Zr-based Bulk Metallic Glass Composites Research Articles

NANOSCALE DIMPLES AND PERIODIC CORRUGATIONS ON FRACTURE SURFACE OF Zr-BASED BULK METALLIC GLASS COMPOSITE

Nanoscale dimples and periodic corrugations are observed on the fracture surface of Zr-based bulk metallic glass composite (BMGC). The nanoscale periodic corrugations display a curved shape, which is different from that observed in previous works. In addition, the crystallization behavior of [Formula: see text][Formula: see text][Formula: see text][Formula: see text] BMG was investigated. The second crystallization event of Zr-Cu-Ni-Al BMG can be controlled by annealing or tuning cooling rate. The in situ Zr-based BMGC was prepared via lowering cooling rate. The Zr-based BMGC displays completely brittleness.

Microstructure and nanomechanical properties of Zr-based bulk metallic glass composites fabricated by laser rapid prototyping

In this study, Zr–Al–Ni–Cu bulk metallic glass composites (BMGCs) were successfully fabricated by laser rapid prototyping and systematically characterized using x-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the studied BMGCs exhibit periodical microstructure along the deposition direction. According to the microstructural characteristics and phase composition, three identified regions are identified, which are classified as the amorphous zone, NiZr2 nanocrystals + amorphous matrix zone and Cu10Zr7 dendrites + CuZr2 nanocrystals zone. The nanomechanical behaviors were investigated by nanoindentation and nanoscratch tests. The elastic modulus and nanoindentation hardness are in the following order: NiZr2 nanocrystals + amorphous matrix zone > Cu10Zr7 dendrites + CuZr2 nanocrystals zone > amorphous zone. This is mainly attributed to the structural relaxation and crystallization of BMG caused by the effect of heat treatment during the repeated processes of laser heating. Moreover, NiZr2 nanocrystals can effectively inhibit the movement of shear band in amorphous matrix, resulting in the enhancement of their strength and hardness.

Work-hardenable Zr-based bulk metallic glass composites reinforced with ex-situ TiNi fibers

A series of work-hardenable bulk metallic glass composites (BMGCs) reinforced with ex-situ continuous TiNi fibers was fabricated with pressure infiltration casting. The BMGCs exhibited a combination of simultaneously enhanced fracture strength, improved plasticity and strong work-hardening ability under compression. More strikingly, the newly developed BMGCs show ductility up to 0.8 ± 0.2% under tension. The ex-situ TiNi fibers not only effectively served as absorbers to prohibit the propagation of shear bands and promote the nucleation of multiple shear bands, but also incorporated the deformation-induced martensitic transformation, resulting in the observed strengthening/toughening. The fracture behavior analysis unveiled that the fracture upon compression is determined by the competition of the critical energy dissipation between shear banding and splitting, whilst the tensile fracture feature is associated with the stress field around the fibers. Additionally, it was revealed that the asymmetry between the tensile and compressive properties was due to the different axial and radial stresses applied on the TiNi fibers under these two loading conditions. Our study not only provides a methodology to develop novel high-performance BMGCs with a controllable microstructure in various alloy systems, but also sheds light on understanding deformation mechanisms and fracture behavior of BMGCs.

Properties of vacuum-laser-welded Ti-based bulk metallic glass and Zr-based bulk metallic glass composite

AbstractIn this work, Ti43.3Zr21.7Ni7.5Be27.5 (at.%) bulk metallic glass and Zr76.11Ti4.20Cu4.51Ni3.16Be1.49Nb10.53 (at.%) bulk metallic glass composite are used to butt-weld identical alloy specimens using a fiber laser beam under a vacuum. Thereafter, various tests are conducted on the welded specimens to evaluate the applicability of the laser welding process to bulk metallic glasses and bulk metallic glass composites. Crystallization is suppressed during the welding process as much as possible, and welded Ti-based bulk metallic glass and Zr-based bulk metallic glass composite exhibit their original properties although some crystalline phases are formed in the welding fusion zone in Ti-based bulk metallic glass. Therefore, laser welding under a vacuum is appraised as a feasible technology to join bulk metallic glasses and bulk metallic glass composites.

