Phase in alloy

B.K. Vulf, Ternary metallic phases in alloys (in Russian). (Izd. Metallurgiya, Moscow, 1964). 

This curve has two branches an inclined branch be, which shows how the parameter of a varies with the composition of a, and a horizontal branch de, which shows that the a phase in alloys 6 and 7 is saturated, because its lattice parameter does not change with change in alloy composition. In fact, alloys 6 and 7 are in a two-phase region at temperature T, and the only difference between them is in the amounts of saturated a they contain. The limit of the a field at temperature Tj is therefore given by the intersection of the two branches of the parameter curve. In this way, we have located one point on the solvus curve, namely x percent B at Tj. 

Figure 8.31 Photomicrographs to illustrate the mechanism hy which sulphide phases in alloys can result in the formation of non-protective oxide scales dm-ing oxidation, (a) Sulphide phases composed of liquid nickel sulphide, A, and chromimn sulphide, B, are preferentially oxidized, (b), to form non-protective oxides O, as well as additional sulphides, B.

And] Andrews, K.W., A New Intermetalhc Phase in Alloy Steels , Nature, 164, 1015-1015 (1949) (Crys. Stracture, Experimental, 2)... 

The lattice parameter for the y phase in alloys quenched from above 1050°C decreases as Ni content increases [1941 Bra]. 

Leo] Leonovich, B.I., Kochurina, O.I., Mikhailov, G.G., Kozyreva, T.D., Thermodynamic Stability of Phases in Alloys of the hon-Chiomium-Carbon System (in Russian), Izv. Vyss. Uchebn. Zaved., Chem. Metall, 3,4-7 (1991) (Phase Relations, Thermodyn., Calculation, 4)... 

While extremely rapid cooling from the liquid state has become a reasonably well establishol metallui ical method in forming new phases in alloys, it is, in the absence of data on polymeric materials, difficult... 

Dezincification refers to the selective leaching of the zinc phase in alloys such as brasses that contain more than 15 percent Zn. The gross appearance and size of a part that has suffered dezincification is often unchanged except for the formation of a copper hue. The part, however, will have become weak and embrittled, and therefore subject to failure without warning. To the trained observer, dezincification is readily recognized under the microscope, and even with the unaided eye, because the red copper color is easily distinguished from the yellow of brass. 

Figure 3 represents the lave phase in SEM microstructure in four samples. SEM analyses indicate great differences on phase precipitation behavior at the grain boundaries in comparison of DE0.7, DEl.l, and DEI.5 alloy with alloy 718. Long needle-like phase is found at grain boundaries in conventional 718 alloy with 0.7% A1 while short rod or granular phase in alloys with 1.1% and 1.5% Al, respectively at as-heat treated condition. 

In addition to RIS, radiation can cause precipitation of second phases in alloys. Typically there are two types of precipitation mechanisms (1) radiation-enhanced mechanism in which the precipitation is thermodynamically favorable and the high concentration of point defects under irradialion allows supersaturated solutes to achieve equilibrium through precipitation at significandy faster rates than under thermal conditions and (2) radiadon-induced mechanism in which the coupling between... 

Introduction Equilibrium phase diagrams are a convenient and concise way of representing the most stable relationships between phases in alloy systems. 

In aging, the alloy is heated below the solvus to permit precipitation of fine particles of a second phase 9 (CuAl ). The solvus represents the boundary on a phase diagram between the soHd-solution region and a region consisting of a second phase in addition to the soHd solution. 

Several of the Al—Li alloys developed in the 1980s contain both magnesium and copper. No quaternary Al—Cu—Li—Mg phase has been found in the alloys. The S -phase in addition to 5 and provides precipitation hardening. 

The SME process can be illustrated by the Cu—Zn system, one of the first SMAs to be studied. A single orientation of the bcc P-phase on cooling goes through an ordering process to a B2 phase. In a disordered alloy, the lattice sites are randomly occupied by both types of atoms, but on ordering the species locate at particular atomic sites, yielding what is called a supedattice. When the B2 phase is cooled below the Mp it transforms to... 

Iron carbide (3 1), Fe C mol wt 179.56 carbon 6.69 wt % density 7.64 g/cm mp 1650°C is obtained from high carbon iron melts as a dark gray air-sensitive powder by anodic isolation with hydrochloric acid. In the microstmcture of steels, cementite appears in the form of etch-resistant grain borders, needles, or lamellae. Fe C powder cannot be sintered with binder metals to produce cemented carbides because Fe C reacts with the binder phase. The hard components in alloy steels, such as chromium steels, are double carbides of the formulas (Cr,Fe)23Cg, (Fe,Cr)2C3, or (Fe,Cr)3C2, that derive from the binary chromium carbides, and can also contain tungsten or molybdenum. These double carbides are related to Tj-carbides, ternary compounds of the general formula M M C where M = iron metal M = refractory transition metal. 

The Tj-carbides are not specifically synthesized, but are of technical importance, occurring in alloy steels, stelUtes, or as embrittling phases in cemented carbides. Other complex carbides in the form of precipitates may form in multicomponent alloys or in high temperature reactor fuels by reaction between the fission products and the moderator graphite, ie, pyrographite-coated fuel kernels. 

---