Search Results for lattice distortion

This chapter, presented in a question-and-answer format, covers many practical aspects of high-entropy alloys (HEAs). It provides clear and concise answers to more than 50 questions, imparting knowledge on alloying elements, heat treatments, diffusion mechanisms, phase formation, lattice distortion, crystal and grain structures, structure-property relationships, microstructure control, and characterization methods. It likewise explains how to calculate the effect of strengthening processes on the mechanical properties of HEAs and offers insights on how to balance strength, ductility, and density for specific applications. It also provides information on twinning behaviors, stacking faults, elastic properties, coating and film deposition methods, manufacturing challenges, and the use of computational techniques for alloy design.

Martensitic steels are produced by quenching carbon steel from the austenite phase into martensite. This chapter provides information on the composition, microstructures, processing, deformation mechanisms, mechanical properties, hot forming, tempering, and special attributes of martensitic steels.

Martensitic (MS) steel is produced by quenching carbon steel from the austenitic phase into martensite. This chapter presents the compositions, microstructures, processing, deformation mechanism, mechanical properties, hot forming process, and attributes of MS steels.

When a metal is alloyed with another metal, either substitutional or interstitial solid solutions are usually formed. This chapter discusses the general characteristics of these solutions and the effects of several alloying elements on the yield strength of pure metals. It presents four rules that give a qualitative estimate of the ability of two metals to form substitutional solid solutions: relative size factor, chemical affinity factor, relative valency factor, and lattice type factor. The chapter provides information on alloys that form an ordered structure during heating. It describes the intermediate phases that are formed during solidification between the two extremes of substitutional solid solution on the one hand and intermetallic compound on the other. The chapter concludes with a section on strain aging in low-carbon steels that allows the interstitial atoms to diffuse to the dislocations and again form atmospheres that pin dislocation movement.

Alloying, heat treating, and work hardening are widely used to control material properties, and though they take different approaches, they all focus on imperfections of one type or other. This chapter provides readers with essential background on these material imperfections and their relevance in design and manufacturing. It begins with a review of compositional impurities, the physical arrangement of atoms in solid solution, and the factors that determine maximum solubility. It then describes different types of structural imperfections, including point, line, and planar defects, and how they respond to applied stresses and strains. The chapter makes extensive use of graphics to illustrate crystal lattice structures and related concepts such as vacancies and interstitial sites, ion migration, volume expansion, antisite defects, edge and screw dislocations, slip planes, twinning planes, and dislocation passage through precipitates. It also points out important structure-property correlations.

Residual, or locked-in internal, stresses are regions of misfit within a metal part or assembly that can cause distortion and fracture just as can the more obvious applied, or service, stresses. This chapter describes the fundamental facts about residual stresses and discusses the basic mechanisms of residual stress formation: thermal, transformational, mechanical, and chemical.

The unique advantages of the nitriding process were recognized by German researchers in the early 1920s. It was used to treat steels for applications that required: high torque, high wear resistance; abrasive wear resistance; corrosion resistance; and high surface compressive strength. This chapter focuses on key process considerations and factors that helped nitriding gain acceptance. These factors include a low-temperature process, no quench requirement, minimal distortion, high hardness values, and resistance to oxidation.

This article discusses the general purpose of alloying and identifies some of the material properties and behaviors that can be improved by adding various elements to the base metal. It explains how alloying can make metals stronger and more resistant to corrosion and wear as well as easier to cast, weld, form, and machine. It also discusses some of the alloying techniques that have been developed to address problems stemming from dissimilarities between the base metal and alloying or inoculate material.

This chapter discusses steel’s compositions, metallurgical phases, microstructures, and heat treatments. It then presents the structure-property relationships of steel. The chapter describes the deformation and strengthening mechanisms of steel. It also presents an overview of deformation processing and annealing.

Several process parameters must be considered to ensure success in achieving desired metallurgical properties and to minimize distortion. This chapter provides a detailed discussion on the liberation of nitrogen, dissociation of the gas at the selected nitriding temperature, why ammonia is used, distortion, and preheat treatment.

This chapter introduces the concepts of mechanical properties and the various underlying metallurgical mechanisms that can be used to alter the strength of materials. The mechanical properties discussed include elasticity, plasticity, creep deformation, fatigue, toughness, and hardness. The strengthening mechanisms covered are solid-solution strengthening, cold working, and dispersion strengthening. The effect of grain size on the yield strength of a material is also discussed.

This chapter provides readers with worked solutions to more than 25 problems related to compositional impurities and structural defects. The problems deal with important issues and challenges such as the design of low-density steels, the causes and effects of distortion in different crystal structures, the ability to predict the movement of dislocations, the influence of impurities on defects, the relationship between gain size and material properties, the identification of specific types of defects, the selection of compatible metals for vacuum environments, and the effect of twinning planes on stacking sequences. The chapter also includes problems on how the formation of precipitates can produce slip planes and how grain boundaries can act as obstacles to dislocation motion.

The tensile test provides a relatively easy, inexpensive technique for developing mechanical property data for the selection, qualification, and utilization of metals and alloys in engineering service. The tensile test requires interpretation, and interpretation requires a knowledge of the factors that influence the test results. This chapter provides a metallurgical perspective for such interpretation. The topics covered include elastic behavior, anelasticity, damping, proportional limit, yield point, ultimate strength, toughness, ductility, strain hardening, and yielding and the onset of plasticity. The chapter describes the effects of grain size on yielding, effect of cold work on hardness and strength, and effects of temperature and strain-rate on the properties of metals and alloys. It provides information on true stress-strain relationships and special tests developed to measure the effects of test/specimen conditions. Finally, the chapter covers the characterization of tensile fractures of ductile metals and alloys.

The building block of all matter, including metals, is the atom. This chapter initially provides information on atomic bonding and the crystal structure of metals and alloys, followed by a description of three crystal lattice structures of metals: face-centered cubic, hexagonal close-packed, and body-centered cubic. It then describes the four main divisions of crystal defects, namely point defects, line defects, planar defects, and volume defects. The chapter provides information on grain boundaries of metals, processes involved in atomic diffusion, and key properties of a solid solution. It also explains the aspects of a phase diagram that shows what phase or phases are present in the alloy under conditions of thermal equilibrium. Finally, a discussion on the applications of equilibrium phase diagrams is presented.

This chapter discusses the compositions, metallurgical phases, microstructure, heat treatment, grades, and structure-property relationships of steels. In addition, it describes the mechanisms involved in deformation, strengthening, and annealing of steels.