Solid solution treatment

Pure AIN has a fracture toughness of 3.4 MPa m1/2 MT and SiC has a fracture toughness of 3 MPa m1/2 MT. The SiC-AIN ceramic alloys, after solid solution treatment, have a toughness of about 3.5 MPa m1/2 MT. After the alloys were annealed in the miscibility region, the fracture... 

Applications of Solid-solution Theory. If a melting curve shows evidence of appreciable solid-solution formation, it may require application of a solid-solution treatment 14,15) to give an accurate impurity value, although Smit (1) has critized one of the treatments 14> Unfortunately, the method often has failed to give an adequate representation of observed melting curves. In some instances, the solid-solution treatment has given an excellent representation of experimental data, but the high sensitivity of the method to small thermometric errors makes the calculated impurity values unreliable. For example, the difference in temperatures observed with 70 and 90% of a sample melted may easily be in error by +0.0005°C. For the solid-solution treatment, such an error would correspond to an uncertainty of 500% in the impurity value for very pure compounds with normal cryoscopic constants, whereas the same 0.0005°C error corresponds to 150% uncertainty if solid insolubility is assumed. 

For instance, when Al-Cu alloys are heat-treated by delayed quenching after solid-solution treatment, copper will diffuse to the grain boundaries. The copper-poor regions formed adjacent the grain boundaries play an anodic role relative to the other regions which have more noble potentials (Galvele and Micheli, 1970). Some aluminum alloys subjected to inadequate quench treatment become susceptible to intergranular corrosion. 

The addition of impurity atoms to a metal results in the formation of a solid solution and/or a new second phase, depending on the kinds of impurity, their concentrations, and the temperature of the alloy. The present discussion is concerned with the notion of a solid solution treatment of the formation of a new phase is deferred to Chapter 9. 

As discussed above, the high-temperature oxidation resistance of Ti3SiC2 above 1100°C is unsatisfactory. Therefore, attempts have been made to improve the high-temperature oxidation behavior of Ti3SiC2. This work can be classified into three categories surface modification, composite preparation, and solid solution treatment. 

Most investigators have focused their attention on a differential segment of the zone between the feed injection and the crystal melter. Analysis of crystal formation and growth in the recoveiy section has received scant attention. Table 22-4 summarizes the scope of the literature treatment for center-fed columns for both solid-solution and eutectic forming systems. 

Of the generic aluminium alloys (see Chapter 1, Table 1.4), the 5000 series derives most of its strength from solution hardening. The Al-Mg phase diagram (Fig. 10.1) shows why at room temperature aluminium can dissolve up to 1.8 wt% magnesium at equilibrium. In practice, Al-Mg alloys can contain as much as 5.5 wt% Mg in solid solution at room temperature - a supersaturation of 5.5 - 1.8 = 3.7 wt%. In order to get this supersaturation the alloy is given the following schedule of heat treatments. 

The morphology of globular type is the most favourable when superplastic deformation is to occur in AI78wt%Zn alloy. This type of structure is formed by decomposition of the a solid solution a -> a + P However, plates usually dominate in the structure of this alloy. To obtain the non-plate or globular type, a special heat treatment is neccesary i.e. the optimal cooling rate as well as the temperature and time of ageing. 

Austenitic steels of the 304S15 type are normally heat treated at 1 050°C and cooled at a fairly rapid rate to remove the effects of cold or hot working, and in this state much of the carbon is in supersaturated solid solution. Reheating to temperatures below the solution treatment temperature leads to the formation of chromium-rich MjjCj precipitates predominantly at the grain boundaries with the production of chromium gradients and reduced corrosion resistance as is the case with the martensitic steels. Any attack is... 

Iron Low-carbon steels Low-carbon alloy steels Decarburised malleable Chromium 980-1 050 (Halide) 1. Gaseous 2. Semi- gaseous 3. Pack 25-75 urn Solid-solution (ferritic) 20-25% Cr Ductile (200-300 HV) Weldable Heat treatment acceptable ... 

Because the appearance of a superlattice is usually well characterized qualitatively in terms of an interaction parameter w which has nothing to do, in the usual treatments, with the melting of the parent solid solution, one does not expect to find a simple relationship between the critical temperature for disordering of the superlattice, and Ts, the solidus temperature of the corresponding solid... 

We have found it possible to formulate a simple treatment of the lead-thallium alloys that accounts satisfactorily for the existence of a maximum in melting-point displaced from the composition PbTls of the ordered structure, and that also accounts in a reasonably satisfactory way for the shapes of the liquidus and solidus curves throughout the range 0—75 atomic percent thallium (Fig. 1). The maximum in these curves occurs at a composition near that for a compound Pb2Tl3 or a compound PbTl2. If either of these compounds existed, it would have to be considered as forming solid solutions with lead and with thallium. The data, however, give no evidence for the existence of such compounds. 

In the case, however, of solid solutions where variability of composition is possible we may expect increased entropy owing to the possibilities of increased randomness of arrangement just as with liquid and gaseous solutions. Also, other special cases might arise where a greater degree of randomness would be possible than in pure, perfect crystals, but such cases could be given a special treatment and would cause no confusion. 

A reference solution is prepared by a dilution method. A known quantity of sample is dissolved in a known volume of the system buffer of known pH the amount of sample is X times less than in the above case in order to avoid precipitation in the formed solution. The spectrum is immediately taken by the UV spectrophotometer, to take advantage of the possibility that solution may be supersaturated (i.e., solid should have precipitated, but because not enough time was allowed for the solid to precipitate, the solution was temporarily clear and free of solid). Mathematical treatment of the spectral data yields the AUC of the reference sample solution, AUQ . The ratio R = AUCS/AUCS is used to automatically recognize the right conditions for solubility determination when the reference has no precipitate, and the sample solution is saturated with precipitate. Under these conditions, solubility is determined from the expression... 

Solution heat treatment. This improves mechanical properties by maximizing the concentration of hardening constituents in the solid solution. 

MJ Pikal, DJW Grant. A theoretical treatment of changes in energy and entropy of solids caused by additives or impurities in solid solution. Int J Pharm 39 243-253, 1987. 

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