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The control of the post-forging cooling rate has been a key issue in the industrial production process of titanium alloys. We investigated texture evolution and variant selection (VS) during β → α transformation through high-temperature compression experiments followed by quantitative control of varying cooling rates. Results show that post-forging...
Citations
... The phase transformation inheritance occurs after ST based on the variant selection effect, and the α p varieties are mainly 80-90 • /<-12-10> and 80-90 • / <01-10>. Furthermore, the density of the deformation texture (000-1) [11][12][13][14][15][16][17][18][19][20] is weakened by the new α p transformation texture (0001) [-1-780] and the recrystallization texture (23-5-3) [11][12][13][14][15][16][17][18][19][20][21][22], but it is inherited at 1.23. However, the α p recrystallization texture significantly restrains the occurrence of the deformation texture inheritance phenomenon at 0.001 s − 1 . ...
... The phase transformation inheritance occurs after ST based on the variant selection effect, and the α p varieties are mainly 80-90 • /<-12-10> and 80-90 • / <01-10>. Furthermore, the density of the deformation texture (000-1) [11][12][13][14][15][16][17][18][19][20] is weakened by the new α p transformation texture (0001) [-1-780] and the recrystallization texture (23-5-3) [11][12][13][14][15][16][17][18][19][20][21][22], but it is inherited at 1.23. However, the α p recrystallization texture significantly restrains the occurrence of the deformation texture inheritance phenomenon at 0.001 s − 1 . ...
... They indicated that {001}<100> and {111}<110> of two texture types act as preferential nucleation sites for recrystallized grains during ST, which nucleate at the deformation texture component {111}<110> by rotating around <110> orientation [13]. The microtexture is very stable during hot processing in the two-phase region [14][15][16]. It is closely related to α p grain evolution, where equiaxed α p grains are of vital importance in microstructure evolution during thermomechanical processing [17,18]. ...
... αGB4 and αGB5 share {0 0 01} and {11-20} planes. The αGB only maintains BOR with one side of the adjacent β grains [40][41][42] , which is prone to recrystallized spheroidization. Furthermore, it also promotes β DRV and β DRX on the same side. ...
... To figure out the effects of reinforcement on the texture characteristics of the Cu matrix, the representative polar figure of the three specimens was also analyzed based on the EBSD results and shown in Fig. 7a-c. It can be seen that the texture of pure Cu is negligible, the deformation texture should be weakened by the sufficient recrystallization allowed by the slow cooling rate after sintering and hot rolling [44]. However, the CNTs/Cu and CNTs@Cr 2 O 3 /Cu composites exhibit slightly stronger texture than pure Cu, which can be attributed to the lowered recrystallization of Cu grains caused by the pinning effects of CNTs and CNTs@Cr 2 O 3 . ...
... Consequently the peritectic solidification is replaced by a β-solidifying pathway as L→L+β→β→β+α→α→α+γ→α 2 +γ [6,7]. As in ordinary titanium alloys, the β→α transformation is predominated by the Burgers orientation relationship (OR) so that a prior large β grain can theoretically transform into twelve α variants [8,9], whereby the ultimate α 2 /γ lamellar colony size can be dramatically reduced. Such a refined microstructure can improve the hot-workability significantly [3]. ...
In this study, the hot deformation behavior of a Ti–42Al-8.5 V alloy with a martensitic staring microstructure was investigated for the first time. For comparison, the same alloy but with a Widmannstatten lamellar structure was also prepared and deformed at identical conditions. It was shown that the martensite exhibited a much lower stress exponent and pronounced flow softening, and the hot-workability was drastically improved. With the aid of the rapid decomposition of the martensite, an excellent fine-grained structure with negligible micro-texture was obtained in a wide temperature-strain rate regime, which was mostly surrounded by high-angle grain boundaries through recrystallization/globularization enhanced by grain boundary sliding. In contrast, the Widmannstatten structure showed a rather poor hot-workability and a retarded refinement efficiency. The deformed microstructure was noticeably non-uniform and micro-textured at nearly all the compression conditions, though the recrystallized grain size was comparable with that of the martensite. To rationalize the distinct deformation behavior of the two starting microstructures, the underlying mechanisms governing the microstructure/orientation evolution were systematically analyzed and discussed. It was suggested that adopting martensite as the starting microstructure may be a potential approach to achieve the optimal microstructural breakdown effect for certain TiAl alloys.
... As it was mentioned, recrystallization was only observed in the core of the neck region. The utilization of a low strain rate during β-phase forging is likely to generate more dynamic recovery (DRV) than dynamic recrystallization (DRX) because, the high self-diffusivity of β-Ti and the decreasing store energy favor easier deformation but lower recrystallization [33][34][35][36][37]. During the final precision forging stage, high heat transfer from the dies allowed for a rapid cooling at the sample surface, which created a temperature gradient with the core. ...
This study investigates direct powder forging (DPF) as a new approach for near-net-shape processing of titanium alloys using a coarse particle size distribution (PSD) between 90 and 250 μm. This route was utilised to takes advantage of DPF’s enclosed nature to make near-net-shape components with conventional forging equipment, making it attractive and viable even for reactive powder such as titanium. In this study, the uncompacted Ti-6Al-4V ELI powder was sealed under vacuum in a stainless-steel canister and hot forged in air to produce a fully dense titanium femoral stem. After the final forging stage, the excess material in the flash region was cut, which efficiently released the canister, revealing the forged part with minimal surface contamination. The as-forged microstructure comprises coarse β grains with a martensitic structure. The subsequent annealing was able to generate a fine and homogenous lamellar microstructure with mechanical properties that respects the surgical implant standard, showing that DPF offers significant potential for forged titanium parts. Therefore, the DPF process provides a suitable alternative to produce titanium components using basic equipment, making it more available to the industry.
Heat treatments with controlled cooling rates have been used to investigate orthorhombic (O) phase precipitation and its variant selection (VS) in Ti–22Al–25Nb alloy, a latest Ti2AlNb-based intermetallic alloy with excellent comprehensive properties. This study uncovers the misorientation types of different O variants mainly belong to two types with a sharing angle of 90° and distinct rotated axis of or . A notable lamellar structure, colony side plates (CSPs), frequently develop on both sides of adjoining B2 grains, which always have a detrimental effect on the final properties. This structure significantly influenced by VS, variants having (001) planes that are paralleled to the common {110} plane of adjacent B2 grains are selected in colony plates on both sides. If the axis of the two B2 grains coincidentally close as well, the colony plates may appear to penetrate the GB. Moreover, the CSPs structure could form on condition of much slow cooling rate after holding in rather high temperature. These findings could provide insights on how to control processing conditions and tailor the lamellar structure to obtain the desired properties.