In-situ synthesis of Zr-based bulk metallic glass composites with periodic amorphous-crystalline microstructure for improved ductility via laser direct deposition

In this paper, design and synthesis of in-situ ZrCuNiAl bulk metallic glass composites (BMGC) from premixed metal powders were achieved using laser direct deposition (LDD). The temperature fields and heating/cooling rates in single-track BMGC were simulated through a validated LDD model, which provided insights for microstructure evolution. Through a proper selection of LDD parameters and precise control of premixed composition, a periodic amorphous-crystalline microstructure was obtained alternatively in the fusion zone (FZ) and heat affected zone (HAZ). In addition to HAZ, composite phase nature was also achieved in FZ where about 4.7 vol% crystals with a size of 100–1000 nm were uniformly formed in the amorphous matrix. Vickers microhardness revealed a higher hardness of 620 HV0.2 in FZ than 450 HV0.2 in HAZ. An optimized overlapping ratio of adjacent tracks at 58 vol% led to 89 vol% FZ in the bulk structure, which resulted in an overall macrohardness of 604 HV. Nanoindentation tests were performed to study the deformation behavior at the micron/sub-micron length scale. The depth-sensing indentation stress-strain data in FZ and HAZ were accurately predicted with an iterative numerical algorithm using finite-element modeling. A correction factor was proposed in this algorithm, which corrected the overestimation of experimental stress by minimizing the difference between experimental and numerical load-depth data. With the composite microstructure, an indentation strain of more than 13% was obtained in both zones.

Compressive mechanical properties and failure modes of Zr-based bulk metallic glass composites containing tungsten springs

A novel kind of Zr-based bulk metallic glass composites (BMGCs) reinforced with tailored volume fractions of tungsten springs were designed. The effect of tungsten springs on the compressive mechanical properties and failure modes of the BMGCs was investigated. As increasing the volume fraction of tungsten springs, the yield strength decreases slightly, however, both the fracture strength and plastic strain increase significantly. The continuity and special geometry shape of the tungsten springs are revealed to account for the enhanced fracture strength and plasticity. The BMGCs with lower volume fractions of tungsten springs exhibit a unique cone-shaped fracture morphology due to the preferential initiation of shear bands in the central metallic glass matrix. While the BMGCs with larger volume fractions of tungsten springs exhibit a mixed shear fracture morphology consisting of four distinct regions. Nevertheless, all the current BMGCs fail in a shear mode, which is obviously different from that of the BMGCs reinforced with longitudinal fibers. The failure modes of the BMGCs can be modified by designing the structure and orientation of the tungsten springs.

Deformation behavior of Ta wire-reinforced Zr-based bulk metallic glass composites

A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix in the form of spirals. The composite exhibits two yield stages under compressive stress, and the samples are compressed into thin pancakes. The micro-cracks originate at the interface between the Ta wire and the metallic glass matrix and propagate perpendicularly to the interface, which then induce multiple shear bands in the metallic glass matrix due to the stress concentration. Shear cracks form in the metallic glass matrix during the continued loading process as a result of the interaction of shear bands. Deformation bands of Ta wires occur under the impact of shear bands. The local stress fields in the composite are changed obviously due to the introduction of the spiral-formed reinforcements. The investigation of the deformation behavior and mechanism suggests a new method for the application of bulk metallic glass composites as the structural materials.

