Zhi-Hong Jia
,
Hui-Lan Huang
,
Xue-Li Wang
,
Yuan Xing
,
Qing Liu
金属学报(英文版)
doi:10.1007/s40195-016-0379-0
Lots of the available literatures on hafnium in aluminum alloys are reviewed. The new binary Al-Hf phase diagram is simply assessed. Two ternary phase diagrams including Al-Hf-Zr and Al-Hf-Sc are accounted for, with emphasis on the aluminum rich part of the diagrams. The relationship between different structure Al3Hf and several different formation mechanisms including the probable phase transformation mechanisms is described. The continuous Al3Hf phase particles can serve as a grain refiner in the Al melt and a precipitate for controlling the grain structure of the alloy and a strengthening precipitate. A series of effects of Fe, Si, Zr, Sc and Li addition on the behavior of Al3Hf and Al alloys are given. Moreover, the effects of Hf on the microstructure and properties of Al alloys, such as hardness and creep, are reviewed. Finally, some views of Hf-containing Al alloys are summarized.
关键词:
Al-Hf
,
Phase
,
diagram
,
Al3Hf
,
precipitate
,
Microstructure
,
Properties
M Liu
,
XM Zhang
,
M.Z. Liu
,
X.M. Mengand Y Y Li(Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)(Metal Material Department
,
Sichuan Union University
,
Chengdu 610065
,
China)
金属学报(英文版)
In this paper by means of TEM and HREM, we found that the presence of r-phase plays the most important role in enabling two way shape memory effect (TWME) to be obtained by the stabilization of stress induced martensite variants (SSIM). This idea is different from the traditional suggestion that strain fields developed by dislocation produced TWME. With prolonged isothermal ageing time, the bainitic tronsforma-tion product α1 precipitated, the amount of γ-phase increased, while the martensite was retained and became less ondered. These factors all reduced TWME. During age-ing, the stacking faults in bainitic product α1 disappeared, which indicated that the bainitic product α1 is a sub-equilibrium phase. The interfaces of α-plates also lost straightness step by step, some plates twisted, bronched and overlapped. Its formation is irreversible in tnorphology and reduces the quantities of martensite. Although the precipitation of r may stabilize some martensite or oppose its growth,α may hinder nucleation of martensite. Thus, it was considered that α-plates were the worst de- stroyed element. These suggestions agreed well with our performance test results in that the transformation temperntures and the amount of TWME changed in the same way with prolonged ageing, firstly increasing and then decreasing after reaching an optimal maximum value.
关键词:
precipitate
,
null
,
null
,
null
S.Q. Zhao
,
Y. Jiang
,
J.X. Dong
,
null
,
null
,
null
金属学报(英文版)
A novel nickel-based superalloy INCONEL 740 was under development for application in ultra-supercritical superheater tubers above 750℃. The precipitation behaviors of ?浊 phase and ?酌' particles of the alloy were investigated through experimental study and phase computation. Experimental results showed that ?浊 phase formed a Widmanst?覿tten pattern structure following long-term exposure at elevated temperatures and that the coarsening of ?酌' particle follows a cube rate law: 3 ∝ t. Thermodynamic calculation results showed that Al and Ti had an important effect on the precipitation behavior of ?酌' and ?浊 phases. Two suggested novel modified alloys, wherein the Al and Ti contents were modified, were designed and melted for the experimental study. The preliminary results indicated that the modified alloys exhibited higher structural stability following long-term exposure at 750℃ till 5000h.
