Effect of continuous cooling on solid phase transformations in TiAl-based alloy during Jominy end-quench test

Grain refinement of cast peritectic TiAl-based alloy by solid-state phase transformations

“…The formation of the grain boundary γ has also been reported by Huang et al [17] in Ti-46Al-8Nb (at.%) alloy cooled from the α phase field at a nominal cooling rate of 40 • C s −1 . The formation of lamellar microstructure in the WQ sample indicates that the cooling rate of 48 • C s −1 is still too low to suppress diffusion assisted transformation of the α phase to the lamellar structure and to promote formation of higher volume fraction of the massive γ M or to preserve untransformed α phase in the microstructure similarly to that observed by several authors [28,31]. identified within the refined grains such as single γ phase and two-phase α 2 + γ, as shown in Figs.…”

“…A grain size up to about 280 µm has been suggested by Kim and Kim [14,51] to maintain an optimal balance between the room and high-temperature mechanical properties of TiAl-based alloys. It should be noted that the fast cooling rates occasionally lead to the formation of short cracks in the OQ and even long cracks in WQ samples [31]. Hence, such type of cooling could not be applied for the grain refinement of cast components in practice.…”

“…The alloying elements showing low diffusivity in both TiAl and Ti 3 Al phases decrease critical cooling rates required for the formation of massive γ M [19]. Some TiAl-based alloys have been specifically designed, as the "air hardenable" requiring only air cooling from the single α phase field to be fully transformed to massive γ M [10,[27][28][29][30][31]. However, many TiAl-based alloys do not exhibit massive transformation or this transformation is shifted to very high cooling rates.…”

“…The as-cast bar was machined to smaller samples with a diameter of 17 mm and length of 26 mm using wire electrical discharge machining. The samples were heated to a solution annealing temperature of 1405 • C at a heating rate of 10 • C min −1 , held at this temperature for 1 h and cooled to room temperature using forced air cooling, oil quenching and water quenching which resulted in average cooling rates of 15, 24 and 48 • C s −1 , respectively [31]. The air cooled (AC), oil quenched (OQ) and water quenched (WQ) samples were subjected to three different heat treatment routes designated as A, B, and C, as seen in Fig.…”

Effects of Water Jet Height and End Dipping on the Cooling Rate and Hardenability in the Jominy End Quench Test

“…To understand the Jominy end quench test, many researchers have studied the overall phenomena of heat transfer; the phase transformation of austenite; and the estimation of hardness with distance from the quenched end during the Jominy test via the mathematical model, numerical algorithm, experimental test, empirical approach, continuous cooling transformation (CCT) diagram, and finite element (FE) method [2,[8][9][10][11][12][13][14][15]. Homberg [8] presented a numerical algorithm for simulating the Jominy end quench test and deriving a CCT diagram based on a model for the diffusive austenite-pearlite coupled with the non-diffusive austenite-martenite phase transition.…”