The atmosphere within a furnace chamber is a basic factor in achieving the desired chemical reactions with metals during heat treating. This article presents the fundamentals of heat treating atmospheres, and describes two groups of atmosphere control, namely, furnace atmosphere control and supply atmosphere control. The two basic types of atmospheric supply systems are generated atmospheres and nitrogen-base atmospheres. The article provides a brief overview of the gas reactions associated with oxidation and carbon control to ensure either carburization, or to prevent decarburization. It demonstrates how the carbon potential control is achieved by controlling water vapor concentration, carbon dioxide concentration, or oxygen partial pressure. The article also describes the various devices and analyzers used to monitor sampled gas from furnace atmospheres, namely, chromatographs, oxygen probes, Orsat analyzers, infrared analyzers, dewpoint analyzers, and hot-wire analyzers. Finally, it discusses the advantages, disadvantages, and limitations of these analyzers.

Radioanalysis is an analytical technique that uses energy emitted by radioactive isotopes to measure the concentration of related elements in test samples. This article begins with a discussion on the principles of radioactive decay and various forms of emission, including alpha and beta-particle emission, positron emission, and gamma and x-ray emission. It compares and contrasts measurement techniques based on various detectors, namely, charged-particle detectors, photon detectors, counting and recording instruments, and radioactive decay spectrometers. It also addresses sample preparation, equipment and process safety, and the handling of radioactive gasses and materials. The article concludes with application examples involving the analysis of rare-earth elements and nuclear fuels.

Heat treating furnaces require different control systems and integration for achieving optimum technical results and enabling safe operation. This article focuses on atmosphere furnaces, with some coverage on controls for vacuum furnaces. Heat treating operations require reliable monitoring and control of motion and position of various mechanical components with the help of mechanical limit switches, proximity sensors, and distance- and position-measuring devices. Using inputs from both flow meters and sensors, such as thermocouples and oxygen sensors, flow measurement control systems must be able to adjust the flow of gases for process optimization. The operator interface of a furnace-control system displays critical information such as the furnace temperature, atmosphere status, alarms, electronic chart recorders, recipe, and maintenance. A supervisory control and data-acquisition (SCADA) system is used to monitor, collect, and store data from multiple pieces of equipment.

Part quality in additive manufacturing (AM) is highly dependent on process control, but there is a lack of adequate AM control methods and standards. Laser powder-bed fusion (L-PBF) is one of the most-used metal AM techniques. This article focuses on the following laser control parameters: laser focus, laser power, laser position, and laser power-position synchronization. It then provides a discussion on laser scan strategies. The article also provides an overview of the AM control framework, the two major sections of which are software and hardware.

This article, to develop an understanding of the underlying mechanisms governing deformation at elevated temperatures, discusses the phenomenological effects resulting from temperature-induced thermodynamic and kinetic changes. It describes the deformation behavior of engineering materials using expressions known as constitutive equations that relate the dependence of stress, temperature, and microstructure on deformation. The article reviews the characteristics of creep deformation and mechanisms of creep, such as power-law creep, low temperature creep, power-law breakdown, diffusional creep, twinning during creep deformation, and deformation mechanism maps. It discusses the creep-strengthening mechanisms for most structural engineering components. The article provides a description of the microstructural modeling of creep in engineering alloys.

Digital radiography is a technique that uses digital detector arrays (linear or area) to capture an X-ray photonic signal and convert it to an electronic signal for display on a computer. This article begins with an overview of real-time radiography and provides a schematic illustration of a typical radioscopic system using an X-ray image intensifier. It discusses the advantages and limitations of real-time radiography. Computed radiography (CR) is one of the radiography techniques that utilizes a reusable detector comprised of photostimuable luminescence (PSL) storage phosphor. The article provides a schematic illustration of a typical storage phosphor imaging plate. It concludes with a discussion on the benefits of digital radiography.

This article discusses two approaches for determining gaseous corrosion rates, one based on indirect (discontinuous) measurements, the other based on direct (continuous) measurements. It explains how corrosion rate data can be obtained indirectly by measuring scale thickness, scale weight per unit surface area, loss of metal thickness, loss of material weight per unit surface area, or weight change of oxidant bonded in the scale per unit surface area as a function of time. It also describes several continuous methods, including volumetric measurements, the manometric method, and thermogravimetric analysis, and the conditions under which they can be used.

The basic elements of control design are safety, process control, process verification, machine control, productivity, repeatability, and ease of setup. Effective systems of quality control/quality assurance are essential for heat treating practices. This article provides information on process control modes, as well as on process signatures of some items that require control, monitoring, verifying, and logging methods. It provides information on programmable logic controllers that have become efficient in machine control and monitoring. The article describes possible noise issues, National Electric Code clearance requirements, monitoring requirements, and machine accuracy that need to be considered when designing induction equipment.

This article describes the viscoelastic behavior of plastics in their solid state only, from the standpoint of the material deforming without fracturing. The consequences of viscoelasticity on the mechanical properties of plastics are described, especially in terms of time-dependencies, as well as the dependence of the viscoelastic character of a plastic on chemical, physical, and compositional variables. By examining the viscoelastic behavior of plastics, the information obtained are then applied in situations in which it may be important to anticipate the long-term properties of a material. This includes assessing the extent of stress decay in materials that are pre-stressed, the noise and vibration transmission characteristics of a material, the amount of heat build-up in a material subjected to cyclic deformation, and the extent a material can recover from any prior deformation. Several qualitative graphs are presented, which highlights the possible differences in the viscoelastic behavior that can exist among plastics.

Corrosion monitoring is important in the operation of modern industrial plants and in the use and maintenance of expensive assets such as bridges and aircrafts, because the damage caused by corrosion and the rate of the deterioration can be huge and the risks devastating. This article discusses the system considerations and installation techniques of different types of direct and indirect techniques in electrochemically based on-line corrosion monitoring process. It describes the importance of probe location and on-line corrosion monitoring techniques with examples.

Gas analysis by mass spectrometry, or gas mass spectrometry, is a useful analytical tool for investigations performed in controlled atmospheres or in vacuum. This article provides sufficient information to determine if gas mass spectrometry can produce the data required and to determine the type of instrument necessary for a particular application. It discusses the working operations of gas mass spectrometer components, namely, the introduction system, ion sources, mass analyzers, and the ion detector. The article also provides information on resolution of a gas mass spectrometer determined by the width of the source slit and the collector slit. Finally, it describes the instrument set-up for gas mass spectrometry, and shows how to analyze the test results of gas mass spectrometry.

The six types of statistical distributions are normal distribution, log normal distribution, Weibull distribution, exponential distribution, binomial distribution, and Poisson distribution. This article discusses the applicability of each distribution, providing information on the probability density function, cumulative distribution function, population mean and variance, and parameter and percentile estimation.

Temperature control in heat treating is of paramount importance in maintaining the quality and achieving the desired metallurgical results. This article provides a detailed account of the factors affecting temperature control in heat treating furnaces, with information on temperature control systems, including contact sensors, noncontact sensors, controllers, energy-flow regulators, measurement instruments, and set-point programmers. Common contact sensors include temperature scales, thermocouples, and resistance temperature detectors, whereas optical pyrometers and on-line radiation thermometers fall under the noncontact type. The article describes two types of instrumentation used in heat treating: field test instruments for temperature-uniformity surveys and system-accuracy tests; and controlling, monitoring, and recording instruments for digital instrumentation.