Research progress of the hottest bulk amorphous al

Research advances in bulk amorphous alloys *

research advances in bulk amorphous alloys

Chu Wei, Chen Guojun

Shougang metallic Research Institute, Beijing 100085 abstract the research advances in the field of bulk amorphous alloy materials are reviewed.the fabrication methods and excellent proper, and then ties of these alloys are described.the principles and influential factors of glass forming ability are also discussed in this paper.

key words bulk amorphous alloy, History and current situation of glass forming ability1 bulk amorphous alloys

amorphous alloys have long-range disordered and short-range ordered structures. Compared with crystalline alloys, they have many unique properties, such as high hardness, high strength, wear resistance, corrosion resistance and high resistance. For soft magnetic alloys, amorphous alloys have better comprehensive magnetic properties than crystalline alloys, that is, they can obtain high saturation magnetization and permeability at the same time

in 1960, duwez et al. First prepared Au Si amorphous alloy by melt quenching method, marking the start of the new material research field of amorphous alloy. In the following three decades, many amorphous alloys of alloy series were obtained by liquid phase quenching technology, which were widely used in different fields. However, the preparation of these amorphous alloys mostly requires an extremely high cooling rate of more than 104k/s, and the thickness is usually limited to 50 μ M, which limits the application range of this kind of material. Although bulk amorphous can be made by powder metallurgy, its overall performance is far lower than that of amorphous particles due to the limitation of molding technology. It has always been the goal of amorphous physics to obtain bulk amorphous directly from liquid phase with strong amorphous forming ability

since 1988, Inoue (Inoue Mingjiu) and others have studied the glass forming ability (GFA) of multi-component amorphous alloy systems, and obtained a series of large blocks of lanthanide, magnesium, hafnium, zirconium, titanium and palladium systems by means of water quenching and mold casting. Ford researchers have thus extended the extensibility of rubber by more than twice that of amorphous alloys, all of which have a wide supercooled liquid phase region, low critical cooling rate (RC) The thickness can reach 75mm. The above bulk amorphous alloys are limited to non-ferrous systems, and ferromagnetism is not obtained. Until 1995, Inoue and others used copper mold casting to obtain two types of ferromagnetic bulk amorphous alloys, namely fe- (al, GA) - (P, C, B, Si, GE) with soft magnetism and Nd Fe Al System with hard magnetism. Later, fe- (CO, Ni) - (Zr, HF, Nb) -b and other alloy systems came out. See Table 1 for details of the above alloy systems and their discovery dates. Table 1 maximum thickness Tmax of bulk amorphous alloy Critical cooling rate RC and Discovery Age alloy system Discovery Age Literature non

iron

magnetic

mg ln - (Cu, Ni) ≈ 10 ≈ [1 it is difficult to form a stable production mode in the domestic market] LN al - (Cu, Ni) ≈ 10 ≈ [2] ln GA - (Cu, Ni) 1989 [2] Zr Al - (Cu, Ni) ≈ 301 ~ 101990 [3] Zr Ti - (Cu, Ni) -Be ≈ 301 ~ 51993 [4] PD Cu Ni P ≈ 750.131996 [5] PD Cu Ni Si 1997 [6] iron

magnetic

property fe- (al, GA) - (P, C, B, Si, GE) ≈ 3 ≈ [7] fe- (Nb, Mo) - (al, GA) - (P, B, SI) 1995 [8] Nd Fe Al ≈ 121995 [9] co- (al, GA) - (P, B, SI) 1996[10] Fe - (CO, Ni) - (Zr, HF, NB) -B ≈ 6 ≈ [11]

2 formation of bulk amorphous alloy

2.1 glass forming ability

according to the homogeneous nucleation and growth theory of spherical crystals in the supercooled liquid region [12], for glass forming ability GFA, there are three factors that dominate, namely viscosity coefficient η，α Factor sum β Factor, where α＝ （N0V）1／3 σ／ΔΗ，β＝Δ S／R。 Where N0 is the Avogadro constant, V is the characteristic volume, σ Is the interface energy of solid/liquid phase, ΔΗ Is enthalpy change, Δ S is the entropy change and R is the gas constant. GFA with η、α and β The proportion of wood pulp imported from the United States increased by 9.19% in 2017. and η With TG/TM (TG is the glass transition temperature, TM is the melting point), α and β along with Δ TX = TX TG (where TX is the crystallization temperature) increases. Therefore, there are two main factors to obtain strong glass forming ability: (1) high TG/TM, (2) large Δ Tx。 From the critical cooling rate RC and maximum thickness Tmax and TG/TM and Δ The relationship between TX can explain this. Fig. 1 Relationship between critical cooling rate RC and maximum thickness Tmax of amorphous alloy and TG/TM [16] FIG. 2 critical cooling rate RC and maximum thickness Tmax of amorphous alloy and Δ TX relationship [15] 2.2 composition characteristics of bulk amorphous alloys

the above-mentioned multicomponent alloy system with strong glass forming ability has the following three common characteristics:

(1) the alloy system is composed of more than three components. According to thermodynamics, increasing the number of components in the alloy can effectively improve the entropy change Δ S. So as to improve the uniformity of nucleation and growth β The value of factor, GFA also increases. In addition, the addition of alloying elements also has an effect on the thermal stability of the alloy. 5. Ti, HF, W, Mn, etc Δ TX decreases, Mo, Nb, Co, Cr, etc Δ TX increases. Therefore, the appropriate addition of Nb, Mo, Cr (generally less than 6at%) can improve the glass forming ability of the alloy [8]

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