刘永长
固态相变、非平衡凝固过程组织控制原理和新型功能结构材料制备
个性化签名
- 姓名:刘永长
- 目前身份:
- 担任导师情况:
- 学位:
-
学术头衔:
博士生导师, 教育部“新世纪优秀人才支持计划”入选者
- 职称:-
-
学科领域:
材料科学
- 研究兴趣:固态相变、非平衡凝固过程组织控制原理和新型功能结构材料制备
天津大学形状记忆材料教育部工程中心主任。1971年10月出生于湖南省新化县。1990年进入西北工业大学学习;1994年、1997年和2000年先后在该校获工学学士、硕士和博士学位;2000年9月至2003年2月在德国科学院金属研究所从事博士后工作;2003年2月加盟天津大学材料科学与工程学院并破格晋升教授,9月被聘为博士生导师;同年4月至8月再次访问德国科学院金属研究所,并创建了长期稳定的科研协作关系;2004年6月至9月、2005年7月至9月和2006年7月至9月为德国科学院金属所客座教授;2005年12月曾在韩国科学技术研究院短期访问;2005年度入选教育部“新世纪优秀人才支持计划”。
研究领域为固态相变、非平衡凝固过程组织控制原理和新型功能结构材料制备,现为美国ASM Materials Properties database committee执委、中国金属学会会员、天津市金属学会常务理事、天津市理化检验学会理事和天津市热处理学会理事。至今已出版专著1部、论文集1本,发表论文100余篇,其中SCI索引51篇,引用107次;EI索引55篇;并获1999年度陕西省新长征突击手、2002年度全国优秀博士学位论文奖、2002年度中国高校科技二等奖、2004年度陕西省科技二等奖和陕西省高校科技一等奖、2005年度天津五四青年奖章、陕西省高校科技二等奖、2006年度霍英东教育基金会高等院校青年教师研究类一等奖和天津青年科技奖等奖励和荣誉。
-
主页访问
2494
-
关注数
0
-
成果阅读
646
-
成果数
10
【期刊论文】Coupled growth behavior in the rapidly solidified Ti-Al peritectic alloys
刘永长, Y.C. Liua, *, G.C. Yanga, X.F. Guoa, b, J. Huangb, Y.H. Zhoua
[10] Liu YC, Sommer F, Mittemeijer EJ. 2002; submitted for publication.,-0001,():
-1年11月30日
Laser melting technology, an ultra-high-temperature gradient direction solidification process, has been adopted on near equal atomic percent Ti-Al peritectic alloys with an effort to achieve the two-phase coupled growth structure. Both the alloy composition range and its local solidification parameters were determined by means of mathematical calculation of local solidification parameters in the melt pool. X-ray, SEM, TEM and optical microscopy techniques were carried out to investigate the microstructure and identify the phase composition. The two-phase (a and r) coupled growth morphology under conditions of high growth velocity and high-temperature gradient was first detected in the laser resolidified Ti-Al peritectic alloys. The aluminum composition range appearing in the coupled growth of a and g phases, lies in Ti-(51.0-54.0) at% Al, a little shift towards the left direction of the hypoperitectic plateau. Microstructural analysis showed that the coupled growth morphology changed from regular lamellar, irregular blocks and equiaxed structures in sequence, with the temperature gradient decreasing during growth. Energy spectrum analysis results showed that not only the solute diffusion but also the dissolution of phase g played an important role in the coupled structure evolution. Rapid eutectic growth KT model (Kurz, Trivedi, Metall Trans. A 22 (1991) 3051) could be used effectively to predict the characteristic lamellar spacing of two-phase coupled structures in Ti-Al peritectic alloys. The transformation from a peritectic, L+a→r, to metastable eutectic reaction, L→a+r, of near equal atomic percent Ti-Al peritectic alloys, induced the formation of two-phase coupled growth morphologies.
Rapid solidification, Coupled growth, Peritectic reaction, Phase selection, Ti-Al alloy
-
25浏览
-
0点赞
-
0收藏
-
0分享
-
210下载
-
0评论
-
引用
【期刊论文】High-velocity banding structure in the laser-resolidified hypoperitectic Ti47Al53 alloy
刘永长, Yongchang Liua, b, *, Gencang Yanga, Yaohe Zhoub
[9] Kempen ATW, Sommer F, Mittemeijer EJ. Acta Mater 2002; 50: 3545.,-0001,():
-1年11月30日
Stability analysis of a growing solid/liquid interface is the fundamental concept of modern solidification theory. Here, serial laser rapid solidification experiments were performed on a hypoperitectic Ti47Al53 alloy to explore the dendritic growth behavior near the limit of high-velocity absolute stability. SEM and TEM techniques were carried out to investigate the microstructure and identify the phase composition. By adopting an improved sampling method of TEM, the growth morphology evolution of the laser-resolidified layer was observed directly and high-velocity banding structure was firstly detected in Ti-Al peritectic alloys. The high-velocity banding structures are parallel to the solid/liquid interface (normal to the growth direction) and made of the oscillation structures grown alternatively in modes of cell and plane morphologies. In light bands with cellular growth mode, all dislocation assembles are parallel to the growth direction and forms the cell boundaries, while all dislocation distributes randomly in dark bands. The determined growth velocity range for the appearance of high-velocity banding structures is about 0.5B1.1ms 1 according to the rapid solidification experiments, and the origin of the banding agrees well with the prediction of the CGZK phenomenological model (Acta Metal. Mater. 40 (1992) 983).
