Metallurgical properties

Eabrication techniques must take into account the metallurgical properties of the metals to be joined and the possibiUty of undesirable diffusion at the interface during hot forming, heat treating, and welding. Compatible alloys, ie, those that do not form intermetaUic compounds upon alloying, eg, nickel and nickel alloys (qv), copper and copper alloys (qv), and stainless steel alloys clad to steel, may be treated by the traditional techniques developed for clads produced by other processes. On the other hand, incompatible combinations, eg, titanium, zirconium, or aluminum to steel, require special techniques designed to limit the production at the interface of undesirable intermetaUics which would jeopardize bond ductihty. 

The alloy niobium titanium (NbTi) and the intermetaUic compound of niobium and tin (Nb.3 Sn) are the most technologically advanced LTS materials presently available. Even though NbTi has a lower critical field and critical current density, it is often selected because its metallurgical properties favor convenient wire fabrication. In contrast, Nb.3Sn is a veiy brittle material and requires wire fabrication under very well-defined temperature conditions. 

To ensure compatibility, detailed engineering descriptions of all materials and their metallurgical properties are needed. General information (e.g., mild steel) does not provide sufficient data to establish compatibility in conductive or corrosive media. 

The unrestricted material acceptance is not intended since physical properties are not the sole measure of acceptability. Metallurgical properties, which affect fabrication and serviceability, must also be considered. 

The choice of alloy for any particular application is determined by the desired physical, mechanical and metallurgical properties. Within these limits, however, a range of materials is usually available. It is essential that at the very earliest stage the choice of materials and the details of design of the installation should be considered from the point of view of corrosion, if the best performance is to be obtained in service. This is particularly true of copper alloys, where protective measures are not normally applied. 

Tinplate and Solder. The tests were carried out to determine the effect of low temperature irradiation on the metallurgical properties of the tinpalte, solder, and soldered lap joints. Two types of tinplate were used 43 kg (95 lb), Type MR-TU and 43 kg (95 lb), Type MR-T2, both coated with No. 25 electrolytic tinplate. The test specimens were 20 X 20 cm panels. 

Further increased sensitivity and accuracy of electronic tools will enable non-destructive evaluation of many metallurgical properties, including composition, interstitial content, residual strain, and many other important variables. A combination of multiple tools will allow for more precise measurement, without the need of testing standards... 

The physical and metallurgical properties of plasma sprayed coatings are generally superior to all other flame spraying methods, with the exceptions of hypersonic combustion and detonation gun systems. 

Cadmium is close to lead and mercury as a metal of current toxicological concern.12346 Extraction of lead and zinc ores, which contain cadmium, pollutes the environment with cadmium. The use of cadmium before 1900 was infrequent however, its valuable metallurgical properties, such as resistance to corrosion, increased its use markedly, for example in the manufacture of alloys and as a coating on steel. It is also now widely used in nickel cadmium ( nicad ) batteries. Coal and other fossil fuels contain cadmium which is released into the environment on combustion. 

The physical properties of the filler metal are based on its metallurgical properties. The composition will determine whether the filler metal is compatible with the metals being joined—capable of wetting them and flowing completely through the joint area. There arc also special... 

A process known as squeeze casting (solidification of liquid metal under pressure) contributes to producing defect-free eastings with improved metallurgical properties. Sec also Casting. 

The economically imporlant coball-comaining minerals exploited ill present are listed in Table I. The metal extraction processes, following the usual pretreatmcnl of the ore, are varied and complicated because the metallurgical properties of cobalt differ insufficiently from those of the associated metals and beeause the eobaltiferous raw materials comprise the sulfide, arsenide, and oxide, or a mixture of these. The final refining stage invariably involves electrolysis. 

Metallurgically influenced corrosion is mainly composed of the corrosion due to chemical composition (alloying elements, metalloids and impurities), metallurgical properties (metallic phases, grain joints) and fabrication procedures (thermal treatments, lamination and welding). Figure 6.24 shows weld zone, dealloying, exfoliation and internal modes of attack. 

Material factors. The main metallurgical properties of importance are alloy composition, distribution of alloying elements and impurities, microstructure and crystal structure, heat treatment, mechanical working, preferred orientation of grains and grain boundaries (texture), mechanical properties (strength, fracture toughness, etc.).31... 

The methods already described have illustrated the wide applicability of flame atomisation techniques to the analysis of non-ferrous alloys. The introduction of electrothermal atomisation has enabled the direct determination of sub-part per million levels of impurities. The presence of very low levels of lead, bismuth and other low melting point metals is known to have a deleterious effect on the metallurgical properties of nickel alloys. 

Physical Properties of Pure Compact Iron.—The properties of iron are affected to such a remarkable and unique extent by the presence of small quantities of alloying elements, chief amongst which is carbon, that these phenomena are an important study in themselves. It is not intended in this section, therefore, to deal with the physical properties of any commercial iron other than the chemically pure and compact metal. For a discussion of the physical and metallurgical properties of various types of commercial iron and its alloys, the reader is referred to Part III. of this volume. Pure iron is a white metal which can be readily machined in a lathe, and even cut with a knife. It crystallises according to the cubic system,3 but crystals are rare, the metal being usually massive. Dendritic crystals may be obtained artificially with branches parallel to the cubic axes.4 Shock apparently assists or induces crystallisation in iron.5... 

A consideration of the influence of cementite upon the metallurgical properties of iron is reserved for later discussion.5... 

Successful operation of the furnace and production of an iron with the desired composition (and hence metallurgical properties) depend so much on making the slag... 

The metallurgical properties of metallic plutonium are even more unfavourable than those of uranium. The melting point of Pu is 639 °C and six solid phases are known. Furthermore, the critical mass of a reactor operating with pure Pu as fuel is below 10 kg, and it would be very difficult to take away the heat from such a small amount of material. A great number of plutonium alloys have been investigated with respect to their possible use as nuclear fuel, but they have not found practical application. 

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