Metal identification alloys

Identification of unknown crystal structures and determination of phase fields by X-rays can be problematical if the characteristic patterns of the various phases are quite similar, for example in some b.c.c. A2-based ordered phases in noble-metal-based alloys. However, in many cases the characteristic patterns of the phases can be quite different and, even if the exact structure is not known, phase fields can still be well established. Exact determination of phase boundaries is possible using lattice-parameter determination and this is a well-established method for identifying solvus lines for terminal solid solutions. The technique simply requires that the lattice parameter of the phase is measured as a function of composition across the phase boimdary. The lattice parameter varies across the single-phase field but in the two-phase field becomes constant. Figure 4.12 shows such a phase-boundary determination for the HfC(i i) phase where results at various temperatures were used to define the phase boundary as a fimction of temperature (Rudy 1969). As can be seen, the position of is defined exactly and the method can be used to identify phase fields across the whole composition range. 

Identification and Quantification of Degradation Products from Coated and Uncoated Metals and Alloys... 

Chemical analyses can be used, but for most metals one needs only to know the major elements such as copper and tin. Chemical identification of metals does not require either high precision or trace sensitivity. X-ray fluorescence has often been used in metal identification and has recently been developed into portable, nondestructive devices for field and museum use. X-ray diffraction can identify metals structurally, but this can be complicated by more than one compound in complex alloys such as steel. 

The first orderly methods of identifying materials were developed by metal manufacturers trade associations. National standards organizations have also created materials identification systems. In the United States, the Unified Number System merges all systems into one method of identifying commercially available metals and alloys. 

In selecting metals and alloys as materials of construction, one must have knowledge of how materials fail, for example is, how they corrode, become brittle with low-temperature operation, or degrade as a result of operating at high temperatures. Corrosion, embrittlement, and other degradation mechanisms such as creep will be described in terms of their threshold values. Transient or upset operating conditions are common causes of failure. Examples include start-ups and shutdowns, loss of coolant, the formation of dew point water, and hot spots due to the formation of scale deposits on heat transfer surfaces. Identification and documentation of all anticipated upset and transient conditions are required. 

X-ray diffraction or X-ray diffractometry (XRD) is a technique that is useful for the analysis of solid crystalline or semicrystaUine materials. Most organic and inorganic compounds, minerals, metals, and alloys, and many types of polymers form crystals and can be analyzed by XRD. XRD can provide the exact crystal structure of a pure single crystal material. In addition, XRD can provide the quahtative and quantitative identification of the molecules present in pure crystalhne powders or mixtures of crystalline powders. 

Identification and quantification of degradation products from metals and alloys... 

Hybrid systems are designed to combine the speed and flexibility of XRD and XRF systems in one spectrometer. Such systems permit more complete characterization of a given crystalline sample. These systems are varied some are XRF systems with a few powder XRD-based channels to identify compounds, such as a system designed with a CaO channel for the cement industry. The combination can go as far as including a complete powder diffractometer and XRF spectrometer for flexible compound identification and quantification. These types of systems are generally used in industries, including metal and alloy production, cement production, mining, and refractory materials production, for both R D and process control. 

It is worthwhile pointing out again that the photo-electrons produced in XPS are incapable of passing through more than perhaps 1 to 5 nm of a solid. Thus, the most important applications of electron spectroscopy, like X-ray microprobe spectroscopy, are for the accumulation of information about surfaces. Examples of some of its uses include identification of active sites and poisons on catalytic surfaces, determination of surface contaminants on semiconductors, analysis of the composition of human skin, and study of oxide surface layers on metals and alloys. 

Base metal Identification of alloy Precise identification of alloy is Identification of alloy by... 

This experimental contribution confirms previous tribological investigations, which showed that phosphate additives were effective under low load conditions (mild wear), whereas sulfides were effective under high load conditions (severe wear). The results are of particular interest in understanding the beneficial roles of some specific additives, in relation to the nature of the contacting surfaces. A major contribution of this study has therefore been identification of the additives that should be chosen for antiwear under extreme pressure conditions, as functions of wear conditions and of the particular metals and alloys in contact. It contains also some interesting observations on how gas/solid reactions can be mediated by tribological activation (i.e., via a scratch), which enhances the reactivity. 

AWS) has issued specifications covering the various filler-metal systems and processes (2), eg, AWS A5.28 which appHes to low alloy steel filler metals for gas-shielded arc welding. A typical specification covers classification of relevant filler metals, chemical composition, mechanical properties, testing procedures, and matters related to manufacture, eg, packaging, identification, and dimensional tolerances. New specifications are issued occasionally, in addition to ca 30 estabUshed specifications. Filler-metal specifications are also issued by the ASME and the Department of Defense (DOD). These specifications are usually similar to the AWS specification, but should be specifically consulted where they apply. 

The corrosion behaviour of different constituents of an alloy is well known, since the etching techniques used in metallography eu e essentially corrosion processes which take advantage of the different corrosion rates of phases as a means of identification, e.g. the grain boundaries are usually etched more rapidly than the rest of the grain owing to the greater reactivity of the disarrayed metal see Sections 1.3 and 20.4). 

Where the end use of the product is known, there is usually preference to use either zinc or aluminium, both technically and because of the works problems associated with use of an alloy (identification, separation of overspray). However, in some countries (such as the United States) where there has been a recent-surge in anti-corrosion uses of metal spraying, a zinc-15%-aluminium alloy wire has been widely used. The original commercial experience was with 65-35% alloys used in powder form. Both have many of the advantages of the parent metals. At one time, the zinc-5%-aluminium alloy was also of interest. These alloy coatings may prove particularly satisfactory for sprayed coatings on articles where service conditions are not known in advance. 

Linear absorption measurements can therefore give the first indication of possible alloy formation. Nevertheless, in systems containing transition metals (Pd-Ag, Co-Ni,. ..) such a simple technique is no longer effective as interband transitions completely mask the SPR peak, resulting in a structurless absorption, which hinders any unambiguous identification of the alloy. In such cases, one has to rely on structural techniques like TEM (selected-area electron diffraction, SAED and energy-dispersive X-ray spectroscopy, EDS) or EXAFS (extended X-ray absorption fine structure) to establish alloy formation. 

---