Microstructural characteristics of as-forged and β-air-cooled Zr-2.5Nb alloy

Multiple characterization and analysis techniques including electron backscatter diffraction（EBSD）, electron channeling contrast（ECC） imaging, transmission electron microscopy（TEM） and microhardness test were jointly employed to investigate microstructural characteristics such as local composition, morphology, grain boundary characteristics and interphase orientation relationship of a forged Zr-2.5Nb alloy before and after β-air-cooling. Results show that the as-forged specimen is composed of equiaxed and lamellar α grains and continuous net-like β-Zr films. After the β-air-cooling, the microstructure of the specimen is featured by basket-weave Widmanst？tten structure, in which the inter-α-plate second phases are nanoscale β-Zr. Analyses for crystallographic orientations reveal that the Burgers relationship has been strictly followed during the β→α cooling. Compared to the as-forged specimen, the hardness of the β-air-cooled specimen is higher, which could be attributed to the decreased structural sizes of both α and β phases, and the increased fraction of high angle boundaries as well.

EBSD Study of Microstructural and Textural Changes of Hot-Rolled Ti–6Al–4V Sheet After Annealing at 800 ℃

In this paper, electron backscatter diffraction and various other characterization and analysis techniques mclucilng X-raydiffraction, electron channeling contrast imaging and energy-dispersive spectrometry were jointly employed to investigatemicrostructural and textural changes of a hot-rolled Ti-6A1-4V （TC4） sheet after annealing at 800 ℃ for 5 h. In addition,the hardness variation induced by the annealing treatment is rationalized based on revealed microstructural and texturalcharacteristics. Results show that the TC4 sheet presents a typical dual-phase （α＋β） microstructure, with α-Ti as themajor phase and short-rod-shaped β-Ti （minority） uniformly distributed throughout the α matrix. Most of α grains cor-respond to the un-recrystallized structures with a typical rolling texture （c//TD and 〈11-20〉//ND） and dense low angleboundaries （LABs）. After the annealing, the stored energy in the as-received specimen is significantly reduced, along withgreatly decreased LABs density. Also, the annealing allows recrystallization and grain growth to occur, leading toweakening of the initial texture. Furthermore, the water quenching immediately after the annealing triggers martensitictransformation, which makes the high-temperature β phases be transformed into submicron α plates. The hardness of theannealed specimen is 320.5 HV, lower than that （367.0 HV） of the as-received specimen, which could be attributed toreduced LABs, grain growth and weakened texture. Nevertheless, the hardening effect from the fine martensitic platescould help to suppress a drastic hardness drop.