The Elements of Metallography

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 Excerpt: ...eutectically at C. Hence their cooling curves show breaks, followed by halting points at tf. As we have seen, the following process takes place at the constant temperature t: Melt E Crystalline variety B ] Melt D. Thus, the heat quantity liberated during the change, and, under the customary assumptions, the length of ... Read More

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 Excerpt: ...eutectically at C. Hence their cooling curves show breaks, followed by halting points at tf. As we have seen, the following process takes place at the constant temperature t: Melt E Crystalline variety B ] Melt D. Thus, the heat quantity liberated during the change, and, under the customary assumptions, the length of the halting point at t as well, is given by the relative quantity of melt E present at this temperature. The maximum value 1 of these halting periods at t is reached at concentration E. From E, this value decreases lineally toward concentrations D and 100 (= pure B), where the zero value obtains. Similarly, the relative quantity of eutectic attains its maximum at concentration C and decreases lineally toward concentrations 0 (= pure A) and 100 (= pure B), where zero is reached. This is depicted in Fig. 49, according to the usual practice, by erection of verticals along the horizontals DEc and aCb. It is characteristic of this diagram that two constant temperature horizontals are present, notwithstanding the entire absence of compounds and polymorphous transformations. The nonexistence of a compound is determined by the fact that the eutectic horizontal aCb extends throughout the whole diagram, and that the relative quantity of eutectic decreases lineally from the eutectic concentration toward both sides. As to the fields of condition, we note that the region of melt above AC DEB is divided into two portions: (1) The field of homogeneous melt above ACDFEB, and (2) The field of two liquid layers, bounded by the solubility curve DFE and the horizontal DE. 0 Weight per cent B 100 Fig. 50. Furthermore, we have two fields with one crystalline variety, namely: (1) The field BEDCb of B crystals and melt, the latter generally consisting of two l... Read Less