材料成型及控制工程外文文獻(xiàn)翻譯（英文）

1、Short CommunicationThe effects of heat treatment on the microstructure and mechanical property of laser melting deposition c-TiAl intermetallic alloysH.P. Qu a,*, P. Li a, S.Q. Zhang a, A. Li a, H.M. Wang a,ba Laboratory

2、 of Laser Materials Processing and Manufacturing, Beijing University of Aeronautics and Astronautics, 37 XueYuan Road, Beijing 100191, PR China b Key Laboratory of Aerospace Materials, Ministry of Education of China, Bei

3、jing University of Aeronautics and Astronautics, 37 XueYuan Road, Beijing 100191, PR Chinaa r t i c l e i n f oArticle history:Received 23 May 2009Accepted 21 October 2009Available online 25 October 2009a b s t r a c tTi

4、–47Al–2.5V–1Cr and Ti–40Al–2Cr (at.%) intermetallic alloys was fabricated by the laser melting depo-sition (LMD) manufacturing process. The microstructure was characterized by optical microscopy (OM),scanning electron mi

5、croscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction(XRD). The room-temperature (RT) tensile properties and Vickers hardness of the as-deposited andheat-treated specimens were evaluated on longitu

6、dinal directions. Results shows that full densitycolumnar grain with fully lamellar (FL) microstructure consisted of c-TiAl and a2-Ti3Al was formed inthe as-deposited c-TiAl samples. The room-temperature tensile strength

7、 of the as-deposited Ti–47Al–2.5V–1Cr alloy is up to approximately 650 MPa in the longitudinal direction and 600 MPa for theas-deposited Ti–40Al–2Cr alloy, while the tensile elongation is approximately 0.6% at most. Diff

8、erentmicrostructure types were obtained in the Ti–47Al–2.5V–1Cr and Ti–40Al–2Cr alloy after heat treatment.The stress–strain curve and the tensile fracture sub-surface indicate that the fracture manner of theas-deposited

9、 and heat-treated specimens was inter-granular manner.Crown Copyright ? 2009 Published by Elsevier Ltd. All rights reserved.1. Introductionc-TiAl intermetallic alloys have been continuously researched as the promising hi

10、gh temperature candidate structural materials due to its high melting point (>1450 ?C), low density (up to 4 g/cm3), high elastic modulus (160–180 GPa) and high creep strength (up to 900 ?C) [1–4]. One of the major li

11、mitations to their structural applications is lack of ductility at ambient temperature. These alloys are also difficult to be processed by conventional man- ufacturing routes such as forging, rolling and welding [5]. The

12、 disadvantage of the conventional casting technologies for TiAl components is its coarse as-cast microstructure that leads to the poor room-temperature mechanical properties. On the other hand, metallurgical defects such

13、 as porosity and shrinkage are inevitable during the conventional slow-cooling solidification process. The shape and the dimension of the products were also restricted by the serious thermal stress-induced casting cracki

14、ng defects due to its low ductility. Although fairly good components could be fabricated by conventional casting process, it is rela- tively too costly and time-consuming. Some other manufacturing and processing routes s

15、uch as spark plasma sintering (SPS) [6,7], semisolid forming from blended elemental powders [8], reactive foil metallurgy [9] and laser engineered net shaping (LENS) [10]have long been researched in order to fabricate hi

16、gh quality TiAl alloy components conveniently. Unfortunately, the nitrogen and oxygen contents are inevitably enhanced during those powder metallurgical processes, further deteriorating ductility of the TiAl alloys. Lase

17、r melting deposition (LMD) is a rapid solidification material additive layered manufacturing technology for building compo- nents from a computer-aided design (CAD) model [11]. During the LMD process, the motion of the h

18、igh power laser beam is con- trolled by CNC system, which was developed from the CAD model of a desired component. The metal powders were injected into the laser focal zone and continuously melt from a powders delivery n

19、ozzle. Successive layers are then stacked to produce the near- net shape components with full density and extremely fine rapidly solidified microstructure due to the high solidification cooling rate. Any complicated shap

20、es and the dimension of the near-net shape components could be conveniently produced by the LMD additive layered manufacturing manner from the CAD files. In the present study, Ti–47Al–2.5V–1Cr and Ti–40Al–2Cr (at.%) inte

21、rmetallic alloys was successfully fabricated by the la- ser melting deposition manufacturing process. Microstructure of the as-deposited and heat-treated specimen was investigated. Vickers hardness and room-temperature t

22、ensile property of the as-deposited specimens on the longitudinal direction was evalu- ated and the tensile fracture surface and sub-surface were characterized.0261-3069/$ - see front matter Crown Copyright ? 2009 Publis

23、hed by Elsevier Ltd. All rights reserved.doi:10.1016/j.matdes.2009.10.045* Corresponding author. Tel.: +86 10 82317102; fax: +86 10 82338131.E-mail address: quhuapeng0926@163.com (H.P. Qu).Materials and Design 31 (2010)

24、2201–2210Contents lists available at ScienceDirectMaterials and Designjournal homepage: www.elsevier.com/locate/matdespressure shielded the melt pool from oxidation and the oxygen content in the chamber is less than 100

25、ppm. The LMD processing parameters are: laser beam power 1500 W, beam diameter 5 mm, beam scanning speed 5 mm/s, single-layer deposition thickness 0.2–0.3 mm, powder delivery rate 4–5.5 g/min. In this work, Ti–47Al–2.5V–

26、Cr and Ti–40Al–2Cr powders with an oxygen content less than 0.1 (wt.%) was produced by vacuum non-contacting plasma melting argon atomization process. The as-cast Ti–6Al–2Zr–Mo–1V and Ti–47Al–2.5V–Cr alloy ingot was mech

27、anically processed to the shape of thin rob with the diameters of about 10 mm and then melted in a vacuum non-contracting plasma melting furnace through a specifically designed nozzle. Ultimately, the molten alloy in the

28、 nozzle was rapidly solidified under the high speed and purity Ar flow to the form of sphericalpowders. The particle size of the fine alloy powders ranges from 70 to 75 lm. On the other hand, the as-cast Ti–6Al–2Zr–Mo–1V

29、 in- got was hot rolled to thin wall-like specimen with the thickness of 8–10 mm as the substrate material (Table 1). The surface of the Ti– 6Al–2Zr–1Mo–1V substrate was pre-polished before laser melting deposition. The

30、as-deposited specimens were sealed in a quartz tube and heat treated in a muffle furnace. Metallographic specimens prepared by standard mechanical polishing method were etched in a mixed solution of 300 ml H2O, 100 ml HN

31、O3 and 100 ml HF. An OLYMPUS BX51M optical microscope, JEM-2100 TEM and a KYKY-2800 SEM fitted with Lea- gue-2000 EDX systems were used to characterize the microstruc- ture and to identify the chemical composition. The V

32、ickers hardness of the gradient zone was measured by using a HXZ-Fig. 3. Microstructure and the lamellar spacing of the as-deposited Ti–47Al–2.5V–1Cr (a, b) and Ti–40Al–2Cr alloy (c, d); the orientation relationship betw