Patent Publication Number: US-2021189530-A1

Title: Plastic single-axis zero-expansion composite material and preparation method thereof

Description:
CROSS-REFERENCE TO THE RELATED APPLICATIONS 
     This application is based upon and claims priority to Chinese Patent Application No. 201911319876.1, filed on Dec. 19, 2019; the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the technical field of high-precision instruments, and particularly relates to a plastic single-axis zero-expansion composite material and preparation method thereof. 
     BACKGROUND 
     Zero-expansion materials, as a functional material, refer to materials whose dimensions do not vary with the temperature, even to a little extent. They are mainly applied to the fields of high-precision instruments, such as optical instrument, microelectronic devices and aerospace. Currently, materials whose shapes and dimensions do not vary with the temperature are urgently needed, to guarantee that the manufactured members have a high dimensional stability, a high precision and a long service life. Low (near zero)-thermal-expansion materials have microscopic dimensions that are approximately constant with the variation of the temperature, and can maintain a volume that does not expand or contract within particular temperature intervals. Therefore, the study on such a type of materials is being paid increasingly more attention. 
     Zero-expansion materials may be generally classified into three types, ceramics, metallic materials and composites. Ceramic materials have poor mechanical properties and exhibit no outstanding property in thermal conduction or electric conduction, which makes them not promotable and applicable in a large scale. Although metallic materials have excellent properties in thermal conduction and electric conduction, there are rare materials among them that have the zero-expansion property, which are mainly intermetallic compounds. However, the inherent brittleness of the intermetallic compounds themselves makes them not applicable in a large scale. Traditional composite materials are generally metal/ceramic-based composite zero-expansion materials prepared by solid-phase sintering. However, such compounding improves the mechanical properties to a limited extent, and the mismatching between the thermal-expansion properties of the two materials themselves results in hot cracks and thus failure. 
     Therefore, it is necessary to develop a plastic single-axis zero-expansion composite material that has a high strength and preparation method thereof, to overcome the disadvantages of the prior art, to solve or alleviate one or more of the above problems. 
     SUMMARY 
     In view of that, the present disclosure provides a plastic single-axis zero-expansion composite material and preparation method thereof, by incorporating an a-Fe second phase into a matrix of R 2 Fe 17 -type intermetallic compound, wherein R refers to a rare earth element. The material has simple synthesis steps and can be easily implemented, and the phase interface formed by the eutectic reaction is more stable than the composite structures obtained by the traditional solid-phase sintering, which realizes the regulation of the thermal expansion, and significantly improves the mechanical properties. 
     In an aspect, the present disclosure provides a preparation method of a plastic single-axis zero-expansion composite material, wherein the preparation method incorporates an α-Fe phase as a second phase into an R 2 Fe 17 -type intermetallic compound, wherein the R 2 Fe 17  exhibits negative thermal expansion, the α-Fe exhibits positive thermal expansion, and the single-axis zero-expansion composite material having a wide temperature zone is obtained by regulating the positive thermal expansion and the negative thermal expansion by controlling a ratio of the two phases and an orientation of the R 2 Fe 17 , wherein R is a rare earth element. 
     In an embodiment according to the above aspect and among potential embodiments, the preparation method comprises the steps of: 
     step 1: providing a raw material of the R 2 Fe 17 -type intermetallic compound and a raw material of the α-Fe phase; 
     step 2: mixing the two raw materials of the step 1; 
     step 3: smelting uniformly the mixed raw materials by using an electric-arc furnace; 
     step 4: annealing the uniformly smelted sample under a protective atmosphere; and 
     step 5: after the annealing has ended, obtaining the single-axis zero-expansion composite material. 
     In an embodiment according to the above aspect and among potential embodiments, the water tanks are evenly distributed or periodically distributed on the copper plate. 
     In an embodiment according to the above aspect and among potential embodiments, in the step 1 both of purities of the raw material of the R 2 Fe 17 -type intermetallic compound and the raw material of the α-Fe phase are &gt;99.5%. 
     In an embodiment according to the above aspect and among potential embodiments, in the step 1 the R 2 Fe 17  phase is of a hexagonal crystal system or a trigonal crystal system, wherein when R is a light rare earth element, R is of a trigonal crystal system, and has a space group of R-3m, and when R is a heavy rare earth element, R is of a hexagonal crystal system, and has a space group of P6 3 /mmC. 
