Alloys compositions

Certain factors are related to the metal (or alloy) itself. Metallurgists try to adjust alloy compositions, transformation sequences and heat treatments in order to obtain the best possible corrosion resistance. 

The influence of the main alloying elements is shown in Table A.3.1. Since the beginning of the 20th century, many studies have tried to quantify the influence of most of the metallic 

Contrary to a common misconception, the purity of the base metal does not improve the corrosion resistance of aluminium. Metal with a very low iron and silicon content (1199) does not resist atmospheric corrosion better than 1070 or 1050. Only at much higher concentrations of iron and silicon (Fe 0.50 and Si 0.25), which was frequently found until the end of the 1940s, will the corrosion resistance be altered. 

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To realize a process integrated quality control the conception shown in fig. 2 was followed. The casting process which is influenced by process parameters like thermal economy, alloy composition or black wash will be pursued with particulary to the problematic nature adjusted sensoring systems. On basic factors orientated sensoring systems like microfocus radioscopy, and tomography will be employed and correlated with sensoring systems which can be applicated under industrial conditions. 

Another method by which metals can be protected from corrosion is called alloying. An alloy is a multicomponent solid solution whose physical and chemical properties can be tailored by varying the alloy composition. 

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

Table 13. High Temperature Eutectic Alloy Compositions...

GaP N, is clearly evident. The addition of N shifts the peak to longer wavelengths and broadens the spectral emission. The curves for the AIGalnP LEDs represent devices of three different alloy compositions, all exhibiting recombination for the conduction band direct minimum. The emission spectmm of the blue InGaN LED exhibits uniquely broad emission, most likely as a result of recombination via deep Zn impurities levels (23). 

Table 8 indicates the compatibiUty of magnesium with a variety of chemicals and common substances. Because the presence of even small amounts of impurities in a chemical substance may result in significantly altered performance, a positive response in the table only means that tests under the actual service conditions are warranted (132). Other factors which may significantly alter magnesium compatibiUty include the presence of galvanic couples, variations in operating temperatures, alloy composition, or humidity levels. 

H. Hucek and M. Wahl, 1990 Handbook ofiInternational Alloy Compositions and Designations, Vol. 1, Titanium, MCIC HB-09, Metals and Ceramics Information Center, BatteUe Columbus Laboratories, Columbus, Ohio, 1990. 

M. Kehler, Handbook ofi International Alloy Compositions and Designations, Vol. 3, Aluminium, Aluminium Vedag, Heyden, Germany, 1981. 

Table 5. Alloy Composition of High Temperature Steels...

In the sputtering process, each surface atomic layer is removed consecutively. If there is no diffusion in the target, the composition of the vapor flux leaving the surface is the same as the composition of the bulk of the material being sputtered, even though the composition of the surface may be different from the bulk. This allows the sputter deposition of alloy compositions, which can not be thermally vaporized as the alloy because of the greatly differing vapor pressures of the alloy constituents. 

Zinc slush-casting alloy compositions are based on the Zn—A1 system. The two commonly used alloys have nominal aluminum contents of 4.75%... 

Greater amounts of copper increase the proportion of needles or stars of Cu Sn in the microstmcture. Increase in antimony above 7.5% results in antimony—tin cubes. Hardness and tensile strength increase with copper and antimony content ductiUty decreases. Low percentages of antimony (3—7%) and copper (2—4%) provide maximum resistance to fatigue cracking in service. Since these low alloy compositions are relatively soft and weak, compromise between fatigue resistance and compressive strength is often necessary. 

Alloy Compositions and Product Forms. The nominal compositions of various cobalt-base wear-resistant alloys are Hsted in Table 5. The six most popular cobalt-base wear alloys are Hsted first. SteUite alloys 1, 6, and 12, derivatives of the original cobalt—chromium—tungsten alloys, are characterized by their carbon and tungsten contents. SteUite aUoy 1 is the hardest, most abrasion resistant, and least ductile. 

Alloy Compositions and Product Forms. SteUite 21, an early type of cobalt-base high temperature alloy, is used primarily for wear resistance. The use of tungsten rather than molybdenum, moderate nickel contents, lower carbon contents, and rare-earth additions typify cobalt-base high temperature alloys of the 1990s as can be seen from Table 5. 

Practical considerations enter into the experimental plan in various other ways. In many programs, variables are introduced at different operational levels. For example, in evaluating the effect of alloy composition, oven temperature, and varnish coat on tensile strength, it may be convenient to make a number of master alloys with each composition, spHt the alloys into separate parts to be subjected to different heat treatments, and then cut the treated samples into subsamples to which different coatings are appHed. Tensile strength measurements are then obtained on all coated subsamples. 

Choices of alternative materials. Corrosion probes are carefully chosen to be as close as possible to the alloy composition, heat treatment, and stress condition of the material that is being monitored. Care must be taken to ensure that the environment at the probe matches the service environment. Choices of other alloys or heat treatments and other conditions must be made by comparison. Laboratory testing or coupon testing in the process stream can be used to examine alternatives to the current material, but the probes and the monitors can only provide information about the conditions which are present during the test exposure and cannot extrapolate beyond those conditions. 

Virtually any cooling water component contacting low-pH water may be corroded. However, there are appreciable differences as to corrosion severity and initiation times depending on alloy composition, kind of acid, and location. 

Sufficient tensile stress. Sufficiency here is difficult to define since it depends on a number of factors such as alloy composition, concentration of corrodent, and temperature. In some cases, stresses near the jdeld strength of the metal are necessary. In other cases, the stresses can be much lower. However, for each combination of environment and alloy system, there appears to be a threshold stress below which SCC will not occur. Threshold stresses can vary from 10 to 70% of yield strength depending on the alloy and environment combination and temperature (Fig. 9.6). 

In any specific environment, only certain alloys are affected. Substitution of more resistant materials does not always necessitate major alloy compositional changes. Adding as little as a few hundredths of a percent of arsenic, for example, can markedly reduce dezincification in cartridge brass. Antimony and phosphorus additions up to 0.1% are similarly efficacious. 

Hence, the evaporation rate of each element will only be in die proportion of the alloy composition at one composition, die congruently vaporizing composition. If drere is a large difference between the vapour pressures of the elements then the element having the higher vapour pressure could be completely evaporated hrst. 

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