Ti-based Bulk Metallic Glass Composites Research Articles

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.

Tuning the microstructure and metastability of β-Ti for simultaneous enhancement of strength and ductility of Ti-based bulk metallic glass composites

A parametric experimental study on the role played by the size, metastability, and volume fraction of the dendritic β-Ti phase on the tensile properties of amorphous matrix composites is conducted. Towards this end, several bulk metallic glass composites (BMGCs) with varying compositions were synthesized, processed under different cooling rates and tensile tested. Results show that the stress induced martensitic transformation, from β to α″, of the dendritic Ti phase enhances the resistance to shear band propagation and, in turn, imparts significant strain hardening capability to the composite. This transformation was found to be favored in BMGCs in which the size of the dendrites is relatively coarse and Co content is ∼1 at.%. Furthermore, a volume fraction of the dendritic phase between 34% and 45% was found to result in optimum combination of strength and ductility. The utility of these microstructural design principles learned from this study was demonstrated by design, synthesis, and testing of a BMGC containing transformable β-Ti with a volume fraction of ∼38% that simultaneously exhibits high strength and ductility.

Tensile properties and deformation micromechanism of Ti-based metallic glass composite containing impurity elements

To study the tensile deformation behavior and deformation micromechanism of Ti-based bulk metallic glass composites (BMGCs) containing high levels of impurity elements, 2 at.% nitrogen or oxygen was introduced into a BMGC with a nominal composition of Ti48Zr20Nb12Cu5Be15. The solid solution strengthening caused by solute atoms and embrittlement due to excess oxygen were examined in detail using transmission electron microscopy observation and theoretical analysis. Special attention was paid to changes occurring at the interface in order to propose a more microscopic interpretation of macroscopic and micron-scale phenomena, such as the two-phase coordinated deformation behavior in the work-hardening stage of the low-tensile plastic composite and the brittle failure mechanism resulting from excessive oxygen content. A precipitation phase of nanoscale polycrystals distributed at the interface was found in the composite with 2 at.% oxygen. The appearance of these harder precipitated polycrystals is conducive to microcrack generation but cannot stop microcrack growth, so it has disastrous effects on the properties of the materials. Adding appropriate solute atoms to Ti-based BMGCs at a suitable dose can be an inexpensive and convenient method of adjusting the mechanical properties in a wide range. This work can provide suggestions for optimizing the impurity element content and preventing embrittlement considering macroscopic and microscopic features.

Identifying the significance of Sn addition on the tribological performance of Ti-based bulk metallic glass composites

Tailoring the properties of an engineering material with low coefficient of friction (COF) and high wear resistance has been a long goal in the tribological research. It is particularly true for the bulk metallic glass composites (BMGCs), which are promising for a large range of advanced applications. Although the materials design and mechanical properties have been extensively investigated, knowledge of their tribological behaviors is still lacking. Ball-on-block wear tests were thus conducted to investigate the effect of Sn addition on the tribological behaviors of Ti45Zr25Nb6Cu5Be17 BMGCs under different normal loads. Nano-indentation and nano-scratch tests were carried out to study the phase-specific wear properties of the crystalline dendrite and amorphous matrix in BMGCs respectively. Preferred wear and delamination in the dendrite phase as a result of the plastic mismatch between the two constituent phases is responsible for the abrasive wear in the Ti47Zr25Nb6Cu5Be17 and Ti46Zr25Nb6Cu5Be17Sn1 BMGCs. While, mechanically driven tribolayer during sliding enables oxidative wear and improved tribological properties in the Ti45Zr25Nb6Cu5Be17Sn2 BMGC. Based on the synergistic mechanical and chemical effects, the underlying relationship between the intrinsic dendrite properties and the wear behaviors of BMGC was revealed.

