Ti-based Metallic Glass Composites Research Articles

Enhancement of tensile plastic stability of Ti-based metallic glass composite with substrate of titanium alloy

The tensile plastic stability of Ti-based metallic glass composites (MGCs) with substrates of titanium alloys was investigated. The findings have shown that the tensile plastic stability of MGC bimetals was significantly dependent on both the yield strength and geometrical dimension of the substrate. The substrate of high-strength Ti6Al4V (T64) alloy can enhance the ductility of the MGC greatly, while the MGC bimetal combined with low-strength pure titanium (PT) displayed worsen plastic stability. Further results showed that the plastic stability of the MGC was enhanced remarkably by increasing the thickness ration of the PT substrate. The enhancement of plasticity stability in the bimetals were explained and discussed from the perspective of normalized strain-hardening rate. These findings indicates that the plastic stability of MGCs can be enhanced by suitable reinforcer with optimized geometrical dimension. • The plastic deformation of Ti-based metallic glasses strongly depends on the mechanical properties of the substrates. • Homogeneous plastic deformation under tension can be realized in the MGC bimetals with substrate of titanium alloy. • The plastic stability of MGC bimetals can be explained by the concept of normalized strain-hardening rate.

Hardening overwhelming softening in Ti-based metallic glass composites upon cold rolling

For in-situ Ti48Zr20Nb12Cu5Be15 metallic glass matrix composites (MGMCs) upon cold rolling, the yield strength is obviously enhanced, and the plasticity instability is effectively alleviated. The increase in yield strength in such kinds of composites is due to the fact that the work hardening of dendrites overwhelms the softening of the amorphous matrix. A quantitative model of predicting yield strengths with rolling straining in MGMCs is successfully established. This provides useful guidances for structural applications of ductile MGMCs.

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.

Tune the mechanical properties of Ti-based metallic glass composites by additions of nitrogen

Different amounts of nitrogen from 1000 to 14,000wtppm were added into the Ti48Zr20Nb12Cu5Be15 bulk metallic glass composites. Results show that addition of nitrogen can increase the yield strength of composites from 1400 to 2350MPa due to the solid solution strengthening effect. The composites still owns certain plastic strain (above 10% when contains 14,000ppm nitrogen) before fracture under compressive test. The reason is attribute to nitrogen shows to be a much weaker activator for the formation of brittle α-Ti phase as compared with oxygen, which make the β-Ti dendrite still softer than that of the glassy phase, thus can enhance the strength of the materials but do not deteriorate the plasticity too much. Our research show that nitrogen can be added into the Ti-based metallic glass composites in a very large range to effectively tune the suitable mechanical properties of Ti-based metallic glass composites, without worrying about the catastrophic failure in the process of deformation.

Revealing homogeneous plastic deformation in dendrite-reinforced Ti-based metallic glass composites under tension

The tensile plastic deformation of dendrite-reinforced Ti-based metallic glass composites (MGCs) was investigated. It was found that there is a critical normalized strain-hardening rate (NSHR) that determines the plastic stability of MGCs: if the NSHR is larger than the critical value, the plastic deformation of the MGCs will be stable, i.e. the necking and strain localization can be effectively suppressed, resulting in homogeneous plastic elongation. In addition, dendrite-reinforce MGCs are verified as being intrinsically ductile, and can be used as good coatings for improving the surface properties of pure titanium or titanium alloys. These findings are helpful in designing, producing, and using MGCs with improved performance properties.

Plastic stability of bimetals composed of Ti-based metallic glass composite and pure titanium

The plastic stability of bimetals composed of a Ti-based metallic glass composite (MGC) and a pure titanium (PT) under tension has been investigated. The results reveal that the plastic stability of the MGC/PT bimetal is strongly dependent on the thickness fraction of the MGC: when the thickness fraction of the MGC decreases to a critical value, a homogeneous plastic deformation occurs in the MGC/PT bimetals, i.e. the strain localization and necking of the MGC is effectively suppressed. This unique phenomenon is explained using the normalized strain-hardening rate, and the quantitative relationship between the normalized strain-hardening rate of the MGC/PT bimetals and the thickness fraction of the MGC is thereby established.

