Patent Publication Number: US-10788064-B2

Title: Composite structure

Description:
TECHNICAL FIELD 
     The present invention relates to a composite structure. 
     BACKGROUND ART 
     Conventionally, a composite structure obtained by joining a plurality of types of structures having different constituent materials has been configured by joining the respective structures by surface joining. In such a composite structure, due to a difference in thermal expansion coefficient between constituent materials of the respective joined structures, thermal stress may be generated on a joining surface to cause cracking or peeling, or the entire composite structure may warp. 
     For example, Patent Document 1 discloses a discharge head configured to suppress warping of an entire composite structure by sintering a base substrate  200  and a piezoelectric body  58  made of materials, coefficients of thermal expansion of which are close to each other, with an individual electrodes  57  interposed therebetween. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: JP 2005-306021 A 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the discharge head of Patent Document 1, thermal expansion coefficients of the base substrate  200  and the piezoelectric body  58  need to be conformed to each other, and materials that can be actually applied are limited. Further, in Patent Document 1, since the individual electrode  57  is simply stacked with the base substrate  200  and the piezoelectric body  58 , there is a possibility that peeling may occur along with heat treatment. 
     Accordingly, an object of the invention is to suppress warping and peeling in a composite structure of structures made of different constituent materials. 
     Solutions to Problems 
     A preferred embodiment of a composite structure according to the invention is a composite structure obtained by joining a first structure and a second structure made of a different material from a material of the first structure, wherein a part of the second structure is incorporated in a cavity of the first structure, and a part of the first structure is incorporated in a cavity of the second structure. 
     Effects of the Invention 
     According to the invention, it is possible to suppress warping and peeling in a composite structure of structures made of different constituent materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a configuration of a conventional composite structure. 
         FIG. 2A  is a perspective view illustrating a first structure included in a composite structure according to Embodiment 1. 
         FIG. 2B  is a perspective view illustrating the composite structure  10  according to Embodiment 1. 
         FIG. 3A  is a perspective view illustrating a composite structure  100  according to Embodiment 2. 
         FIG. 3B  is a diagram separately illustrating a structure  101  included in the composite structure  100 . 
         FIG. 4  is a diagram for description of a method of manufacturing the composite structure  10 . 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
       FIG. 1  is a perspective view illustrating a configuration of a conventional composite structure. As illustrated in  FIG. 1 , a conventional composite structure  20  is configured by joining a structure  11  and a structure  12 , which are made of different constituent materials, at a joining surface  13 . When the structure  11  and the structure  12  are joined and heat treated, thermal stress a generated in an X direction and a Y direction on the joining surface  13  is expressed by the following Equation (1).
 
[Formula 1]
 
σ= E ×( T   1   −T   2 )×|β 1 −β 2 |   (1)
 
