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, ...

No abstract

No abstract

Coatings of hydroxyapatite (HA) on the porous-surfaced Ti compact have been conducted by electrostatic spray deposition (EDS). The precursor solution for the HA coating by ESD was prepared by mixing nano-scaled HA powder with ethyl alcohol. As-deposited HA films on the substrate were heat-treated (400 ~ 900 °C) and their physical characteristics were investigated by Scanning Electronic Microscopy (SEM), X-ray Diffractometer (XRD), and X-ray Photoelectronic Spectroscopy (XPS). As-deposited HA films were consisted of HA particles which were uniformly distributed on the Ti substrate, showing a porous structure. By heat treatment, HA particles were agglomerated each other and melted to form a highly dense and homogeneous coating layer consisted of equiaxed nano-scaled grains. HA coatings on the porous-surfaced Ti compact consisted of highly crystalline apatite phase with the Ca/P ratio of about 1.67 were successfully obtained by using ESD.

No abstract