JP6374333B2 - Crucible and method for producing single crystal sapphire using the same - Google Patents

Description

  The present invention relates to a crucible and a method for producing single crystal sapphire using the same, and more particularly to a crucible containing molybdenum and a method for producing single crystal sapphire using the same.

  Conventional crucibles are disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2-251285), Patent Document 2 (Japanese Patent Laid-Open No. 2-254285), Patent Document 3 (Japanese Patent No. 3828651), and Patent Document 4 (Japanese Patent No. 3917208). Gazette), patent document 5 (JP 2011-127150 A), and patent document 6 (JP 2012-107782 A).

Japanese Patent Laid-Open No. 2-251085 JP-A-2-254285 Japanese Patent No. 3828651 Japanese Patent No. 3917208 JP 2011-127150 A JP 2012-107782 A

  Patent Document 1 discloses an invention relating to a molybdenum single crystal crucible and a method for producing the same. In the upper left column of page (2), “However, the molybdenum crucible produced by the above method is in use at 2000 to 2200 ° C. Recrystallization occurs, and the crystal grains become abnormally large. As a result, the leakage of the molten metal occurs during use of the crucible.

  Patent Document 2 discloses an invention related to a molybdenum crucible and a method for manufacturing the same. In [Upper left column of page (2)], “Problems to be solved by the invention” is described as “However, a molybdenum crucible is 2000 ° C. to 2200 ° C. During use at a high temperature, secondary recrystallization occurs, the recrystallized grain size grows to about several centimeters to 10 cm, and the grain boundary penetrates from the inner wall surface to the outer wall surface. There is a description that “the area becomes smaller”.

  Patent Document 3 discloses an invention related to a molybdenum forged molded part and a method for producing the same. In paragraph [0021], “To make the material flow smooth, the oxygen content in the sintered body is usually 40 to 40%. There is a description that “the total carbon amount is 10 ppm or less and the crystal grain size is 80 μm or less” while it is 80 ppm compared to 30 ppm or less.

Patent Document 4 discloses an invention related to a crucible made of tungsten-molybdenum alloy and a method for manufacturing the same. In claim 2, “... after the strain relief annealing, further heat treatment is performed in a vacuum at a temperature of 2000 ° C. or higher. And a seventh step of configuring the molybdenum crystal grains to have a grain size in the range of more than 1 mm and not more than 15 mm. . Furthermore, in paragraph [0003], “However, the weakening of the crystal grain boundary of the material causes cracks and cracks in the grain boundary, and the melted material in the crucible leaks out from such a part, making it unusable. Is described. In paragraph [0006], there is a problem that “a sufficient countermeasure is not taken with respect to the occurrence of damage such as cracks due to heat on the outer wall of the crucible, and it is not possible to avoid intrusion of the material to be melted into the grain boundary. Is described. In claim 3, there is a description that “the temperature range of the heating and holding in the fourth step is 900 ° C. to 950 ° C.”. In claim 4, there is a statement that "in the strain relief annealing process in the sixth step, the temperature condition is in the range of 800 ° C to 900 ° C in a hydrogen atmosphere or 1000 ° C or higher in a vacuum". In paragraph [0008], “In the case of this molybdenum crucible, the crucible size that is actually required recently, for example, the diameter (inner diameter) is about 60 mm to 220 mm and the height is about 30 mm to 100 mm. There are even large-sized ones ”. In paragraph [0019], “The squeezing process is a process that creates an opportunity to occlude gas, and may be vacuum-heated before use. This is a blister that may be generated as a separate factor from cracking. It is effective for prevention measures ". In paragraph [0033], “In addition, after the strain relief annealing process in the previous sixth step, the tungsten-molybdenum alloy crucible is subjected to a temperature of 2000 ° C. and a degree of vacuum of 10 −6 Torr. There is a description of "vacuum high temperature heat treatment was performed under conditions of (10 ^-6 × 133 Pa)".

  Patent Document 5 discloses an invention related to a tungsten-molybdenum alloy crucible and a method for manufacturing the same. Claim 5 describes that "the oxygen distribution in a unit area of 500 μm × 500 μm is distributed more in the tungsten crystal region than in the molybdenum crystal region”. In paragraph [0017], “The impurity components other than tungsten and molybdenum are preferably 0.1% by mass or less, and more preferably 0.05% by mass or less. As a typical impurity component, iron is 0.01 wt%. % (100 wtppm) or less and the other metal components are preferably 0.04 wt% (400 wtppm) or less in total. Needless to say, the smaller the impurity components, the better. " In paragraph [0033], “One of the reasons why the life of the crucible is reduced is the“ bulging ”phenomenon in which oxygen has advanced to the molybdenum crystal surface. There is a description of “blowing occurs”.