High strength beta titanium alloys: New design approach

A novel approach for development of high strength and ductile beta titanium alloys was proposed and successfully applied. The microstructure of the designed alloys is fully composed of a bcc β-Ti phase exhibiting dendritic morphology. The new Ti68.8Nb13.6Cr5.1Co6Al6.5 (at%) alloy (BETAtough alloy) exhibits a maximum tensile strength of 1290±50MPa along with 21±3% of fracture strain. The specific energy absorption value upon mechanical deformation of the BETAtough alloy exceeds that of Ti-based metallic glass composites and commercial high strength Ti-based alloys. The deformation behavior of the new alloys was correlated with their microstructure by means of in-situ studies of the microstructure evolution upon tensile loading in a scanning electron microscope.

Enhanced mechanical properties of Ti-based metallic glass composites prepared under medium vacuum system

The Ti48Zr20Nb12Cu5Be15 bulk metallic glass composites were prepared by copper mold casting under medium vacuum conditions (0.15Pa–25Pa). The addition of impurity elements neither induces the phase transformation of β-Ti→α-Ti, nor changes the microstructure of the Ti-BMG composites when the oxygen level is low. However, some tiny α-Ti crystals separate out from the interface between the dendritic second phases and glassy matrix when the oxygen content is 7500ppm. The impurity elements concentrated in the BMGs lead to a sharp decrease of GFA when the average oxygen level is above 4500ppm. The impurity elements absorbed in the β-Ti phase can induce a significant solid-solution strengthening effect, which results in an enhanced strength. With the average oxygen level further increases, the higher shear modulus and hardness of β-Zr phase, because of the excessive solid-solution hardening effect of oxygen, may lose the ability to arrest the shear bands. The brittle tiny α-Ti crystals can deteriorate the mechanical property of the composite.

Tensile deformation of a Ti-based metallic glass composite lamella confined by commercially pure titanium

The tensile plastic deformation behaviour of a Ti-based metallic glass composite (MGC) lamella confined by commercially pure titanium (CPT) is investigated. It is found that a uniform plastic deformation is achieved in the CPT-confined MGC lamella, where the strain localization and necking is effectively suppressed. The MGC lamella sustains a true tensile strain exceeding 10% before fracture. A deformation mechanism of the amorphous/crystalline interface is proposed to interpret the plastic deformation of the MGC/CPT structure. The revealed significant intrinsic plasticity of the MGC suggests its potential application as an excellent coating for bulk ductile materials.

Ti Particles Dispersed Ti-Based Metallic Glass Matrix Composite Prepared by Spark Plasma Sintering

Using spark plasma sintering (SPS) process, Ti particles dispersed Ti40Zr10Cu36Pd14 metallic glass (MG) matrix composites were fabricated. The X-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and compressive tests were used for examining the microstructure and properties of the composites. The experiment results showed that the as-sintered composite exhibited mainly dense structure. The Ti-based MG and pure Ti particles were coalesced together closely. There was no distinct gap or interface between the Ti-based MG matrix and pure Ti particles. No crystallization was observed in the Ti-based glassy matrix. The addition of Ti particles improved the plasticity of the Ti-based MG composite, while had no significant influence on the thermal stability of MG matrix. [doi:10.2320/matertrans.MF201311]

Effect of Carbon-Nanotube Addition on Thermal Stability of Ti-Based Metallic Glass Composites

The preparation of Ti50Cu28Ni15Sn7 metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The thermal stability of the amorphous matrix is affected by the presence of the CNT particles. Changes in Tg and Tx suggest deviations in the chemical composition of the glassy matrix due to a partial dissolution of the CNT species in the amorphous phase. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/ Ti50Cu28Ni15Sn7 metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

Enhanced plasticity in Mg-based bulk metallic glass composite reinforced with ductile Nb particles

The authors report the synthesis of Mg-based metallic glass composite reinforced with Nb particles which are simply added during melting process. The ductile Nb particles effectively impede shear band propagation and upon yielding, deformed Nb particles distribute the load uniformly to the surrounding glassy matrix to promote the initiation and branching of abundant secondary shear bands. In contrast to the previous Mg-based metallic glass composites which fracture with very little plasticity, the composite shows great resistance to crack growth. The high strength of 900MPa and large plasticity of 12.1±2% have made it comparable to excellent Zr- or Ti-based metallic glass composite.