Phase diagram calculations for high-temperature structural materials

Modelling of the Microsegregation in CMSX-4 Superalloy and its Homogenisation During Heat Treatment

“…In the present case it is clear that Re and Ta segregate in different directions, so that the magnitude of the quantity (CT,, -Cne) can be used as a basis for estimating the solid fraction fs to which it corresponds. A criterion based upon the Ta and Re concentrations is further supported by predictions made using a database of thermodynamic parameters [22], which indicate that the composition of these elements changes monotonically with increasing fraction of solid, even past the eutectic temperature, see the following section. The procedure employed [30] involves (i) the sorting of the datapoints into ascending order on the basis of the local value of (CTa -Cne), (ii) the assignment of an integer i lying between unity and N on this basis, where N is the number of datapoints collected, and the quantity fs placed equal to (i -l)/(N -1) which is assumed to equate to the fraction solidified at this point and (iii) the compu- reasonably good agreement between the values found here, and values reported elsewhere [31,32].…”

“…Values of the interdiffusion coefficients for Ni-Mo were estimated from [1 '7,18] and for Ni-Co from [19,20]. For modelling purposes, atomic mobilities were evaluated using the method reported in [al], with care being taken to ensure consistency with a databank of thermodynamic parameters for the superalloys [22]. The mobilities given by Engstrom & Agren [23] for the ternary Ni-Cr-Al system were accepted.…”

“…The experimentally determined solidification paths given in Figure 4 have been compared with the predictions made using the Thermocalc software [33] and a database of thermodynamic parameters [22]. For the purposes of the present analyses, one assumes that only the liquid, y and y' phases play a part in the reaction.…”

Local variations of the chemistry in as‐cast γ‐TiAl (TiBx) alloys and its consequence for thermomechanical treatments

“…During the last decade extensive research has shown that we are close to a breakthrough for applications of gtitanium aluminides in industrial and aviation gas turbines (Austin & Kelly, 1996). According to the binary Ti-Al phase diagram (Saunders, 1995), typical g-TiAl alloys with nearly equiatomic compositions pass through several phase fields during solidification. This phenomenon can be used to generate a variety of different microstructures consisting of g-TiAl and a small volume fraction of a-Ti 3 Al (Kim, 1995;Appel & Wagner, 1998).…”

Constitution

“…Of the solid state phases austenite, d-ferrite, carbides, nitrides and sigma phase are to be expected. To cope with such a complex alloy system the commercial software program THERMO-CALC TM , version R with TCFE4 database [1] was used to calculate the constitution of multi-component HIS.It depends on experimental data and theoretical models covering a wide range of steel compositions by minimizing the Gibb's free energy [2]. The program provides phase diagrams as isothermal or isoplethal sections through a system.…”