US20070253856A1

US20070253856A1 - Low Cost Amorphous Steel

Info

Publication number: US20070253856A1
Application number: US11/628,574
Authority: US
Inventors: Kenneth Vecchio; Justin Cheney
Original assignee: University of California
Current assignee: University of California
Priority date: 2004-09-27
Filing date: 2005-09-27
Publication date: 2007-11-01
Also published as: WO2006037093A3; KR20090092346A; KR20070045324A; JP2008514815A; WO2006037093A2; KR100933849B1; EP1794337A2; CN101014728B; EP1794337A4; US20110284135A1; CA2577718A1; CN101014728A

Abstract

Design and fabrication processes and compositions for iron-based bulk metallic glass materials or amorphous steels. Examples of bulk metallic glasses based on the described compositions may contain approximately 59 to 70 atomic percent of iron, which is allowed with approximately 10 to 20 atomic percent of metalloid elements and approximately 10 to 25 atomic percent of refractory metals. The amorphous steels may exhibit X-ray diffraction patterns as shown in FIG. 1. The compositions can be designed using theoretical calculations of the liquidus temperature to have substantial amounts of refractory metals, while still maintaining a depressed liquidus temperature. The alloying elements are molybdenum, tungsten, chromium, boron, and carbon. Some of the alloys are ferromagnetic at room temperature, while others are non-ferromagnetic. These amorphous steels have increased specific strengths and corrosion resistance compared to conventional high strength steels.

Description

This application claims the priority of U.S. Provisional Patent Application No. 60/613,780 entitled “LOW COST AMORPHOUS STEEL” and filed Sep. 27, 2004.

BACKGROUND

This application relates to compositions of amorphous metallic materials and bulk metallic glasses (BMGs).
Amorphous metallic materials made of multiple components are amorphous with a non-crystalline structure and are also known as “metallic glass” materials. Such materials are very different in structure and behaviors from many metallic materials with crystalline structures. Notably, an amorphous metallic material is usually stronger than a crystalline alloy of the same or similar composition. Bulk metallic glasses are a specific type of amorphous materials or metallic glass made directly from the liquid state without any crystalline phase and exhibit slow critical cooling rates, e.g., less than 100 K/s, high material strength and high resistance to corrosion. Bulk metallic glasses may be produced by various processes, e.g., rapid solidification of molten alloys at a rate that the atoms of the multiple components do not have sufficient time to align and form crystalline structures. Alloys with high amorphous formability can be cooled at slower rates and thus be made into larger volumes. The amorphous formability of an alloy can be described by its thermal characteristics, namely the relationship between its glass transition temperature and its crystallization temperature, and by the difference between its liquidus temperature and its ideal solution melting temperature. Amorphous formability increases when the difference between the glass transition temperature and crystallization temperature increases, and when the difference between its liquidus temperature and ideal solution melting temperature increases.
Various known iron-based amorphous alloy compositions suitable for making non-bulk metallic glasses) have relatively limited amorphous formability and are used for various applications, such as transformers, sensor applications, and magnetic recording heads and devices. These and other applications have limited demands on the sizes and volumes of the amorphous alloys, which need to be produced. By contrast, iron-based bulk metallic glasses can be formulated to be fabricated at slower critical cooling rates, allowing thicker sections or more complex shapes to be formed. These Fe-based BMGs can have strength and hardness far exceeding conventional high strength materials with crystalline structures and thus can be used as structural materials in applications that demand high strength and hardness or enhanced formability.
Some iron-based bulk metallic glasses have been made using iron concentrations ranging from 50 to 70 atomic percent. Metalloid elements, such as carbon, boron, or phosphorous, have been used in combination with refractory metals to form bulk amorphous alloys. The alloys can be produced into volumes ranging from millimeter sized sheets or cylinders. A reduced glass transition temperature on the order of 0.6 and a supercooled liquid region greater than approximately 20K indicates high amorphous formability in Fe-based alloys.

