**2.1. Fiber-reinforced BMGMCs**

The fiber-reinforced BMGMCs mainly focus on tungsten fiber, steel fiber and carbon fiber [28–34]. Dandliker et al. have firstly fabricated the tungsten and carbon-steel continuous wire reinforced Zr-based BMGMCs by quenching the metallic melt to a glass after infiltrating the reinforcement [28]. The continuous long fibers in the glass matrix can efficiently hinder the propagation of main shear bands, improving the plastic strain from 0% of monolithic BMG to over 2% of those reinforced with steel wires. Kim et al. have successfully fabricated carbon

**Figure 3.** (a) Backscattered SEM image of carbon fiber reinforced bulk metallic glass composite; (b) dark field TEM of the interfacial region between a carbon fiber and the matrix.

fiber reinforced Zr-based BMGMCs by infiltrating the alloy melt to the bundle of carbon fibers in a quartz tube which are cleaned and preheated [30]. **Figure 3a** shows the backscattered SEM image of the carbon fiber reinforced composite. The carbon fibers are uniformly distributed in the matrix and the matrix appears to be uniform and free of heterogeneity. The volume fraction of carbon fibers is about 50% and the diameter is about 5 μm. They also found that a carbide reaction zone is formed surrounding the carbon fibers, as shown in **Figure 3b**, starting from the carbon fibers, a diffusion zone of Ni, Cu within the fiber, a crystallize reaction zone of (Zr + Ti)C and ZrC, to the BMG matrix. Qiu et al. cast the sample in a resistive furnace by melting the ingots in an evacuated quartz tube packed with the tungsten fibers, followed by pressure infiltration [34]. After pressurization the tube was quenched in a supersaturated brine solution. The nominal diameter of the fibers is 250 μm. The volume fraction of the fibers varies from 10 to 70%.

shows the uniformly distributed WC particles in the metallic glass matrix with the volume fraction of 10%. The matrix composition is chosen for several reasons. A relatively low melting temperature suppresses the chemical interactions between the reinforcement particles and the glass. A low glass transition temperature decreases differential thermal stresses which

Metallic Glass Matrix Composites

57

http://dx.doi.org/10.5772/intechopen.76526

Zhang et al. have introduced Ta particles into Zr-Cu-Al-Ag BMG matrix, the average size of Ta particles is about 40 μm and the volume fraction varies from 5 to 20% [36]. The composite is prepared by induction melting the Zr-Cu-Al-Ag alloy together with Ta powder in a quartz tube and subsequently injecting through a nozzle into a copper mold. **Figure 5a** shows the SEM images of the as-cast BMGMCs containing 10% Ta, consisting of homogeneously dispersed particles embedded in the metallic glass matrix. **Figure 5b** shows the compressive stress-strain curves of the composites containing 5–20% Ta. The monolithic glassy alloy fails immediately after yielding at 1885 MPa. However, the composites exhibit apparent work hardening and plastic strain. For 10% Ta-containing composite, the yield strength, fracture strength and plastic strain are 1717, 2600 MPa and 31%, respectively. The composite containing 20% Ta shows no plasticity which may originate from the crystallization of the matrix. Ta particles play an important role in the initiation and propagation of the multiple shear bands. The differences in Young's modulus between Ta particles and glassy matrix generates highstress concentration occurs at the interfaces, which promotes the initiation of shear bands at

arise between the reinforcement and the matrix during freezing and cooling.

**Figure 4.** An optical micrograph showing uniformly distributed WC particles in the matrix.

the interface prior to the formation of shear bands on the maximum shear surface.

Pan et al. have added Nb particles into Mg-based BMG matrix to fabricate the ex-situ particle-reinforced BMGMCs [43]. The size of Nb particles is 20–50 μm, the volume fraction varies from 4 to 8%. The particles are added during inductively melting the master alloy. The composite alloy is remelted by induction in a quartz tube and injected with argon pressure into copper molds. **Figure 5c** shows the SEM micrograph of the cross-sectional surface of the composite with 8% Nb particles, which exhibits the uniform distribution of the particles

During compression test, unlike the catastrophic fracture of monolithic BMG, the composites reinforced with tungsten fibers shows yielding and plastic deformation. The yielding strength also increases with a higher volume fraction of fibers. They also found that the failure mode changes with various volume fractions of fibers. The monolithic glass fractures on 45° planes. As the volume fraction of fiber increases, failure mode shifts from shear to localized buckling and tilting.