     In an embodiment according to the above aspect and among potential embodiments, the step 4 comprises placing the obtained sample under the protective atmosphere, and annealing at 1100° C. for at least 24 h, wherein the protective atmosphere is vacuum or an inert gas. 
     In an embodiment according to the above aspect and among potential embodiments, the R 2 Fe 17 -type intermetallic compound is a matrix phase, the α-Fe phase is a plastic second phase, and the plastic second phase is incorporated to improve a mechanical behavior of the matrix phase, and by synergy between the two phases, inhibit an intrinsic brittleness of the intermetallic compound. 
     According to the above aspect, there is further provided a plastic single-axis zero-expansion composite material, wherein a chemical formula of the single-axis zero-expansion composite material is R x Fe 1-x , wherein 0&lt;x≤0.09, and R is a rare earth element. 
     In an embodiment according to the above aspect and among potential embodiments, a same copper plate has an average taper change rate of the taper of 0.5%-2.5% in the entire length. 
     In an embodiment according to the above aspect and among potential embodiments, the single-axis zero-expansion composite material comprises Ho 0.04 Fe 0.96 , and the Ho 0.4 Fe 0.96  exhibits a characteristic of zero expansion within a temperature interval of 100-335 K, wherein a coefficient of linear expansion α 1  is 0.19×10 −6 . 
     As compared with the prior art, the present disclosure can obtain the following technical effects: 
     1. The high-strength zero-expansion composite material according to the present disclosure has shapes and dimensions that do not vary with the temperature, and has a high dimensional stability, a high precision and a long service life. The low (near zero)-thermal-expansion material has microscopic dimensions that are approximately constant with the variation of the temperature, and can maintain a volume that does not expand or contract within particular temperature intervals. 
     2. The zero-expansion composite material according to the present disclosure is a zero-expansion composite material that has excellent mechanical properties, which overcomes the intrinsic brittleness of traditional intermetallic compounds, and has higher thermal conductivity and electric conductivity than those of conventional ceramic materials. Furthermore, the raw materials are more inexpensive than intermetallic compounds, which enables the large-scaled application of the composite material. 
     Certainly, the implementation of either product according to the present disclosure may not necessarily achieve all of the above-described technical effects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly describe the technical solutions of the embodiments of the present disclosure, the drawings that are required to be used in the embodiments will be described below briefly. Apparently, the drawings described below are merely some of the embodiments of the present disclosure, and a person skilled in the art can obtain other drawings according to those drawings without paying creative work. 
         FIG. 1  is a finely finished X-ray diffraction pattern of the powder of Ho 0.04 Fe 0.96 , one of the zero-expansion composite material according to the present disclosure when R=Ho, at 300 K; 
         FIG. 2  is diagrams of the crystal structures of the R 2 Fe 17  phase and the α-Fe phase according to the present disclosure; 
         FIG. 3  is plots of the linear expansion of the R x Fe 1-x  (R=Ho, and x=0.03, 0.04, 0.05, 0.07 and 0.09) according to the present disclosure; and 
         FIG. 4  is an engineering stress-strain curve of the Ho 0.04 Fe 0.96  according to the present disclosure at 300 K. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In order to better understand the technical solutions of the present disclosure, the embodiments of the present disclosure will be described below in detail with reference to the drawings. 
     It should be understood that the described embodiments are merely some of the embodiments of the present disclosure, and are not all of the embodiments. All of the other embodiments that a person skilled in the art obtains on the basis of the embodiments in the present disclosure without paying creative work fall within the protection scope of the present disclosure. 
     The terms used in the embodiments of the present disclosure are merely for the purpose of describing the particular embodiments, and are not intended to limit the present disclosure. The terms “a”, “an”, “said” and “the” used in the singular forms in the embodiments and the appended claims of the present disclosure are intended to encompass the plural forms, unless expressly indicated otherwise in the context. 
     The present disclosure provides a plastic single-axis zero-expansion composite material. A chemical formula of the single-axis zero-expansion composite material is R x Fe 1-x , wherein 0&lt;x≤0.09, and R is a rare earth element. The single-axis zero-expansion composite material comprises Ho 0.04 Fe 0.96 , and the Ho 0.04 Fe 0.96  exhibits a characteristic of zero expansion within a temperature interval of 100-335 K, wherein a coefficient of linear expansion α 1  is 0.19×10 −6 . 
