Microstructural and Textural Differences Induced by Water and Furnace Cooling in Commercially Pure Zr Annealed in the α + β Region

Linjiang Chai,Tingting Wang,Yi Ren,Bo Song,Ning Guo,Liangyu Chen 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.4

In this work, a commercially pure Zr sheet with a typical bimodal basal texture was annealed in an α + β region and thensubjected to Different coolings (in water and furnace). Microstructures and textures of both the as-received and the heat-treatedspecimens were investigated by electron channeling contrast imaging and electron backscatter diff raction techniques. Resultsshow that a duplex microstructure consisting of untransformed bulk α grains and twinned martensitic plates is produced inthe water-cooled specimen, which possesses a weakened texture compared to the initial one. For the specimen cooled in furnace,however, a uniform microstructure fully comprised of coarser equiaxed grains with a strengthened texture is obtained. Analyses reveal that the rapid cooling in water could suppress variant selection behaviors during β → α transformation andallow α plates with scattered orientations to be nucleated inside β phases, contributing to the weakened texture. In contrast,during slow cooling in furnace, β boundaries would act as preferred nucleation sites of α embryos, resulting in a strong variantselection that accounts for the intensifi ed texture.

Development of Grain Boundary Character Distribution in Medium‑Strained 316L Stainless Steel During Annealing

Weijiu Huang,Shanshan Yuan,Linjiang Chai,Luyao Jiang,Haiding Liu,Fangjun Wang,Dongzhe Wang,Junjun Wang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2

A medium-strained (13% cold-drawing) 316L austenitic stainless steel rod was subjected to annealing between 750 and1100 °C. Electron backscatter diffraction and electron channeling contrast imaging techniques were jointly employed toinvestigate the development of microstructures and grain boundary character distribution during the annealing treatments. Results show that annealing at temperatures below 900 °C does not evidently change microstructures of the as-drawn specimen. Full recrystallization is observed after the temperature reaches 1000 °C and the deformation microstructures are replacedby fine and uniform recrystallized grains. A large number of annealing twins (with Σ3 misorientation) are produced by therecrystallization, leading to markedly increased fractions of special boundaries (fSB). The maximum fSB is found to be 67.3%in the present study. In addition, for the recrystallized grains, rapid growth is noticed at relatively high temperatures due toeasy migration of grain boundaries.

Preparation and Characterization of Mg Alloy Rods with Gradient Microstructure by Torsion Deformation

Bo Song,Huaizhi Zhao,Linjiang Chai,Ning Guo,Hucheng Pan,Hongbing Chen,Renlong Xin 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.5

Extruded AZ31 Mg alloy rods were subject to free-end torsion deformation at room temperature. The microstructure features of the torsion deformed samples were characterized using electron backscatter diffraction technique. Mg rods with gradient microstructure can be fabricated by torsion deformation. Inhomogeneous distribution of microstructure along the radial direction of the twisted rods is attributed to the linearly increasing strain accumulation and strain rate from core to surface. With increasing equivalent strain, both the amount of {10- 12} twins and dislocation density increase and the c-axes of texture tend to rotate towards torsion axis. Although both dislocation slips and {10-12} twinning can be activated during torsion, dislocation slips are considered as the dominated deformation mechanism and responsible for the change of macro-texture for present torsion deformation. {10-12} twins and dislocations in the twisted samples can generate refinement hardening and dislocation hardening, respectively, to increase the hardness value.

Effects of pulsed laser surface remelting on microstructure, hardness and lead-bismuth corrosion behavior of a ferrite/martensitic steel

Hao Wang,Qian Yuan,Linjiang Chai,Ke Zhao,Ning Guo,Jun Xiao,Xing Yin,Bin Tang,Yuqiong Li,Shaoyu Qiu 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.6

A typical ferritic/martensitic (F/M) steel sheet was subjected to pulsed laser surface remelting (LSR) andcorrosion test in lead-bismuth eutectic (LBE) at 550 C. There present two modification zones withdistinct microstructures in the LSRed specimen: (1) remelted zone (RZ) consisting of both bulk d-ferritegrains and martensitic plates and (2) heat-affected zone (HAZ) below the RZ, mainly composed ofmartensitic plates and high-density precipitates. Martensitic transformation occurs in both the RZ andthe HAZ with the Kurdjumov-Sachs and Nishiyama-Wassermann orientation relationships followedconcurrently, resulting in scattered orientations and specific misorientation characteristics. Hardnessesof the RZ and the HAZ are 364 ± 7 HV and 451 ± 15 HV, respectively, considerably higher than that of thematrix (267 ± 3 HV). In oxygen-saturated and oxygen-depleted LBE, thicknesses of oxide layers developed on both the as-received and the LSRed specimens increase with prolonging corrosion time (oxidelayers always thinner under the oxygen-depleted condition). The corrosion resistance of the LSRed F/Msteel in oxygen-saturated LBE is improved, which can be attributed to the grain-refinement acceleratedformation of dense FeeCr spinel. In oxygen-depleted LBE, the growth of oxide layers is very low withboth types of specimens showing similar corrosion resistance

