Effect of infiltrating time on interfacial reaction and properties of tungsten particles reinforced Zr-based bulk metallic glass composites

The tungsten particles reinforced Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit 1 alloy) bulk metallic glass composites (BMGCs) were prepared by the melt infiltrating casting method with the infiltrating time of 1, 5 and 10 min, respectively. The changes of interfacial reaction and compression properties of the bulk metallic glass composites with different infiltrating times were studied. Results show that with the increase of infiltrating time, tiny nanocrystals are generated at the interfacial boundary of tungsten particles and the amorphous matrix, and the size of tiny crystals increases with the infiltrating time. When the infiltrating time is 10 min, polygonal crystals with a larger size are also generated within the amorphous matrix. The compressive strength of the composites also increases with the infiltrating time. When the infiltrating time is 10 min, the compressive strength of the composite reaches 2,030 MPa and the compression strain is 44%. The fracture morphology of the composite materials is in a vein-like pattern and the melting phenomenon is found on the fracture surface. In addition, the density of the shear bands during the compressive tests of the composite materials increases with the infiltrating time.

High strain rate induced embrittlement of Zr-based bulk metallic glass

Quasi-static and high strain rate mechanical behavior of the Zr_ 1.25Ti_ 13.75Ni_ 10Cu_ 12.5Be_ 22.5 bulk metallic glass was determined covering strain rates from 1.02×10 -4s -1 to 3.258×103s -1. By use of split hopkinson pressure bar(SHPB) equipment, it is found that the alloy fractures in the high strain rate period with a strength well below that of its quasi-static counterpart and thus a strain rate induced embrittlement happens. Considering the glassy nature of the alloy and with careful analysis of the fracture morphology, dynamic damage accumulated in the high speed deformation period is suggested to be the reason for this embrittlement.

Dynamic strength behavior of a Zr-based bulk metallic glass under shock loading

Dynamic strength behavior of Zr51Ti5NiloCu25A19 bulk metallic glass （BMG） up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirm- ing the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.

Testing of High-Strength Zr-Based Bulk Metallic Glass with the Split Hopkinson Pressure Bar

The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown that at high strain rates beyond about 1 000 s^-1, uniform deformation within the metallic glass specimen could not be achieved and dispersion in the transmitted pulse can lead to discrepancies in measuring the dynamic failure strength of the present Zr-based bulk metallic glass. Based on these reasons, a copper insert was placed between the strike bar and the input bar to obtain reliable and consistent experimental data for testing of the Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass using the SHPB. Negative strain rate sensitivity was found in the present Zr-based bulk metallic glass.

In Vivo Investigation of Zr-Based Bulk Metallic Glasses Sub-Periosteally Implanted on the Bone Surface

Bulk metallic glasses (BMG) show higher strength and lower Young’s modulus than SUS 316L stainless steel and Ti-6Al-4V alloys. This study aimed to investigate the reaction of Zr-based BMG sub-periosteally implanted on the surface of the rat femur, thereby evaluate the possibility of the BMG as biomaterials for osteosynthetic devices. Zr65Al7.5Ni10Cu17.5 BMG ribbons with 10 mm length, 2 mm width and 0.5 mm thickness were implanted sub-periosteally on the femur surface in three male Wistar rats for 6 weeks. Systemic effects were evaluated by measuring Cu and Ni levels in the blood, and local effects were evaluated by the histological observation of the surrounding soft tissues in contact with the BMG. The reaction of the surface of the BMG was examined with scanning electron microscopy. No increase of Cu and Ni levels in the blood was recognized. In the scanning electron microscopy observation, spherical deposits which were considered as sodium chloride crystals were observed. Neither breakage nor pitting corrosion was noted. BMG will be a promising metallic biomaterial for osteosynthetic device that must be removed.

Novel titanium particles reinforced Zr-based bulk metallic glass composites prepared by infiltration casting

A novel Ti/Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 composite was successfully prepared by infiltrating the melt into sintered Ti preform. It shows that the introduction of Ti particles into the composite results in an increase in elastic strain to 3% and an enhancement of the strength up to 2.1 GPa. High specific strength has been obtained because of the decrease in density of the composite. It is suggested that an improvement in the mechanical properties of the composite may be attributed to the generation of multiple shear bands and some deformation in the Ti particles.