Effect of MoSi2 Content on Dry Sliding Tribological Properties of Zr-Based Bulk Metallic Glass Composites

Zr55Cu30Al10Ni5 bulk metallic glass and its composites were prepared by suction casting into a copper mold. The effect of MoSi2 content on the tribological behavior of Zr55Cu30Al10Ni5 BMG was studied by using a high-speed reciprocating friction and wear tester. The results indicate that the friction coefficient and wear resistance of the BMGs can be improved by a certain amount of crystalline phase induced by MoSi2 content from 1 to 3% and deteriorated with MoSi2 content of 4%. The wear mechanism of both the metallic glass and its composite is abrasive wear. The mechanism of crystalline phase-dependent tribological properties of the composite was discussed based on the wear track and mechanical properties in the present work. The wear behavior of Zr55Cu30Al10Ni5 BMG and its composite indicates that a good combination of the toughness and the hardness can make the composite be well wear resistant.

3D printing of crack-free high strength Zr-based bulk metallic glass composite by selective laser melting

3D printing of crack-free bulk metallic glasses remains challenge due to the generation of huge thermal stress during the selective laser melting and their intrinsic brittleness. Herein, Zr55Cu30Ni5Al10 system was selected and 3D printed by selective laser melting technique. The results indicated that bulk metallic glassy composite comprises a large fraction (about 83%) of amorphous phase and minor fraction of intermetallic compounds with free of cracks were successfully fabricated. The 3D printed metallic glassy composite exhibited high strength over 1500 MPa. Experiment combined with finite-element-method simulation not only revealed the mechanism of crystallization at heat affected zones, but demonstrated that low thermal stress reduce the risk of micro-cracks generation and fracture toughness plays a crucial role in suppression the crack propagation during selective laser melting process.

Significantly enhanced drilling ability of the orthopedic drill made of Zr-based bulk metallic glass composite

Zr-based bulk metallic glass composite (BMGC) presents superior unique properties, including high hardness, high fracture strength, high toughness, large elastic limit, excellent corrosion resistance, and was believed as a promising material for medical-tool applications. In this study, the 4 mm diameter rods of ZrCuAlAgSi-based (Zr-based) BMGC containing ex-situ Ta particles were successfully fabricated by two-step arc melting and suction casting method. These Zr-based BMGC rods was ascertained their amorphous nature by X-ray diffraction and differential scanning calorimetry analyses, and then machined into the orthopedic drill bits with 2 mm in diameter. The drilling tests of the commercial and Zr-based BMGC orthopedic drill bits were conducted by a specially designed indentation-drilling rig. The data of thrust force as a function of drilling distance between drill and porcine bone was recorded and analyzed to evaluate the drilling ability of the Zr-based BMGC made and commercial orthopedic drills, respectively. As a result, the Zr-based BMGC made drill presents 73% reduced thrust force than the commercial one, this indicates that the Zr-based BMGC made drill has less friction force and performs much better drilling ability.

Effect of the volume fraction of the ex-situ reinforced Ta additions on the microstructure and properties of laser-welded Zr-based bulk metallic glass composites

To investigate the effect of the volume fraction of the ex-situ reinforced Ta additions on the weldability of Zr–Cu–Ag–Al bulk metallic glass composites (BMGCs), in this study, different Ta contents (0–6 vol%) of BMGCs are welded using the Nd:YAG pulsed laser technique with preselected welding parameters. After welding, the microstructure (including the parent material (PM), weld fusion zone (WFZ) and heat-affected zone (HAZ)), mechanical and thermal properties of the test samples are investigated.The test results show, for all BMGC welds, the micro-sized Ta particles in the PM, WFZ and HAZ to be covered by a crystallized interfacial layer (IL), ZrCu. For both un-welded and laser-welded BMGCs, as the Ta contents increase, the glass transformation temperature (Tg) increases, which in turn reduces the glass formation ability (GFA) indices, ΔTx, γ and γm. However, when compared to that of un-welded BMGC, the GFA index, ΔTx, of the laser-welded BMGCs is slightly improved. However, the γ, and γm of the BMGC welds seem not to be affected.In addition, due to the characteristics of the rapid thermal cycle of the laser welding process, two smaller sizes of Ta, nano-sized (mainly on the surface of WFZ) and sub micro-sized Ta, are found in the WFZ. These sub-micro-sized Ta particles normally locate near the micro-sized Ta, which tends to slightly reduce the hardness in this area.Furthermore, an increase in the volume fraction of Ta (0–6 vol%) in the BMGCs does not encourage the formation of the harmful crystalline phase in the amorphous matrix after the laser welding process. It is observed that, other than the IL (ZrCu) on the micro-sized Ta particles, no other type of crystalline is observed in the amorphous matrix of the laser-welded BMGCs.

