1 INTRODUCTIONNi based superalloys are presently used as gasturbine components in power plants and in aircraftengines<1 3>. Since 1970s, Al has been added toNi Cr alloy for producing the hard elastic alloysused as wear resistant components in instru ments<4>. This is an important development in Ni Cr alloy. With the increasing demands for the al loys with high hardness and toughness, Ni Cr Alalloys are designed to meet the requirement. Dueto the addition of Ce element, forgeable tempera ture was decreased, and grains were refined, andthe inclusions were removed<5>.LIU<6, 7> have preformed extensive research onthe behavior of Ni Cr Al hard elastic alloy. Theirresults indicated that a number of Cr (
α) richphase were found aroundγ′phase with tiny grainsand dispersed distribution when aged at 550
℃ for5 h. But Cr (α) rich phase was not observed inthis work. Ni Cr Al alloys were usually producedby vacuum melting and cast process. But reports a bout Ni Cr Al alloy prepared by electron beam physical vapor deposition(EB PVD), which is of ten used to produce the thermal barrier coatings(TBCs)<8 11>, are few.Electron beam physical vapor deposition (EB PVD) technology is a potential technique for pro ducing near theoretical density and oxide free con densates<12 14>. Due to its high deposition rate, easycontrol for chemical constitution and pollution freeto environment, Ni Cr Al alloy with 0. 5 mm inthickness was deposited by EB PVD process. Inthis work, microstructure and mechanical proper ties of an EB PVD formed Ni Cr Al alloy are stud ied.2 EXPERIMENTALNi Cr Al alloy was prepared by EB PVD. Thechemical composition of Ni Cr Al ingots is Ni 22Cr 5Al 0. 6Y ( mass fraction, %). The processof the preparation of deposited alloy by EB PVD isshown in Fig.1.Before the alloy was fabricated, the resistanceadhesive layer with about 15μm in thicknessFig.1 Schematic diagram ofEB PVD process of Ni Cr Al alloyshould be deposited to prevent bonding betweensubstrate and condensate. The Ni Cr Al ingots of100 mm in diameter and 200 mm in length werefilled in a water cooled crucible. A stainless steeldisk substrate of 800 mm in diameter and 20 mm inthickness was mounted on the vertical axis. Thesubstrate was heated by electron beam and thetemperature was kept at 900 ℃. The degree ofvacuum was 5 × 10-4 Pa during evaporation.Thickness of the alloy could be controlled by adjus ting the beam current, the upward speed of the in gots and rotation speed of the substrate. The rota tion speed of the substrate was 36 r/min. The dep osition rate of the alloy was 1.8 μm/min. In thiswork, the Ni Cr Al alloy with 0.5 mm in thicknesswas prepared by EB PVD, and aged at 760 ℃ for16 and 120 h.The SEM samples of the tested alloy wereground to 13μm and mechanically polished, thenetched with a solution of HCl, HNO3, HF andH2O. The TEM samples were mechanicallythinned down to 50 100 μm in thickness, andelectropolised with a solution of 7% perchloric acidand ethanol at -30 -20 ℃ by a double jet elec tropoliser. Tensile tests at room temperature werecarried out by Instron 5500.3 RESULTS AND DISCUSSION3.1 Microstructures of tested alloyMicrostructures in the deposited condition areshown in Fig.2. Based on the AFM and TEM ima ges given in Fig.2, grain size on the surface of va por deposited alloy is in the range of 70 255 nm,and average size is about 185 nm. However, aver age size of the alloy annealed at 760℃ for 16 h is a bout 4 μm(Fig. 3 (a)). Convergent beam diffrac tion shows that the as deposited alloy has singlephase and a laminated structure is observed in thecross section of as deposited alloy, as shown inFig.2(b). After annealing at 760 ℃ for 16 h, thelaminated structure dissolves and the individualgrain can be seen clearly. Schulz et al<15> EB PVD deposited a ceria stabilize
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