     In the above Formula (1), “E” denotes an equivalent elasticity factor in the constituent material of the structure  11  and the constituent material of the structure  12 , “β 1 ” denotes a thermal expansion coefficient in the constituent material of the structure  11 , “β 2 ” denotes a thermal expansion coefficient in the constituent material of the structure  12 , “T 1 ” denotes a temperature at the time of joining the structure  11  and the structure  12 , and “T 2 ” is a temperature before joining. 
     As shown in Formula (1), as a difference between the thermal expansion coefficient β 1  of the structure  11  and the thermal expansion coefficient β 2  of the structure  12  increases, the thermal stress generated at the joining surface  13  increases, and peeling occurs on the joining surface  13 , or warping occurs in the structure  11  or the structure  12 . 
     Embodiment 1 
     Next, a composite structure according to Embodiment 1 will be described with reference to  FIG. 2A  and  FIG. 2B .  FIG. 2A  is a perspective view illustrating a structure  1  corresponding to a first structure (hereinafter simply referred to as the structure  1 ) included in the composite structure according to Embodiment 1. As illustrated in  FIG. 2A , the structure  1  includes a base  1   a  and a lattice  1   b  protruding from the base  1   a . Each of the base  1   a  and the lattice  1   b  has a rectangular parallelepiped shape as a whole, and the lattice  1   b  is formed to be narrower than the base  1   a.    
     In  FIG. 2A , reference symbol  1   c  corresponds to a connecting surface between the base  1   a  and the lattice  1   b . In more detail, the lattice  1   b  is integrally formed with the base  1   a  through the connecting surface  1   c , and a cavity  1   d  is formed in a center portion thereof. The lattice  1   b  has a pair of leg portions  1   b   1  erected from the base  1   a  and a ceiling portion  1   b   2  formed between the leg portions  1   b   1  so as to face the base  1   a . The cavity  1   d  is formed in a space surrounded by the leg portions  1   b   1 , the ceiling portion  1   b   2  and the base  1   a.    
       FIG. 2B  is a perspective view illustrating a composite structure  10  according to Embodiment 1. The composite structure  10  is a composite structure obtained by joining the structure  1  to a structure  2  corresponding to a second structure (hereinafter simply referred to as the structure  2 ). The structure  2  is a structure made of a different constituent material from that of the structure  1  and has the same shape as the structure  1  (see  FIG. 2A ). That is, reference symbols  2   a ,  2   b ,  2   b   1 ,  2   b   2 ,  2   c , and  2   d  of the structure  2  correspond to reference symbols  1   a ,  1   b ,  1   b   1 ,  1   b   2 ,  1   c , and  1   d  of the structure  1 , and description thereof will be omitted. For example, a metal body may be used as the structure  1  and the structure  2 . 
     The structure  2  is joined to the structure  1  while being disposed in a z direction of  FIG. 2B  with respect to the structure  1  such that a protruding direction of a lattice  2   b  is opposite to a protruding direction of the lattice  1   b  of the structure  1 . As illustrated in  FIG. 2B , in the structure  1 , the ceiling portion  1   b   2  of the lattice  1   b  is incorporated in a cavity  2   d  of the structure  2 . Further, in the structure  2 , a ceiling portion  2   b   2  of the lattice  2   b  is incorporated in the cavity  1   d  of the structure  1 . 
     In  FIG. 2B , a surface including a joining surface  3   a   1  between the base  1   a  of the structure  1  and the lattice  2   b  of the structure  2  is indicated by a boundary surface  3   a , a surface including a joining surface between the ceiling portion  1   b   2  of the lattice  1   b  of the structure  1  and the ceiling portion  2   b   2  of the lattice  2   b  of the structure  2  is indicated by a boundary surface  3   b , and a surface including a joining surface  3   c   1  between the base  2   a  of the structure  2  and the lattice  1   b  of the structure is indicated by a boundary surface  3   c.    
     For example, the boundary surface  3   a  has the connecting surface  1   c  between the base  1   a  and the lattice  1   b  adjacent to the joining surface  3   a   1  between the base  1   a  and the lattice  2   b . As described above, in the structure  1 , the base  1   a  and the lattice  1   b  are integrally formed using the same constituent material. Therefore, the boundary surface  3   a  has the connecting surface  1   c  integrally formed using a constituent material of the structure  1  adjacent to the joining surface  3   a   1  on which dissimilar materials are joined to each other. 
     In a region of the connecting surface  1   c  integrally formed using the same constituent material, no difference in thermal expansion coefficient occurs, and thermal stress is not generated during heat treatment. For this reason, thermal stress generated during heat treatment may be reduced on the boundary surface  3   a  of the composite structure  10  when compared to the joining surface  13  (see  FIG. 1 ) formed solely by a joining surface between the structure  11  and the structure  12  made of different constituent materials. 
     The thermal stress on the boundary surface of the composite structure  10  is calculated by Formula (2) below. In more detail, when the structure  1  and the structure  2  are subjected to heat treatment while being joined to each other in a mode illustrated in  FIG. 2B , average thermal stress σ a  generated in the X direction and the Y direction on the boundary surface  3   a  is expressed by the following Formula (2). 
     
       
         
           
             
               
                 
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     In the above Formula (2), “α” denotes thermal stress calculated by the above Formula (1), “S 1 ” denotes an area of the joining surface  3   a   1  between the base  1   a  and the lattice  2   b , and “S 2 ” denotes an area of the connecting surface  1   c  between the base  1   a  and the lattice  1   b  of the structure  1 . 
     Considering a shape of the composite structure  10  associated with the above Formula (2), since both S 1  and S 2  are positive values, a relationship of Formula (3) below holds for an area ratio S 1 /(S 1 +S 2 ). 
     
       
         
           
             
               
                 
