Ce-based amorphous metallic plastic

The present invention belongs to the field of amorphous metal alloys and especially concerns a Ce based amorphous metallic plastic.

Compared with metallic glasses, polymeric glasses have superior glass forming ability, low glass transition temperature (T g ) and wider supercooled liquid region (ΔT, defined as the difference between T g and the onset crystallization temperature T x ), thus have a very wide range of applicability. The thermoplasticity nature of common glassy polymers is exploited in molding and imprinting. Since chemical scientists invented the thermoplastics in 1940's, they became the basic materials for the 2 nd industrial revolution. Although their strength is only about one fiftieth of that of steels, thermoplastics products became very cheap because they could be prepared repeatedly using the same mold at a temperature near room temperature. Now thermoplastics are widely used in our daily lives.

In the early 1960's, non-crystalline alloys (so called metallic glasses) were firstly fabricated in laboratories. Compared with polymers, metallic glasses also have advantages in mechanical, electrical, magnetic and chemical properties. Amorphous metal alloys have a supercooled liquid region ΔT above T g . When an amorphous metal alloy was heated into this region, it still keeps its glassy state and does not crystallized immediately. In general, the wider range of ΔT suggests better deformability of the supercooled state. Therefore, the stability against crystallization is crucial for deformation of an amorphous metal alloy in its supercoolied state. The stability during a heating process is closely related with the critical cooling rate necessary for forming a glass from its liquid. For a good glass former, it is expected that the time-temperature-transformation (TTT) curve will move toward the long time direction.

The conventional melt-spin glasses have a limited ΔT and could not be used to investigate the related properties of the supercooled liquid region. In the early 1990's, bulk metallic glasses (BMGs) with large size up to millimeters even centimeter scales in three dimensions were developed using conventional casting methods. For most of BMGs, their values of ΔT are larger than 45 K and even larger than 100 K in some case. The supercooled liquids of these BMGs show typical Newtonian flow characteristics at low strain rates or low stresses and the maximum elongation could reach about 15000%. For crystalline alloys, they are unable to deform as easily as the viscous supercooled liquids of BMGs, which are capable of remaining the glassy structure and original properties even after large plastic deformation. The unique combination of these superior properties and homogeneous microstructure makes BMGs a new type of engineering materials in applications such as manufacturing the micro-electro-mechanical components. Meanwhile, high strain rates and superplasticity are suitable for quality control, thus make it possible for the mass production.

For most of the known BMGs, however, their industrial applications are still impeded by the limitation of alloy size and the lack of workability and machinability. The polymerlike exploitation of the supercooled viscous flow of many BMGs was also postponed due to low T g and low stability against crystallization. Additionally, some BMGs based on noble metals like Pd, Pt and Au can only be used in the experimental laboratory because of their high cost although they have good glass forming ability and superplasticity in the supercooled liquid region.

The present invention is aimed to overcome the problems in the known BMGs and thus to provide a new type of BMGs named Ce-based amorphous metallic plastics. These problems are the limitation of the small size, poor workability and machinability, the limitation in exploitation of the viscous supercooled liquid due to high T g and low crystallization resistance and the high cost in some BMGs containing the noble metals such as Pd, Pt and Au. The present amorphous metallic plastics have extremely low T g , wide supercooled liquid region ΔT and low cost coming from the cheap raw materials having low purity.

The invention is realized using the following techniques and methods.

The invention provides amorphous metallic plastics based on Cerium which can be represented by the following formula:

Ce a Al b M c

in which 55≦a≦75, 5≦b≦25, 10≦c≦25, and a+b+c=100.

The M can be one of three elements Co, Cu and Ni.

The purities of the said Ce, Al and M are no less than 99.5.wt. % (weight percent).

The present invention provides Ce-based amorphous metallic plastics which can be represented by the following formula:

Ce d Al e Cu f Z g

in which 55≦d≦75, 5≦e≦15, 15≦f≦25, 0.01≦g≦10, and d+e+f+g=100.

Z is one element selected from Co, Fe, Hf, Mg, Mo, Nb, Sc, Ta, Ti, W, Zn and Zr.