High-tenacity in-situ Ti/Zr-based bulk metallic glasses composites fabricated by industrial high-pressure die casting

The glass-forming ability and mechanical properties of metallic glasses and their composites are well known to be sensitive to the preparation conditions and are highly deteriorated by industrial preparing conditions such as low-purity raw materials and low vacuum.Here,we showed that a series of in-situ bulk metallic glass composites(BMGCs)which exhibit excellent ductility and segmental work hardening were successfully developed utilizing a high vacuum high-pressure die casting(HV-HPDC)technology along with industrial-grade raw materials.The tensile properties of these BMGCs are systematically investigated and correlated with the alloy microstructure.As compared with the copper mold suction casting method,the volume fraction difference of the dendrite phase for the BMGCs with the same composition is not significant when fabricated by the HV-HPDC,whereas the size of theβ-phase is generally larger.Insitu BMGCs with the composition of Ti_(48)Zr_(20)(V_(12/17)Cu_(5/17))19 Be 13 obtained by the HV-HPDC process show ductility up to 11.3%under tension at room temperature and exhibit a certain amount of work hardening.Two conditions need to be met to enable the BMGCs,which are prepared by vacuum die-casting to retain favorable ductility:(1)The volume fraction ofβphase stays below 62%±2%;(2)The equiaxed crystals with a more uniform size in the range of 5-10μm.Meanwhile,the results of the present study provided guidance for developing BMGCs with good ductile properties under industrial conditions.

Toughening additive manufactured Zr-based bulk metallic glass composites by martensite phase transformation

Additive manufacturing technology based on laser powder bed fusion(LPBF)offers a novel approach for fabricating bulk metallic glass(BMG)products without restriction in size and geometry.Nevertheless,the BMGs prepared by LPBF usually suffered from less plasticity and poorer fracture toughness as compared to their cast counterparts due to partial crystallization in heat-affected zones(HAZs).Since crystallization in HAZs is hard to avoid completely in LPBF BMGs,it is desirable to design a suitable alloy system,in which only ductile crystalline phase,instead of brittle intermetallics,is formed in HAZs.This unique structure could effectively increase the toughness/plasticity of the LPBF BMGs.To achieve this goal,a quaternary BMG system with a composition of Zr 47.5 Cu 45.5 Al 5 Co_(2)is adopted and subjected to LPBF.It is found that nearly a single phase of B_(2)-ZrCu is precipitated in HAZs,while a fully amorphous phase is formed in molten pools(MPs).This B_(2)phase reinforced BMG composite exhibits excellent mechanical properties with enhanced plasticity and toughness.Furthermore,it is easy to modulate the mechanical properties by altering the amount of the B_(2)phase via adjusting the laser energy input.Finally,the best combination of strength,plasticity,and notch toughness is obtained in the BMG composite containing 27.4%B_(2)phase and 72.6%amorphous phase,which exhibits yield strength(σ_(s))of 1423 MPa,plastic strain(ε_(p))of 4.65%,and notch toughness(K_(q))of 53.9 MPa m 1/2.Furthermore,a notable strain-hardening is also observed.The improvement of plasticity/toughness and appearance of strain-hardening behavior are mainly due to the martensite phase transformation from the B_(2)phase to the Cm phase during plastic deformation(i.e.,the phase transformation-induced plasticity effect).The current work provides a guide for making advanced BMGs and BMG composites by additive manufacturing.

Strong dependency of the tribological behavior of CuZr-based bulk metallic glasses on relative humidity in ambient air

Thanks to their outstanding mechanical properties,Bulk Metallic Glasses(BMGs)are new alternatives to traditional crystalline metals for mechanical and micromechanical applications including power transmission.However,the tribological properties of BMGs are still poorly understood,mostly because their amorphous nature induces counter intuitive responses to friction and wear.In the present study,four different BMGs(Cu_(47)Zr_(46)Al_(7),Zr_(46)Cu_(45)Al_(7)Nb_(2),Zr_(60)Cu_(28)Al_(12),and Zr_(61)Cu_(25)Al_(12)Ti_(2))underwent ball-on-disc friction tests against 100Cr6 steel balls(American Iron and Steel Institute(AISI)52100)at different relative humidities(RHs)ranging from 20%to 80%.Controlling humidity enabled to observe a high repeatability of the friction and wear responses of the BMG.Interestingly,the friction coefficient decreased by a factor of 2 when the humidity was increased,and the wear rate of BMGs was particularly low thanks to a 3rd-body tribolayer that forms on the BMG surface,composed of oxidized wear particles originating from the ball.The morphology of this tribolayer is highly correlated to humidity.The study also identifies how the tribolayer is built up from the initial contact until the steady state is achieved.