Effect of Nb content on corrosion behavior of Ti-based bulk metallic glass composites in different solutions

The effect of Nb content on the corrosion behavior of in-situ (Ti0.45Zr0.31Be0.17Cu0.07)100−xNbx (x = 4, 6, 8, 10, and 12) was evaluated in 0.5 mol/L H2SO4, 0.6 mol/L NaCl, and 1 mol/L NaOH solutions. A dual-phase microstructure which composed of an amorphous matrix and dendrites was observed. Electrochemical measurements in each corrosion medium showed the same trend. The corrosion resistance first increased and then decreased with the addition of Nb content from 4 to 12 at.%. The results show the best corrosion resistance in terms of × = 8 for the alloys. Notably, Nb addition improved the pitting-corrosion resistance of samples in a chloride-containing solution, whereas spontaneous passivation occurred in chloride-free solutions. A preferential solution was observed in the amorphous matrix region in NaCl solution, but a part of dark spots and dents appeared on the surface after the polarization in chloride-free solutions. X-ray photoelectron spectroscopic measurements showed that Nb addition promoted the formation of metal oxide on the surface film, thus inducing a superior corrosion resistance for the bulk metallic glass matrix composites.

The design and mechanical behaviors of in-situ formed ductile dendrite Ti-based bulk metallic glass composites with tailored composition and mechanisms

Up to now, few work has concerned about the composition design strategy in the field of in-situ dendrite bulk metallic glass composites (BMGCs) for the difficulty to mediate single element in the multi-component system. In this work, an innovative composition design strategy was proposed, and a novel series of in-situ β dendrite reinforced Ti-based BMGCs were prepared. It was found that the real composition of the in-situ formed dendrites and amorphous phase is well consistent with the designed one. Accordingly, the dendrite composition is tailored monotonically and precisely, while the composition and volume fraction keep similar for the amorphous matrix in the composites. The microstructure of the dendrites and the mechanical properties and mechanisms of the overall composites are essentially controlled by the dendrite composition. According to the corresponding deformation mechanisms which transform from stress-induced martensitic transformation and mechanical twinning to dislocation slip, these alloys can be classified into two groups: the stress-induced martensitic transformation type and the none-phase transformation type. The composition design strategy proposed in this work and the correlation between the dendrite composition and the mechanical mechanisms may provide useful guidance for the development of in-situ β dendrite reinforced BMGCs with optimized mechanical properties.

Dynamic compressive response of a dendrite-reinforced Ti-based bulk metallic glass composite

Dynamic compressive response of a dendrite-reinforced Ti-based bulk metallic glass composite is investigated. Strain rate dependencies of the max strength and strain energy density are illustrated. The inherent mechanisms are revealed by studying the dynamic deformation behaviors at lower and higher strain rates. Under high-rate loading, the deformation and fracture of the soft crystalline dendrites and the hard amorphous matrix are characterized, respectively. Then, their contributions to the failure of the composite material are discussed. Finally, the dynamic damage efficiency of the composite material is addressed.

Modulating mechanical properties of Ti-based bulk metallic glass composites by tailoring dendrite composition with Sn addition

The design of highly processable metallic glass matrix composites (MGMCs) is driven by optimizing the mechanical properties such as strength and ductility. In this work, by using X-ray diffraction (XRD), scan electron microscopy (SEM), energy dispersive spectroscope (EDS), transmission electron microscopy (TEM) and compressive testing, we reported that the microstructure and mechanical properties of Ti-based MGMCs can be tuned by a minor addition of Sn. The results revealed a critical content for Sn (i.e., 3 at.%), below which (i.e., 1 at.%-3 at.%), the MGMCs can be strengthened without losing their plasticity. While excessive addition of Sn (i.e., 4 at.%-5 at.%) would degrade severely the plasticity of MGMCs. The Sn element which mainly distributes in the dendrite-phase was found to affect significantly the intrinsic properties of the β-Ti dendrite-phase and should account for the variation of the yield strength and plasticity of MGMCs. Thus, the competing effect between dendrite-phase and glass-matrix in plastic deformation has been discussed in detail. The current work provides further insights to develop MGMCs with enhanced yield strength and graceful plasticity through optimal element addition.