Dynamic mechanical behavior of a Zr-based bulk metallic glass composite

Dynamic mechanical analysis (DMA) was used to study the viscoelastic properties of a Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 (LM2) bulk metallic glass (BMG) matrix composite. The temperature spectrum and the frequency spectrum were tested by three point bending. We revealed that the relaxation process of the LM2 composite is different from the single amorphous alloys. The unique superimposition of glass transition (α-relaxation) and β-phase transformation during DMA results in double peaks on the loss modulus evolution and a plateau on the storage modulus evolution. The numerical analysis of the isothermal spectrum suggests that the dynamic relaxation behavior of the LM2 composite cannot be described by a single classical relaxation model. A coupling model is instead proposed to well quantify the coupling effect of the α-relaxation and β-phase transformation in the LM2 BMG composite. Our findings provide an insight into understanding the more complex structural relaxation of BMG composite than monolithic BMGs.

On the compressive failure of tungsten fiber reinforced Zr-based bulk metallic glass composite

In this paper, a combination of experimentation and analysis is used to identify and study the mechanisms that govern the failure of tungsten fiber reinforced Zr41.2Ti13.8Cu10Ni12.5Be22.5 bulk metallic glass composite. In the experimental part, quasi-static and dynamic compressive behaviors of this composite with various fiber volume fractions were systematically investigated. For this composite under uniaxial compression, both the microstructure and strain rate are found to affect the compressive failure behavior. With the increasing fiber volume fraction, or with the decreasing strain rate, the failure mode of the composite switches from shear to splitting. Motivated by the experimental findings, an energy competition mechanism is proposed to unveil these fundamental behaviors of the tungsten fiber reinforced bulk metallic glass composite. The critical energy dissipations for shear banding and splitting of the composite are derived as the functions of tungsten fiber volume fraction and strain rate. It is found that the failure behavior of the composite is decided by the energy competition between shear banding and splitting.

Critical obstacle size to deflect shear banding in Zr-based bulk metallic glass composites

The Zr53Cu22Ni9Al8Ta8 bulk metallic glass composite (BMGC) rods have been reported to present superior plastic strain up to 30% at room temperature. The remarkable plasticity is demonstrated to be contributed by the in-situ Ta-rich precipitates in micro-sized (10–20 micro-meter) plus nano-sized (5–15 nm) scales, homogeneously distributed in the amorphous matrix. These Ta-rich particles act as discrete obstacles, separating and restricting the highly localized shear-banding, avoiding catastrophic shear-through of the whole sample and dramatically enhancing plasticity, as compared with the ZrCuNiAl monolithic BMG. To explore the critical particle size that can effectively deflect the shear banding, the Zr-based BMGC rods were plastically deformed to different strain levels (3%–25%) before fracture for investigating the interaction between the Ta-rich particles (micro- and nano-sized) and shear banding. The results suggest that the critical size of single particle or particle cluster for deflecting the shear band is greater than 20 nm and less than 100 nm. The best estimation suggests about 80 ± 20 nm.

Atomic interaction mechanism for designing the interface of W/Zr-based bulk metallic glass composites.

The interaction between active element Zr and W damages the W fibers and the interface and decreases the mechanical properties, especially the tensile strength of the W fibers reinforced Zr-based bulk metallic glass composites (BMGCs). From the viewpoint of atomic interaction, the W-Zr interaction can be restrained by adding minor elements that have stronger interaction with W into the alloy. The calculation about atomic interaction energy indicates that Ta and Nb preferred to segregate on the W substrate surface. Sessile drop experiment proves the prediction and corresponding in-situ coating appears at the interface. Besides, the atomic interaction mechanism was proven to be effective in many other systems by the sessile drop technique. Considering the interfacial morphology, Nb was added into the alloy to fabricate W/Zr-based BMGCs. As expected, the Nb addition effectively suppressed the W-Zr reaction and damage to W fibers. Both the compressive and tensile properties are improved obviously.

