Cryogenic temperatures cause many structural alloys to become brittle, which is an unacceptable condition in most structural applications and is rectified by optimizing the weld composition. Although nonmatching weld compositions are most appropriate, differences between the welds and parent material in terms of thermal contraction, corrosion, and other factors must be considered. This article discusses these differences and describes the effect of these factors on the choice of the weld filler metal. It also provides a detailed discussion on the effects of cryogenic services on mechanical properties of the parent metal.

This is an introductory article to special welding and joining topics focusing on various unique aspects related to three major joining technologies, namely, welding, brazing, and soldering.

This article provides a discussion on the mechanical properties of metals, ceramics, and polymers and fiber-reinforced polymer composites at low temperatures. It reviews the factors to be considered in tensile and compression testing of these materials. The article details the equipment used for low-temperature tensile and compression tests with illustrations. It concludes with a discussion on the various test methods and their ASTM standard for compression and tension testing.

Cold treating of steel can be used to enhance the transformation of austenite to martensite and improve the stress relief of castings and machined parts. Cryogenic treatment of steel is a distinct process that uses extreme cold to modify the performance of materials. This article explains the practices employed and equipment used in the cold treatment of steel. It also presents the results of using cryogenic treatment to enhance steel properties.

The presence of macroscopic residual stresses in heat treatable aluminum alloys can give rise to machining distortion, dimensional instability, and increased susceptibility to in-service fatigue and stress-corrosion cracking. This article details the residual-stress magnitudes and distributions introduced into aluminum alloys by thermal operations associated with heat treatment. The available technologies by which residual stresses in aluminum alloys can be relieved are also described. The article shows why thermal stress relief is not a feasible stress-reduction technology for precipitation-hardened alloys. It examines the consequences of aging treatments on the residual stress, namely, annealing, precipitation heat treatment, and cryogenic treatment. The article provides information on uphill quenching, which attempts to reverse thermal gradients encountered during quenching. It examines how quench-induced residual stresses in heat treatable aluminum alloys are reduced when sufficient load is applied to cause plastic deformation. The article also shows how plastic deformation reduces residual stress.

This article examines residual stresses in quenched and surface-hardened steels by focusing on its theoretical background, formation mechanisms of residual stress, effects of tempering and cryogenic cooling on residual stress, effects of residual stress on the service performance of components, and measurement, computation, and relaxation of residual stress.

This article aims to summarize the work on cryogenic strength and toughness and to present the fractography of aluminum alloys. It presents case studies on the importance of understanding the fractography of aluminum alloys and the role of microstructure in the appearance of fractographic features, with variables comprised of in-plane/through-thickness anisotropy, test temperature, heat treatment condition, and the effect of welding.

This article describes the fracture toughness behavior of austenitic stainless steels and their welds at ambient, elevated, and cryogenic temperatures. Minimum expected toughness values are provided for use in fracture mechanics evaluations. The article explains the effect of crack orientation, strain rate, thermal aging, and neutron irradiation on base metal and weld toughness. It discusses the effect of cold-work-induced strengthening on fracture toughness. The article examines the fracture toughness behavior of aged base metal and welding-induced heat-affected zones. It concludes with a discussion on the Charpy energy correlations for aged stainless steels.

High-potential high-alloy tool steels (HATS) containing martensitic microstructure with undissolved hard phases are achieved by a number of complex heat treating cycles, predominantly tempering. This article focuses on three tempering treatments, namely, salt bath heat treatment, austenitizing, and vacuum heat treatment. It explains the result of these tempering processes with HSS M2 grade of HATS.

Metal-induced embrittlement is a phenomenon in which the ductility or fracture stress of a solid metal is reduced by surface contact with another metal in either liquid or solid form. This article summarizes the characteristics of solid metal induced embrittlement (SMIE) and liquid metal induced embrittlement (LMIE). It describes the unique features that assist in arriving at a clear conclusion whether SMIE or LMIE is the most probable cause of the problem. The article briefly reviews some commercial alloy systems where LMIE or SMIE has been documented. It also provides some examples of cracking due to these phenomena, either in manufacturing or in service.

This article describes the process of materials selection in relation to the design process, such as materials selection for a new design and materials substitution for an existing design. It reviews the performance characteristics of materials using prototype tests or field tests to determine their performance under actual service conditions. The article describes the selection of a material in relation to the manufacturing process and presents the factors that influence materials selection based on costs and related aspects. These factors include metallurgical requirements, dimensions, processing, quantity, packing, marking, and loading. The article discusses how the needs for materials data evolve as a design proceeds from conceptual to detail design. It describes the methods of materials selection, namely, cost per unit property method, weighted property index method, and limits on properties method.

The extrusion alloy 7005 is used as extruded structural members, where welded or brazed assemblies require moderately high strength and high fracture toughness. This datasheet provides information on key alloy metallurgy, processing effects on physical and mechanical properties, and fabrication characteristics of this 7xxx series alloy.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of miscellaneous metals and alloys and in identifying and interpreting the morphology of fracture surfaces. The metals and alloys covered include tungsten, iridium, magnesium-base, iron-base, molybdenum-base, and tantalum-base materials. The fractographs illustrate fatigue striations, slow-bending fracture, quasi-cleavage fracture, corrosion-fatigue fracture, fatigue crack, intergranular cleavage, microvoid coalescence, tension-overload fracture, crack propagation, impact fracture, and high-cycle fatigue failure.