Dynamic response and damage evolution of Zr-based bulk metallic glass under shock loading

Dynamic response and damage evolution of Zr_(70)Cu_(13)Ni_(9.8)Al_(3.6)Nb_(3.4)Y_(0.2) bulk metallic glass(Zr-based BMG)under impact pressure ranging from 4.03 GPa to 27.22 GPa were studied.The Hugoniot Elastic Limit(HEL)and the spalling Strength(σ_(sp))were measured as 7.09 GPa and 2.28 GPa,and the curve of impact velocity(D)and particle velocity(u)were also obtained.Under the strain rate of~10^(5)s^(-1),local crystallization phenomenon was observed.As increasing the impact pressure,the failure mode of Zr-based BMG changed from spallation to fragmentation caused by the combination of spalling cracks and longitudinal cracks.Cone-cup structures were also observed in the internal spalling zone via nano-CT characterization.When increasing the impact pressure,the thickness of Zr-based BMG increased after impact and the remelting and cladding layers were also observed on the fracture surfaces.The fragments of the specimen were welded after impact due to the high temperature remelting,which causes plastic deformation of Zr-based BMG under shock loading.

Effect of the cooling rate on plastic deformability of a Zr-based bulk metallic glass

The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Zr65Cu17.5Ni10Al7.5 BMGs as-cast or lathed from different sizes as-cast samples was characterized, and they exhibited different plastic strains. The compressive plastic strain increases with the decreasing diameter of the as-cast specimens, i.e. with increasing the cooling rate. It is suggested that free volume content in the BMGs, which is related to the cooling rate during the rapid solidification, could play an important role in the deformation process of the BMGs.

Deformation behavior of Zr-based bulk metallic glass and composite in the supercooled liquid region

A Zr-based bulk metallic glass (BMG) with a composition of (Zr75Cu25)78.5Ta4Ni10Al7.5 and a bulk metallic glass matrix composite (BMGC) with a composition of (Zr75Cu25)74.5Ta8Ni10Al7.5 have been prepared by copper-mold casting. The compres-sive deformation behavior of the BMG and BMGC was investigated in the super-cooled region at different temperatures and various strain rates ranging from 8×10-4s-1 to 8×10-2s-1. It was found that both the strain rate and test temperature signifi-cantly affect the deformation behavior of the two alloys. The deformation follows Newtonian flow at low strain rates but non-Newtonian flow at high strain rates. The deformation mechanism for the two kinds of alloys was discussed in terms of the transition state theory.

Characterization of plastic flow in two Zr-based bulk metallic glasses

Plastic deformation behaviors of Zr65Al10Ni10Cu15 and Zr52.5Al10Ni10Cu15Be12.5 bulk metallic glasses (BMGs) are studied by using the depth-sensing nanoindentation, microindentation and uniaxial compression. The Be-containing BMG exhibits a signifi- cantly improved overall plastic strain compared with the Be-free alloy during compressive tests. Both BMGs show a loading-rate-dependent serrated flow during nanoindentation measurements, but the Be-containing alloy exhibits a much lower critical loading rate for the disappearance of the serration than the Be-free BMG. The shear band patterns de- veloped during plastic deformation are investigated by microindentation technique, wherein much higher shear band density is found in the Be-containing alloy than in the Be-free alloy, indicating an easier nucleation of shear bands in the former BMG. The dif- ference in the plastic deformation behavior of the two BMGs can be explained by a free volume model.

Compressive fracture characteristics of Zr-based bulk metallic glass

The compressive fracture characteristics of Zr-based bulk metallic glass under uniaxial compression tests are studied.The zigzag rheological behavior is observed in the compression stress-strain curves of amorphous alloys.At room temperature the uniaxial compression fracture takes place along the plane which is at a 45-degree angle to the direction of the compressive stress.The microstructure of a typical fracture pattern is the vein network.A unique,finger-like vein pattern is found to exist at the fracture surface of Zr-based bulk metallic glass.

