Publication Date)
  • De Gruyter

    (Publisher)

  A kinetics model based on Avrami theory is developed to obtain chateristics of precipitate microstructure at given aging time. Fitting only the rate constants in the precipitation kinetics model, the macroscopic strength predictions of the hier-archical multiscale model are found to correspond reasonably well with available experimental data. Keywords: Al alloy, age hardening curve, Precipitation Hardening, solute hardening, atomistic simulation, molecular dynamics, dislocation-obstacle interaction 3.1 Introduction Modern high strength aluminum alloys are used for structural components in aero-space, automotive, civil, and sports industries. Precipitation Hardening is a common method to obtain high mechanical strength, wherein microscopic precipitates retard the motion of dislocations, thereby retarding the plastic flow and hence increasing the alloy’s yield strength. This phenomena was first discovered by Alfred Wilm [1] in the early 20 th century. In fact, this phenomenon had previously been inadvertently utilized by the Wright brothers during their historic flight of 1903 [2]. During the last century, phenomenal advancements have taken place to improve our understanding of this behavior [3, 4], and its utilization to manufacture ever strong alloys, with the most recent precipitation hardened Al alloys demonstrating strengths approaching 1 GPa [5, 6]. Initial works involved the development of dislocation theory [7–9] and the observation of nanometer-sized solute clusters by X-ray scattering [10, 11] and trans-mission electron microscopy (TEM) [12]. Despite such advancements, a physics based model is still lacking that can predict age hardening curves reliably without experi-mental input, and this chapter presents an atomistics based hierarchical multiscale model to predict age hardening curves and discusses the remaining challenges. © 2013 The Minerals, Metals & Materials Society and ASM International.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Fundamentals of Magnesium Alloy Metallurgy

  • Mihriban O Pekguleryuz, Karl Kainer, A. Arslan Kaya(Authors)
  • 2013(Publication Date)
  • Woodhead Publishing

    (Publisher)

  4

  Understanding precipitation processes in magnesium alloys

  C.L. Mendis,     Helmholtz Zentrum Geesthacht, Germany (formerly of National Institute for Materials Science, Japan)

  K. Hono,     National Institute for Materials Science, Japan

  Abstract:

  Recent interest in developing high strength wrought magnesium alloys has revived studies of precipitation processes in magnesium alloys, as they can be used to control recrystallized microstructure and to add yield strength by age hardening after processing of wrought magnesium. In this chapter, we describe the basic information necessary for controlling precipitate microstructures by aging. Thereafter, precipitation processes and microalloying effects in representative age-hardenable magnesium alloys are reviewed.

  Key words precipitation solid state phase transformations age hardening

  4.1 Introduction

  Magnesium alloys have attracted renewed interest as light alloys, to substitute some conventional structural materials for weight reduction in vehicles such as cars, trucks, trains and aircrafts. Cast alloys, widely used in interior and power-train components, account for more than 99% of magnesium alloys used today, while only a small number of wrought products are utilized. This is because magnesium alloys lack formability for wrought applications, and their high cost discourages the use of magnesium alloys for automotive applications.

  Rare earth (RE) elements, such as CeGd, Nd and Y, are often used as major alloying elements in cast magnesium alloys because of their relatively high solubility in Mg and their effectiveness in Precipitation Hardening and creep resistance. In fact, several Mg–RE alloys show a notable age hardening response, which can lead to substantial strengthening in Mg (Khoarashahi, 1997 ; Nie and Muddle, 2000 ;

  Lorimer et al.,

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Precipitation Hardening

  • J. W. Martin(Author)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  If after such solution heat-treat-ment the alloy is then rapidly cooled to room temperature by quenching into water or other fluid, the separation of the 0-phase (of approximate composition CuAl 2 ) is suppressed, and an un-stable supersaturated solid solution is produced. Merica et al. suggested that hardening resulted from precipitation of the second 3 4 Precipitation Hardening phase taking place when the quenched alloy is aged for a sufficient time, and that the precipitate was in the form of a fine submicroscopic dispersion. Since that date the search for new age-hardenable alloys became susceptible to a scientific approach. The main requirements for strengthening were first clearly stated by Jeffries and Archer in their classic paper of 1921. They considered not only Merica's results with duralumin, but a wide range of dispersion-hardened structures such as cementite in steel, cuprous oxide in copper, and also their own powder metallurgically produced ThO a in tungsten. They laid the founda-tions of the principles of this type of alloy, and proposed that strengthening is obtained by slip interference within the grains due to the keying effect of the dispersed hard particles, and that the effect increases with the fineness of subdivision of the hard constituent (for a given amount of the phase), further suggesting that the strengthening reaches a maximum at an average particle size denoted by the term critical dispersion. With a given amount of precipitate, larger particles would have less strengthen-ing effect because there would be fewer keys: this would explain why at some ageing temperatures the hardness increased initially and then decreased as the particles coalesced beyond the critical dispersion size. 1.2. More Recent Developments Since these early years, aluminium-based alloys (and alumin-ium-copper alloys in particular) have been those most widely studied.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Mechanical Behavior of Materials

  • Marc André Meyers, Krishan Kumar Chawla(Authors)
  • 2008(Publication Date)
  • Cambridge University Press

    (Publisher)

