Zhiguang LIU
,
Jianting GUO
,
Nanlin SHI and Zhuangqi HU(State Key Lab. for RSA
,
Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)
材料科学技术（英文）
The mixture of pure nickel and aluminum powders in the composition of Ni50AI50 was subjected to high energy ball milling. The high energy ball milling to 30 h resulted in the formation of a nanocrystalline NiAl with a grain size of about 10 nm. The as-milled NiAl powder was hot-pressed and the compact with a density of 90% was obtained. It was showed that heating to900℃ and holding for more than 2 h failed to induce the coarsening of the fine nanocrystalin the material, the tendency of grain growth was weak. Compression testing showed that thecompression ductility at room temperature reached about 7%. The ductility increased with theexperimental temperature while the strength decreased drastically at elevated temperature.
关键词:
Xinghao DU
,
Jianting GUO
,
Bide ZHOU
,
Liangyue XIONG
材料科学技术（英文）
In order to study the subboundaries evolution in superplastically deformed NiAl, the positron lifetime change during superplastic deformation process was measured. It is shown that the superplastic deformation of NiAl has not influence on its τ2, the newly recrystallized grain boundaries formed during entire superplastic deformation process belong to the calegory of subboundaries and have not contribution to the superplastic strain.
关键词:
NiAl
,
null
,
null
,
null
Weili REN
,
Jianting GUO
,
Gusong LI
,
Jiyang ZHOU
材料科学技术（英文）
The influence of strain rate and temperature on the tensile behavior of as-cast and HIPed NiAl-9Mo eutectic alloy was investigated in the temperature range of 700~950℃ and over a strain rate range from 2.08×10-4 s-1 to 2.08×10-2 s-1. The results indicate that HIP process causes an enhancement in ductility and a decrease in ultimate tensile strength (UTS), yield strength (YS), average strain hardening rate as well as a drop in brittle to ductile transition temperature(BDTT) under the same condition. It is noticed that the BDTT of as-cast NiAl-9Mo is more dependent on strain rate than that of HIPed one. The brittle to ductile transition process of the alloy is related to a sharp drop in strain hardening rate. Regardless of strain rate, the fracture morphology changes from cleavage in NiAl phase and debonding along NiAl/Mo interface below the BDTT to microvoid coalescence above BDTT. The apparent activation energy of the BDT of HIPed and as-cast material are calculated to be 327 and 263 kJ/mol, respectively, suggesting that the mechanism is associated with lattice diffusion in NiAl phase.
关键词:
NiAl-9Mo
,
null
,
null
,
null
Qiang GAO
,
Jianting GUO
,
Kaiwen HUAI
,
Hutian LI
,
Junshan ZHANG
材料科学技术（英文）
Effect of 0.1 wt pct Dy addition on microstructure and compressive behavior of NiAl-28Cr-5.8Mo-0.2 Hf eutectic alloy was investigated. The results showed that remarkable lamellar refinement can be achieved with the addition of 0.1 wt pct Dy. The Dy addition results in the decrease in Young's modulus of alloy and the enhancement of the compressive strength and ductility of alloy at all testing temperatures. The lamellar refinement, the increased dislocation networks located at the interfaces of NiAl/Cr(Mo) and the strengthening of cell boundary are benefical to the improvement of compressive properties of the alloy.
关键词:
NiAl-28Cr-5.8Mo-0.2Hf
,
null
,
null
,
null
Lanzhang ZHOU
,
Jianting GUO
材料科学技术（英文）
Reaction-milled NiAl-TiB2 composite was fabricated by mechanical alloying elemental powders and hot pressing. TiB2 particles are distributed mostly in grain boundaries of the matrix. The compressive strain to failure of the composite at RT is about twice that of cast NiAl. The compressive yield stress at high temperatures is about 4.5 times higher than that of extruded NiAl, and is also much stronger than XD NiAl-TiB2 composites. Deformation behavior between 1000-1100℃ with different strain rates has been investigated.