Modulating work-hardening behaviors and tensile plasticity of in-situ formed ductile dendrite Ti-based bulk metallic glass composites with tailored dendrite composition

A novel series of in-situ dendrite Ti-based bulk metallic glass composites (BMGCs) were obtained. The Mo content of the dendrites monotonically increases from nil to 10.5at% while the dendrite volume fraction and the composition of the amorphous matrix remain nearly invariant. It was found that the mechanical behaviors varied tremendously simply by changing the Mo content. Thus, the correlation between the composition and the mechanical behaviors under tension has been determined for in-situ dendrite Ti-based BMGCs for the first time.

Influence of spherical particles and interfacial stress distribution on viscous flow behavior of Ti‐Cu‐Ni‐Zr‐Sn bulk metallic glass composites

Bulk metallic glass composites containing micro-scale B2 particles are subject to investigation with regards to the influence of B2 particles and interfacial stress and strain distribution on the viscous flow behavior at a super-cooled liquid state. An increased volume fraction of B2 particles leads to an increase of minimum viscosity and influences viscous flow behavior before crystallization. In high temperature deformation, the bulk metallic glass shows homogeneous deformation feature. However, the heterogeneous deformation feature is found in thermoplastically deformed bulk metallic glass composite. The strong stain accumulation and sluggish viscous flow occur around B2 particles, which are caused by the heterogeneous stress distribution linked to stress concentration and shear stress impediment around B2 particles. The sluggish viscous flow of super-cooled liquids around B2 particles during high temperature deformation induces an increase of viscosity and strongly affects the viscous flow behavior of Ti-based bulk metallic glass composites containing micro-scale spherical B2 particles.

Strain rate sensitivity and deformation behavior in a Ti-based bulk metallic glass composite

The Ti45Zr25Nb6Sn2Cu5Be17 bulk metallic glass composite was investigated by uniaxial quasi-static compression and tension tests under strain rates from 1×10−4s−1 to 1×10−2s−1 at the room temperature. The deformation behavior was characterized by analyzing the lateral and fracture surfaces. With the increase of strain rate, the yielding stress and plasticity decrease significantly, indicating negative strain rate sensitivity. At higher strain rates, the thermal softening effect is more prominent and the yielding stress is lower, while lower strain rates, the shear band toughness of the dendrites is higher than that of the glass matrix. Then the dislocations have sufficient time to be generated, multiplied and aggregated, thereby the shear banding can be retarded and hindered efficiently by dendrites. Furthermore, the primary shear bands are able to block more effectively the secondary ones, which results in more uniform distribution of plastic strain and thereby higher plasticity. The current work shows that the coordination of the shear band toughness of the dendrites and the glass matrix and the stable extension of the shear bands are of primary importance for obtaining excellent mechanical properties.

β-type Ti-based bulk metallic glass composites with tailored structural metastability

Abstract Bulk metallic glass composites (BMGCs) containing an in-situ formed metastable β phase (β-type BMGCs) being capable of transforming to martensites, are a promising class of alloys. Nonetheless, the influence of the structural metastability of β phases on the deformation mechanisms of BMGCs remains largely unclear. This, however, is crucial for understanding and optimizing plastic deformability. In this study, three Ti-based β-type BMGCs with nominal compositions of (Ti0.505Zr0.353Fe0.028Be0.114)100−xCux (x = 1, 5, 8) have been developed, in each of which the β-Ti phase has a different metastability. For x = 8, the β phase precipitates exclusively and does not transform martensitically during deformation. At the lowest Cu content (x = 1), however, the β phase contains a high density of fine ω phase upon quenching, which hinders the deformation-induced martensitic transformation. β phases in both BMGCs deform plastically by dislocation glide. Only when x = 5 does the β phase undergo the martensitic transformation to α″-Ti due to an appropriate degree of metastability. The reversible phase transformation between β and α″ followed by twinning in α″ on continuing deformation leads to a “double yielding” behavior and results in strong work-hardening capability as well as superelasticity during compression (cyclic loading) tests.