#### **2.2. Particle-reinforced BMGMCs**

The particle-reinforce BMGMCs includes ceramic particles, metal particles and the matrix includes Zr-based, Ti-based and Mg-based alloy system [35–43].

Choi-Yim and Johnson have firstly introduced ceramic particle such as SiC, WC and TiC, and the metal particles W and Ta into Zr-based and Cu-based BMG matrix [35]. A mixture of the pre-alloyed metallic glass forming elements and secondary phase material are combined by induction melting the glass forming alloy together with the solid secondary phase material on a water-cooled copper boat under a Ti-gettered argon atmosphere. The volume fractions of particles range from 5 to 30% and the sizes of the particles vary between 20 and 80 μm. **Figure 4**

**Figure 4.** An optical micrograph showing uniformly distributed WC particles in the matrix.

fiber reinforced Zr-based BMGMCs by infiltrating the alloy melt to the bundle of carbon fibers in a quartz tube which are cleaned and preheated [30]. **Figure 3a** shows the backscattered SEM image of the carbon fiber reinforced composite. The carbon fibers are uniformly distributed in the matrix and the matrix appears to be uniform and free of heterogeneity. The volume fraction of carbon fibers is about 50% and the diameter is about 5 μm. They also found that a carbide reaction zone is formed surrounding the carbon fibers, as shown in **Figure 3b**, starting from the carbon fibers, a diffusion zone of Ni, Cu within the fiber, a crystallize reaction zone of (Zr + Ti)C and ZrC, to the BMG matrix. Qiu et al. cast the sample in a resistive furnace by melting the ingots in an evacuated quartz tube packed with the tungsten fibers, followed by pressure infiltration [34]. After pressurization the tube was quenched in a supersaturated brine solution. The nominal diameter of the fibers is 250 μm. The volume fraction of the fibers

**Figure 3.** (a) Backscattered SEM image of carbon fiber reinforced bulk metallic glass composite; (b) dark field TEM of the

During compression test, unlike the catastrophic fracture of monolithic BMG, the composites reinforced with tungsten fibers shows yielding and plastic deformation. The yielding strength also increases with a higher volume fraction of fibers. They also found that the failure mode changes with various volume fractions of fibers. The monolithic glass fractures on 45° planes. As the volume fraction of fiber increases, failure mode shifts from shear to localized buckling

The particle-reinforce BMGMCs includes ceramic particles, metal particles and the matrix

Choi-Yim and Johnson have firstly introduced ceramic particle such as SiC, WC and TiC, and the metal particles W and Ta into Zr-based and Cu-based BMG matrix [35]. A mixture of the pre-alloyed metallic glass forming elements and secondary phase material are combined by induction melting the glass forming alloy together with the solid secondary phase material on a water-cooled copper boat under a Ti-gettered argon atmosphere. The volume fractions of particles range from 5 to 30% and the sizes of the particles vary between 20 and 80 μm. **Figure 4**

includes Zr-based, Ti-based and Mg-based alloy system [35–43].

varies from 10 to 70%.

**2.2. Particle-reinforced BMGMCs**

interfacial region between a carbon fiber and the matrix.

56 Metallic Glasses - Properties and Processing

and tilting.

shows the uniformly distributed WC particles in the metallic glass matrix with the volume fraction of 10%. The matrix composition is chosen for several reasons. A relatively low melting temperature suppresses the chemical interactions between the reinforcement particles and the glass. A low glass transition temperature decreases differential thermal stresses which arise between the reinforcement and the matrix during freezing and cooling.

Zhang et al. have introduced Ta particles into Zr-Cu-Al-Ag BMG matrix, the average size of Ta particles is about 40 μm and the volume fraction varies from 5 to 20% [36]. The composite is prepared by induction melting the Zr-Cu-Al-Ag alloy together with Ta powder in a quartz tube and subsequently injecting through a nozzle into a copper mold. **Figure 5a** shows the SEM images of the as-cast BMGMCs containing 10% Ta, consisting of homogeneously dispersed particles embedded in the metallic glass matrix. **Figure 5b** shows the compressive stress-strain curves of the composites containing 5–20% Ta. The monolithic glassy alloy fails immediately after yielding at 1885 MPa. However, the composites exhibit apparent work hardening and plastic strain. For 10% Ta-containing composite, the yield strength, fracture strength and plastic strain are 1717, 2600 MPa and 31%, respectively. The composite containing 20% Ta shows no plasticity which may originate from the crystallization of the matrix. Ta particles play an important role in the initiation and propagation of the multiple shear bands. The differences in Young's modulus between Ta particles and glassy matrix generates highstress concentration occurs at the interfaces, which promotes the initiation of shear bands at the interface prior to the formation of shear bands on the maximum shear surface.

