This chapter summarizes the progress that has been made in the study of high-entropy alloy (HEA) systems and the process-structure-property relationships that define them. It describes the various ways HEAs can be strengthened and explains how alloying elements influence tensile and yield strength, fracture toughness, and fracture strength. It discusses the stages of plastic deformation in HEAs and the role of dislocations and twinning in the evolution of microstructure. It reviews some of the work that has been done on fatigue behaviors and the methods developed to assess fatigue performance. It discusses the influence of defects on fatigue life, the effect of temperature and grain size on fatigue-crack propagation, and the role of nanotwinning in crack-growth retardation. It describes the methods used to produce HEAs in bulk and powder form and to apply them as protective coatings and films. It also identifies potential applications based on properties such as strength, hardness, density, wear resistance, high-temperature stability, and biocompatibility.

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.

This chapter describes the basics of energy and entropy and “free energy.” Fundamentals of internal energy U , the enthalpy H , entropy S , free energies G , and F of a substance are presented. The chapter also presents the thermal vibration model to promote a better understanding of the U , S , and F of the crystal. It covers basic concepts of thermodynamics of magnetic transition and discusses the role and the meaning of magnetic transition in iron and steel. The chapter concludes with a general discussion on an amorphous phase from a thermodynamic viewpoint.

This chapter presents an overview of families of brazing alloys that one is likely to encounter in a manufacturing environment. It discusses the metallurgical aspects of brazing and includes a survey of brazing alloy systems. A discussion of deleterious and beneficial impurities is provided with examples. The chapter also describes the application of phase diagrams to brazing.

This chapter discusses joining atmospheres that are used for brazing, along with their advantages and disadvantages. It discusses the processes, advantages, and disadvantages of chemical fluxing, self-fluxing, and fluxless brazing. Information on stop-off compounds that are considered as the antithesis of fluxes is also provided.

This chapter considers the role of materials in brazing operations and the manner in which they impact on the choice of processing conditions and their optimization. The concepts covered are metallurgical and mechanical constraints, and constraints imposed by the components and their solutions as well as service environment considerations.

Brazes for carat gold jewelry must meet or exceed the fineness/caratage of the component piece parts of the assembly in order for it to meet the national fineness/caratage standards and marking or hallmarking regulations for jewelry. This chapter concentrates on brazes for gold jewelry. It provides understanding of the metallurgy of gold jewelry alloys and includes a discussion of brazes for carat gold jewelry. The chapter also provides information on traditional gold jewelry brazes, the target properties of filler metals for carat gold jewelry and describes the characteristics of novel 22 carat gold solders.

This chapter discusses the process, principles, and modeling of the diffusion brazing system. The applications of diffusion brazing to wide-gap joining and layer manufacturing are also discussed.

This chapter discusses the processes involved in the wetting, spreading, and chemical interaction of a braze on a nonmetal. The chapter reviews the key materials and process issues relating to the joining of nonmetals using active brazing. Emphasis is placed on the differences in brazing to metals by established methods. The chapter also describes the designing process and properties of metal/nonmetal joints.

This appendix contains abbreviations and symbols related to brazing.

This appendix contains a brief list of general references related to brazing technology.

This chapter briefly reviews the history of brazing from ancient times to the early 20th century.

Brazing and soldering jointly represent one of several methods for joining solid materials. This chapter summarizes the principal characteristics of the various joining methods. It then discusses key parameters of brazing including surface energy and tension, wetting and contact angle, fluid flow, filler spreading characteristics, surface roughness of components, dissolution of parent materials, new phase formations, significance of the joint gap, and the strength of metals. The chapter also describes issues in processing aspects that must be considered when designing a joint, and the health, safety, and environmental aspects of brazing.

This chapter presents an overview and survey of solder alloy systems. Extensive reference is made to phase diagrams and their interpretation. The chapter describes the effect of metallic impurities on different solders. The chapter concludes with a review of the key characteristics of eutectic alloys and of the factors most effective at depressing the melting point of solders by eutectic alloying.

Materials used in joining, whether solders, fluxes, or atmospheres, are becoming increasingly subjected to restrictions on the grounds of health, safety, and pollution concerns. These regulations can limit the choice of materials and processes that are deemed acceptable for industrial use. The chapter addresses this issue with a focus on soldering fluxes. The chapter also describes factors related to soldering under a protective atmosphere, provides information on chemical fluxes for soldering of various metals, and discusses the processes involved in fluxless soldering processes.

This chapter considers the materials and processing aspects of soldering and the manner in which these interrelate in the development of joining processes. It discusses the processes involved in eliminating or suppressing metallurgical and mechanical constraints as well as constraints imposed by the components.

This chapter presents several materials and processes related to soldering technology. It first provides information on lead-free solders, followed by sections devoted to flip-chip processes, diffusion soldering, and modeling. Scanning acoustic microscopy and fine-focus x-ray techniques are also discussed. The chapter describes several evaluation procedures and tests developed to measure solderability and standards for process calibration. The chapter also describes the characteristics of reinforced solders, amalgams used as solders, and other strategies to boost the strength of solders. Further, the chapter considers methods for quantifying the mechanical integrity of joints and predicting their dimensional stability under specified environmental conditions. It discusses the effects of rare earth elements on the properties of solders. The chapter concludes with information on advanced joint characterization techniques.

This appendix contains a brief list of general references related to soldering technology.