Metal-induced embrittlement is a phenomenon in which the ductility or the fracture stress of a solid metal is reduced by surface contact with another metal in either the liquid or solid form. This article summarizes some of the characteristics of liquid-metal- and solid-metal-induced embrittlement. This phenomenon shares many of these characteristics with other modes of environmentally induced cracking, such as hydrogen embrittlement and stress-corrosion cracking. The discussion covers the occurrence, failure analysis, and service failures of the embrittlement. The article also briefly reviews some commercial alloy systems in which liquid-metal-induced embrittlement or solid-metal-induced embrittlement has been documented and describes some examples of cracking due to these phenomena, either in manufacturing or in service.

Aluminum alloys, particularly the heat-treatable alloys, are sensitive to weld cracking. Anticipation of these characteristics and general knowledge of these materials assist in selection of suitable method for welding heat-treatable aluminum alloys. This article provides a general description of the metallurgy, characteristics, and applications of heat-treatable aluminum alloys and a detailed discussion on the characteristics of heat-treatable aluminum alloys, their resulting impact on the weld quality and property, along with the methods of avoiding or reducing the impacts. The impact created in the weld quality includes crack sensitivity, liquation cracking, porosity, and heat-affected zone degradation. The article provides an overview of filler alloy selection for reducing weld crack sensitivity and increasing weld strength, ductility, and corrosion resistance in the welds of heat-treatable aluminum alloys.

The high-alloy irons can be categorized into two main groups: the high-alloy graphitic irons (covering both gray and ductile grades) and the high-alloy white irons. High-alloy irons are used in applications with demanding requirements, such as high resistance to wear, heat, and corrosion, or for combined properties. This article discusses the specification and selection of high-alloy irons. The common alloying elements and their effect on the stable and metastable eutectic temperatures are listed in a table. The article provides information on the compositions, properties and applications of high-alloy graphitic irons and high-alloy white irons.

Titanium and its alloys are used in various applications owing to its high strength, stiffness, good toughness, low density, and good corrosion resistance. This article discusses the applications of titanium and titanium alloys in gas turbine engine components, aerospace pressure vessels, optic-system support structures, prosthetic devices, and applications requiring corrosion resistance and high strength. It explains the effects of alloying elements in titanium alloys as they play an important role in controlling the microstructure and properties and describes the secondary phases and martensitic transformations formed in titanium alloy systems. Information on commercial and semicommercial grades and alloys of titanium is tabulated. The article also discusses the different grades of titanium alloys such as alpha, near-alpha alloys, alpha-beta alloys, beta alloys, and advanced titanium alloys (titanium-matrix composites and titanium aluminides).

Thermal inspection comprises all methods in which heat-sensing devices or substances are used to detect irregular temperatures. Inspection of workpieces can be used to detect flaws and undesirable distribution of heat during service. Though there are several methods of thermal inspection and many types of temperature-measuring devices and substances, this article focuses only on thermography, which is the mapping of isotherms, or contours of equal temperature, over a test surface, and on thermometry, which is the measurement of temperature. Thermography techniques can be classified as contact thermographic methods using cholesteric liquid crystals, thermally quenched phosphors, and heat-sensitive paints, and noncontact techniques using hand-held infrared scanners, high-resolution infrared imaging systems, and thermal wave interferometer systems. Contact thermometric inspection devices include bolometers, thermocouples, thermopiles, and meltable substances, whereas radiometers and pyrometers come under the noncontact category.

Austenitic stainless steels exhibit a single-phase, face-centered cubic structure that is maintained over a wide range of temperatures. This article reviews the compositions of standard and nonstandard austenitic stainless steels. It summarizes the important aspects of solidification behavior and microstructural evolution that dictate weld-metal ferrite content and morphology. The article describes weld defect formation, namely, solidification cracking, heat-affected zone liquation cracking, weld-metal liquation cracking, copper contamination cracking, ductility dip cracking, and weld porosity. It discusses four general types of corrosive attack: intergranular attack, stress-corrosion cracking, pitting and crevice corrosion, and microbiologically influenced corrosion. The article concludes with information on weld thermal treatments such as preheat and interpass heat treatments and postweld heat treatment.

Thermocouple devices are the most widely used devices for measurement of temperature in the metals industry. Favorable characteristics of these devices include good accuracy, suitability over a wide temperature range, fast thermal response, ruggedness, high reliability, low cost, and great versatility of application. Thermocouples are grouped into two broad categories, namely, standard thermocouples, including five base-metal thermocouples and three noble-metal thermocouples that have been given letter designations, and nonstandard thermocouples, including iridium-rhodium, platinum-molybdenum, platinel, and tungsten-rhenium thermocouples. This article discusses the basic principles, classification, and properties of thermocouples, and the techniques for insulating and protecting thermocouple wires from the operating environment.