Wear Behavior of Mechanically Alloyed Ti-Based Bulk Metallic Glass Composites Containing Carbon Nanotubes

The present paper reports the preparation and wear behavior of mechanically alloyed Ti-based bulk metallic glass composites containing carbon nanotube (CNT) particles. The differential scanning calorimeter results show that the thermal stability of the amorphous matrix is affected by the presence of CNT particles. Changes in glass transition temperature (Tg) and crystallization temperature (Tx) suggest that deviations in the chemical composition of the amorphous matrix occurred because of a partial dissolution of the CNT species into the amorphous phase. Although the hardness of CNT/Ti50Cu28Ni15Sn7 bulk metallic glass composites is increased with the addition of CNT particles, the wear resistance of such composites is not directly proportional to their hardness, and does not follow the standard wear law. A worn surface under a high applied load shows that the 12 vol. % CNT/Ti50Cu28Ni15Sn7 bulk metallic glass composite suffers severe wear compared with monolithic Ti50Cu28Ni15Sn7 bulk metallic glass.

The wear properties of Ti-based bulk metallic glass composites containing carbon particles

Abstract This paper reports the preparation and wear behavior of mechanically alloyed Ti-based bulk metallic glass composites containing carbon particles. The carbon/Ti 50 Cu 28 Ni 15 Sn 7 metallic glass composite powders are formed by two-stage mechanical alloying (MA) process. The bulk metallic glass composite was successfully prepared by vacuum hot pressing of as-milled carbon/Ti 50 Cu 28 Ni 15 Sn 7 metallic glass composite powders. The differential scanning calorimeter (DSC) results show that the thermal stability of the amorphous matrix is affected by the presence of the carbon particles. Changes in T g and T x suggest deviations in the chemical composition of the amorphous matrix that were developed due to a partial dissolution of the carbon species into the amorphous phase. Although the hardness of carbon/Ti 50 Cu 28 Ni 15 Sn 7 bulk metallic glass composite is increased with carbon addition, but their wear resistances is not directly proportional to hardness and does not follow the standard wear law. The increase in the wear rate of a carbon/Ti 50 Cu 28 Ni 15 Sn 7 bulk metallic glass composite with high carbon content may be attributed to the residual porosity and in-situ formed hard TiC particles formed in situ in the matrix of the composite.

Effect of transition metal elements (Cu, Ni, Co and Fe) on the mechanical properties of Ti-based bulk metallic glass composites

A series of Ti-based Ti45Zr25Nb6Sn2TM5Be17 (at.%, TM = Cu, Ni, Co and Fe) BMG composites were studied to show the effect of transition metal elements on the microstructure, intrinsic properties and mechanical properties of Ti-based BMG composites. The research shows that the transition metal elements are distributed mainly in the glass-matrix, substitution of which influences significantly the Young's modulus and hardness of glass-matrix. Different from the load-bearing model, the yielding strength of the BMG composites relates highly to not only the yielding strength of the dendrite-phase but also that of the glass-matrix. The plasticity of the BMG composites is highly dependent on the average stress concentration factor of the dendrite-phase. A useful rule for preparing of BMG composite with high strength and excellent plasticity is herein proposed, where tailoring simultaneously the properties of dendrite-phase and glass-matrix is suggested to be a better choice to obtain a good compromise between strength and plasticity.

Effects of Sn addition on mechanical properties of Ti-based bulk metallic glass composites

Ti-based bulk metallic glass (BMG) composites were prepared by a minor addition of Sn to match the Young's modulus of dendrite-phase and glass-matrix, and prepared by suction casting into a water-cooled copper mold. The largest compressive fracture strain of 28.07% and the highest fracture strength of 1820MPa are obtained simultaneously in the Ti45Zr25Nb6Cu5Be17Sn2 BMG composite. The average stress concentration factor of dendrite-phase, which characterizes the concentrated stress in the dendrite-phase that is transferred to the glass-matrix through the interface, is found to be highly related to the mechanical properties and thus would be a guide for matching the Young's modulus. The microscopic deformation mechanism shows that the high average stress concentration factor of dendrite-phase promotes the transfer of concentrated stress from the dendrite-phase to the glass-matrix, thus leading to the formation of multiple shear bands. Matching the Young's modulus of dendrite-phase and glass-matrix is concluded to be a useful recipe to prepare the BMG composites with excellent mechanical properties.