     The present disclosure further provides a preparation method of a plastic single-axis zero-expansion composite material, wherein the preparation method incorporates an α-Fe phase as a second phase into an R 2 Fe 17 -type intermetallic compound, wherein the R 2 Fe 17  exhibits negative thermal expansion, the α-Fe exhibits positive thermal expansion, and the plastic single-axis zero-expansion composite material having a wide temperature zone is obtained by regulating the positive thermal expansion and the negative thermal expansion by controlling a ratio of the two phases and an orientation of the R 2 Fe 17 . 
     The preparation method comprises the steps of: 
     step 1: providing a raw material of the R 2 Fe 17 -type intermetallic compound and a raw material of the α-Fe phase, wherein both of the purities of the raw materials are &gt;99.5%, the R 2 Fe 17  phase is of a hexagonal crystal system or a trigonal crystal system, wherein when R is a light rare earth element, R is of a trigonal crystal system, and has a space group of R-3m, and when R is a heavy rare earth element, R is of a hexagonal crystal system, and has a space group of P6 3 /mmC, and the α-Fe phase is of a cubic crystal system, and has a space group of Im-3m; 
     step 2: mixing the two raw materials of the step 1; 
     step 3: smelting uniformly the mixed raw materials by using an electric-arc furnace; 
     step 4: placing the obtained uniformly smelted sample under a protective atmosphere, and annealing at 1100° C. for at least 24 h, wherein the protective atmosphere is vacuum or an inert gas; and 
     step 5: after the annealing has ended, obtaining the single-axis zero-expansion composite material. 
     In the preparation method according to the present disclosure, the R 2 Fe 17 -type intermetallic compound is a matrix phase, the α-Fe phase is a plastic second phase, and the plastic second phase is incorporated to improve a mechanical behavior of the matrix phase, and by synergy between the two phases, effectively inhibit the intrinsic brittleness of the intermetallic compound, and realize a great improvement on the mechanical properties. 
     Example 1 
     A block of the single-axis zero-expansion composite material according to the present disclosure, in which the composition is Ho 0.04 Fe 0.96 , was synthesized by using the electric-arc-furnace smelting process, wherein the reaction equation is as follows: 
       0.04×Ho+0.96Fe=Ho 0.04 Fe 0.96  
 
     The particular operation was performed according to the following steps: 
     10 g of the raw materials of Ho and Fe at the molar ratio of 0.04:0.96 was weighed. The raw materials were placed into an electric-arc furnace, the furnace was vacuumed (to the vacuum degree of &lt;2.5×10 −3  Pa), and under that vacuum condition or the protection of an inert gas the system was smelted for 3 times for 1 min each time, which may optionally be assisted by electromagnetic stirring to homogenize the alloy. The obtained sample was placed under vacuum or an inert atmosphere and annealed at 1100° C. for at least 24 h. The result of X-ray diffraction indicated that the obtained product is of an Ho 0.04 Fe 0.96  composite phase, and has no impurity. 
     Example 2 
     A block of the single-axis zero-expansion composite material according to the present disclosure, in which the composition is E r0.04 Fe 0.96 , was synthesized by using the electric-arc-furnace smelting process, wherein the reaction equation is as follows: 
       0.04×Er+0.96Fe=E r0.04 Fe 0.96  
 
     The particular operation was performed according to the following steps: 
     10 g of the raw materials of Er and Fe at the molar ratio of 0.04:0.96 was weighed. The raw materials were placed into an electric-arc furnace, the furnace was vacuumed (to the vacuum degree of &lt;2.5×10 −3  Pa), and under that vacuum condition or the protection of an inert gas the system was smelted for 3 times for 1 min each time, which may optionally be assisted by electromagnetic stirring to homogenize the alloy. The obtained sample was placed under vacuum or an inert atmosphere and annealed at 1100° C. for at least 24 h. The result of X-ray diffraction indicated that the obtained product is of an E r0.04 Fe 0.96  composite phase, and has no impurity. 
