Thin Solid Films
The effects of Ti/TiN bi- and multilayered films on the fatigue performance of the Ti46Al8Nb alloy were investigated. Ti/TiN films with a total thickness of 1 mu m were deposited on the Ti46Al8Nb alloy substrate by the hollow cathode deposition method. The samples were examined with various analytical techniques including nanoindentation, scratch test, stripping layer substrate curvature test and scanning electron microscopy. The results show that multilayered Ti/TiN films can enhance the fatigue strength of the Ti46Al8Nb alloy, whereas bilayered films have no obvious effect. Compared with the bilayer, the multilayer exhibits higher hardness, higher residual compressive stress and higher adhesion strength to the substrate. It is also demonstrated that the multilayer is responsible for retarding fatigue crack growth. All the superior properties make the hard Ti/TiN multilayer to be an effective protection coating for the enhanced fatigue strength of the brittle substrate. (C) 2010 Elsevier B.V. All rights reserved.
关键词:
Fatigue strength;Ti/TiN multilayer;TiAl alloy;Residual stress;Nanohardness;Adhesion;temperature fatigue;residual-stresses;tial alloy;coatings;microstructure;behavior;pvd;hardness;tension;steels
Corrosion Science
The oxidation process of Ti-45Al-8Nb-0.2W-0.2B-0.02Y (at%) can be divided into three stages during 100 h at 900 degrees C. The change of ion diffusion path leads to the discontinuity of the oxidation curve between the second and third stage. Different stages of oxidation morphology have been investigated combined with TEM and STEM. AlNb2 phase forms at the interface of oxide scale/base alloy. Contrary to a continuous formation of 'x' phase in gamma-TiAl with Nb free at the interface of oxide scale/base alloy. AlNb2 phase hinder continuous 'x' phase formation, which can promote TiAl oxidation protection. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
alloy;STEM;oxidation;gamma-titanium aluminide;high-temperature air;tial-based alloys;intermetallic alloys;ternary-system;behavior;phase;scales;si
LI Dong ZHOU Jing CHANG Xin GUAN Shaoxuan Institute of Metal Research
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Academia Sinica
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Shenyang
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China
金属学报(英文版)
Study was made of the behaviour of ordering transformation in Ti_3AI-Nb alloy,including the ordering at high temperatures,the transformation of high temperature β-phase during cooling,and the decomposition of metastable β-phase during aging.The results show that the ordered primary α_2 and high temperature β in alloy form at 1060℃.The transformation of high temperature β-phase proceed by β→α_2+ω type during cooling,and the decomposition of metastable β and ω type proceeded by(β+ω)_(metustabte)→(α_2+β)_(stable)during aging at 700℃.
关键词:
Ti_3Al-Nb alloy
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材料科学技术（英文）
It has been found from the analysis of X-ray diffraction and the observation of TEM that the metastable ordered orthorhombic martensite alpha(0) '' phase in the rapidly solidified Ti3Al-2Nb alloy transforms to various phases at different aging temperatures. When the alloy aged at temperature of 500 degrees C for 20 min, the alpha(0) '' phase decomposition into B2 and O phases is related to the stress in the alloy. When the aged temperature above 600 degrees C, the alpha(0) '' phase transforms to alpha(2) phase by both shearing and chemical ordering.
关键词:
P.Guan
金属学报(英文版)
The directionally solidified samples of an ultra-high temperature Nb-Si- Ti-Hf-Cr-Al alloy have been prepared with the use of an electron beam floating zone melting (EBFZM)furnace, and their microstructural characteristics have been analyzed. All the primary dendrites of Nb solid solution (Nbss), euteetic colonies of Nbss plus (Nb, Ti)3 Si//(Nb, Ti)5 Si3 and chains of (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates align along the growth direction of the samples. With increasing of the withdrawing rate, the microstructure is refined, and the amounts of Nbss+(Nb, Ti)3 Si/(Nb, Ti)5 Si3 euteetic colonies and (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates increase. There appear nodes in the (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates.
关键词:
ultra-high temperature alloy
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null
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ZHANG Jianwei
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LIANG Xiaobo
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CHENG Yunjun
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LI Shiqiong
钢铁研究学报(英文版)
Microstructure and tensile properties of the Ti-23Al-17Nb alloy sheets rolling at （α2＋B2＋O）phase field with the various heat treatments were studied. Before rolling the microstructure of B2 phase particles embedded in O phase continuity matrix is acquired. The B2 phases deform more greatly and recrystallize more easily than α2/ O phases during the same rolling step. The (α2＋B2) two-phase equiaxed microstructure is obtain by solution treatment at (α2＋B2) phase field. The B2 phases become the continuity matrix by recrystallization and growing up of B2 grains and the anisotropy caused by rolling disappears. The microstructure obtained by solution treatment has more excellent tensile properties than the microstructure gained by subsequent aging treatment at (O＋B2) phase field because the O phases precipitate as the block structure during aging and the B2 matrix continuity is broken down.
关键词:
Ti-23Al-27Nb;rolling sheets;microstructure;property
Transactions of Nonferrous Metals Society of China
Thermo-mechanical fatigue tests were carried out on the gamma-TiAl alloy in the temperature range of 500-800 degrees C under mechanical strain control in order to evaluate its cyclic deformation behaviors at elevated temperature. Cyclic deformation curves, stress-strain hysteresis loops under different temperature-strain cycles were analyzed and dislocation configurations were also observed by TEM. The mechanisms of cyclic hardening or softening during thermo-mechanical fatigue (TMF) tests were also discussed. Results showed that thermo-mechanical fatigue lives largely depended on the applied mechanical strain amplitudes, applied types of strain and temperature. On the hysteresis loops appeared two apparent asymmetries: one was zero asymmetry and the other was tensile and compressive asymmetry. Dislocations configuration and slip behaviors were contributed to cyclic hardening or cyclic softening.
关键词:
titanium-aluminium alloy;thermo-mechanical fatigue;cyclic stress;response;hysteresis loop;dislocation;gamma-tial alloy
D Song
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G.Y Zeng and X. Y Sun (Material Testing Centre
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Northeastern University
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Shenyang 110006
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China Manuscript received 24 August 1995
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in revised form 30 March 1996)
金属学报(英文版)
In the present paper, the microstructures of the two-phase alloy specimens of Ti-48AlMn-Nb, deformed at room temperature, 700℃and 900℃,have been investigated by using an EM400T transmission electron microscope. For specimens deformed at room temperature it is observed that (1/2) [011] superdislocation, normal (1/2) [110] dislocations, stacking fault band and a few twins etc. formed mainly in r-phase and a (1/2) [011] superdislocation preferentially decomposes into two partial dislocations with an antiphase boundary between them, which makes the dislocation difficult to move. The normal (1/2) [110] dislocations move with a long dragging tail behind them and have a low mobility In addition, the existence of a few twins implies a low mobility of (1/6) <112> twin dislocations, which leads to low plasticity of the allow. For samples deformed above 700℃,(1/2) [110] dislocations are in majority in the r-phase and exhibit short and bending dislocation segments without dragging tails,which may have resulted from an increased mobility of (1/2) [110] dislocations due to thermal activation. Meanwhile, (1/2) [011]superdislocation disappears, the mobility of (1/6)<112> dislocations is greatly increased, and thus a lot of twins are produced in r-phase. These make the plasticity of the alloy notably enhanced. The laminated structures in the alloy may be transformed into stacking fault bands during deformation at room temperature and the deformation above 700℃leads to the generation of a great quantity of twins.
关键词:
: dislocation
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