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Synthesis And Properties Of Ti-Zr-Ni-Cu-Be Bulk Amorphous Alloy

Posted on:2007-06-26Degree:MasterType:Thesis
Country:ChinaCandidate:J N MeiFull Text:PDF
GTID:2121360182979023Subject:Materials Processing Engineering
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Bulk amorphous alloys are of scientific interest in material science field due to their unique mechanical, physical and chemical properties associated with the long-range disorder and short-range order atomic structure. In this paper, we predicted the range in Ti-Zr-Ni ternary system in which bulk metallic glasses can be formed based on thermodynamics;further, we analyzed the glass forming ability of Ti-Zr-Ni-Cu-Be system combining phase diagram analysis and A. Inoue's "three empirical rules". And then, glass forming ability, thermal stability, crystallization behavior, mechanical properties and compressive fracture mechanism of Ti40Zr25Ni8Cu9Be18 bulk amorphous alloy together with the effects of Nb and Ta addition on the microstructure and properties of it were all researched in detail.According to the multi-chemical short-range order domain (MCSRO) model, the range of forming amorphous in Ti-Zr-Ni ternary system was identified to be Ti=0.3-0.5, Zr=0.3-0.5, Ni=0.1-0.25.Ti40Zr25Ni8Cu9Be18 bulk amorphous alloy could be fabricated by arc melting and suction casting method with the diameter of 3mm, whose glass transition temperature Tg and the onset crystallization temperature Txl were 599K and 653K, respectively. And its supercooled liquid region △Tx, reduced glass transition temperature Trg(Tg/T1) and y parameter value were 54K, 0.588 and 0.404, respectively. Ti40Zr25Ni8Cu9Be18 bulk amorphous alloy exhibited good mechanical properties, whose yield strength, compressive strength, plastic strain and elastic modulus were 1555MPa, 1760MPa, 4.4% and 78GPa, respectively. The fracture took place almost along the maximum shear plane, inclined by about 41° to the direction of the applied load. The fracture surface showed a well-developed shear dimples along the shear direction.Crystallization kinetics research indicated that the glass transition and crystallization behavior showed the typical characteristic of kinetics. The process ofcrystallization contained two steps of crystallization reactions corresponding to the precipitation of quasicrystalline phase in the amorphous matrix, the transition from quasicrystalline phase to Laves phase and direct precipitation of Laves phase in the remaining amorphous matrix, respectively. Additionally, the activation enthalpy of the glass relaxation E% was 201.78KJ/mol, and the effective activation energies of the phase transformation Ep\, EP2 were 213.04KJ/mol and 378.55 KJ/mol, respectively.The addition of Nb (<5%) prompted the precipitation of quasicrystalline phase;however, with the increasing of Nb content (>5%), CuTi phase was easy to form in the amorphous matrix. On the other hand, with the increasing of Nb content from 0 to 10%, the microstructure evolution of as-cast Ti-Zr-Ni-Cu-Be-Nb alloy in diameter 3mm was as followed: amorphous (NbO)—?amorphous + quasicrystalline (Nb3-5)—>amorphous (Nb8)—?amorphous+CuTi nanocrystalline (NblO). When the Nb content was 8%, the alloy showed relative good mechanical properties, whose compressive strength and plastic strain were 1969MPa and 1.93%, respectively.The addition of Ta (0-8%) prompted the precipitation of quasicrystalline phase, CuTi2 phase and bcc P-Ti solid solution. With the increasing of Ta content from 0 to 8%, the microstructure evolution of as-cast Ti-Zr-Ni-Cu-Be-Ta alloy in diameter 3mm was as followed: amorphous (TaO-3)—^amorphous + quasicrystalline + CuTi2 (Ta5)—?amorphous + quasicrystalline + CuTi2 + dentritic P-Ti (Ta8). When the Ta content is 5%, the compressive fracture strength is up to 1856MPa due to the nano-quasicrystalline precipitated in the amorphous matrix. With the further increasing of Ta content (5-8%), although the ductile dentritic P-Ti solid solution was precipitated in the amorphous matrix, the strength and plasticity decreased to a great extent resulted from the quasicrystalline phase and CuTi2 phase growing up.
Keywords/Search Tags:titanium alloy, bulk amorphous alloy, glass forming ability, thermal stability, crystallization behavior, microstructure, properties
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