The purities of the said Ce, Al, Cu and Z are no less than 99.5.wt. % (weight percent).

Furthermore, the present invention provides Ce-based amorphous metallic plastics which can be represented by the following formula:

Ce h Al i Cu j Ni k .

in which 55≦h≦75, 5≦i≦15, 15≦j≦25, 0.01≦k≦55, and h+i+j+k=100.

The purities of the Ce, Al, Cu and Ni are no less than 99.5.wt. % (weight percent).

The above-described Ce-based amorphous metallic plastics can be prepared using the conventional method known in the field of metallic glasses. Specifically, the preparation method includes the following steps:

1) Preparation of mother ingots: In a Ti-absorbed arc melting furnace under Argon atmosphere, a mixture of elements Ce, Al and M according to the above formula Ce a Al b M c , or a mixture of Ce, Al, Cu and Z according to the above formula Ce d Al e Cu f Z g , or a mixture of Ce, Al, Cu and Ni according to the above formula Ce h Al i Cu j Ni k is blended and melted until homogeneity, and then cooled to form a mother ingot.

2) Suction casting: In a Ti-absorbed arc melting furnace under Argon atmosphere, the mother ingot prepared in the first step is remelted and then suction casted into a copper mold with different cavities to form a sample in the form of rod or sheet.

It should be stressed that many modifications and changes can be made to the present invention without departing the spirit and scope thereof. Although what the instant invention illustrates is to produce Ce-based amorphous metallic plastics by forming an amorphous ingot in a way of suction casting, it is well-known to the person ordinarily skilled in the art that any suitable technique for fabricating non-crystalline alloys or any related casting method under a protective atmosphere such as spray casting, single- or twin-roll melt-spinning, planar flow casting and metal pulverization and so on can also be used to prepare Ce-based amorphous metallic plastics.

For the present Ce based amorphous metallic plastics, the amorphous nature and the volume fraction of the amorphous phase can be determined and evaluated using known techniques such as X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). In the examples of the present invention, XRD measurements were carried out on a MAC M03 XHF diffractometer with Cu K a radiation and HRTEM measurements on a TECNAI-F20 instrument operated at 200 kV. The thin foils for the HRTEM measurements were prepared by mechanical thinning and chemical polishing.

Similarly, any suitable methods can also be used to examine the thermal properties of the Ce-based amorphous metallic alloys. By way of an example, the thermal properties of our samples were determined by differential scanning calorimetry (DSC) under a purified argon atmosphere in a Perkin-Elmer DSC-7, calibrated for temperature and energy with high-purity indium and zinc. Both isothermal and continuous heating (at a rate of 10 K min −1 ) were used

The mechanical properties and density data, etc of the present Ce based alloys can be measured using many universal instruments. In the present invention, the mechanical properties including yield strength and elastic strain were measured at room temperature and at 90° C. by an MTS 880 system. Compression tests were conducted at a strain rate of 1×10 −3 s − . Acoustic velocities were determined by a pulse echo overlap method on a MATEC 6600 ultrasonic system with a measuring sensitivity of 0.5 ns and a frequency of 10 MHz. Young's modulus E, bulk modulus B, Poisson's ratio v and shear modulus G were derived from the acoustic velocities. The density was determined by the Archimedean technique and the accuracy lies within 0.1%. Vickers hardness was measured with a Polyvar Met microhardness tester using a load of 1.96 N. The electrical resistance of the sample at room temperature was measured on a PPMS 6000 instrument (Quantum Design Instrument, Inc.).

The Ce based amorphous metallic plastics defined in the present invention should contain the amorphous phase with a volume fraction of at least 50%. In most cases, the Ce based amorphous metallic plastics prepared according to the present invention have a single amorphous phase, a wide supercooled liquid region ΔT of no less than 20 K and a low T g of no more than 430 K. These thermal parameters (ΔT and T g ) can be examined using DSC method at a scanning rate of 10 K/min.

