Deformation-induced martensitic transformation in Cu–Zr–(Al,Ti) bulk metallic glass composites

Abstract

Plastic deformation of Cu-Zr-(Al,Ti) bulk metallic glass (BMG) composites induces a martensitic phase transformation from the B2 to the B19 0 CuZr phase. Addition of Ti to binary Cu-Zr increases the temperature above which the B2 CuZr phase becomes stable. This affects the phase formation upon quenching in Cu-Zr-Ti BMG composites. The deformation-induced martensitic transformation is believed to cause the strong work hardening and to contribute to the large compressive deformability with plastic strains up to 15%. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Binary Cu-Zr alloys have been known since the early 1980s and much research has been done on them [1][2][3][4][5][6][7][8]. They exhibit two interesting and unique characteristics: (i) even binary Cu-Zr melts solidify into bulk metallic glasses (BMGs) [4,5,8]; and (ii) the equiatomic CuZr intermetallic compound can undergo a martensitic transformation from a cubic primitive B2 to a monoclinic B19 0 phase similarly to the well-known transformation that occurs in the NiTi system [9][10][11]. As the transformation from austenite (B2) to martensite (B19 0 ) is reversible, a shape memory effect (SME) arises in the CuZr alloy [10,12]. The addition of third elements such as Ti or Al significantly improves the glass-forming ability [13][14][15] and allows casting of larger specimens of fully glassy material. Alloys on the Cu-rich side, e.g. Cu 64 Zr 36 [3][4][5], show poor plasticity, whereas Cu 50 Zr 50 or compositions in its vicinity show an appreciable plastic strain [4,8]. Once the alloy composition has been optimized the plastic strain can be increased by the introduction of second-phase particles [16]. Structural heterogeneities such as nano-and micrometersized crystals have been found to be beneficial for the enhancement of macroscopic deformability [17][18][19].Thus, the combination of both the structural heterogeneities and the ability to undergo a diffusionless and hence very fast shear transformation promises interesting mechanical properties in Cu-Zr-based alloys. It is important to note here that the B2 CuZr phase can only be obtained from the glassy state by proper adjustment of the cooling rate. Annealing treatments of glassy alloys lead to the formation of metastable phases or the precipitation of the equilibrium phases, depending on the composition [20].To the best of the authors' knowledge only the formation of martensite in Cu-Zr-based partially glassy alloys upon quenching has been reported so far [19,[21][22][23][24]. This is due to the stresses in the material that occur during the solidification process that usually trigger martensite formation. In this paper we report for the first time the B2 to B19 0 transformation after plastically deforming partially crystalline Cu-Zr-Ti and Cu-Zr-Al bulk specimens. Furthermore, we investigate the effect of the addition of Ti and Al to the Cu-Zr system on the martensite transformation characteristics.Cu 50 Zr 50Àx Ti x (0 6 x 6 10) and (Cu 0.5 Zr 0.5 ) 100Àx Al x (x = 5, 6, ...

Phase formation, glass forming ability, mechanical and thermal properties of Cu50Zr50−x Al x (0⩽x⩽11.0) glass forming alloys

“…Thus the composition with best GFA locates at Cu 50 Zr 47 Al 3 among Cu 50 Zr 50−x Al x (0x11.0) alloys. On the other hand, B19 ' CuZr phase is more stable than B2 CuZr phase [5,34]. The mixing enthalpy is larger for Al-Zr than for Cu-Zr, indicating that the bonding is stronger for the former than for the latter.…”

“…It results in partial even full collapse of B2 CuZr phase by Al addition. In addition, there exists a transformation: CuZr → Cu 10 Zr 7 + CuZr 2 [5]. Thus Cu 10 Zr 7 and CuZr 2 phases can simultaneously form when Al6.0, as shown in Fig.…”

“…Kuo et al [13] investigated the effect of V on the phase formation and plasticity in Cu 47. 5 Zr 47.5 Al 5 glassy alloy and found that V minor addition improved the plasticity by doubling the fracture strain to 9.4% in (Cu 47.5 Zr 47.5 Al 5 ) 99 V 1 due to the formation of B2-CuZr precipitates. Recently, Cai et al [14] found that the substitution of Ti by Ni significantly influences the GFA, mechanical, electrical and thermal properties of Cu 50 Zr 40 Ti 10 glassy alloy.…”

“…Cu-based bulk metallic glasses (BMGs) have been extensively investigated due to their interestingly properties including work hardening [1], martensitic transformation [2][3][4][5], magnetism [6], catalytic activity [7,8], cryogenic temperature plasticity [9] and room-temperature plasticity [10][11][12][13][14], which enable their applications as structural and functional materials.…”

Combinatorial Influence of Bimodal Size of B2 TiCu Compounds on Plasticity of Ti-Cu-Ni-Zr-Sn-Si Bulk Metallic Glass Composites

“…[22][23][24] Regarding enhancement of the plasticity of the BMG composites, more recently, there have been some interesting reports on the transformation-mediated ductility in CuZr-based BMGs and composites. [25][26][27] From these reports, it is worth noting that both the dynamically crystallized and pre-existing B2 CuZr compound transform into martensitic B19' phase during deformation. This implies that the martensitic phase transformation from B2 into B19' effectively releases the local stress concentration around the shear transformation zone (STZ).…”