Pan et al. have added Nb particles into Mg-based BMG matrix to fabricate the ex-situ particle-reinforced BMGMCs [43]. The size of Nb particles is 20–50 μm, the volume fraction varies from 4 to 8%. The particles are added during inductively melting the master alloy. The composite alloy is remelted by induction in a quartz tube and injected with argon pressure into copper molds. **Figure 5c** shows the SEM micrograph of the cross-sectional surface of the composite with 8% Nb particles, which exhibits the uniform distribution of the particles

**Figure 5.** (a) SEM image of the as-cast BMGMC containing 10% Ta; (b) compressive stress-strain curves of the BMGMCs containing 0–20% Ta; (c) SEM image of the composite containing 8% Nb (inset shows the XRD pattern); (d) compressive stress-strain curves for single phase BMG and Nb-containing composite (4 and 8%).

Jang et al. have introduced porous Mo particles into Mg-Cu-Gd-Ag BMG matrix [45]. During master alloy melting, high purity porous Mo particles with a spherical shape and a size of 20–70 μm are added in the matrix alloy. The volume fraction of porous Mo particles ranges from 10 to 25%. For the introduced porous particles, the overall microstructure of the composite is separated into larger-scale compartment, ~50 μm between Mo particles, and the fine-scale compartment, 1–5 μm within one porous Mo particle, as shown in **Figure 7a** and **b**. The composites containing 20–25 vol% porous Mo particles exhibit superior mechanical performance with ultimate compression stress up to 0.95 and 1.1 GPa and plastic strain up to 10%, as shown in **Figure 7c**. Unlike solid particles, the crack propagation in the present composite is arrested by the porous Mo particles. For the porous nature of the reinforcing phase, the numbers of particles are calculated to be 1.4 times higher than those with solid ones, i.e., the mean interspacing of the porous Mo particles is less than that of the solid Mo ones. This should favor to the confining the shear-banding behavior, thus enable more halting propagation of the shear bands. The porous Mo particles separates and restricts the highly localized shear banding into many isolated small regions, and can confine lots of microsized compartments of the matrix within porous particles, which results in the formation of multiple shear bands within or around the porous particles, promoting the deformation to distribute more uniformly across the sample. Guo et al. have used an original method, so-called top-down process, to fabricate porous NiTi shape memory alloy (SMA) powders [46]. In this process, the multiphase precursor powder of Ni-Ti-Gd is firstly produced with B2-NiTi and Ni-Gd phase, then by leaching in nitric acid solution to remove Ni-Gd phase and leaving pore in the powder, as shown in **Figure 8a**. The size and interspacing between NiTi within one porous particle are as small as 200 nm. The porous NiTi powders are subsequently added to Mg-Cu-Gd-Ag glass former liquid to fabricate the BMGMC, as shown in **Figure 8b**, with volume fraction ranged from 5 to 20%. The porous particles are homogeneously distributed in the glassy matrix. The composites containing 20 vol% porous NiTi particles exhibits the best mechanical properties, including a true plastic strain of up to 10.6% and a fracture stress of up to 1173 MPa, as shown in **Figure 8c**. Similar to porous Mo, many microcracks are confined in the inter-particle regions and should result from local shear banding within the amorphous matrix. Furthermore, compared with solid particles, the porous particles can generate

**Figure 6.** (a) Pore distributed BMG rods, water quenched from a melt held at 853 K for 3 h under 4 MPa hydrogen; (b)

Metallic Glass Matrix Composites

59

http://dx.doi.org/10.5772/intechopen.76526

tensile and compressive stress-strain curves of pore reinforced BMGMCs with different porosities.

without interfacial reaction. **Figure 5b** shows stress-strain curves for monolithic BMG and Nb-containing composite with 4 and 8% Nb particles. The BMG fails just after the elastic limit of 2%, but the composites yield at about 900 MPa and exhibit significantly plastic strain as well as work hardening and softening. The overall engineering plastic strain is determined to be about 12.1% for 8% Nb-containing composite. Ductile Nb particles serve as obstacles to impede shear bands propagation. When encountering an Nb particle, the shear band has to be either blocked or bypass around the particle due to the strong bonding between the particles and the matrix. Furthermore, if the sear deformation travels into the ductile Nb particles, the particle can dramatically plastic deform by dislocation mode to absorb the shear strain and prevent the catastrophic failure from taking place by the free propagation of unstable shear bands.
