孙军
主要研究领域为材料微观组织与力学性能,涉及材料损伤断裂的约束效应,材料界面裂纹行为与界面屏蔽及材料形变/相变及其微尺度效应、先进结构金属材料与块体非晶合金的高性能化和材料介观性能表征及其尺度效应等课题。
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- 姓名:孙军
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学术头衔:
博士生导师, “973”、“863”首席科学家, 国家杰出青年科学基金获得者 优秀教师/优秀教育工作者,
- 职称:-
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学科领域:
材料科学
- 研究兴趣:主要研究领域为材料微观组织与力学性能,涉及材料损伤断裂的约束效应,材料界面裂纹行为与界面屏蔽及材料形变/相变及其微尺度效应、先进结构金属材料与块体非晶合金的高性能化和材料介观性能表征及其尺度效应等课题。
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12
【期刊论文】Origin of 2-stage R-phase transformation in low-temperature aged Ni-rich Ti-Ni alloys
孙军, Yumei Zhoua, b, Jian Zhanga, Genlian Fana, Xiangdong Dinga, Jun Suna, Xiaobing Rena, c, *, Kazuhiro Otsukaa
Acta Materialia 53(2005)5365-5377,-0001,():
-1年11月30日
After aging at intermediate temperatures (400-500℃), Ni-rich Ti-Ni alloys undergo an abnormal 3-stage martensitic transformation behavior (1-stage R and 2-stage B190), which stems from a preferential Ti3Ni4 precipitation around grain boundary. On the other hand, if aged at low-temperatures (250-300℃), they undergo 2-stage R-phase transformation, but the origin of this strange phenomenon is unclear. In the present study, we made a systematic study of this phenomenon by considering the grain boundary effect and composition effect. We found that all single crystals undergo 1-stage R-phase transformation; in contrast, the transformation behavior of polycrystals is dependent on Ni content: low-Ni (50.6Ni, 51Ni) polycrystals undergo 2-stage R-phase transformation while high-Ni (52Ni) polycrystals undergo 1-stage R-phase transformation. The abnormal 2-stage R-phase transformation is attributed to a large-scale compositiona lheterogeneity in B2 matrix between grain boundary region and grain interior, due to the heterogeneity in precipitate density between the grain boundary and grain interior. But for high-Ni polycrystals, precipitates are essentially homogeneously distributed across the whole grain and this leads to normal 1-stage R-phase transformation. The different transformation behavior of low-Ni and high-Ni polycrystals stems from a competition between two opposing tendencies: (1) for preferential precipitation in the grain boundary; (2) for homogeneous precipitation across the whole grain with high-Ni content. The difference between the effect of intermediate-temperature and low-temperature aging lies in the difference in the ability for long-range diffusion of Ni (from the grain interior to the grain boundary), which results in whether or not Ti3Ni4 precipitates can form in the grain interior. Our results lead to a unified explanation for different transformation behaviors of both low-temperature and intermediate-temperature aged alloys in terms of the kinetics of precipitation in supersaturated polycrystals.
Ti-Ni, Martensitic transformation, Shape memory alloys, R-phase transformation, Multi-stage transformation
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孙军, G. Liua, G.J. Zhanga, X.D. Dinga, J. Suna, K.H. Chenb
/Materials Science and Engineering A344(2003)113-124,-0001,():
-1年11月30日
For the heat-treatable aluminum alloys containing plate or rod/needle-shaped precipitates, a previous model was modified to present quantitative relationships between the yield strengths of the alloys and the sizes, volume percentages of precipitates, related to aging temperature and aging time as well as alloy compositions, while the strengthening of the precipitates was coupled with the whole evolution process, i.e. nucleation, growth and coarsening, of the precipitates. It was found that the aging yield strengths have been well predicted by the model for a series of aged Al-Cu binary alloys, 6061 alloys and Al-Zn-Mg alloys. It was also experimentally proved that the model was suitable to evaluate the aging strengthening of the precipitates for an Al-Cu-Mg alloy and an Al-Mg /Si alloy. Furthermore, a detailed discussion has been made to the variation of aspect ratio of precipitates, relative to its strengthening response, with aging parameters and alloy compositions.
