After shaping and first-stage binder removal, the component (with remaining backbone binder) is heated to the sintering temperature. Further heating induces densification, evident as dimensional shrinkage, pore rounding, and improved strength. This chapter begins with a discussion on the events that are contributing to sintering densification, followed by a discussion on the driving forces, such as surface energy, and high-temperature atomic motion as well as the factors affecting these processes. The process of microstructure evolution in sintering is then described, followed by a discussion on the tools used for measuring bulk properties to monitor sintering and density. The effects of key parameters, such as particle size, oxygen content, sintering atmosphere, and peak temperature, on the sintered properties are discussed. Further, the chapter covers sintering cycles and sintering practices adopted as well as provides information on dimensional control and related concerns of sintering. Cost issues associated with sintering are finally covered.

Fabricated powder metallurgy (P/M) parts are evaluated and tested at several stages during manufacturing for part acceptance and process control. The various types of tests included are dimensional evaluation, density measurements, hardness testing, mechanical testing, and nondestructive testing. This chapter is a detailed account of these testing methods. It describes the four most common types of defects in P/M parts, namely ejection cracks, density variations, microlaminations, and poor sintering. The chapter discusses the capabilities and limitations of various nondestructive evaluation methods to flaw detection in P/M parts. The nondestructive evaluation methods covered are mechanical proof testing, metallography, liquid penetrant crack detection, filtered particle crack detection, magnetic particle crack inspection, direct current resistivity testing, x-ray radiography, computed tomography, gamma-ray density determination, and ultrasonic techniques.

This chapter introduces the key powder fabrication attributes to assist in the identification of the right powders for an application. First, it describes the characteristics of engineering powders such as particle size distribution, powder shape and packing density, surface area, powder flow and rheology, and chemical analysis. The chapter then describes the general categories of powder fabrication methods, namely mechanical comminution, electrochemical precipitation, thermochemical reaction, and phase change and atomization. It provides information on the two largest contributors to powder price, namely raw material cost and conversion cost. The applicability of various processes to specific material systems is mentioned throughout this chapter.

This chapter is a detailed account of various attributes related to mixing and testing of powder-binder feedstocks. Mixing parameters and their effects on feedstock properties is discussed. The attributes reviewed include mixture homogeneity, wetting, powder-binder ratio, feedstock density, elastic modulus, rheological behavior, particle size, formulation control, feedstock mixing, and feedstock properties. The chapter also provides information on the processes involved in feedstock preparation and testing.

This chapter discusses the sintering process for stainless steel powders and its influence on corrosion resistance. It begins with a review of sintering furnaces and atmospheres and the effect of temperature and density on compact properties such as conductivity, ductility, and strength. It then describes the relationship between sintered density and corrosion resistance and how it varies for different types of powders and operating environments. The chapter also explains how stainless steel powders respond to different sintering atmospheres, including hydrogen, hydrogen-nitrogen, and vacuum, and liquid-phase sintering processes.

This appendix contains a table listing the symbol, atomic number, atomic weight, melting temperature, density, atomic radius, and crystal structure of various elements.

This appendix contains a table listing density, thermal conductivity, linear expansion, electrical resistivity, and Young's modulus of various materials.

This chapter discusses the advantages of using powder metallurgy to produce magnetic materials, particularly its ability to control chemistry and near-net shape. It also explains how process parameters and powder characteristics influence the physical and magnetic properties of common stainless steels.

This appendix contains tables listing the physical and mechanical properties of stainless steel engineering alloys. The physical properties covered are density, modulus of elasticity, coefficient of thermal expansion, thermal conductivity, specific heat, and electrical resistivity. The mechanical properties listed include yield strength, tensile strength, elongation and hardness.

This appendix provides crystal structure and property data for alloying elements used in superalloys.

The physical properties of a material are those properties that can be measured or characterized without the application of force and without changing material identity. This chapter discusses in detail the common physical properties of metals, namely density, electrical properties, thermal properties, magnetic properties, and optical properties. Some physical properties for a number of metals are given in a table.

