Milling of materials, whether hard and brittle or soft and ductile, is of prime interest and of economic importance to the powder metallurgy (PM) industry. This article discusses the principles of milling, milling parameters, and the powder characteristics required for the process. It discusses the changes in powder particle morphology that occur during milling of metal powders produced by various processes such as microforging, fracturing, agglomeration, and deagglomeration. The article also provides useful information on milling equipment such as tumbler ball mills, vibratory ball mills, attrition mills, and hammer and rod mills.

Rough grinding and polishing of specimens are required to prepare fiber-reinforced composite samples for optical analysis. This article discusses the consumables, process variables, and the equipment that influence the sample preparation procedure. It describes the hand and automated grinding methods. The article summarizes the rough and final polishing steps for both hand and automated techniques. Common artifacts that may be created during grinding and polishing steps of composite samples are reviewed. These include scratches, fiber pull-out, matrix smears, streaks, erosion of different phases, and fiber and sample edge rounding and relief.

This article focuses on the sample preparation methods for titanium honeycomb composites, boron fiber composites, and titanium/polymeric composite hybrids. These include mounting, sectioning, grinding, and polishing. The article also provides information on the sample preparation of unstaged and staged prepreg materials for optical analysis.

Particle size and size distribution have a significant effect on the behavior of metal powders during their processing. This article provides an overview of the sample preparation process for particle size measurement, which is a key step in the measurement of particle size distributions. Common particle size measuring techniques discussed in this article include sieve analysis, quantitative image analysis, laser diffraction, sedimentation methods, aerodynamic time-of-flight method, electrical zone sensing, and photon correlation spectroscopy. The advantages and disadvantages of these methods are reviewed.

This article discusses the pressing and sintering of various refractory metal powders for the production of intermediate products as well as special cases of finished products. The metal powders considered include tungsten, molybdenum, tantalum, niobium and their alloys, as well as rhenium.

This article describes the various aspects relating to the selection and preparation of ultrathin-section specimens of fiber-reinforced polymeric composites for examination by transmitted light microscopy. It provides information on the contrast-enhancement methods used by transmitted-light microscopy and optimization of microscope conditions. Examples of composite ultrathin sections analyzed using transmitted-light microscopy contrast methods are also presented.

This article summarizes sampling of powders, which includes the sampling of stored material and flowing streams, sample reduction and evaluation, and weight of sample required. It also summarizes the classification of powders. Classifiers are divided into two categories: counterflow equilibrium and crossflow separation. Classification methods are used to exclude certain powder sizes from a powder distribution and to obtain particular powder distributions. For example, sieving methods are used to obtain particular powder distributions and to obtain narrow size ranges of a powder. The article summarizes the sieving methods for powders. The sieving methods include hand sieving, machine sieving, manual wet sieving, air jet sieving, sonic sifter, wet sieving by machine, the Seishin robot sifter, automated systems, and ultrasonic machine sieving. The article outlines the sieve types and the process variables of the sieving process. An appendix reviews dispersion of powders in liquids.

This article explains how ceramic powders are made. It begins by briefly describing the raw materials used in structural clay products, whitewares, refractories, and advanced ceramics. It then examines various additives that promote uniformity at different stages of the process. After a description of the comminution process (wet and dry milling methods), it discusses batching and mixing operations and granulation methods. The article also deals with the effect of process variables and the steps involved in chemical synthesis, including preparation from solution and gas-phase reactions, filtration and washing, and powder recovery techniques. It concludes with a discussion on characterization, centering on size distribution analysis, specific surface area, density, porosity chemical composition, phase, and surface composition.

The primary market for metal powder is the production of powder metallurgy (PM) parts, which are dominated primarily by iron and copper powders. This article reviews the chemical and pyrotechnics applications of ferrous and nonferrous powders. It describes the characteristics of iron powder used in oxygen scavengers and chemical reactive warmers and heaters. Metal powders used as fuels in solid propellants, pyrotechnic devices, explosives, and similar applications are reviewed. Atomized aluminum, magnesium, tungsten, and zirconium powders are also discussed.