Direct Observation on the Evolution of Shear Banding and Buckling in Tungsten Fiber Reinforced Zr-Based Bulk Metallic Glass Composite

The evolution of micro-damage and deformation of each phase in the composite plays a pivotal role in the clarification of deformation mechanism of composite. However, limited model and mechanical experiments were conducted to reveal the evolution of the deformation of the two phases in the tungsten fiber reinforced Zr-based bulk metallic glass composite. In this study, quasi-static compressive tests were performed on this composite. For the first time, the evolution of micro-damage and deformation of the two phases in this composite, i.e., shear banding of the metallic glass matrix and buckling deformation of the tungsten fiber, were investigated systematically by controlling the loading process at different degrees of deformation. It is found that under uniaxial compression, buckling of the tungsten fiber occurs first, while the metallic glass matrix deforms homogeneously. Upon further loading, shear bands initiate from the fiber/matrix interface and propagate in the metallic glass matrix. Finally, the composite fractures in a mixed mode, with splitting in the tungsten fiber, along with shear fracture in the metallic glass matrix. Through the analysis on the stress state in the composite and resistance to shear banding of the two phases during compressive deformation, the possible deformation mechanism of the composite is unveiled. The deformation map of the composite, which covers from elastic deformation to final fracture, is obtained as well.

EBSD Analysis for Microstructure Characterization of Zr-based Bulk Metallic Glass Composites

EBSD Analysis for Microstructure Characterization of Zr-based Bulk Metallic Glass Composites

Dynamic shear punch behavior of tungsten fiber reinforced Zr-based bulk metallic glass matrix composites

Dynamic shear punch tests were carried out on the tungsten fiber reinforced Zr-based bulk metallic glass composites. The experimental results show that with the increasing fiber volume fraction, the failure mode of the composites switches from shear to tensile fracture. A new failure criterion, based on the Tsai-Hill criterion and the unified failure criterion for bulk metallic glasses, is proposed to characterize fracture behavior of this bulk metallic glass composite. It is found that the shear-to-normal strength ratio α controls the transition of failure mode of this metallic glass composite. The underlying mechanism of the transition of failure mode is discussed as well.

Microstructure evolution in the Zr-based bulk metallic glass composites by additions of oxygen

The effects of oxygen on the microstructure evolution and glass forming ability of the Zr60Ti20Cu5.6Ni4.4Be10 alloy are investigated. The results show that the entire alloys doped with various oxygen levels exhibit type glass composites. With the increase in the oxygen, the precipitated phase changes from ω-Zr+β-Zr to α-Zr. It is worth noting that the oxygen is segregated in these precipitated crystals, the glass matrix contains very low oxygen level and keeps good glass formation. This founding gives us a new clue to avoid the oxygen detrimental to glass formation just by designing appropriate metallic glass composites.

Interfacial analysis of the ex-situ reinforced phase of a laser spot welded Zr-based bulk metallic glass composite

To study the interfacial reaction of the ex-situ reinforced phase (Ta) of a Zr-based ((Zr48Cu36Al8Ag8)Si0.75+Ta5) bulk metallic glass composite after laser spot welding, the interfacial regions of the reinforced phases located at specific zones in the welds including the parent material, weld fusion zone and heat affected zone were investigated. Specimen preparation from the specific zones for transmission electron microscopy analysis was performed using the focused ion beam technique. The test results showed that the reinforced phases in the parent material, weld fusion zone and heat affected zone were all covered by an interfacial layer. From microstructure analysis, and referring to the phase diagram, it was clear that the thin layers are an intermetallic compound ZrCu phase. However, due to their different formation processes, those layers show the different morphologies or thicknesses.