Effects of β Air Cooling and Subsequent Cold Rolling on Microstructure and Hardness of Zr702 Sheet

Haotian Guan,Lingguo Zeng,Zhijun Li,Linjiang Chai,Yufan Zhu,Yueyuan Wang,Qin Huang,Ke Chen,Liang‑yu Chen,Ning Guo 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.2

In this work, a Zr702 sheet was subjected to β air cooling and then rolled to 15% reduction at room temperature, with theirdetailed microstructural characteristics characterized by electron channeling contrast imaging and electron backscatterdiffraction techniques. Results show that after the β air cooling, the prior equiaxed grains in the as-received material arecompletely transformed into Widmanstätten structures featured by coarse plates with typical phase transformation misorientationsbetween them. The subsequent 15% rolling allows both slip and twinning (especially the {10–12} type) to beactivated readily, leading to significant grain refinement and the appearance of misorientation angle peaks around 3°–5° and85°. Analyses on kernel average misorientations reveal that there exist very low residual strains in the β-air-cooled specimenwhile they are markedly increased after the 15% rolling and preferably distributed near low-angle and twin boundaries. Hardnessmeasurements show that the specimen hardness is evidently decreased from ~ 199 to ~ 170 HV after the β air cooling,which can be attributed to grain coarsening and the scattered orientations associated with the slow β → α transformation. For the 15%-rolled specimen, however, effective grain refinement by twinning and denser low-angle boundaries jointly leadto ~ 35% hardness increment to ~ 228 HV.

Influence of δ' Phase with GP‑I Zones Fillings on Slip Behavior and Cold Rolling Texture in AA2099

Xusheng Yang,Weijiu Huang,Xianghui Zhu,Fei Guo,Yanlong Ma,Linjiang Chai,Ran Zhang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9

The cold rolling texture of AA2099 sheets was strongly influenced by the prior heat treatment. Two typical heat treatments,including solid solution (T4) and underaging (T6) were utilized to control slip behavior by different precipitates during coldrolling. A much weaker texture with an orientation scatter towards higher Φ angles was found in the as-rolled T6 specimen(T6R). Slip behavior was analyzed using geometry necessary boundaries distribution. Results show that the T6R specimenexperienced a strong co-planar slip compared to the as-rolled T4 specimen. Prosperity of co-planar slips and limitation ofco-direction slips were main reasons for the weakening of Copper texture component in the T6R specimen. The distinguishslip behavior was caused by existence of δ' phase with GP-I zones fillings in the T6 specimen. This phase could be easilysheared by dislocations and then promoted co-planar slips in further deformation.

Influence of Initial Textures on Microstructure and Mechanical Properties of Commercially Pure TA2 Titanium Sheet Pre-Strained by Cryorolling

Changhao Wang,Yu Luo,Jinru Luo,Xiao Song,Wei Zhang,Pinghuai Wang,Zhenghao Liu,Maoyin Wang,Xinghui He,Linjiang Chai 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.4

Titanium alloys are one of the most important structural materials for the aerospace applications, which bring active studyon microstructural and mechanical optimization of the alloys. In the present study, commercial TA2 titanium sheets withdifferent initial textures were rolled to a strain of 4% at liquid nitrogen temperature. Microstructures of the rolled sheets werecharacterized using a scanning electron microscope equipped with an EBSD detector and their mechanical properties weretested through quasi-static uniaxial tension tests at room temperature. The influence of the initial texture on the microstructureand mechanical performance of the cryorolled sheet were discussed. Twinning is found to occur in the TA2 sheets after rollingeven at a small strain. Initial texture is an important factor affecting both numbers and types of the twins. {11–22} contractiontwinning is always the dominating type of twins for all three sheets having different initial textures. A lot of {11–22}and {11–24} twins can be found in the sheets with the initial texture of C-axes//ND, while the sheet with an initial texture ofC-axes away from the ND contains few twins, with a high density of dislocations developed instead. Along with contractiontwinning, many {10–12} and {11–21} twins are detected in the sheet with the initial texture of C-axes⊥ND. The cryorolledsheet having the densest twins shows the best mechanical properties, indicating a beneficial effect of a small pre-strain.