Semisolid casting is a near-net shape manufacturing process capable of producing thick- and thin-walled complex-shaped components having excellent mechanical and functional performance. This article begins with a discussion on the history of semisolid processing and the advantages claimed for semisolid casting. It describes the four notable processes used to produce semisolid castings: thixocasting, rheocasting, thixomolding, and wrought processes. Most commercial aluminum semisolid casters use either thixocasting or rheocasting. The article discusses the die design, process conditions, and simulation for semisolid casting. It concludes with a review of several components produced by each of the various semisolid casting processes.

This article presents a detailed account of the processes involved in vat-photopolymerization-based fabrication of ceramics, namely bioceramics, structural ceramics, piezoelectric ceramics, optical ceramics, and polymer-derived ceramics. Information and methods of material preparation, curing characteristics, green-part fabrication, property identification, process design and planning, and quality control and optimization are introduced. The article also provides information on postprocessing techniques, namely debinding and sintering, as well as on the phenomenon of shrinkage and compensation.

This article provides information on the microstructure of powder metal alloys and the special handling requirements of porous materials. It covers selection, sectioning, mounting, grinding, and polishing, and describes procedures, such as washing, liquid removal, and impregnation, meant to preserve pore structures and keep them open for analysis. The article compares and contrasts the microstructures of nearly 50 powder metal alloys, using them to illustrate the effect of consolidation and compaction methods as well as particle size, composition, and shape. It discusses imaging equipment and techniques and provides data on etchants and etching procedures.

The residual porosity in sintered refractory metal ingots is usually eliminated by different densification processes, such as thermomechanical processes. This article focuses on thermomechanical processing of tungsten, molybdenum, and tantalum. It provides an overview of liquid-phase sintering of tungsten heavy alloys and describes the infiltration of tungsten and molybdenum for attaining full density. The article concludes by providing information on hot isostatic pressing of refractory metal alloys to full density.

Ceramic-matrix composites (CMCs) have ability to withstand high temperatures and have superior damage tolerance over monolithic ceramics. This article describes important processing techniques for CMCs: cold pressing, sintering, hot pressing, reaction-bonding, directed oxidation, in situ chemical reaction techniques, sol-gel techniques, pyrolysis, polymer infiltration, self-propagating high-temperature synthesis, and electrophoretic deposition. The advantages and disadvantages of each technique are highlighted to provide a comprehensive understanding of the achievements and challenges that remain in this area.

The two major types of beryllium-containing alloys are copper-berylliums and nickel-berylliums. The most widely used beryllium-containing alloys are wrought copper-berylliums, which provide good strength while retaining useful levels of electrical and thermal conductivity. This article provides information on the specimen preparation procedures, macroexamination, microexamination, and microstructures of beryllium, copper-beryllium alloys, as well as nickel-beryllium alloys. It also discusses health and safety measures associated with the specimen preparation of beryllium and beryllium-containing alloys.

This article outlines the beam/sample interactions and the basic instrumental design of a scanning electron microscopy (SEM), which include the electron gun, probeforming column (consisting of magnetic electron lenses, apertures, and scanning coils), electron detectors, and vacuum system. It discusses the contrasts mechanisms used for imaging and analyzing materials in the SEM. These include the topographic contrast, compositional contrast, and electron channeling pattern and orientation contrast. Special instrumentation and accessory equipment used at elevated pressures and during the X-ray microanalysis are reviewed. The article also provides information on the sample preparation procedure and the materials applications of the SEM.

This article describes the microstructure and metallographic practices used for medium- to high-carbon steels as well as for low-alloy steels. It explains the microstructural constituents of plain carbon and low-alloy steels, including ferrite, pearlite, and cementite. The article provides information on how to reveal the various constituents using proven metallographic procedures for both macrostructural and microstructural examination. Emphasis is placed on the specimen preparation procedures such as sectioning, mounting, grinding, and polishing. The article illustrates the use of proven etching techniques for plain carbon and low-alloy steels.

Metal powders are used as fuels in solid propellants, fillers in various materials, such as polymers or other binder systems, and for material substitution. They are also used in food enrichment, environmental remediation market, and magnetic, electrical, and medical application areas. This article reviews some of the diverse and emerging applications of ferrous and nonferrous powders. It also discusses the functions of copier powders and the processes used frequently for copier powder coating.