关键词:
Xinghao DU
,
Jianting GUO
材料科学技术（英文）
A multiphase NiAl-28Cr-5.85Mo-0.15Hf alloy, which was directionally solidified (DS) in an Al2O3-SiO2 mold by standard Bridgman method and then underwent prolonged solution and aging treatment was prepared. The microstructure, tensile properties as well as tensile creep of the heat-treated alloy at different temperatures were studied. The alloy was composed of NiAl, Cr(Mo) and Hf-rich phase and small amount of fine Heusler phase (Ni2AlHf). Although the present alloy exhibited high tensile strength at low temperature, it was weaker than that of system with high content Hf but still stronger than that of many NiAl-based alloys at high temperatures. The fracture toughness is lower than that of DS NiAl-28Cr-6Mo alloy. Nevertheless, advantageous effects on the mechanical properties, $i.e$. the decrease in brittle-to-ductile transition temperature (BDTT) were obtained for the low content of Hf. The obtained creep curves exhibit conventional shape: a short primary creep and long accelerated creep stages. The rupture properties of the heat-treated alloy follow the Monkman-Grant relationship, which exhibits similar creep behavior to that of NiAl/Cr(Mo) system with high Hf content.
关键词:
NiAl/Cr(Mo
,
null
,
null
,
null
,
null
,
null
Rongshi CHEN
,
Jianting GUO
,
Wenlong ZHOU
,
Liangyue XIONG
材料科学技术（英文）
In order to understand the point defect structure in NiAl Intermetallic compound, the positron lifetime in binary Ni100-xAlx (53 greater than or equal to x greater than or equal to 45) and ternary B2 Ni50-xCoxAl50 (x=0, 5, 10, 15) intermetallic compounds as a function of composition were measured. It is shown that the positron lifetime spectra of these compounds can be consistently expressed by single-component lifetimes. The positron lifetime value in ternary Ni50-xCoxAl50 alloy is independent of Co content and equal to that detected in both stoichiometric and Al-rich NiAl. From an analysis of the present results, it is suggested that the constant lifetime of tau approximate to 180 ps should be ascribed to saturation trapping and annihilation of positron exclusively at Ni vacancy, no evidence for the presence of Al vacancy is available.
关键词:
Guangye ZHANG
,
Xinghao DU
,
Jianting GUO
,
Hengqiang YE
材料科学技术（英文）
Brittle-to-ductile transition (BDT) behavior and creep behavior of extruded NiAl-25Cr alloy at elevated temperatures were investigated. The results reveal that the alloy exhibits obvious BDT behavior with the increase in temperature and BDT temperature (BDTT) is sensitive to initial strain rate. When the initial strain rate increases by two orders of magnitude, BDTT has an increase of approximate 80 K. The creep data in the temperature range of 1073～1123 K reveal two distinct regions of creep behavior in this material. At lower temperature, the creep characteristics are consistent with structural controlled creep process where creep deformation is controlled by dislocation climb. At higher temperature, the creep characteristics are consistent with mobility-controlled deformation where viscous glide of dislocations controls creep. The apparent activation energy determined by creep in both regions exceeds the value for lattice self-diffusion in NiAl by a considerable amount. This can be explained in terms of the simultaneous deformation of second phase particles (γ'-Ni3Al and α-Cr phase) along NiAl matrix during creep.
关键词:
NiAl
,
null
,
null
,
null
,
null
Jieshan HOU
,
Jianting GUO
,
Lanzhang ZHOU
材料科学技术（英文）
Derived from Russian alloy CHS88U, six experimental Ni-base alloys named as A to F in the Ni-Cr-Co-W-Ti-Al-Hf system are designed, evaluated and processed. One of these alloys, F, shows excellent high temperature tensile strength and ductility with superior creep rupture properties. As predicted by using modeling tools such as PHACOM and NEW PHACOMP, there is hardly the tendency for formation of topologically close-packed phase (TCP) phase in alloy F. Furthermore, through microstructural observation, it is also found that no TCP phase is formed in alloy F after long-time exposure at high temperature. So alloy F has well balance of phase stability and mechanical properties in view of application for gas turbines. It is proved that d-electron approach can be applied for design and development of nickel-base superalloys for gas turbine application.
关键词:
Conventional Ni-base superalloy
,
null
,
null
,
null