SUMMARY

This application describes compositions of and techniques for designing and manufacturing iron-based amorphous steel alloys with a significantly high iron content and high glass formability that are suitable for forming bulk metallic glasses. For example, a composition suitable for bulk metallic glasses described in this application may include 59 to 70 atomic percent of iron, 10 to 20 atomic percent of metalloid elements, and 10 to 25 atomic percent of refractory metals, where the iron, metalloid elements and refractory metals are alloyed with one another to form an amorphous phase material. One exemplary formulation for iron-based metallic glass materials is
Fe_78-a-b-cC_dB_eCr_aMo_bW_c
where (a+b+c)≦17, ‘a’ ranges from 0 to 10 (e.g., 2 to 10), ‘b’ from 2 to 8, ‘c’ from 0 to 6, ‘d’ from 10 to 20, and ‘e’ from 3 to 10. The values of a, b, c, d, and e are selected so that the atomic percent of iron exceeds 59 atomic %. One specific example is Fe_78-a-b-cC₁₂B₁₀Cr_aMo_bW_c.
Bulk metallic glass materials based on the above formulation may be designed by computing the liquidus temperatures based upon the concentrations of alloying elements and optimizing the compositions. This method determines alloys with high glass formability by using theoretical phase diagram calculations of multi component alloys.
As another example, this application describes a composite material that includes 59 to 70 atomic percent of iron, 10 to 20 atomic percent of a plurality metalloid elements, and 10 to 25 atomic percent of a plurality of refractory metals. The iron, metalloid elements and refractory metals are alloyed with one another to form an amorphous phase material.
A process for producing a bulk metallic glass based on a composition disclosed here is described as an example. First, a mixture of the components including iron, refractory metals, carbon and boron is melted into an ingot (e.g., using an arc melting process). The molten final ingot is solidified to form a bulk amorphous metallic material. The solidification may be conducted rapidly using a chill casting technique. This fabrication process can be used to make Fe-based alloys into amorphous samples with 0.5 mm in thickness in its minimum dimension. This process can also be used to produce, among other compositions, a steel of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂with a high iron content and a large supercooled liquid region greater than about 50K.
These and other compositions and their properties and fabrications are described in the attached drawings, the detailed description, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows measured X-ray diffraction patterns showing amorphous structures of a) Fe₆₀C₁₅B₈Mo₁₀Cr₄W₃, b) Fe₆₀C₁₈B₅Mo₁₀Cr₄W₃, c) Fe₅₉C₁₂B₁₀Mo₁₁Cr₅W₃, d) Fe₆₁C₁₂B₁₀Mo₁₀Cr₄W₃, e) Fe₆₁C₁₂B₇Mo₁₁Cr₃W₃, Fe₆₈C₁₂B₃Mo₁₀Cr₅W₂, f) Fe₆₈C₁₀B₁₀C₄Mo₆W₂, and g) Fe₆₄C₁₀B₈Mo₁₁Cr₄W₃, Fe₆₈C₁₀B₈Mo₁₁W₃, where the vertical axis is the measured strength of the diffraction signal and the horizontal axis is the measured angle which is twice of the diffraction angle.
FIG. 2 shows the measured X-ray diffraction pattern showing the amorphous structure of (Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂)₉₈Y₂.
FIG. 3 shows the measured X-ray diffraction pattern showing the amorphous structure of (Fe₅₇C₁₀B₁₀Cr₁₃Mo₇W₃)₉₈Y₂.
FIG. 4 shows the measured X-ray diffraction pattern showing the amorphous structure of Fe₆₁C₁₂B₁₀Cr₄Mo₁₀W₃.
FIG. 5 shows the measured X-ray diffraction pattern showing the amorphous structure of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂.
FIG. 6 shows thermal mechanical analysis (TMA) results for Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂where the glass transition temperature Tg is indicated by an arrow.
FIG. 7 shows differential thermal analysis (DTA) results for Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂where glass transition and crystallization temperatures are indicated by arrows.

