Liquidmetal Technologies Inc (LQMT)

[joshuaeyu]

Good read for those who cares about detail.

http://pcsmaa.nimte.ac.cn/uploadfiles/site20/201601/20160128190812-7654312966.pdf

10. Applications

From above descriptions, it is clear that BMGs or MGMCs have an interesting combination of properties. They exhibit very high strength (both in tension and compression), large elastic elonga- tion limit, very high hardness, and excellent corrosion resistance, etc.
For the applications, Kumar et al. [563] discussed the advantages of using metallic glasses in miniature applications. Size-dependent properties suggest that applications on length scales from 1 nm to 5 mm would benefit the most from BMGs. These applications are in the fields of MEMS (microelectromecha- nical system), NEMS (nanoelectromechanical systems), biomedical implants, precision microparts, surgical tools, and micromachines.
As different applications require various forms of glassy materials, the BMG alloy compositions are produced in the form of rods, sheets, plates, spheres, pipes, etc. Fig. 77 show some BMG- product photos fabricated directly from their molten state by DongGuan Eontec Co., Ltd. in China [564]. Fig. 77(a) exhibits some jewelries made from BMGs. Fig. 77(b)–(d) show the photographs of mobile phone skeletons (iPhone 6S+ mid frame) in different forms and shapes, in which Zr- and Cu-based BMGs are synthesized (Note that all the products are not artificially polished). The high yielding (or fracture) strength, low Young’s modulus, large elastic strain limit, and easy formability in the supercooled liquid region are the main attributes of BMGs that make them attractive for structural applications. This attribute of BMG alloys has been extensively exploited to produce different types of parts with complex shapes such as gears, coiled springs, and other complex parts [565]. The superior corrosion resistance of BMGs over their crystalline counterparts plays a major role in chemical applications. BMGs have been specifically considered as most appropriate materials for fuel cell separators. Fuel-cell systems are known to have a higher efficiency in comparison to internal combustion engines by directly converting the chemical energy of fuels to electrical energy. There has been recent progress in the development of proton-exchange membrane fuel cells (PEMFCs) by utilizing the superior corrosion resistance and viscous deformability of BMGs. Besides, in the field of biomedical applications, implants that ‘biocorrode’ are of considerable interest. Deploying them not only abrogates the need for the implantremoval surgery, but also circumvents the long-term negative effects of permanent implants [497–499,566,567]. In addition, the outstanding soft magnetic properties of the Fe-based melt-spun ribbons or BMGs have found applications in power-distribution transformers and several other applications [565]. Recently, Krautz et al. [568] reported on novel magnetocaloric composites based on La(Fe,Si)13 particles in an amorphous metallic matrix, showing a promising route for the production of compact refrigerant bodies that can be easily extended to other brittle giant magnetocaloric materials whose performance depends strongly on particle size.
The broad application of BMGs will go on. In comparison, the high strength together with high toughness in MGMCs render them potential candidates for applications in the field of structural engineering. The following is a design route for the development of high-performance knives [569].
Quality knives are typically fabricated from high-strength steel alloys. Depending on the applications, there are different require- ments for mechanical and physical properties that cause problems for steel alloys. For example, diver’s knives are generally used in salt water, which causes rust in steel knives. Titanium diver’s knives are a popular alternative due to their salt water corrosion resistance, but are too soft to maintain a sharp cutting edge. Steel knives are also magnetic, which is undesirable for military applications where the knives are used as a tactical tool for diffusing magnetic mines. The solution to the deficiencies of titanium and steel knives is to fabricate them using MGMCs. They can be cast into net or near-net shaped knives with a combination of properties that exceed both titanium and steels, which are based on titanium. The knife has a self- sharpening edge, and can retain an edge during service. And it is hard, non-magnetic, corrosion-resistant against a variety of corro- sive environments, and tough (to allow for prying), which can be cast into a net-shape with a mirror finish and a complex shape with an excellent wear resistance, and low density, as shown in Fig. 78 [569]. Examples of a variety of net-shaped parts of the Ti-based MGMC DV1 (TiZrVCuBe) show how complex shapes can be cast with Ti-based composites. Bolts, washers, hollow tubes, and rods are demonstrated in Fig. 79(a) [570]. A 75 g plate of DV1 with 3.5 mm thickness and the feedstock from which it is created are shown in Fig. 79(b). Fig. 79(c) presents a two-layered composite including the DV1 MGMC and bcc Zr–Ti–Nb alloy. The structure is bent in a three- point-bend apparatus to 12.5 degree before delaminating occurred on one side. Significant plastic deformation in MGMCs is observed at the bending midpoint [164]. As presented in Section 1, various processing methods can be used to directly cast in-situ MGMCs with complex shapes, as shown in Fig. 80 [571]. The structural applications in MGMCs bear similarities to the monolithic BMGs. It should be noted that the special applications in strategic fields, such as the defense and aerospace, are for ex-situ Wf- reinforced MGMCs. The adiabatic shear-band failure mechanism of ex-situ Wf-reinforced MGMCs at high strain rates suggests that they can be used in the kinetic-energy penetrator applications.

