|Title of Invention||
"METHOD OF INCREASING A CRYTALLIZATION ONSET TEMPERATURE OF AN IRON BASED ALLOY"
|Abstract||An alloy design approach to modify and improve existing iron based glasses. The modification is related to increasing the stability of the glass, which results in increased crystallization temperature, and increasing the reduced crystallization temperature (Tcrystaiiization/Tmeiting), which leads to a critical cooling rate for metallic glass formation. The modification to the iron alloys includes the addition of lanthanide elements, including gadolinium. The resulting properties of such a modified alloy are compared to those of an unmodified alloy in Figure 1. Figure 1.|
|Full Text||Method of Modifying Iron Based Glasses To Inreasse Crystallization Temperature Without Changing Melting Temperature
Crow Reference fa Related Applications
This application claims priority to U.S. Provisional Application No. 60/446,398 filed February 14,2003.
Field of Invention
The present invention relates generally to metallic glasses, and more particularly to a method.of increasing crystallization temperature, while minimally affecting melting temperature. Hie resultant glass has a reduced critical cooling rate which allows the formation of the glass structure by a larger number of standard industrial processing techniques, thereby enhancing me functionality of the metallic glass.
It has been known for at least 30 yean, since the discovery of Metglasses (iron based glass forming compositions used for transformer core applications) mat iron based alloys could be made to be metallic glasses. However, with few exceptions, these iron based glassy alloys have had very poor glass forming ability, and the amorphous state could only be produced at very high cooling rates (>106 K/B). Thus, these alloys can only be processed by techniques which give very rapid cooling such as drop impect or melt-spining techniques.
All metal glasses are metastable and given enough activation energy they will transform into a crystalline state. The kinetics of the transformationof a metallic glass to a crystalline material is governed by both temperature and time. In conventional TTT (Time-Temperature-Transformation) plots, the transformation often exhibits C-curve kinetics. At the peak transformation temperature, the devitrification (transformation from an amorphous glass to a crystalline structure) is extremely rapid, but as the temperature is reduced the devitrification occurs at an increasingly slower rate. When me crystallization temperature of the metallic glass is increased, the TTT curve is effectively shifted up (to higher temperature). Accordingly, any given temperature will be lower on (he TTT curve indicating a longer devitrification rate and, therefore, a more stable metal glass structure. These changes manifest as an increase in me available operating temperature and a dramatic lengthening of
stable time at any particular temperature before crystallization is initiated. The result of increasing the crystallization temperature ia an increase in the utility of the metal glass for a given* elevated service temperature.
Increasing the crystallization temperature of a metal glass may increase the range of suitable applications for metal glass. Higher crystallization temperature may allow the glass to be used in elevated temperature environments, such as under the hood applications in automobiles, advanced military engines, or industrial power plants. Additionally, higher crystallization temperatures may increase me likelihood that a glass will not crystallize even after extended periods of time in environments where the temperature is below the metal glass's crystallization temperature. This may be eapecially important fbr applications such as storage of nuclear waste at low temperature, but for extremely long periods of time, perhaps for thousands of years.
Similarly, increasing the .stability of (he glass may allow thicker deposits of glass to be produced and may also enable the use of mon efficient, effective, and diverse industrial processing methoda. For example, when an alloy melt ia spray formed, the deposit which is formed undergoes two distinct cooling regimes. The atomized spray cools very quickly, in the range of 10 to 10s K/s, which facilitates the formation of a glassy deposit Secondarily, the accumulated glass deposit cools from the application temperature (temperature of the spray as it is deposited) down to room temperature. However, the deposition rates may often be anywhere fiom one to several tons per hour causing the glass deposit to build up very rapidly. The secondary cooling of the deposit down to room temperature the cooling of the atomized spray, typically in the range of 50 to 200 K/s. Such a rapid build up of heated material in combination with the relatively slow cooling rate may cause the temperature of the deposit to increase, as the thermal mass increases. If the alloy is cooled below the glass transition temperature before crystallization is initiated, then the subsequent secondary slow cooling will not affect the glass content However, often the deposit can heat up to 600 to 700°C and at such temperatures, me glass may begin to crystallize. Thus, this crystallization can be avoided if the stability of the glass (i.e. the crystallization temperature) is increased.