DETAILED DESCRIPTION

Designing of bulk metallic glass compositions having multiple elements with desired material properties is technically difficult in part because the complexities of the interactions and effects of the different elements. In such a complex material, a change in any aspect of the composition, such as the quantity of one element or a substitution of one element with another element, may significantly affect the property of the final metallic glass material. Due to such complexity, many known metallic glass compositions are results of trial and error. The Fe-based metallic glass compositions described in this application were designed based on a systematic approach to selection of metalloid elements and refractory metal elements in combinations with iron to search for compositions with high glass formability represented by a large difference between a low glass transition temperature and a high crystallization temperature and a large difference between the liquidus temperature and the ideal solution melting temperature which the weighted average of the melting temperatures of different elements in the mixture.
Under this approach to designing a specific bulk metallic glass, the liquidus temperatures are calculated based upon the concentrations of different alloying elements selected as the constituents of the bulk metallic glass. The compositions are then optimized based on the respective resulting liquidus temperatures. The concentrations of refractory metal elements such as molybdenum and chromium added to the Fe-based alloy can also be optimized such that the final alloy has 1) a high or maximum viscosity due to high concentrations of added refractory metals, and 2) a low or minimum liquidus temperature. The compositions are selected to achieve low liquidus temperatures and high ideal solution melting temperatures so that a candidate composition has a large difference between the liquidus temperature and the ideal solution melting temperature. Such candidate compositions can maintain their liquidus phase over a large temperature range within which a relatively slow cooling process can be used to achieve the amorphous phase in a bulk material. Among the candidate compositions with a large difference between the liquidus temperature and the ideal solution melting temperature, compositions with a large difference between a low glass transition temperature and a high crystallization temperature are further identified and selected as candidates for the final metallic glass composition. This numerical and systematic design approach works well in predicting the compositions of existing amorphous alloys and was used to design the compositions of the examples described below.
One application of the above design approach is metallic glass compositions based on the metal iron, which is relatively inexpensive and widely available. Such iron-based metallic glass materials can be designed to achieve good glass formability at a reasonably low price to allow for mass production and uses in a wide variety of applications. The compositions of iron-rich amorphous alloys described here can be used to reach an amorphous state under a modest cooling rate, thus forming bulk metallic glass materials. Several examples of such bulk metallic glasses described here have a content of iron of approximately from 59 to 70 atomic percent and are also referred to as amorphous steels. In these examples, the iron is further alloyed with 10 to 20 atomic percent metalloid elements and 10 to 25 percent refractory metals. The compositions are chosen using theoretical calculations of the liquidus temperature. The alloys are designed to have a sufficient amount of refractory metals to stabilize the amorphous structure, while still maintaining a depressed liquidus temperature. In some implementations, the principal alloying elements may be molybdenum, tungsten, chromium, boron, and carbon. Some of the resulting alloys are ferromagnetic at the room temperature, while others are non-ferromagnetic. These amorphous steels have increased specific strengths and corrosion resistance compared to conventional high strength steels. The amorphous structure of these alloys imparts unique physical and mechanical properties to these alloys, which are not obtained in their crystalline alloy forms.
Notably, the compositions described here have a higher Fe content than other Fe-based bulk metallic glass materials and do not use expensive alloying elements found in other Fe-based bulk metallic glass materials to make the material amorphous under slow cooling conditions. The compositions of the present amorphous steels are significantly closer to standard steel alloy compositions than other Fe-based bulk metallic glasses and thus are much more attractive to scale up production by using various steel production techniques, processes and equipment including existing techniques, processes and equipment. In comparison, various commercial bulk metallic glasses use Zr-based materials and therefore are expensive to produce. The present compositions use iron, one of the cheapest and widely available metallic elements, as a major component and thus significantly reduce the cost of the materials.
One formulation of the present compositions can be expressed as
Fe_78-a-b-cC_dB_eCr_aMo_bW_c,
where the subscript parameters represent the relative atomic % of the different elements. Based on the above described systematic design approach, the relative quantities of the elements are limited by the following conditions: (a+b+c)≦17; ‘a’ ranges from 0 to 10; ‘b’ from 2 to 8; ‘c’ from 0 to 6; ‘a’ from 10 to 20; and ‘e’ from 3 to 10. In addition, the values of a, b, c, d, and e are selected so that the atomic percent of iron exceeds 59 atomic %. One amorphous material based on this composition is Fe_78-a-b-cC₁₂B₁₀Cr_aMo_bW_cfor d=12 and e=10.