     The zero-expansion material Ho 0.04 Fe 0.96  that was obtained in Example 1 was measured with respect to the linear expansion, and it exhibits the characteristic of zero expansion within the temperature interval of 100-335 K, wherein the coefficient of linear expansion (cu) is 0.19×10 −6 . Furthermore, its mechanical properties were measured, and it exhibits excellent mechanical properties, wherein its yield strength reaches 700 Mpa, and its plastic elongation is up to 15%. 
       FIG. 1  is a finely finished X-ray diffraction pattern of the powder of Ho 0.04 Fe 0.96 , one of the zero-expansion composite material according to the present disclosure when R=Ho, at 300 K. It can be seen from the pattern that the X-ray diffraction pattern that was simulated based on its crystal structure and the X-ray diffraction pattern obtained in the experiment were consistent, which proves the correctness of the structural model of the zero-expansion composite material according to the present disclosure. 
       FIG. 2  is diagrams of the crystal structures of the R 2 Fe 17  phase and the α-Fe phase according to the present disclosure. The crystal structures according to the present disclosure are hexagonal phase or trigonal phase of the rare-earth rich R 2 Fe 17  type, and the body-centered cubic phase formed by the single Fe element. 
       FIG. 3  is plots of the linear expansion of the R x Fe 1-x  (R=Ho, and x=0.03, 0.04, 0.05, 0.07 and 0.09) according to the present disclosure. From the linear-expansion curve of the Ho x Fe 1-x  according to the present disclosure, it can be known that regulating the molar ratio of Ho:Fe can realize the regulation of the thermal expansion from negative to positive, and at the composition of Ho 0.04 Fe 0.96  it exhibits the characteristic of zero expansion, wherein at 100-335 K the coefficient of thermal expansion is 0.19×10 −6 . 
       FIG. 4  is an engineering stress-strain curve of the Ho 0.04 Fe 0.96  according to the present disclosure at 300K. From the engineering stress-strain curve according to the present disclosure, it can be known that the zero-expansion composite material exhibits excellent mechanical properties, wherein its yield strength reaches 700 Mpa, and its plastic elongation is up to 15%. 
     The above description describes in detail the plastic single-axis zero-expansion composite material and preparation method thereof according to the embodiments of the present application. The description of the above embodiments is merely intended to facilitate to understand the method according to the present application and its core concept. Moreover, for a person skilled in the art, on the basis of the concept of the present application, the particular embodiments and the range of application may be varied. In conclusion, the contents of the description should not be understood as limiting the present application. 
     The description and the claims employ certain words to refer to particular elements. A person skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same one element. The description and the claims do not distinguish the elements according to the difference of the names, but use the difference in the functions of the elements as the criteria of distinguishing. For example, throughout the description and the claims the “comprise” and the “include” are open-ended terms, so they should be interpreted as “including but not limited to”. The “substantially” refers to that, within an acceptable range of error, a person skilled in the art can, within the range of error, solve the technical problem and essentially reach the technical effects. The subsequent description is the preferable embodiments of the present application, but the description is for the purpose of explaining the general principle of the present application, and is not intended to limit the scope of the present application. The protection scope of the present application should be defined by the appended claims. 
     It should also be noted that the terms “comprise” and “include” or any variants thereof are intended to encompass non-exclusive inclusions, so that a product or system comprising a series of elements does not only comprise those elements, but also further comprises other elements not explicitly listed, or further comprises elements that are inherent to such a product or system. Unless further limitation is set forth, an element defined by the wording “comprising a . . . ” does not exclude additional the same element in the product or system comprising the element. 
     It should be understood that the term “and/or” as used herein is merely the description on the associated relation of associated objects, and indicates the existence of three relations. For example, A and/or B may indicate the sole existence of A, the sole existence of B and the existence of both of A and B. In addition, the symbol “/” as used herein generally refers to that the preceding and subsequent associated objects are of a relation of “or”. 
     The above description illustrates and describes some preferable embodiments of the present application. However, as stated above, it should be understood that the present application is not limited to the forms disclosed herein, and should not be deemed as the exclusion of other embodiments. Instead, the present application may be used for various other combinations, modifications and circumstances, and can be modified within the scope of the concept of the present application by employing the above teaching or the techniques and knowledge in the relevant fields. Moreover, any modification or variation made by a person skilled in the art does not depart from the spirit and scope of the present application, and should fall within the protection scope of the appended claims of the present application.