There are many important parameters used to determine or predict the ability of an alloy to Forma metallic glass, including the reduced glass .or reduced crystallization temperature, the presence of a deep cutectic, a negative heat of mixing, atomic diameter
ratios,and relative ratios of alloying dements. However, one parameter that has been very successful in predicting glass forming ability is the reduced glass temperature, which is the rutio of theglass trasition temperature.The use of reduced glass
temperature as a tool for predicting glass farming ability has been widely supported by
When dealing with alloys in -which the glass crystallizes during heating before the glass transition ternperature is reduced, crystallization temprature,i.e., the ratio of the crystallization temperature to the melting temperature, can be utilized as an important benchmark. A higher reduced glass transition or reduced glass crystallization temperature indicates a decrease in. the critical cooling rate necessary for formation of metallic glass. As the critical cooling rate is reduced the metallic glass melt can be processed by a larger number of standard industrial processing techniques, thereby greatly enhancing the functionality of the metallic glass.
A method for increasing the crystallization temperature of an iron based glass alloy comprising supplying an iron baaed glass alloy wherein said eJtoy has a melting temperature and crystallization temperature,. adding to said iron based glass alloy lanthamde element; and increasing said crystallization temperature by addition of said lanthanide element.
Brief Description of die Drawing*
The various aspects and advantages of the present invention are described in part with reference to exemplary embodiments, which description should be understood in conjunction with the accornpanying figures wherein:
Figure 1 is a differential thermal analysis plot showing the glass to crystalline transition for ALLOY A alky and gadolinium modified ALLOY A alloy; and
Figure 2 Is a differential thermal analysis plot' showing the glass to crystalline transition for ALLOY B alloy and gadolinium modified ALLOY B alloy.
Description of the Preferred Embodiments of the Invention This invention is directed at the incorpciation of lanthanide additions, such as gadolinium, into iron based alloys, thereby facilitating the ability of the alloy composition to
form a metallic glass, Specifically, ther amorphous glass state may be developed at lower critical cooling rates, with an increasein the crystallization temperature of me Composition.
The present invention ultimately is an alloy design approach that may be utilized to modify and improve existing iron based glasses. Specifically, me property modification is related to two distinct properties. First, the present invention may allow me increase in the stability of me glass which results in increased crystallization temperature. Second, consistent with the present invention, me reduced crystallization temperature i.the ratio of , may be increased leading to a reduced critical cooling rate Cor metallic glass formation. the combined characteristics of the invention may lead to increases in the glass Forming ability of an existing melt and stabilization of the glass which is created
Thiscombined effect may enable technological exploitation of iron based metallic glasses by making me iron glass susceptible to a wide variety of processing 'approaches and many different kinds of applications.
The alloys for producing iron based glasses incorporate lanthanide additions, which are me elements of atomio number 58-71, namely cerium, praseodymium, neodymium, samarium, europium, gadolinium terbium, . dysprosium holnuum, erbium,
thulium, ytterbium, and lutetium, although lanthanum (atomio number 57) may also be included in toe lanthanide series. The incorporation of the lanthnide additions modify the physical properties of the glass, including increasing the crystallization temperature and increasing the reduced crystallization temperature. This approach can be applied generally to any existing iron based metallic glass Preferably the lanthanide additions are combined at levels in the range of 0,10 atomio % to SO.O atomic %, and more preferably at levels hi the range of 1.0 atomio % to 10.0 atomic %> including all 0.1 atomio % intervals therebetween,
The iron alloys modified by gadolinium additions may bo susceptible to many processing methods which cannot currently successfully produce metallic glass deposits, including weld on hard facing, spray forming, spray rolling, die-casting, and float glass processing. It should be noted,' however, mat each particular process will have an average cooling rate, making it important to design an alloy such that the critical cooling rate for gla« formation of the alloy is less than the avenge cooling rate achieved in a particular processing method. Achieving a critical cooling rate mat is less than the process cooling rate will allow glass to be formed by the particular processing technique.
