Melting incipient

Fig. 4 Stress-strain rate behavior of several mechanically alloyed materials, showing the increase of m values at temperatures corresponding to the incipient melting point for each alloys (data from Ref. [11]).

Fig. 5 Elongation-to-failure as a function of testing temperature for MA materials. /The left and right arrows on each curve indicate the incipient melting point and solidus temperature, respectively.

At medium speeds, contact of the high spots will cause incipient melting and surface welding. The rise in surface temperature will encourage the breakdown of the lubricant film and the resultant scoring which is distinctive will cause rapid wear. 

The next stage, baking, begins at about 600°C, when small amounts of flux within the clay mixture melt and induce incipient melting of the surrounding clay, which is therefore converted to glass (see Chapter 3). The melting, or vitrification process, starts at isolated sites within the clay mixture... 

Arrow Tg, Start of devitrification arrow 7arn, start of ante-melting arrow Tmv start of incipient melting (Fig. 1 from [1.103]). 

C/min) all freezable water is crystallized, or if the rewarming is interrupted before the melting starts and the product cooled down again to e. g. -150 °C, the rewarming curves resemble that in Fig. 1.33. There is no water left, which can crystallize at Td. There are only two events, which are denoted (as by Mac Kenzie) with antemelting and incipient melting. 

Figure 5,45 P-T stability curve of phlogopite compared with the incipient melting curves of granite and basalt. Reprinted from H. S. Yoder and H. R Eugster, Geochimica et Cos-mochimica Acta, 6, 157-185, copyright 1954, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

The P-T stability curve of muscovite intersects the incipient melting curve of granite in hydrous conditions at about 2.3 kbar total pressure and T = 650 °C. Thus, muscovite may crystallize as a primary phase from granitic melts above these P and T conditions (interstitial poikihtic crystals) or may form by reaction with pristine solid phases at lower P and T (muscovite as dispersed phase within feldspars, for instance). In this second type of occurrence, the following two equilibria are of particular importance ... 

Figure 5.47 Extrinsic stability curves for muscovite and paragonite, based on (A) equilibria 5.139 and 5.144 (quartz absent) and (B) equilibria 5.140 and 5.145 (quartz present). Incipient melting curves of granite for = 0.5 to 1, and stability curves of Al2Si05 polymorphs according to Richardson et al. (1969), are superimposed.

Figure 5.48 Extrinsic stability limits of muscovite, based on equilibrium 5.140 for variable amounts of H2O component in fluid. Also shown are incipient melting curves of granite for various h20 isopleths and stability curves of Al2Si05 polymorphs, according to Holdaway (1971) From Kerrick (1972), American Journal of Science, 212, 946-58. Reprinted with permission of American Journal of Science.

In terms of practical use, one of the most important features of phase equilibria can often be the effect of composition on some critical temperature. This can be a liquidus or solidus or a solid-state transformation temperature, such as the /3-transus temperature, (T ), in a Ti alloy. The solidus value can be critical, as solution heat-treatment windows may be limited by incipient melting. In some materials a solid-state transformation temperature may be of prime importance. For example, in Ti alloys it may be specified that thermomechanical processing is performed at some well-defined temperature below the / -transus temperature. The CALPHAD route provides a method where such temperatures can be quickly and reliably calculated. 

Material Melting Temperature ( C) Vaporization Temperature (°C) Pressure to Cause Incipient Melting (Mbar) Pressure to Cause Complete Melting (Mbar) Pressure to Cause Vaporization (Mbar)... 

Figure 1 Schematic evolution of the freeze-drying process. Temperatures (upper curve) and water content (lower curve) are indicated versus time. In the temperature diagram cs = maximum temperature of complete solidification 7 = minimum temperature of incipient melting = absolute limit for fast process = maximum allowed temperature for the dry product RMF, final requested residual moisture.

Product temperature during primary drying should be consistently maintained below the level where incipient melting or collapse is observed. 

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