A1., Dendrites, A1., Directional solidification, A1., Interfaces, A1., Morphological stability, B1., Alloys
-
77浏览
-
0点赞
-
0收藏
-
0分享
-
124下载
-
0评论
-
引用
【期刊论文】Abnormal austenite-ferrite transformation behaviour in substitutional Fe-based alloys
刘永长, Y.C. Liu, F. Sommer ∗, E.J. Mittemeijer
[8] Honeycombe RWK, Bhadeshia HKDH. Steels microstructure and properties. London: Edward Arnold, 1995.,-0001,():
-1年11月30日
The r→a phase transformation behaviours of Fe-Co and Fe-Mn alloys were systematically investigated by dilatometry and Differential Thermal Analysis (DTA). Two kinds of transformation kinetics, called normal and abnormal, were recognized for the first time and classified according to the variation of the ferrite formation rate. These transformation characteristics were observed for both isothermally and isochronally conducted annealing experiments. A transition, from abnormal to normal transformation kinetics, occurs for Fe-1.79at.%Co when successive heat treatment cycles are executed, which contrasts with Fe-2.26at.%Mn for which only normal transformation kinetics occurs after each of all successive heat treatment cycles. A possible mechanism for the appearance of abnormal transformation kinetics is given, which is based on the austenite grain size. Light microscopical analysis indicates a repeated nucleation of ferrite in front of the migrating g/a interface.
Austenite-ferrite phase transformation, Substitutional Fe-based alloys, Annealing, Dilatometry, DTA
-
54浏览
-
0点赞
-
0收藏
-
0分享
-
196下载
-
0评论
-
引用
【期刊论文】Microstructural evolution of rapidly solidified Ti-Al peritectic alloy
刘永长, Yongchang Liua, *, Feng Lana, Gencang Yangb, Yaohe Zhoub
[7] Li CM, Sommer F, Mittemeijer EJ. Z Metall 2001; 92: 326.,-0001,():
-1年11月30日
Primary cellular/dendritic spacing of the solidified structures plays an important role on the microstructure control under rapid solidification conditions. In order to clarify the phase evolution and growth mechanism of peritectic reaction, here laser resolidification experiments, with different growth velocity, have been performed on Ti–Al peritectic alloys. By taking both the transverse and longitudinal sections of the directional growth cells/dendrites in the laser traces, the primary phase formation and average primary cellular/dendritic spacing, as well as the corresponding solidification velocity are quantitatively determined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). With the solidification velocity increasing, the separating primary phase evolves from single-phase a, two-phase (a+g), g, and the corresponding primary cellular/dendritic spacing decreases gradually. All experimental observations of primary spacing evolution, in all single phase regions, agree well with that predicted by rapid dendritic growth model.
A1., Dendrites, A1., Directional Solidification, A1., Morphological stability, B1., Titanium compounds
-
42浏览
-
0点赞
-
0收藏
-
0分享
-
318下载
-
0评论
-
引用
【期刊论文】Abnormal austenite-ferrite transformation behaviour of pure iron
刘永长, Y. C. LIUy, F. SOMMERz and E. J. MITTEMEIJER
[6] Wilson EA. Metal Science 1984; 18: 471.,-0001,():
-1年11月30日
The isochronal and isothermal austenite (r)→ferrite (a) transformation of pure iron was measured by high-resolution dilatometry and differential thermal analysis. Both abnormal and normal transformation kinetics were recognized for the first time in pure iron according to the variation in the ferrite formation rate. The occurrence of the type of r→a transformation strongly depends on the grain size; the transformation type changes from abnormal to normal with decreasing grain size. The abnormal transformation process involves the occurrence of additional peaks in the transformation rate for the first stage of the transformation. A phase transformation model, involving repeated nucleation (autocatalytic nucleation), interface-controlled continuous growth and incorporating correction for impingement, has been employed successfully to describe the observed kinetics of the abnormal transformation.
-
78浏览
-
0点赞
-
0收藏
-
0分享
-
355下载
-
0评论
-
引用
【期刊论文】Microstructural control of metastable phase in rapidly solidified Ti-45Al-2Cr-2Nb alloy
刘永长, Y. C. LIU, Q. Z. SHI, G. C. YANG, Y. H. ZHOU
[5] der Ven A, Delaey L. Progress in Materials Science 1996; 40: 181.,-0001,():
-1年11月30日
-
47浏览
-
0点赞
-
0收藏
-
0分享
-
90下载
-
0评论
-
引用
刘永长, Y.C. Liu, F. Sommer∗, E.J. Mittemeijer
[4] Zhao JC, Notis MR. Mater Sci & Eng R 1995; 15: 135.,-0001,():
-1年11月30日
Differential dilatometry is a technique for precise measurements of the thermal dilatation of materials. A procedure has been presented for calibration of the differential dilatometric measurement signal (length change as a function of temperature), both upon heating and cooling. Measurements of the thermal expansion of pure iron up to 1223Khave been performed by a high-resolution differential dilatometer (resolution in length measurement of about 10 nm). The magnetic contribution to the length change has been introduced for the first time in an analytic expression for the linear thermal expansion coefficient of ferritic iron. The dilatation signal has been calibrated on heating and cooling using a sapphire specimen for which recommended dilatation data are available. The ferro- to paramagnetic transition (characterized by the Curie point temperature) has been adopted successfully to calibrate the temperature in dilatometric measurements upon heating and cooling.