11. Conclusions

The development of various ex-situ and in-situ MGMCs is reviewed in this paper. Since the first amorphous alloy was synthesized in the Au-Si system in 1960, people are trying to search for the BMGs with the large glass-forming ability in different alloy systems. Up to now, there have been many alloy systems, such as Zr, Ti, La, Mg, Cu, Ni, Fe, Pd, and Gd-based etc., which have the critical diameters over than 1 cm. These BMGs could be fabricated by various processing methods, including the copper-mould suction casting, Bridgman solidification, spark plasma sintering, electromagnetic-vibration process, pulsed-laser forming, low-pressure die-casting, melt atomization and spray deposition, continuous casting, etc. And the copper-mold suction casting is the most common method to fabricate BMGs, and most developed BMGs are based on this method all over the world.
Although a series of excellent mechanical properties have been explored gradually, the intrinsic room-temperature brittleness of monolithic BMGs is yet to be solved until the appearance of ex-situ and in-situ MGMCs since the 1990s. After foundation of plastic- deformation models, such as free-volume, STZ, and TTZ models, the shear-banding behavior, which is associated with the catastrophic failure at room temperature, is widely accept to explain the brittleness. However, in ex-situ and in-situ MGMCs, the secondary phases can effectively hamper the fast propagation of shear bands, and the improved toughness at room temperature is generally obtained. It should be noted that there exists mechanical asymmetry during the quasi-static uniaxial compression and tension for not only BMGs but also MGMCs. Specially, there is almost no work hardening during tension of ex-situ and in-situ MGMCs, even if the large compressive plasticity together with the macroscopic work hardening is obtained. Based on this asymme- try, the deformation micromechanisms upon compression and tension are analyzed in detail. Besides, on the basis of the background that it is inevitable for the engineering materials serving upon dynamic loading, the dynamic compression, tension, and shear punching behaviors of ex-situ and in-situ MGMCs are studied.
The deformation behaviors of MGMCs at cryogenic and high temperatures are experimentally and theoretically discussed. The fatigue results of BMGs and MGMCs are summarized and compared. In particular, the four-point-bending and tension– tension results of in-situ dendrite/MGMCs and the corresponding mechanisms are carefully explored. Note that the fatigue behavior in shape-memory MGMCs is first reported here. Though the advancement has been achieved in the study of mechanical properties, deeper understanding, such as deformation models, should be developed in order to widen the potential applications. Apart from the deformation, the corrosion and wear properties of ex-situ and in-situ MGMCs have been mentioned. And the composite thin-film metallic glasses together with Ni- and Cu- coated BMGs are investigated. The corresponding deformation model is illustrated by experiments and simulations. Lastly, the applications of MGMCs now and in future are discussed.

12. Future work

Although numerous efforts have been paid on the in-situ and ex- situ MGMCs during the past years, especially on the aspect of structural engineering, such as deformation, more work should be unfolded in order to pave a way for actual applications. Attempts to bridge high toughness and high strengths on the MGMCs have always been the goal of the previous, present, and future research.
The asymmetry in mechanical properties under compressive and tensile loadings exists, e.g., distinguished plasticity accompa- nied by the work-hardening behavior under compressive loading, but fully softening after yielding under tensile loading. For structural applications at room temperature, homogeneous deformation with the work-hardening behavior is highly expected. How to obtain homogeneous deformation is poorly understood to design MGMCs with high toughness. Based on these safety evaluations, deformation mechanisms should be explored exten- sively in the future. Besides, the service surrounding is complex for materials. More investigations on the deformation behavior can be concentrated under the high-speeding dynamic loading, such as dynamic compressive, tensile, and shearing loading at varied temperatures, such as cryogenic or high temperatures beyond the glass-transition temperature. Up to now, almost all the research activities on MGMCs are based on the as-cast samples. It is well known that it is inevitable to obtain micro-scaled casting pores in conventional alloys, and the rolling process is widely employed to remove the pores [572]. Previously, Cao et al. have demonstrated that the plasticity of BMGs after cold rolling is remarkably enhanced [573]. Thus, people may pay more attention to the rolling effect on MGMCs, which can remove the casting pores, and enhance the plasticity [574]. Additionally, lightweight is of interest for MGMCs with high specific strengths, such as Mg-, Ca-, and Ti- based MGMCs [570,575,576].
Except for the consideration on structural properties, functional properties should be vital [563,577–579], and developed for special applications, such as soft magnetism, high electroconduct- ibility, high thermal conductivity, shape memory, etc.

Acknowledgments

All the authors thank Prof. Y.W. Chung’s great invitation. We are indebted to many researchers in this field with whom we have had valuable and stimulating discussions, and whose work provided the inspiration for writing this overview. We wish to thank in particular Dr. M.Q. Jiang from the Institute of Mechanics, Chinese Academy of Sciences for providing the original artwork for the deformation model including TTZ and STZ theories, Dr. J. Bai from Northwestern Polytechnical University for his writing on fracture toughness, and Dr. H. Wu from the Central South University for his writing on wear behavior. Drs. Y.S. Wang and H.J. Yang from Taiyuan University of Technology give their contributions on the writings.
J.W.Q. would like to acknowledge the financial support of National Natural Science Foundation of China (nos. 51101110 and 51371122), the Program for the Innovative Talents of Higher Learning Institutions of Shanxi (2013), the Youth Natural Science Foundation of Shanxi Province, China (no. 2015021005), and the opening project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology), and the opening project number is KFJJ15-19M. P.K.L. would appreciate the National Science Foundation (DMR-0909037, CMMI-0900291 and CMMI-1100080), the Department of Energy (DOE) Office of Nuclear Energy’s Nuclear Energy University Programs (NEUP, grant no. 00119262), the DOE Office of Fossil Energy, NETL (DE- FE0008855, DE-FE-0011194, and DE-FE-0024054), with Drs C.V. Cooper, A. Ardell, Z.M. Taleff, R.O. Jenseng Jr, L. Tian, V. Cedro, R. Dunst, S. Lesica, J. Mullen, and S. Markovich as program managers, and the support from the U.S. Army Office Project (W911NF-13-1- 0438) with the program manager, Dr S.N. Mathaudhu.



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Professor Li serves as an analyst for the Institute of Metal Research at the Chinese Academy of Sciences and serves part-time as a professor at several universities in China.