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     From the above, the average thermal stress a on the boundary surface  3   a  in the composite structure  10  is reduced when compared with the thermal stress σ on the joining surface  13  in the conventional composite structure  20 . The above-mentioned point holds true for the boundary surface  3   b  and the boundary surface  3   c.    
     As described above, in the composite structure  10  of Embodiment 1, a part of the structure  2  is incorporated in the cavity  1   d  of the structure  1 , and a part of the structure  1  is incorporated in the cavity  2   d  of the structure  2 . Thus, both the structures  1  and  2  are joined in a state in which a positional relationship thereof is constrained. For this reason, during heat treatment of the composite structure  10 , it is possible to suppress deformation of the structure  1  or the structure  2 , peeling of both the structures associated with the deformation, and warping of the entire composite structure  10 . 
     Further, as described above, since the composite structure  10  has a region (for example, the connecting surface  1   c ) integrally formed using the same constituent material on the boundary surfaces  3   a ,  3   b , and  3   c , thermal stress applied to the whole respective boundary surfaces is reduced during heat treatment. In this way, thermal stress applied to the structure  1  and the structure  2  forming each boundary surface is reduced, and thus it is possible to suppress deformation of the structure  1  and the structure  2 , peeling of both the structures associated with the deformation, warping of the entire composite structure  10 , and a crack of the structure  1  and the structure  2 . 
     Embodiment 2 
     Next, a description will be given of a composite structure  100  according to Embodiment 2 with reference to FIG.  3 A and  FIG. 3B .  FIG. 3A  is a perspective view illustrating the composite structure  100  of Embodiment 2. The composite structure  100  includes a structure  101  and a structure  102 . 
       FIG. 3B  separately illustrates a configuration of the structure  101 . 
     The structure  101  is obtained by connecting structures  1  illustrated in  FIG. 2A  in an x direction a y direction of  FIG. 3A . Hereinafter, in  FIG. 3A , units corresponding to the structure  1  illustrated in  FIG. 2A  will be denoted as unit structures  1   p   1 ,  1   p   2 , . . . ,  1   p   n . For example, the unit structure  1   p   2  adjacent to the unit structure  1   p   1  is connected to the unit structure  1   p   2  while sharing a part of the lattice  1   b  of the unit structure  1   p   1 . Thereafter, similarly thereto, the unit structures  1   p   1 ,  1   p   2 , . . . ,  1   p   n  are connected in the x direction and the y direction to form the structure  101 . 
     The structure  102  is a structure made of a different constituent material from that of the structure  101 , and has the same shape as that of the structure  101 . That is, reference symbols  2   p   1 ,  2   p   2 , . . . ,  2   p   n  of the structure  102  correspond to reference symbols  1   p   1 ,  1   p   2 , . . . ,  1   p   n , and description thereof will be omitted. Similarly to Embodiment 1, for example, a metal body may be used as the structure  101  and the structure  102 . 
     The structure  102  is joined to the structure  101  while being disposed in a z direction of  FIG. 3A  with respect to the structure  101  such that a protruding direction of a lattice  2   b  of each unit structure  2   p   n  is opposite to a protruding direction of a lattice  1   b  of each unit structure  1   p   n  of the structure  101 . 
     As illustrated in  FIG. 3A , in the structure  101 , a ceiling portion  1   b   2  of the lattice  1   b  of each unit structure  1   p   n  is incorporated in a cavity  2   d  of each unit structure  2   p , of the structure  102 . Further, in the structure  102 , a ceiling portion  2   b   2  of the lattice  2   b  of each unit structure  2   p   n  is incorporated in a cavity  1   d  of each unit structure  1   p   n  of the structure  101 . In this way, the composite structure  100  is formed as a structure obtained by connecting a plurality of unit structures corresponding to the composite structure  10  illustrated in  FIG. 2B . 
     In  FIG. 3A , a layer in which the lattice  2   b  of each unit structure  2   p   n  of the structure  102  is formed inside the cavity  1   d  of each unit structure p n , of the structure  101  is set to a mixed layer  4   c , and a layer in which the lattice  1   b  of each unit structure  1   p   n  of the structure  101  is formed inside the cavity  2   d  of each unit structure  2   p   n  of the structure  102  is set to a mixed layer  4   d . In addition, in the structure  101 , a layer formed by a connecting body of a base  1   a  of each unit structure  1   p   n  is set to a first monolayer  4   a . In the structure  102 , a layer formed by a connecting body of a base  2   a  of each unit structure  2   p   n  is set to a second monolayer  4   b . In addition, a boundary surface  3   a  is set between the monolayer  4   a  and the mixed layer  4   c , a boundary surface  3   b  is set between the mixed layer  4   c  and the mixed layer  4   d , and a boundary surface  3   c  is set between the mixed layer  4   d  and the monolayer  4   b.    
     As illustrated in  FIG. 3A , for example, on the boundary surface  3   a , the composite structure  100  alternately has a joining surface  3   a   1  between the lattice  2   b  of each unit structure  2   p   r  and the monolayer  4   a  (base  1   a ) and a connecting surface  1   c  between the lattice  1   b  of each unit structure  1   p   n  and the monolayer  4   a  (base  1   a ). 
     As described above, in the structure  101 , the lattice  1   b  of each unit structure  1   p   n  and the monolayer  4   a  (base  1   a ) are integrally formed using the same constituent material. Therefore, the boundary surface  3   a  has the connecting surface  1   c  integrally formed using a constituent material of the substrate  101  adjacent to the joining surface  3   a   1  on which different materials are joined to each other. 
