JPH0474314B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to tungsten or molybdenum multilayer crystals. [Prior Art] Tungsten and molybdenum belong to group a of the periodic table, and are body-centered cubic lattice transition metals with atomic numbers of 74 and 42, located in the third and second long periods, respectively. Tungsten has the highest melting point of all metal elements
It has a melting point of 3380℃, while molybdenum has a melting point of 2615℃, respectively, which are representative of high melting point rare metals. In addition, the first metallurgical property of tungsten and molybdenum is the ability to withstand high temperatures of 2000°C or higher in a non-oxidizing atmosphere, that is, they are super heat-resistant metal materials that exhibit excellent high-temperature strength. Are known. However, both metals are typical metal materials that have not yet been developed for effective use or put into practical use, except for wire rods. The reason for this is that when tungsten and molybdenum are in a polycrystalline state, their moldability is extremely poor below room temperature.
DBTT (ductile, brittle transition temperature) or higher, each 3
%, due to showing an elongation of 20% or less. Furthermore, when used at high temperatures, polycrystalline tungsten and molybdenum cause coarsening of crystal grains and recrystallization embrittlement, making it impossible to fully demonstrate the characteristics as super heat-resistant materials mentioned above. This is one of the reasons why it is restricted. [Problems to be Solved by the Invention] Generally, molybdenum and tungsten materials are used under harsh conditions at high temperatures and for long periods of time, so once a fracture crack occurs, the polycrystalline state may suffer from recrystallization embrittlement. Rapid destruction occurs at grain boundaries. On the other hand, in order to eliminate the drawbacks of polycrystalline molybdenum and tungsten mentioned above, the recrystallization method is used to
Tungsten with coarse crystals (Japanese Patent Application Laid-Open No. 61-6197
Patent No.) and single crystallized molybdenum (Patent No.
No. 1420928) is known. In this way, single crystallized tungsten and molybdenum may undergo cleavage fracture all at once, and therefore cannot be said to be sufficiently reliable as a material. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide tungsten and molybdenum materials that have strength, particularly sagging resistance and reliability, without recrystallization brittleness at high temperatures. In the case of a multilayer crystal made of these molybdenum and tungsten materials, even if fracture fracture occurs on the crystal surface, there are grain boundaries between the crystal grains of each layer and the crystal orientation is different. This results in increased strength and reliability of the material, without causing confinement in the crystals in each layer and leading to rapid fracture. Therefore, if it is possible to provide multiple crystals with grain boundaries parallel to the plates, it will be possible to use them in general reactor materials such as atomic route materials that require high-temperature strength and reliability, and the field of application will expand. , significantly expanded. Therefore, another technical object of the present invention is to provide a method for manufacturing tungsten or molybdenum multiple crystals that can easily manufacture the tungsten or molybdenum multiple crystals. [Means for Solving the Problems] According to the present invention, it is composed of two or more multilayers having crystal grain boundaries parallel to the plate plane, and the layers that overlap each other in these multilayers have crystallographic orientations that are different from each other. A tungsten or molybdenum multilayer crystal is obtained, which is characterized by having single crystal states with different tungsten or molybdenum crystals. According to the present invention, a multilayer crystal is manufactured by laminating and molding tungsten or molybdenum polycrystals to form a molded body, and annealing the molded body to exhibit a crystal state in which adjacent layers have mutually aligned crystal orientations. method is obtained. Specifically, when producing tungsten or molybdenum multilayer crystals, tungsten oxide or molybdenum oxide powder containing 0.03 to 1.55 wt% of CaO or MgO is directly processed by powder metallurgy in a reducing atmosphere. It is produced by a method of producing polycrystalline metal powder, or by a method of producing a sintered body using a powder metallurgy method, and pulverizing the sintered body to produce polycrystalline metal powder. Next, this polycrystalline metal powder is pressure-molded to form a green compact. Such compacted powder bodies are stacked one on top of the other, and in a reducing atmosphere such as hydrogen,
By sintering, a sintered body in which each layer has a different crystallographic orientation is obtained. Subsequently, this sintered body is subjected to hot and warm rolling processing to form a plate-shaped composite in a reducing atmosphere such as hydrogen at a temperature within the range of 1800 to 2300°C, preferably 1 to 2300°C. It was confirmed that by annealing for 3 hours, a multilayered crystal body having a single crystal state in which the layers overlapped with each other had different crystallographic orientations was obtained. Furthermore, in the present invention, if the amount of molybdenum or tagsten added to the metal powder is 0.003 wt% or less, no grain boundaries exist in the multilayer crystal. Furthermore, if the amount added is 0.232wt% or more,
Since a composite of single crystal and polycrystalline layers is obtained,
It is preferable that the amount added is within the range of 0.003 to 0.115 wt%. [Examples] The present invention will be described below based on Examples. Since the present invention can be similarly applied to both tungsten and molybdenum, the following examples will be described without limiting to either of them. First, tungsten oxide or molybdenum oxide powder is
Calcium oxide and magnesium oxide were added in various proportions by a wet method to prepare a plurality of types of raw material powders. Next, this raw material powder was made into polycrystalline metal powder using a powder metallurgy method. These metal powders with different amounts added were formed into plate shapes, then laminated and press-molded at a pressure of 3 tons/cm ² to obtain a molded body with a multilayer structure as shown in FIG. Each layer of the molded body as shown in this figure has the same additive concentration of calcium oxide and magnesium oxide, and each layer 2, 4 has a different additive concentration than layers 1, 3, and 5, and is mutually equal. It has an additive concentration. In this way, a composite green compact having a multilayer structure was obtained. Next, this composite powder compact was sintered in a hydrogen atmosphere at 1800 to 2300°C to obtain a multilayered sintered body. Furthermore, this sintered body is subjected to hot working at a temperature within the range of 1200 to 1600℃, and then heated to 500 to 1000℃.
The final rolling reduction was 70.
% or more, with a thickness of 2 to 5 mm and a width of
A rolled product with a length of 20 mm and a length of 150 mm was obtained. This rolled product was annealed in a hydrogen atmosphere at a temperature in the range of 1800 to 2300°C for 1 to 3 hours. Table 1 shows the crystal state and temperature at that time. In Table 1, C ₀ is CaO of each layer 1, 3, and 5.
and the amount of MgO added to the metal powder, weight%
It is constant at 0.003wt%. On the other hand, C ₁ is each layer 2, 4
Indicates the amount of CaO and MgO added to the metal powder,
It is varied in the range of 0.012 to 0.155wt%. 1st
For comparison, samples with C1 of 0.05 to 0.08 wt% (Comparative Example 1) and 0.232 to 0.310 wt% (Comparative Example 2) are also shown in the table. As a result, as shown in Comparative Example 1, when C ₁ is 0.005 to 0.008 wt%,
It has been found that the crystalline state of the laminate is a single crystal without grain boundaries, and that it is difficult to form the desired multilayer crystal.

