Lixing HUO
,
Furong CHEN
,
Yufeng ZHANG
,
Li ZHANG
,
Fangjun LIU
,
Gang CHEN
材料科学技术（英文）
The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath martensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.
关键词:
Post-weld heat treatment
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Lixing HUO
,
Furong CHEN
,
Yufeng ZHANG
,
Li ZHANG
,
Fangjun LIU
,
Gang CHEN
材料科学技术（英文）
A three-dimensional finite-element model (FEM) used for calculating electron beam (EB) welding temperature and stresses fields of thin plates of BT20 titanium has been developed in which the nonlinear thermophysical and thermo-mechanical properties of the material has been considered. The welding temperature field, the distributions of residual stresses in as-welded (AW) and electron beam local post-weld heat treatment (EBLPWHT) conditions have been successfully simulated. The results show that: (1) In the weld center, the maximum magnitude of residual tensile stresses of BT20 thin plates of Ti alloy is equal to 60%~70% of its yield strength δs. (2) The residual tensile stresses in weld center can be even decreased after EBLPWHT and the longitudinal tensile stresses are decreased about 50% compared to joints in AW conditions. (3) The numerical calculating results of residual stresses by using FEM are basically in agreement with the experimental results. Combined with numerical calculating results, the effects of electron beam welding and EBLPWHT on the distribution of welding residual stresses in thin plates of BT20 have been analyzed in detail.
关键词:
Electron beam local heat treatment
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Jie WEI
,
Yubao LI
,
Yi ZUO
,
Xueling PENG
,
Li ZHANG
材料科学技术（英文）
A new method of calcium nitrate and sodium phosphate as reactants was employed to prepare biomimetic apatite nanocrystals by a simple heating treatment in water. The structure and properties of the apatite crystals were investigated by TEM, XRD, IR, ICP and TG. It is found that the apatite nanocrystals contain OH-, CO32-, Na+ and HPO42- ions in their crystal structure. The crystal water is removed during heating from 200℃ to 400℃. CO32- and HPO42- are decomposed at 600℃ to 800℃, also there is lattice water lost at this temperature stage. The morphology of the apatite nanocrystals is needle-like with a length less than 80 nm. The size and crystallinity of the apatite nanocrystals increase with water treatment temperature and time. Compared to the apatite crystals sintered at 800℃, water treated apatite nanocrystals are poorly crystallized apatite. The results indicate that the apatite nanocrystals have similarity in composition, structure, morphology and crystallinity to that of bone apatite crystals. It can be used to make apatite crystals/polymer biomimetic bone repair materials or for other biomedical applications.
关键词:
Biomimetic
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