关键词:
superalloy
,
null
,
null
,
null
W.H. Tian
金属学报(英文版)
The microstructures of Cr modified Al3 Ti containing Al2 Ti and L10-AlTi precipitateshave been investigated in terms of transmission electron microscopy ( TEM). Fine pre-cipitation of Al2 Ti (Ga2Hf type structure) and L 1o-AlTi(Cr) occurs in L l2-Al3 Ti(Cr)by aging around 973K. The aging behavior was investigated by microhardness mea-surements. TEM observations revealed that plate-like Al2 Ti precipitates lie on { 100}planes of the L12-Al3 Ti(Cr) matrix with the c axis of the tetragonal phase perpendic-ular to the thin plate. As contrast with Al2 Ti precipitates, L1o-AlTi(Cr) precipitatesform thin plate and lie on {100} planes of L12-Al3Ti(Cr) matrix at the initial agingtime and for long time aging the habit plane of the thin plate deviated from {100}plane and finally formed a kinked plate. The coherency stresses across the precipi-tate/matrix interface are considered to be the main factor controlling the precipitatemorphology.``
关键词:
titanium aluminide
,
null
,
null
,
null
,
null
FU Changpu HAN Yong Shaanxi Mechanical Engineering Institute
,
Xi'an
,
China FU Changpu
,
associate professor
,
Department of Materials Engineering
,
Shaanxi Mechanical Engineering Institute
,
Xi'an 710048
,
China
金属学报(英文版)
Studies were made of the effect of tempering at temperatures from 25 to 750℃ for 0.5 to 100 h on changes of hardness,precipitated phase and its alloying element content as well as activation energy of tempering for quenched steel 20Cr11MoVNbNB.Tempering of the steel at temperatures below 400℃ may be controlled by the diffusion of C atoms in α-Fe,and above 400℃,by diffusion of Cr,also Mo or V,in α-Fe.
关键词:
steel 20Cr11MoVNbNB
,
null
,
null
,
null
W.H. Tian
金属学报(英文版)
Microstructural variations and correlated hardness changes in B2-ordered NiAl containing fine precipitation of Ni2AlTi have been investigated by means of transmission electron microscopy (TEM) and hardness tests. The amount of age hardening is not large as compared to the large microstructural variations during aging. TEM observations have revealed that the L21-type Ni2AlTi precipitates keep a lattice coherency with the NiAl matrix at the beginning of aging. By longer periods of aging Ni2AlTi precipitates lose their coherency and change their morphology to the globular ones surrounded by misfit dislocations. The temperature dependence of the yield strength of precipitate-containing B2-ordered NiAl was investigated by compression tests over the temperature range of 873-1273K. The fine precipitation of Ni2AlTi was found to enhance greatly the yield strength and the high-temperature strength is comparison with that of superalloy Mar-M200.
关键词:
NiAl intermetallics
,
null
,
null
,
null
,
null
W.H. Tian*
金属学报(英文版)
A transmission electron microscopy (TEM) investigation has been performed on the dislocation pinning in L12-ordered Ni3(Al,Ti) containing disordered γ precipitates. The morphology of defor?鄄mation induced dislocations in the γ' base alloys containing fine dispersion of disordered γ was investigated by means of weak-beam electron microscopy. The superdislocations are strongly at?鄄tracted to the disordered particles and dissociate on the (111) plane in the γ particles, while they dissociate on the (010) plane in the γ' matrix. The disordered γ precipitates play an important role as a pinning point during the cross-slip of superdislocations from (111) to (010) planes in the γ' matrix and restrain the cross-slip of superdislocations. The interaction of superdislocations with disordered particles causes the formation of superkinks, jogs and closed loops.
关键词:
superdislocation
,
precipitates
,
attractiv
X.M.Meng
,
L.L.He
,
D.X.Li
金属学报(英文版)
The structure change of γ-TiAl intermetallic alloy irradiated by 50keV xenon ionswith a dose of 7.6×1018ions/m2 was studied in a high voltage transmission electronmicroscope at room temperature.Some precipitates appeared in the γ-TiAl grains,which have a hexagonal structure with a=0.283nm and c=0.462nm,and seems to bethe disordered Al2 Ti3 phase.The orientation relationship between the precipitates andmatrix is (0001)P//(111 )γ-TiAl and [21 1 0]P//[011]γ-TiA1.
关键词:
γ-TiAl alloy
,
null
,
null