[Table] This shows that when the content of calcium oxide and magnesium oxide is 0.008wt% or less, the _C0 layer and _C1
This is because grain growth cannot be suppressed at layer boundaries because the difference in pinning effect on grain growth between layers is small. Furthermore, as Comparative Example 2, C ₀ is 0.03wt% and C ₁ is
A composite of a single crystal layer and a polycrystalline layer was formed in the layer containing 0.232 wt% or more. In this way, when the amount of calcium oxide and magnesium oxide added is 0.232wt% or more,
It can be inferred that this is because the addition amount of calcium oxide and magnesium oxide is large, so the pinning effect on crystal grain growth is strong, and grain growth is suppressed. On the other hand, C ₀ given as an example is
Within the range of 0.03 wt% and _C1 of 0.012 to 0.155 wt%, each layer of the 5-layer is single crystal, and
It was confirmed that grain boundaries existed within each layer. It has been found that the samples according to these examples have sag resistance without causing recrystallization embrittlement even at high temperatures, and have high reliability without causing rapid fracture propagation even at the time of fracture. [Effects of the Invention] As explained above, according to the present invention, a tungsten or molybdenum multilayer crystal containing at least one of calcium oxide and magnesium oxide in a total amount of 0.003 to 0.115 wt% has excellent sagging resistance and It does not have rapid fracture propagation and has a wide range of uses as an ultra-high temperature heat-resistant material for nuclear reactors, fusion reactor materials, general reactor materials, etc. Furthermore, according to the present invention, the total amount of at least one of calcium oxide and magnesium oxide is
A tungsten or molybdenum multilayer crystal material having one or more parallel crystal grain boundaries on a plate surface is obtained by laminating and annealing a tungsten or molybdenum green compact containing 0.003 to 0.115 wt%. An object of the present invention is to provide a method for manufacturing a multilayer crystal.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a molybdenum or tungsten polycrystal according to an embodiment of the present invention. In the figure, 1, 3, and 5 are C ₀ layers, and 2 and 4 are C ₁ layers.

Claims (1)

[Claims] 1. Consisting of two or more multilayers having grain boundaries parallel to the plate surface, each adjacent layer among the multilayers is in a single crystal state with mutually different crystallographic orientations. A tungsten or molybdenum multilayer crystal comprising: 2 Multiple layers of polycrystals of either tungsten or molybdenum containing different additives are laminated and molded, and then adjacent layers are formed in a single crystal state with different crystallographic orientations. A method for producing a multilayer crystal of tungsten or molybdenum, which comprises annealing the crystal. 3. A raw material preparation step of producing a polycrystalline metal powder containing 0.03 to 0.155 wt% by weight of at least one of calcium oxide and magnesium oxide as an additive to tungsten or molybdenum, and press molding the metal powder. a lamination step of forming a multi-layered composite compact; a sintering step of sintering the composite compact in a reducing atmosphere to obtain a multi-layered compact; and after processing the sintered compact, 1800~2300℃ in reducing atmosphere
A method for producing a tungsten or molybdenum multilayer crystal, comprising an annealing step of performing annealing at a temperature within the range of .