Differential dilatometer, Calibration, Heating, Cooling, Linear thermal expansion, Curie temperature
-
79浏览
-
0点赞
-
0收藏
-
0分享
-
328下载
-
0评论
-
引用
刘永长, Y.C. Liu , F. Sommer*, E.J. Mittemeijer
[3] Huang W, Hillert M. Metall & Mater Trans A 1996; 27: 480.,-0001,():
-1年11月30日
The kinetics of the recently discovered abnormal austenite (c)-ferrite (a) transformation of substitutional Fe-Co and Fe-Mn alloys were measured by dilatometry and compared with the, also measured, corresponding normal transformation behaviour. A phase transformation model, involving site saturation, interface-controlled continuous growth and incorporating an impingement correction, has been employed to extract the migration velocity of the c/a interface. It was found that the normal transformation process could be well described assuming a constant nucleus density and interface migration velocity. The thus assessed misfitaccommodation, deformation Gibbs energy is of the same order of magnitude as the chemical Gibbs energy change driving the transformation. A large austenite grain size was shown to be the precondition for the occurrence of abnormal kinetics. The abnormal transformation process involves the occurrence of additional peaks in the transformation rate for the first stage of the transformation. An autocatalytic type of nucleation was successfully incorporated in the above model to describe the occurrence of the repeated nucleation during the abnormal transformation.
Pase transformation kinetics, Interface migration, Iron alloys, Autocatalytic nucleation, Thermodynamics
-
76浏览
-
0点赞
-
0收藏
-
0分享
-
102下载
-
0评论
-
引用
【期刊论文】Preparation of metastable phase materials: nucleation and growth kinetics considerations
刘永长, Yongchang Liua, *, Qingzhi Shia, Gencang Yangb, Yaohe Zhoub
[2] Reed RC, Bhadeshia HKDH. Mater Sci & Tech 1992; 8: 421.,-0001,():
-1年11月30日
Separation of metastable phase, involving the melt undercooling before the onset of nucleation and the growth (solidification) velocity of competing phases, lies at the core of Rapid Solidification Processing. To clarify the dependences of metastable phase formation on the initial undercooling degree and solidification rate in the rapidly solidified alloys, three alloys, Ti50Al50, Ti47Al53 and Ti44Al56, were prepared and investigated by undercooling and laser resolidification experiments. The corresponding undercooling window and solidification velocity range for different competing phases were determined from the rapidly solidified samples by precise microstructural analysis. In Ti50Al50 and Ti47Al53 alloys, the primary phase changes from h to a and g phase with increasing undercooling, and it evolves from a to g phase with increasing solidification velocity. However, phase g acts as the primary phase in the achievable undercooling and solidification velocity ranges of Ti44Al56 alloy. Two surface treatment methods, in view of nucleation and growth kinetics, were proposed to obtain metastable phase structures.
Intermetallic compounds, Surfaces, Crystal growth, Microstructure
-
59浏览
-
0点赞
-
0收藏
-
0分享
-
125下载
-
0评论
-
引用
刘永长, Y.C. Liu a, b, F. Sommer a, *, E.J. Mittemeijer a
[1] Lange WF, Enomoto M, Aaronson HI. Metall & Mater Trans A 1988; 19: 427.,-0001,():
-1年11月30日
The kinetics of the isochronal austenite (r)→ferrite (a) transformation of ultralow-carbon Fe-C alloy were investigated for cooling rates in the range 5-20 Kmin-1 by high-resolution dilatometry and differential thermal analysis. The starting temperature of the transformation decreases with increasing cooling rate. The transformation kinetics, as characterized by the formation rate of product (ferrite) phase, varies greatly with cooling rate. At a small cooling rate of 5 K min 1 the transformation rate curve has a multiple-peaked nature. Upon increasing the cooling rate from 5 to 20 K min 1, the first transformation rate maxima vanish gradually, and finally so-called normal transformation behavior, characterized by the (remaining) one maximum in the transformation rate curve, is observed. On the basis of microstructural analysis and thermodynamic and kinetic reasoning, it is shown that the first transformation rate maxima pertain to diffusion-controlled ferrite growth, whereas the later single, main transformation rate maximum is due to interface-controlled, massive transformation.
Austenite-ferrite transformation, Interstitial Fe-based alloys, Growth, Annealing, Dilatometer
-
109浏览
-
0点赞
-
0收藏
-
0分享
-
237下载
-
0评论
-
引用