Soldering of Zr-based bulk metallic glass and copper by Au-12Ge eutectic alloy

Zr-based bulk metallic glass and copper with different surface roughness were soldered using low temperature eutectic Au-12 Ge(wt%) solder on a thermomechanical simulator. The cross-sectional microstructures of the brazed joints were analyzed by scanning electron microscopy(SEM) and transmission electron microscope(TEM) in detail, and the compositional distribution along the interface was analyzed by energy-dispersive spectrometer(EDS). Results show that the surface roughness of base metals plays an important role in the quality of the brazed joint because the surface roughness can enlarge the effective contact area, which can improve the brazing surface quality between two materials. A moderate roughness of treated Zr-based metallic glass of 18 μm is shown to be the best for the soldering, while the surface roughness has a weak effect on the soldering behavior of Au-12 Ge solder on copper. After soldering, long-range diffusion of atoms occurs between the base metal and solder, and five distinct regions are formed at the joint region.

Cutting Characteristics of Zr-Based Bulk Metallic Glass

Cutting behavior exerts a considerable influence on the fabrication of bulk metallic glass(BMG) components. In this study,the influences of machining parameters(i.e.,depth of cutting,feed rate,and spindle rate) on the turned surface of a Zr-based BMG after observing the 3D morphologies of this surface were characterized.The results showed that the influence of the spindle rate on the surface morphologies is more substantial as compared to the depth of cutting and the feed rate. Nanoscratch tests were conducted to further characterize the separation mechanism of the chips,which revealed that the chips are torn off the surface of a BMG because of inhomogeneous localized maximum shear stress.

Microstructure and compressive/tensile characteristic of large size Zr-based bulk metallic glass prepared by laser solid forming

The large size, crack-free Zr_(55)Cu_(30)Al_(10)Ni_(5) bulk metallic glass(BMGs) with the diameter of 54 mm and the height of 15 mm was built by laser solid forming additive manufacturing technology, whose size is larger than the critical diameter by casting. The microstructure, tensile and compressive deformation behaviors and fracture morphology of laser solid formed Zr_(55)Cu_(30)Al_(10)Ni_5 BMGs were investigated. It is found that the crystallization mainly occurs in the heat-affected zones of deposition layers, which consist of Al_5Ni_3Zr_2, NiZr_2, ZrCu, CuZr_2 phases. The content of amorphous phase in the deposit is about 63%.Under the compressive loading, the deposit presents no plasticity before fracture occurs. The fracture process is mainly controlled by the shear stress and the compressive shear fracture angles of about39?. The compressive strength reaches 1452 MPa, which is equivalent to that of as-Cast Zr_(55)Cu_(30)Al_(10)Ni_5 BMGs, and there exist vein-like patterns, river-like patterns and smooth regions at the compressive fractography. Under the tensile loading, the deposit presents the brittle fracture pattern without plastic deformation. The fracture process exhibits normal fracture model, and the tensile shear fracture angle of about 90?. The tensile strength is only about 609 MPa, and the tensile fractography mainly consists of micro-scaled cores and vein-like patterns, dimple-like patterns, chocolate-like patterns and smooth regions. The results further verified the feasibility and large potential of laser additive manufacturing on fabrication and industrial application of large-scale BMGs parts.

Relationship between composite structures and compressive properties in CuZr-based bulk metallic glass system

Bulk metallic glass (BMG) composites with the austenite B2 phase as reinforcement macroscopically showed strain hardening behavior due to the plasticity induced by martensitic transformation during deformation. Relationship between characteristics of the B2-CuZr reinforcing phase and uniaxial compressive properties of CuZr-based BMG composites was studied. Mechanical properties of these BMG composites were found to depend on not only the reinforced phases but also the amorphous matrix,and the yield and fracture strength can be roughly estimated by the rule of mixture principle. Distribution of the reinforced B2-CuZr phase has an important impact on the compressive plasticity even for the composites with a similar volume fraction of the crystalline phase.

Plastic deformation of a Zr-based bulk metallic glass fabricated by selective laser melting

Fully amorphous Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_(5) bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa and a reproducible plastic strain of about 0.5% were obtained for cylindrical SLM samples.The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass.This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation.Despite these heterogeneities,the shear bands are straight and form in the plane of maximum shear stress.Additive manufacturing,hence,might not only allow for producing large BMG samples with complex geometries but also for manipulating their deformation behaviour through tailoring porosity and structural heterogeneity.

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.