This chapter reviews failure aspects of structural ferrous powder metallurgy (PM) parts, which form the bulk of the PM industry. The focus is on conventional PM technology of parts in the density range of 6 to 7.2 g/cc. The chapter briefly introduces the processing steps that are essential to understanding failure analysis of PM parts. This is followed by a section on case hardening of PM parts. The methods used for analyzing the failures are then discussed. Some case studies are given that illustrate different failures and the methods of prevention of these failures.

This chapter discusses the context in which metallography is used and some of the challenges of analyzing three-dimensional structures from a two-dimensional perspective. It describes the hierarchical nature of metals, the formation of grain boundaries, and the notable characteristics of microstructure. It explains how microstructure can be represented qualitatively by points, lines, surfaces, and volumes associated to a large extent with grain contact, and how qualitative features (including grains) can be quantified based on cross-sectional area, volume fraction, density, distribution, and other such metrics.

With cold work, mechanical strength (measured either by yield strength or ultimate tensile strength) increases and ductility (measured by elongation, reduction of area, or fracture toughness) normally decreases. This chapter discusses the mechanisms that produce these changes and the factors that influence them. It explains how cold working increases dislocation density and how that affects the stress-strain characteristics of steel, particularly the onset of deformation. It describes the effects of deformation on ferrite, austenite, cementite, and pearlite, and how to optimize their microstructure for various applications through controlled deformation. It also provides information on subcritical annealing, the examination and control of texture, the use of optical microscopy to monitor the effects of recrystallization, and the effect of cold working on threaded fasteners, nails, and filaments used to manufacture cords.

This chapter discusses the properties and applications of beryllium intermetallic compounds. It describes the crystal structure of key beryllides, the metals they contain, and important properties such as high-temperature strength, thermal conductivity and expansion, oxidation resistance, and density. It explains how beryllide intermetallics are formed using sputter deposition, diffusion, and powder metal methods.

Beryllium is an important additive in the production of amorphous metal alloys, achieving low density and high strength. It also plays a role in amorphous alloys that can be slowly cooled and still retain their amorphous structure. This chapter provides information on the development of amorphous alloys that contain beryllium and the applications for which they are suited.

This chapter provides an overview of the physical metallurgy of beryllium, discussing phases and phase transformations, physical and mechanical properties, heat treatment, and alloying. It explains how the atomic structure of beryllium, particularly its sp hybrid state, contributes to the anisotropy of elastic constants and slip properties, resulting in a specific stiffness, or modulus-to-density ratio, six times higher than that of any other structural material.

This chapter discusses the principles and procedures of electrochemical measurements used to investigate corrosion behaviors. It begins by presenting a diagram of a basic potentiostatic circuit, which consists of a working electrode and an auxiliary or counter electrode suspended in an electrolytic solution. It describes how corrosion potentials and current densities are measured and explains how to deal with various sources of error. It also explains how electrochemical impedance measurements are used and describes the underlying theory and procedures in some detail.

Beryllium is an extraordinary metal with an unusual combination of physical and mechanical properties. It has low density, high stiffness, and excellent dimensional stability. It is also transparent to x-rays and can be machined to extremely close tolerances. This chapter discusses the properties, compositions, and processing characteristics of beryllium and its alloys. It provides information on powder production and consolidation, commercial designations and grades, wrought products, and forming processes. It also discusses the issue of corrosion, the use of protective treatments and coatings, and health and safety concerns.

This chapter discusses the basic principles of induction heating and related engineering considerations. It describes the design and operation of induction coils, the magnitude and distribution of magnetic fields, and the forces that generate eddy currents in metals. It explains how induced electrical current causes metal to heat in proportion to their electrical resistance and how it affects temperature dependent properties such as resistivity and specific heat and, in turn, heating rates and efficiencies. It also discusses the effect of hysteresis and explains why eddy currents tend to be confined to the outer surface of the workpiece, a phenomenon known as the skin effect. The chapter includes several data plots showing how the depth of heating varies with frequency and how heating time, power density, and thermal conduction rate correspond with hardening depth.