Aluminum alloys, Aging, Plate/, disc-or rod/, needle-shaped precipitates, Yield strength modeling, Aspect ratio
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【期刊论文】Microstructural evolution of previously deformed ZA27 alloy during partial remelting
孙军, T.J. Chena, b, *, Y. Haob, J. Suna
Materials Science and Engineering A337(2002)73-81,-0001,():
-1年11月30日
The microstructural evolution process of previously deformed ZA27 alloy during partial remelting was studied. After being compressed by a ratio of 20% in length at 250℃, the microstructure of ZA27 alloy changed from developed dendrites to coarsened short dendrites and near-equiaxed grains, then in turn to united pieces, big lumps, small pieces, polygon particulates, and finally to spherical grains that would grow and agglomerate and become larger in size and irregular in shape during following partial remelting at semi-solid temperature of 460℃. The structure evolution resulted from the eutectics first melted between boundaries of the primary grains and then penetrated into polygon boundaries that formed due to recrystallization, resulting in the separation of the primary grains into small polygon grains, followed by spheroidizing. This process was mainly discussed through analyzing the phase transformations occurred during partial remelting.
Semi-solid forming, Previously deformed ZA27 alloy, Microstructural evolution, Phase transformation, Partial remelting
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【期刊论文】Formation of Zr-based bulk metallic glasses from low purity materials by scandium addition
孙军, F. Jianga, b, Z.J. Wanga, Z.B. Zhanga, J. Suna, *
Scripta Materialia 53(2005)487-491,-0001,():
-1年11月30日
Zr55Al10Cu30Ni5 bulk metallic glass (BMG) is formed by using low purity sponge zirconium, instead of high purity zirconium, and other high purity raw materials with a small amount of scandium addition. The results show that glass forming ability and thermal stability of the Zr55Al10Cu30Ni5 alloy are improved with scandium addition. Compressive fracture strength is similar to that of BMG alloy produced with high purity raw materials. However, plasticity of BMGs with sponge zirconium and scandium addition deteriorates.
Bulk metallic glass, Low purity, Scandium addition, Thermal stability, Glass forming ability
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【期刊论文】Fatigue crack propagation normal to a plasticity mismatched bimaterial interface
孙军, F. Jiang, Z.L. Deng, K. Zhao, J. Sun*
Materials Science and Engineering A356(2003)258-266,-0001,():
-1年11月30日
Plasticity mismatched bimaterial specimens were made by explosive cladding with stainless steel and mild steel. Fatigue crack propagation normal to a bimetallic interface was experimentally investigated under a four-point bending condition. The results showed that material plasticity mismatch either promoted the crack growth as crack advanced to the interface from higher strength material side or retarded it as crack grew to the interface from lower strength material side. However, the cracks are always subjected to the interface shielding because of the interaction of the interface with the crack tip plastic zone for both cases above. For the present four-point bending specimens, the cracks can penetrate the next layer as the crack approaches the interface from either the higher or the lower yield strength side as long as the load levels are high enough. The effects of specimen geometry and dimensions on the fatigue crack deflection near to the interface are also discussed.
Bimetallic laminate, Plasticity mismatch, Fatigue crack growth
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孙军, Gang Liua, b, *, Jun Suna, Ce-Wen Nanb, Kang-Hua Chenc
Acta Materialia 53(2005)3459-3468,-0001,():
-1年11月30日
Solution and quench treatments are very important for the heat-treatable aluminum alloys because any change in these treatments will induce a trade-off in volume fraction between the constituents and precipitates and so will cause a change in the mechanical properties. In this paper, three types of solution+quench treatments were applied to two kinds of aluminum alloys, i.e., the Al-Cu-Mg alloy that contains disc/plate-shaped precipitates and the Al-Mg-Si alloy that contains rod/needle-shaped precipitates, to change the relative content between the constituents and the precipitates and to develop different coupling of the constituent and precipitates. The specimen treated with an enhanced solution or a stepped solution is found to exhibit a significant increase in yield strength, ductility, and fracture toughness. A multiscale model is presented to quantitatively estimate the coupled influence of the constituents and precipitates on the mechanical properties by combining with a strengthening model. The experimentally observed non-monotonic dependence of ductility on the trade-off in volume fraction between the constituents and precipitates is reasonably explained by using this multiscale model. In addition, the influence of stress triaxiality level on the ductility and fracture toughness is also calculated. All the calculations are in quite good agreement with the experimental results.