The Ce based amorphous metallic alloys in this invention have an extremely low T g close to room temperature, a wide supercooled liquid region and high stability against crystallization, thus can be deformed homogeneously in their viscous supercooled liquid state in low temperatures like the near boiling point of water. This polymerlike superplasticity (homogenous deformation) of these Ce based amorphous metallic alloys makes them very easy to form or imprint a complex product with an amorphous structure. For example, in this invention, a precise shape or article can be imprinted on the surface of a Ce based amorphous metallic sample in near boiling water under a pressure of 30˜300 MPa.

Generally, compared with the prior arts, the present Ce based amorphous metallic plastics contain Ce as a main component and also several addition elements like Al, Co, Cu, Fe, and Nb, and have advantages as follows:

1. They have high glass forming ability, and easily cast into bulk glasses with different sizes ranging from millimeter to centimeter; 2. They have extremely low T g and can deform like polymeric thermoplastics; 3. They have wide supercooled liquid regions and high thermal stability against crystallization, thus are suitable for industrial production (i.e. a long manufacturing time before crystallization); 4. They have high thermostability at low temperatures near the boiling point of water in their supercooled liquid states, thus are able to deform repeatedly in a precise die. 5. They contain the addition components selected from commonly used metals like Al, Co, Cu, Fe, Zn, Nb and so on, which can obviously decrease the cost of materials.

FIG. 1 shows the appearance of Ce-based amorphous metallic plastics of the present invention. A Ce 70 Al 10 Cu 20 glassy sheet with a size of 1.5×12×70 mm 3 (A) is the sample prepared in Example 1. An as-cast Ce 68 Al 10 Cu 20 Nb 2 glassy rod of 8 mm in diameter (B) is prepared in Example 3.

FIG. 2 shows XRD results of a Ce 70 Al 10 Cu 20 glassy sheet of 2 mm in diameter (A) with a size of 1.5×12×70 mm 3 prepared in Example 1 and an as-cast Ce 68 Al 10 Cu 20 Nb 2 glassy rod of 8 mm in diameter (B) prepared in Example 3.

FIG. 3 shows HRTEM image and selected-area electron diffraction pattern for the 1 mm diameter Ce 70 Al 10 Cu 20 as-cast sample prepared in Example 1, showing a single glassy phase with no evidence for nanocrystallization.

FIG. 4 shows DSC results at a heating rate of 10 K/min for the Ce 70 Al 10 Cu 20 glassy sample (A) prepared in Example 1 and the Ce 68 Al 10 Cu 20 Nb 2 glassy sample (B) prepared in Example 3.

The inset picture in the right corner in FIG. 4 shows isothermal DSC traces for Ce 70 Al 10 Cu 20 glass (prepared in Example 1) held at 120° C.: (a) immediately after casting, and (b) after three months at room temperature (20-38° C.).

FIG. 5 shows the time-temperature-transformation (TTT) diagram for crystallization of Ce 70 Al 10 Cu 20 glass in Example 1. Isothermal DSC traces have been used to estimate the times to 1% (open circle) and 99% (solid circle) crystallized at each temperature. The dashed line extrapolated to room temperature (˜20° C.) shows the onset time for crystallization at that temperature to be ˜10 10 s (˜200 years).

FIG. 6 shows the true stress-true strain curve of a 2 mm diameter Ce 70 Al 10 Cu 20 glassy rod (in Example 1) tested under compression at RT and at 90° C.

The inset of FIG. 6 shows the starting sample, 2 mm in diameter and 3 mm in height, on the left and the sample compressed at 90° C., 5 mm in diameter and 0.3 mm in height, on the right.

FIG. 7 shows the 1 mm diameter glassy rods (prepared in Example 1) formed into letters by simple manipulation in near-boiling water.

FIG. 8 shows the impression of a UK five-pence coin made on the surface of a Ce 70 Al 10 Cu 20 glassy sheet (prepared in Example 1) held in near-boiling water, demonstrating excellent imprintability and viscous deformability.

FIG. 9 shows XRD results of the 10 mm diameter as-cast Ce 69.5 Al 10 Cu 20 Co 0.5 glassy rod prepared in Example 2.

FIG. 10 shows DSC results at a scanning rate of 10 K/min for the 10 mm diameter as-cast Ce 69.5 Al 10 Cu 20 Co 0.5 glassy rod prepared in Example 2.