Study on Microstructure Evolution of TC18 Titanium Alloy During Continuous Cooling Process
ZHAI Jiangbo1,2, TU Junzhe1, QIN Weidong2, JI Shengli2, XU Jianwei1, ZENG Weidong1,*
1 School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China 2 Shandong Hongshan Aviation Forging Co., Ltd., Yantai 265713, Shandong, China
Abstract: Controlling the morphological characteristics of α-phase precipitation following β annealing is the pivotal factor governing the attainment of superior damage tolerance performance. This work presents a systematic investigation of the precipitation behavior and associated microstructural evolution of α-phase in TC18 titanium alloy during continuous cooling processes. Comprehensive experimental characterization demonstrates that reduced cooling rates facilitate both enhanced α-phase precipitation and pronounced coarsening of α platelets. Notably, grain boundary α (αGB) exhibits preferential precipitation, followed by Widmansttten α laths (αW), which manifest through two distinct formation pathways:extension from αGB into adjacent grain interiors (αWGB) and autonomous nucleation within β grains (αWI). Crystallographic orientation analysis reveals that αGB preferentially maintains the Burgers orientation relationship (BOR) with a single adjacent β grain, while unique variants simultaneously satisfying the BOR with both neighboring grains emerge when adjacent β grains share (110) crystallographic planes. Subsequent growth behavior shows that αGB extends exclusively into BOR-compliant β grains to form αWGB, preserving orientation continuity with the parent αGB. In addition, intra-granular αWI rigorously adheres to BOR principles, exhibiting the complete spectrum of 12 orientation variants. Therefore, this work statistically analyzes the influence of cooling rate on the variant types of intragranular αWI. At a cooling rate of 0.3 ℃·s-1, the (011)β//(0001)α, [111]β//[1120]α variant dominates precipitation, whereas below 0.1 ℃·s-1, preferential growth occurs for both (101)β//(0001)α, [111]β//[1120]α and (110)β//(0001)α, [111]β//[1120]α variants. These findings provide a parameter basis for optimizing the TC18 alloy heat treatment processes to regulate α-phase distribution.
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2026, Vol. 40 