Aluminum alloys, Toughness, Ductility, Precipitation, Modeling
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孙军, Lin He*, Jun Sun
Scripta Materialia 54(2006)1081-1085,-0001,():
-1年11月30日
Zr52. 5Cu17.9 Ni14.6 Al10Ti5 bulk metallic glass prepared using sponge zirconium was microalloyed with 0.1 at.%B+0.2 at.%-Si+0.1 at.%Pb. The effect of microalloying on the glass-forming ability and thermal stability of the alloy is studied. The crystallization kinetic parameters are determined by means of a Kissinger plot. The interrelation between these parameters is discussed.
Metallic glasses, Glass-forming ability, Thermal stability, Crystallization kinetics
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35浏览
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【期刊论文】Ductile-brittle transition of pure Al-interlayer sandwiched by high strength Al alloy
孙军, L.H. Han, L. Li, J. Sun∗
Materials Science and Engineering A 403(2005)165-173,-0001,():
-1年11月30日
Four point bending test (FPB) was conducted to investigate the unusual ductile–brittle transition (DBT) of pure Al sheet with decreasing thickness, sandwiched by 2024 alloy through explosive cladding. The results show that, with the decrease in thickness of Al-interlayer restricted by parallel interfaces, obvious differences appear for the measured load-displacement curves, and fracture toughness characterized by critical J integral drops down remarkably. Correspondingly, brittle cleavage patterns, mainly belong to {100} besides a very few {1 1 0}, were observed on the fracture surfaces and increase gradually in the fraction as decreasing in the thickness of Al-interlayer. A finite element simulation showed that the crack-tip plastic zone spreads rapidly in the Al sheet and advances along the ligament confined by the two interfaces. With either decreased thickness or increased load, the stress triaxiality and maximum principal tensile stress ahead of crack-tip continue to increase, which make the materials become more brittle.
Pure Al sheet, Interface constraint, Ductile to brittle transition
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孙军, L.H. Han , L. Li, J. Sun*
Scripta Materialia 52(2005)1157-1162,-0001,():
-1年11月30日
The ductile-brittle transition of pure Al sheet, sandwiched by 2024 Al alloy through explosive cladding, was investigated at decreasing thicknesses through experimental and numerical methods. The results showed that this transition resulted from confined plastic deformation and consequent high triaxial tensile stress in the Al interlayer.
Multilayers, Aluminium, Ductile to brittle transition
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【期刊论文】Diffusive healing of intergranular fatigue microcracks in iron during annealing
孙军, H.L. Zhang, J. Sun∗
Materials Science and Engineering A 382(2004)171-180,-0001,():
-1年11月30日
Micron-sized internal cracks were introduced into pure iron via plastic-strain-controlled low cycle fatigue (LCF) loadings. The cracks on grain boundaries were found to have a regular shape of penny-like. The length of the cracks is less than 30m, and the thickness less than 3m. The aspect ratio of diameter-to-thickness is within a range of 5-45. The as-fatigued specimens were annealed for 7h in vacuum at 1173K. Scanning electron microscopy (SEM) observations show that the intergranular microcrack first changes as an unduloid-like shape at 2h of annealing time, then evolves into an array of "circular voids" at 5h, with some isolated voids scarcely observed at 7h. Finite element method (FEM) simulations predict that the intergranular penny-shaped microcrack would evolve into a spherical void when its aspect ratio is less than 19.5, and the evolution time is also quantitatively given. The shrinkage time of the spherical voids evolved from the parent microcrack is predicted by a modified Speight-Beere model. The shrinkage rate of the intergranular spherical voids is faster not only than that of a single intergranular spherical void, but also than that of the intragranular spherical voids.
Fatigue crack, Morphological evolution, Spherical void, Diffusion, Iron
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