Underlying factors determining grain morphologies in high-strength titanium alloys processed by additive manufacturing

Abstract

In recent research, additions of solute to Ti and some Ti-based alloys have been employed to produce equiaxed microstructures when processing these materials using additive manufacturing. The present study develops a computational scheme for guiding the selection of such alloying additions, and the minimum amounts required, to effect the columnar to equiaxed microstructural transition. We put forward two physical mechanisms that may produce this transition; the first and more commonly discussed is based on growth restriction factors, and the second on the increased freezing range effected by the alloying addition coupled with the imposed rapid cooling rates associated with AM techniques. We show in the research described here, involving a number of model binary as well as complex multi-component Ti alloys, and the use of two different AM approaches, that the latter mechanism is more reliable regarding prediction of the grain morphology resulting from given solute additions.

Ultrauniform, strong, and ductile 3D-printed titanium alloy through bifunctional alloy design

“…The total Q and Δ T FR values based on the real chemical composition of Ti-5553 are calculated to be about 10.4 K and 10.9 K, respectively ( 30 ) (table S3). These values are far below those reported in other studies to achieve substantial grain refinement by solute—for example, Q = 62 K and Δ T FR = 603 K in Ti−8.5Cu ( 9 , 42 ). Therefore, it is unsurprising that the L-PBF–produced Ti-5553 shows the typical columnar grain structure (Fig.…”

Additively Manufactured Alnico Permanent Magnet Materials—A Review

“…The types of microstructures that can be obtained for various combinations of G and R are schematically presented in Figure 11. The solidification range of a material is one of the critical factors along with the kinetics of the solidification (thermal gradient, solidification growth velocity, cooling rate), local composition, etc., which exerts a substantial influence on the type of microstructure that ultimately develops [75,76]. The solidification ranges of various Alnico alloys are given in Table 2 (obtained from the CALPHAD database).…”

“…Understanding and controlling all these thermokinetics and composition-related parameters are therefore essential for tailoring microstructures to achieve specific material characteristics and performance attributes. Although the combined effects of all these parameters are very complex, several researchers have attempted to break down such complexity by approaching it in the most simplistic manner by separating the effect of each of these parameters [57,66,73,[75][76][77][78]. Majority of these efforts have emphasized the effect of solidification range on grain morphologies.…”

“…Majority of these efforts have emphasized the effect of solidification range on grain morphologies. When the solidification range is high, there is a greater amount of undercooling provided during solidification, which leads to the high nucleation density; thus, alloys with a high solidification range lead to the development of an equiaxed microstructure [76]. The Alnico-8H alloy with a high solidification range of 283 °C (obtained from the CALPHAD database) is likely to develop an equiaxed microstructure due to the high nucleation density in the AM samples.…”