A novel method to prepare columnar grains of TiAl alloys by controlling induction heating

Directional recrystallisation processing: a review

“…The grain length and width both increased with increasing hot zone width. Further, they predicted that the upper hot zone velocity limit for columnar grain propagation was higher than that for columnar grain formation and increasing the hot zone velocity during directional recrystallisation would lead to a growth front breakdown, see Figure 19 [94], a result recently confirmed experimentally by Yang and Baker [54]. Badmos et al [94] also showed that using a wider hot zone helps prevent breakdown of the growth front.…”

“…The heating source, cooling method and temperature gradient noted in various papers are listed in Table 2. For furnaces where the heating unit moves when the sample is static [6,18,[20][21][22][23]25,28,30,31,33,35,50], the temperature gradient often changes continuously during processing since the distance between the heating unit and heat sink changes; while for furnaces where the sample travels when the heating unit is static [8,[35][36][37][38][39][40][41][43][44][45][46]48,49,[52][53][54][55][56][57][58], the temperature gradient is usually constant as long as the sample is long enough. It is clear that static heating unit design is better for directional recrystallisation research since the temperature gradient is well controlled.…”

“…A transverse temperature gradient can be present in some directional annealing studies, especially with large samples and using induction heating, in which a transverse temperature gradient is induced by the skin effect. Using the finite element method, Liu et al [54] showed that for a five-turn induction coil furnace (cross-section of 60 × 60 mm 2 ), a transverse temperature gradient was observed when the iron sample diameter was larger than 20 mm and that it increased with increasing sample Air-impingement cooling 844 [15] Induction coil Ambient air cooling 25 [35] Focused light radiation Ambient air cooling 50 [35][36][37]43,53,53,55,56] Focused light radiation Water-cooled copper 1000 [38][39][40][41][42]44,48] Induction coil Liquid Ga-In cooling bath 200-350 [45,47] Resistance heating Ambient air cooling 82 [46] Induction coil Water cooling bath 900 [49] Induction coil Water-cooled chill block 200 [55] Induction coil Water cooling bath 680 [57] Induction coil Ambient air cooling 180 diameter. Thus, a transverse temperature gradient can undoubtedly affect the directional recrystallised structure in different parts of the material.…”

“…A transverse temperature gradient can be present in some directional annealing studies, especially with large samples and using induction heating, in which a transverse temperature gradient is induced by the skin effect. Using the finite element method, Liu et al [54] showed that for a five-turn induction coil furnace (cross-section of 60 × 60 mm 2 ), a transverse temperature gradient was observed when the iron sample diameter was larger than 20 mm and that it increased with increasing sample diameter. Thus, a transverse temperature gradient can undoubtedly affect the directional recrystallised structure in different parts of the material.…”

Experimental and numerical study of the effect of coil structure on induction nitriding temperature field

“…14 Therefore, it is very important to control the temperature distribution of the heated workpiece during the induction heating process. However, some challenges associated with the coil structure design 15,16 and selection of parameters, 17,18 including the heating time, current density, and current frequency, should be overcome during induction heating. Meanwhile, this process is complicated and relies on the trial-and-error method.…”