The alloys based on the above compositions may be produced by melting mixtures of high purity elements. For example, the melting may be performed in an arc furnace under an argon atmosphere. The alloy ingot is fabricated from iron as the main metal element, refractory elements such as Cr, W, and Mo, and metalloid elements such as carbon and boron. Specific quantities of these elements are selected based on the above prescription. The mixture of these elements with predetermined relative quantities may be melted together to form an ingot by, e.g., using arc melting and other meting methods. The ingot is re-melted several times to ensure homogeneity of the ingot and then cast into a chilled casting mold to produce a desired shape in an amorphous structure. The melting may be performed in an electric furnace, an induction-melting furnace, or any other melting technique that allows the elements in the above-described compositions to be melted together. The heat for the melting may generate from various processes such as induction heating, furnace heating, or arc melting.
For example, the arc melting method was used to successfully produce the following bulk metallic glass material samples with dimensions of at least of 0.635 mm: Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂Y₂, Fe₅₇C₁₀B₁₀Cr₁₃Mo₇W₃Y₂, Fe₆₁C₁₂B₁₀Cr₄Mo₁₀W₃, Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂, Fe₆₀C₁₅B₈Mo₁₀Cr₄W₃, Fe₆₀C₁₈B₅Mo₁₀Cr₄W₃, Fe₆₁C₁₂B₇Mo₁₁Cr₅W₄, Fe₆₁C₁₂B₁₀Mo₁₁Cr₃W₃, Fe₆₄C₁₀B₈Mo₁₁Cr₄W₃, and Fe₆₈C₁₀B₈Mo₁₁W₃. The samples were suction cast into a copper sleeve. Two sleeves of different thicknesses of 0.025″ and 0.050″ were used. The amorphous nature of the cast alloys was verified using X-ray diffraction. Thermal properties were obtained using a differential thermal analyzer (DTA), a differential scanning calorimeter (DSC), and a thermal mechanical analyzer (TMA). Two classes of iron-rich amorphous steels were produced; one class contains yttrium, and the other lacks yttrium. The alloys produced without the use of yttrium represent the optimum alloys in terms of their low cost manufacturability. In addition, these alloys are composed of elements that are relatively resistant to oxidation, further increasing their manufacture potential.
FIGS. 1 through 7 show various measured results of these samples. FIGS. 1 through 5 are measured X-ray diffraction patterns showing amorphous structures of the samples. FIG. 6 is measured TMA data for the sample with a composition of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂where the vertical axis is the TMA probe position and the location where the probe falls down is used as a measure of the glass transition temperature Tg. FIG. 7 shows differential thermal analysis (DTA) results for Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂where the vertical axis is the heat flow used during the measurement. The sharp transitions in DTA indicate when reactions occur, either endotherms or exotherms, indicative of crystallization, or melting, and even the very small transition at the start reflecting the glass transition. The specific DTA measurement in FIG. 7 shows the difference between the glass transition temperature (Tg) and the crystallization temperature (T×1) to be in excess of 50K, which is an indicator of a good glass forming ability.
The compositions of amorphous steel described here have higher levels of iron in combination with low cost refractory metals and metalloid elements than various amorphous steels made by others. Therefore, the applications of such high iron content amorphous steels are more favorable to replace conventional high strength structural steels than other amorphous steels. In particular, the composition of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂has a high iron content of 68 atomic % and uses low cost alloying elements of C, B, Cr, Mo and W to exhibit a large supercooled liquid region, greater than approximately 50K. Therefore, this composition is suitable for bulk production for industrial applications.
The Fe-rich materials based on the present compositions may be used in a wide range of applications. The relatively high amorphous formability of these materials makes them desirable materials for a wide range of applications including but not limited to sporting goods such as tennis rackets reinforcements, skis, baseball bats, golf club heads, consumer and other electronics such as device cases, antennas, and thermal solutions for high-strength, light-weight, components and parts used in mobile devices such as notebook computers, cell phones, portable PDA's, MP3 players, portable memory devices, multimedia players, components and parts used in avionics devices, and automotive parts and devices. The Fe-rich materials based on the present compositions may also be used as low cost alternatives to titanium and other specialty alloys in various aerospace, industrial, and automotive applications such as springs and actuators, and various corrosion resistant applications. In addition, the compositions may also be used to form non-ferromagnetic structural materials in military applications for avoiding magnetic triggering of mines. Furthermore, the present compositions may be used for biomedical implants, transformer cores, etc. Many other structural material applications are certainly possible.
In summary, only a few implementations are disclosed. However, it is understood that variations and enhancements may be made.