     In a region of the connecting surface  1   c  integrally formed using the same constituent material, no difference in thermal expansion coefficient occurs, and thermal stress is not generated during heat treatment. For this reason, thermal stress generated during heat treatment may be reduced as a whole on the boundary surface  3   a  of the composite structure  100  when compared to the joining surface  13  (see  FIG. 1 ) formed solely by the joining surface between the structure  11  and the structure  12  made of different constituent materials. 
     Similarly to Embodiment 1, thermal stress on the boundary surface of the composite structure  100  is calculated by the above Formula (2). In more detail, when the structure  1  and the structure  2  are subjected to heat treatment while being joined to each other in a mode illustrated in  FIG. 3A , average thermal stress σ a  generated in the X direction and the Y direction on the boundary surface  3   a  is expressed by the above Formula (2). 
     In the above Formula (2), “S 1 ” denotes a sum of areas of joining surfaces  3   a   1  between lattices  2   b  of respective unit structures  2   p   n  and monolayers  4   a  (bases  1   a ), and “S 2 ” denotes a sum of areas of connecting surfaces  1   c  between lattices  1   b  of respective unit structures  1   p   n  and monolayers  4   a  (bases  1   a ). In Embodiment 2, considering a shape of the composite structure  100 , since both S 1  and S 2  are positive values, a relationship of the above Formula (3) holds for an area ratio S 1 /(S 1 +S 2 ). 
     From the above, the average thermal stress σ a  on the boundary surface  3   a  in the composite structure  100  is reduced when compared with the thermal stress σ on the joining surface  13  in the conventional composite structure  20 . The above-mentioned point holds true for the boundary surface  3   b  and the boundary surface  3   c.    
     As described above, in the composite structure  100 , the structure  101  and the structure  102  are joined in a state in which a positional relationship thereof is constrained. Thus, during heat treatment of the composite structure  100 , it is possible to suppress deformation of the structure  101  or the structure  102 , peeling of both the structures associated with the deformation, and warping of the entire composite structure  100 . 
     Further, since the composite structure  100  has a region (for example, the connecting surface  1   c ) integrally formed using the same constituent material on the boundary surfaces  3   a ,  3   b , and  3   c , thermal stress applied to the whole respective boundary surfaces is reduced during heat treatment. In this way, thermal stress applied to the structure  101  and the structure  102  forming each boundary surface is reduced, and thus it is possible to suppress deformation of the structure  101  and the structure  102 , peeling of both the structures associated with the deformation, warping of the entire composite structure  100 , and a crack of the structure  101  and the structure  102 . 
     In addition, the composite structure  100  of Embodiment 2 has configuration in which a plurality of unit structures corresponding to the composite structure  10  illustrated in  FIG. 2B  is connected, and thus it is possible to obtain an effect that thermal stress is reduced in a wide range of the composite structure. 
     As illustrated in  FIG. 2B  and  FIG. 3A , it is preferable to use structures having the same shape as the respective joined structures since the composite structure may be easily and efficiently manufactured, and stable structures may be obtained in the obtained composite structure. However, the composite structure may be manufactured using structures having different shapes as the respective structures. 
     In addition, as illustrated in  FIG. 2B  and  FIG. 3A , it is preferable to dispose a part of a lattice of each structure inside a cavity of another structure substantially without any gap since stable structures may be obtained in the composite structure. However, the composite structure may be manufactured in a state in which a gap is formed between the cavity and the lattice. 
     In addition,  FIG. 2B  and  FIG. 3A  illustrate an example in which a structure having a cavity whose cross-sectional shape is a rectangular shape is used as each structure. However, for example, a structure having a cavity whose cross-sectional shape is a circular shape, a triangular shape, etc. other than the rectangular shape may be used. 
     Next, a description will be given of a method of manufacturing the composite structure  10  illustrated in  FIG. 2B  with reference to  FIG. 4 . First, a lower region  1   b - 1  of the lattice  1   b  is formed on the base  1   a  using built-up welding. The lower region  1   b - 1  of the lattice  1   b  is formed at a position corresponding to a position illustrated in  FIG. 4  on the base  1   a . Subsequently, an upper region  2   b - 2  of the lattice  2   b  is formed using built-up welding from one end side to the other end side of the base  1   a  to fill a region sandwiched by the lower region  1   b - 1  of the lattice  1   b.    
     Subsequently, a lower region  2   b - 1  of the lattice  2   b  is formed on the base  2   a  using built-up welding. The lower region  2   b - 1  of the lattice  2   b  is formed at a position corresponding to a position illustrated in  FIG. 4  on the base  2   a . Subsequently, an upper region  1   b - 2  of the lattice  1   b  is formed using built-up welding from one end side to the other end side of the base  2   a  to fill a region sandwiched by the lower region  2   b - 1  of the lattice  2   b.    
     Subsequently, the composite structure  10  is obtained by joining the base  1   a  and the base  2   a  such that built-up welding surfaces face each other.