Mechanical behavior and wear performance of a Ti-based bulk metallic glass composite containing dendritic and intermetallic phases

A biocompatible bulk metallic glass composite (BMGC) alloy with a nominal composition of Ti56Zr6Cu19.8Pd8.4Sn1.8Nb8 was designed to obtain microstructure consisting of β-Ti dendrites and glassy matrix. It was found that Nb-rich β-Ti dendrites were the primary phase in the alloy, and extra discontinuous island-like Ti2Cu phase was also produced in the glassy matrix. The BMGC alloy presented higher yield strength, remarkably increased plasticity and pronounced work-hardening characteristic. Furthermore, excellent sliding wear resistance was exhibited by the alloy due to the work-hardening capability and the contribution of the Ti2Cu intermetallic phase.

Two-phase quasi-equilibrium in β-type Ti-based bulk metallic glass composites.

The microstructural evolution of cast Ti/Zr-based bulk metallic glass composites (BMGCs) containing β-Ti still remains ambiguous. This is why to date the strategies and alloys suitable for producing such BMGCs with precisely controllable volume fractions and crystallite sizes are still rather limited. In this work, a Ti-based BMGC containing β-Ti was developed in the Ti-Zr-Cu-Co-Be system. The glassy matrix of this BMGC possesses an exceptional glass-forming ability and as a consequence, the volume fractions as well as the composition of the β-Ti dendrites remain constant over a wide range of cooling rates. This finding can be explained in terms of a two-phase quasi-equilibrium between the supercooled liquid and β-Ti, which the system attains on cooling. The two-phase quasi-equilibrium allows predicting the crystalline and glassy volume fractions by means of the lever rule and we succeeded in reproducing these values by slight variations in the alloy composition at a fixed cooling rate. The two-phase quasi-equilibrium could be of critical importance for understanding and designing the microstructures of BMGCs containing the β-phase. Its implications on the nucleation and growth of the crystalline phase are elaborated.

Deformation behaviors of a Ti-based bulk metallic glass composite in the dendrite softening region

Deformation behaviors of the Ti50Zr20Nb12Cu5Be13 bulk metallic glass composite in the dendrite softening region have been investigated using uniaxial compressive and tensile tests. All the compressive stress–strain curves show work-hardening phenomenon with the same tendency, the tensile stress–strain curves show work-softening phenomenon. The strain rate sensitivity exponent ranges from 0.061 to 0.072 in the compressive tests, and 0.33 to 0.38 in the tensile tests. The activation volume of the Ti50Zr20Nb12Cu5Be13 bulk metallic glass composite at 710K ranges from 1.6nm3 to 2.5nm3 under compressive tests and 1.0nm3 to 2.7nm3 under tensile tests, indicating that there is a migration of atomic group (about 170–180 atoms) during the deformation. The dendrite of the Ti50Zr20Nb12Cu5Be13 BMGC has been well spheroidized and undergoes severe plasticity deformation after the deformation in the dendrite softening region.

Deformation behavior of a Ti-based bulk metallic glass composite in the supercooled liquid region

Deformation behavior of the Ti50Zr20Nb12Cu5Be13 bulk metallic glass composite in the supercooled liquid region have been investigated by uniaxial compressive as well as tensile tests. The results indicated that all stress–strain curves show work-hardening and work-softening phenomenon. The high temperature deformation behavior is sensitive to strain rate and temperature. Rheological behavior of Ti50Zr20Nb12Cu5Be13 bulk metallic glass composite was analyzed by activation volume quantitatively, which implied that the Ti50Zr20Nb12Cu5Be13 has better rheological behavior than that of conventional Ti alloy, but not as good as Ti-based bulk metallic glass. In addition, dendrite morphology of the Ti50Zr20Nb12Cu5Be13 almost does not change after deformation, and tensile fracture is full of dimples.