Claims

1. A composite material, comprising a plurality of components defined by:

Fe_78-a-b-cC_dB_eCr_aMo_bW_c

wherein (a+b+c)≦17, a ranges from 0 to 10, b from 2 to 8, c from 0 to 6, d from 10 to 20, and e from 3 to 10 and wherein values of a, b, c, d and e are selected so that the atomic percent of iron exceeds 59 atomic %.

2. The material as in claim 1, further comprising Y and wherein a composition of the components is Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂Y₂.

3. The material as in claim 1, further comprising Y and wherein a composition of the components is Fe₅₇C₁₀B₁₀Cr₁₃Mo₇W₃Y₂.

4. The material as in claim 1, wherein a composition of the components is Fe₆₁C₁₂B₁₀Cr₄Mo₁₀W₃.

5. The material as in claim 1, wherein a composition of the components is Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂.

6. The material as in claim 1, wherein a composition of the components is Fe₆₀C₁₅B₈Mo₁₀Cr₄W₃.

7. The material in claim 1, wherein a composition of the components is Fe₆₀C₁₈B₅Mo₁₀Cr₄W₃.

8. The material as in claim 1, wherein a composition of the components is Fe₆₁C₁₂B₇Mo₁₁Cr₅W₄.

9. The material as in claim 1, wherein a composition of the components is Fe₆₁C₁₂B₁₀Mo₁₁Cr₃W₃.

10. The material in claim 1, wherein a composition of the components is Fe₆₄C₁₀B₈Mo₁₁Cr₄W₃.

11. The material in claim 1, wherein a composition of the components is Fe₆₈C₁₀B₈Mo₁₁Cr₄W₃.

12. The material in claim 1, wherein a composition of the components is Fe₅₉C₁₂B₁₀Mo₁₁Cr₅W₃.

13. The material in claim 1, wherein a composition of the components is Fe₆₁C₁₂B₁₀Mo₁₀Cr₄W₃.

14. The material in claim 1, wherein a composition of the components is Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂.

15. The material in claim 1, wherein a composition of the components is Fe_78-a-b-cC₁₂B₁₀Cr_aMo_bW_c.

16. A method for producing a material in claim 1, comprising:

melting a mixture of the components into an ingot;

re-melting the ingot to produce a homogeneous molten alloy; and

solidifying the molten ingot to form a bulk amorphous material.

17. The method in claim 16, wherein an arc melting process is used to perform the melting.

18. The method in claim 16, wherein an induction melting process is used to perform the melting.

19. A composite material, comprising:

59 to 70 atomic percent of iron;

10 to 20 atomic percent of a plurality metalloid elements; and

10 to 25 atomic percent of a plurality of refractory metals;

wherein the iron, metalloid elements and refractory metals are alloyed with one another to form an amorphous phase material.

20. The material as in claim 19, further comprising yttrium which is alloyed with the iron, metalloid elements and refractory metals.

21. The material as in claim 19, wherein the metalloid elements comprise C and B.

22. The material as in claim 19, wherein the refractory elements comprise Cr, W and Mo.