  Figure 10.13 illustrates the differences between strengthening by precipitation and by dispersion-hardening. Nickel-based superalloys IN792 and MAR M-200 are precipitation-hardened by γ or γ precipitates having compos-itions of Ni 3 Nb and Ni 3 Al, respectively. The TD nickel, on the other hand, contains a fine dispersion of ThO 2 , a high-melting-point oxide that is insoluble in the matrix. At lower temperatures (up to 1,000 ◦ C), Precipitation Hardening is more effective; however, at approximately 1,100 ◦ C, the precipitates dissolve in the matrix and the strength is drastically reduced. The dispersoids continue to be effective strength-eners at still higher temperatures. The strengthening in these systems, hardened by either pre-cipitates or dispersoids, has its origin in the interaction of dis-locations with the particles. In general, the interaction depends on the dimensions, strength, spacing, and amount of the precipitate. The detailed behavior, of course, differs from system to system. Let us first describe the phenomenon of precipitation-, or age-, harden-ing. The supersaturated solid solution is obtained by sudden cooling from a sufficiently high temperature at which the alloy has a single phase. The heat treatment that causes precipitation of the solute is called aging . The process may be applied to a number of alloy systems. Although the specific behavior varies with the alloy, the alloy must, at least: 574 SOLID SOLUTION, PRECIPITATION, AND DISPERSION STRENGTHENING 800 700 660 ° 600 500 400 300 200 100 1 1 2 % Cu, atomic 3 4 2 4 Liquid 3 α + θ α α + L 5 Copper, wt. % (b) (a) Temperature, ° C 6 7 8 9 10 700 600 Al Al + Li Al 602 5.2 Liquid Al + Liquid Lithium, wt. % Temperature, ° C 0 1 2 3 4 5 6 500 400 300 200 100 0 Fig. 10.14 (a) Phase diagram of the Al-rich end of the Al–Cu system. (b) Phase diagram of the Al-rich end of Al–Li system. 1. Form a monophase solid solution at high temperatures.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Precipitation Hardening

  Theory and Applications

  • J. W. Martin(Author)
  • 2012(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  ( oo)B is the solute content at a grain boundary in equilibrium with an infinitely large precipitate. A is the parameter defined by B is the parameter defined by B = 2ln (1/f) 22 Precipitation Hardening where (1B is the grain-boundary energy, f is the fraction of the grain boundary covered by precipitates. Experimentally it is found that in the vast majority of cases the kinetics are diffusion-controlled, that is, the mobility of the interface does not limit the reaction. 1.2.9 Calorimetry of precipitation processes Calorimetric techniques have been used to study precipitation in age-hardening alloys since the 1930s. In recent years differential scanning calorimetry (nSC) has been widely employed for this purpose. Modem microcomputer-based thermal analysis systems are available which are able to perform a programmed experiment, collect, record and analyse data, and display or transmit the results automatically. Essentially the difference in heat input into a test specimen and a reference specimen of equal thermal mass is measured while the specimen and reference material are subjected to a controlled temperature programme. A feedback control system measures the temperatures of the specimen and reference material and ensures that they remain the same. The differential heat flow to the specimen and reference material is monitored, thus readily distinguishing (exothermic) precipitation reactions from (endothermic) dissolu-tion reactions. For example, Papazian [10] studied the ageing sequence in the aluminium alloy 2219, which is nominally Al with 6.3 wt % Cu and small amounts of several other elements. Its age hardening behaviour is comparable to that of the pure binary AI-Cu system, with the sequence: supersaturated a ~ GP zones ~ S ~ Sf ~ S Papazian first measured the characteristics in the nsc of the individual precipitate phases, by comparing the nsc and TEM results from samples that had been aged such that only one precipitate phase was present.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Maraging Steels

  Modelling of Microstructure, Properties and Applications

  • W Sha, Z Guo(Authors)
  • 2009(Publication Date)
  • Woodhead Publishing

    (Publisher)

  141 8 Precipitation Hardening stainless steels Abstract : The precipitation process in wrought PH13-8 steel during ageing is the main topic of this chapter. The precipitates formed are enriched in nickel and aluminium, and depleted of iron and chromium, but the composition is far from the stoichiometric NiAl phase. They may take on different shapes at different temperatures. The hardening effects observed during the early stages of ageing should be caused by the redistribution of atoms such as iron, chromium, nickel and aluminium. Particle coarsening takes place simultaneously with the development of the composition of the NiAl-enriched precipitates. Other topics include the use of small-angle neutron scattering, and the effects of intercritical annealing. Key words : atom probe, microstructure, ageing, toughness, grain refinement. 8.1 Microstructural evolution in PH13-8 after ageing The hardness of PH13-8 (Fe–0.97Al–12.43Cr–2.15Mo–8.39Ni) reaches a peak after 30 minutes at 593°C, but still increases after ageing for 4 hours at 510°C (Fig. 8.1). The ageing behaviour of this wrought PH13-8 stainless steel is significantly different from cast PH13-8 steel. There is no contrast in the field-ion microscopy (FIM) image at peak hardness after ageing at 593°C (Fig. 8.2), where, for maraging and PH steels, austenite normally shows a contrast. Atom probe data is obtained from the instrument in the form of a sequence of the mass-to-charge ratio of each of the ions evaporated. The 510 ∞ C 593 ∞ C As quenched 0 10 100 1000 Ageing time (min) HV2 550 500 450 400 350 300 8.1 Age hardening curves at 510°C and 593°C of PH13-8 steel 142 Maraging steels three-dimensional (3D) atom probe (3DAP) instrument allows a high mass resolution, through the introduction of a reflectron-based energy-compensation system. In the example mass spectrum shown in Fig. 8.3, a minor problem is the exact coincidence of 58 Fe 2+ and 58 Ni 2+ , and 64 Ni 2+ and 96 Mo 3+ peaks.

  Sign up to read

  Learn more about book