Two metal alloys consistent with the present invention were prepared by making Od additions at a content of 8 ac% relative to the alloy to two different alloys, ALLOY A and ALLOY B. The compoaMoa of these alloys is given in Table 1, below. The resultant (3d modified alloys are, herein, respectively referred to as Gd modified ALLOY A and Od modified ALLOY B, the compositions of which are also detailed in Table 1.
The Od modified alloysALLOY A and Od modified ALLOY B were compared to samples of the unmodified alloys, ALLOY A and ALLOY B using differential thermal analyris (DTA). Referring to Figures 1 and 2, the DTA plots indicate mat, in both cases, the Oil modified ALLOY A and Gd modified ALLOY B alloys exhibit an increase in the crystallization temperature relative to the unmodified alloys ALLOY A and Dar 35. In the case of me Od modified ALLOY B alloy compared to the ALLOY B alloy, illustrated in Figure 2, the crystallization temperature is raised over 100°C. It is also noted that no previous iron alloy has been shown to have a crystallization temperature over 700°C The crystallization onset temperatures fat all of the exemplary alloys are given m Table 2.
While not illustrated in the figures, the results of the DTA analysis indicate that the Qd additions resulted in tittle change in melting temperature of the modified alloys relative to the unmodified alloys. The melting temperatures for all of the exemplary alloys are also given in Table 2. Since the crystallization temperature of the alloys is raised but the melting temperature is largely unchanged, the result is an increase in me reduced crystallization temperature.The Gd addition to the alloy increased the reduced crystallization temperature from 0.5 to 0.61 for the ALLOY A series alloys (unmodified alloy to Od modified alloy) and from 0.56 to 0.61 in me ALLOY B series alloys (unmodified alloy to Gd modified alloy).
W e Claim
1. A method for increasing a crystallization onset temperature of an iron based alloy comprising:
supplying an iron based alloy comprising 30-90 atomic percent iron characterized in that said alloy having a crystallization temperature less than 675 °C and a reduced crystallization temperature, wherein said reduced crystallization temperature is the ratio of the crystallization temperature to the melting temperature;
adding to said iron based alloy a lanthanide element, the concentration of said lanthanide element added to said iron based glass alloy is in the range of 0.10 atomic % to 50.0 atomic %;
increasing said crystallization onset temperature above 675°C by the addition of said lanthanide element, and increasing said reduced crystallization temperature up to approximately 22%.
2. The method as claimed in claim 1 wherein said melting temperature of said iron based glass alloy prior to addition of said lanthanide element is substantially the same as to the melting point of the alloy subsequent to addition of said lanthanide element.
3. The method as claimed in claim 1 wherein the concentration of said lanthanide element added to said iron based glass alloy is in the range of 1.0 atomic % to 10.0 atomic %.
4. The method as claimed in claim 1 wherein said lanthanide element is selected from the Lanthanide series consisting of cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, lanthanum, and mixtures thereof.
|Indian Patent Application Number||3612/DELNP/2005|
|PG Journal Number||33/2010|
|Date of Filing||16-Aug-2005|
|Name of Patentee||THE NANOSTEEL COMPANY|
|Applicant Address||MAITLAND PROMENADE, 485 NORTH KELLER ROAD, SUITE 100 MAITLAND, FLORIDA 32751 USA.|
|PCT International Classification Number||C21C|
|PCT International Application Number||PCT/US2004/004510|
|PCT International Filing date||2004-02-13|