  Patent Document 6 discloses an invention relating to a crucible and a method for producing a sapphire single crystal using the crucible. In claim 6, the oxygen content is 10 to 2000 wtppm. 5. The crucible according to any one of 5). In paragraph [0004], “When a refractory metal crucible is used at a high temperature, a phenomenon called“ bulging ”in which impurity oxygen expands inside the sintered body occurs, resulting in a short life of the crucible. There was a description. In paragraph [0013], “The impurity components other than tungsten and molybdenum are preferably 0.1% by mass or less, and more preferably 0.05% by mass or less. It is preferable that the total amount of the other metal components is 0.04 wt% or less and the nitrogen content is 0.01 wt% or less. It goes without saying that the smaller the impurity components, the better. In paragraph [0017], “It is preferable that the crucible has an oxygen content of 10 to 2000 wtppm. This oxygen content is a value obtained by adding both impurity oxygen and oxygen of the oxygen-adsorbing metal oxide.” Is described. In paragraph [0021], there is a description that "a high melting point metal powder having an oxygen content of 10 to 1000 wtppm is used. Even if the oxygen content is less than 10 wtppm, it can be used as a raw material powder". .

  However, the crucibles described in Patent Documents 1 to 6 have a problem that the melt in the crucible leaks when used at a high temperature.

  Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide a crucible capable of preventing melt leakage and a method for producing single crystal sapphire using the crucible. .

  The crucible according to the present invention is a crucible manufactured by forging containing 40 mass% or more of molybdenum, the total content of C, N and O is 200 mass ppm or less, and the angle R of the boundary between the bottom surface and the side surface Part hardness is 150HV or more and 300HV or less, C content is 30 mass ppm or less, N content is 20 mass ppm or less, and O content is 150 mass ppm or less.

  According to the present invention, it is possible to provide a crucible capable of preventing melt leakage and a method for producing single crystal sapphire using the crucible.

It is sectional drawing of the crucible according to embodiment.

[Description of Embodiment of Present Invention]
First, the contents of the embodiments of the present invention will be listed and described.

  The crucible is a crucible manufactured by forging containing 40% by mass or more of molybdenum, the total content of C, N and O is 200 ppm by mass or less, and the hardness at the corner R of the boundary between the bottom surface and the side surface Is 150 HV or more and 300 HV or less, the C content is 30 mass ppm or less, the N content is 20 mass ppm or less, and the O content is 150 mass ppm or less.

Preferably, heat treatment is performed before and after forging.
Preferably, the heat treatment is performed in a vacuum atmosphere.

  The method for producing single crystal sapphire includes the step of filling the crucible according to any one of the above with alumina powder, and the step of forming single crystal sapphire in the crucible by solidifying the alumina powder after heating and melting. With.

[Details of the embodiment of the present invention]
Specific examples of the crucible according to the embodiment of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

  The present inventor has examined why melt leakage occurs in a crucible containing molybdenum.

  Molybdenum crucibles are frequently used for sapphire single crystal growth. Because it is used in a high-temperature environment above the melting point of alumina (2050 ° C), leakage of alumina melt accompanying sliding of the molybdenum crystal grain interface coarsened with recrystallization grain growth, or from a rupture part accompanying swelling Problems such as melt leakage have occurred.

  When molybdenum metal is used in a high temperature environment, a recrystallized grain growth phenomenon occurs and crystal grains become coarse. Crystal grains originally having a size of about several μm to several hundreds of μm are transformed into crystal grains having a size of about several mm to several cm to several tens of cm when used at a high temperature. This factor is considered to be the effect of residual strain accumulated with plastic working or the effect of impurities contained.

  The inventor has focused on gas impurities, particularly oxygen impurities, among the contained impurities. It is said that oxygen is one of the causes of swelling (Patent Document 5). Considering that the problem of blistering can be reduced by reducing the oxygen content, attention was paid to high-temperature heat treatment in a vacuum as a method for easily reducing the oxygen content. A technique for adjusting the crystal grain size by applying this treatment is disclosed (Patent Document 4), but it is not a technique for actively reducing oxygen impurities. It has been found that swelling problems can be reduced by setting the oxygen content to 150 mass ppm or less by high-temperature heat treatment in vacuum.

  Patent Document 1 discloses a molybdenum single crystal crucible in which the entire crucible is substantially composed of one crystal and a method for manufacturing the same as a solution to this problem. This method is a technique suitable for application to a small crucible having a diameter of several centimeters and a height of several centimeters, but a recent large-sized crucible (for example, a range of 20 to 50 cm in diameter and a height of 20 to 60 cm). (Approx. Range) is difficult to apply.

  Patent Document 2 discloses a molybdenum crucible that fits into a grain growth of about several millimeters by devising a flat forging method in order to prevent recrystallized grain growth. Although this method can obtain a forging material by simple flat forging, a post-process for finishing the forging material into a crucible shape by machining such as lathe cutting or milling is essential, and it is necessary to consume a large amount of molybdenum material. Yes, manufacturing cost is high.

  Patent Document 3 discloses a molybdenum crucible by a die forging method and a manufacturing method thereof. This is a method for forming a crucible shape by forging a molybdenum powder sintered material with a forging device having a male mold and a female mold, and it can be said to be near-net processing and provide a technique capable of extending the life of the crucible. This method, that is, the upsetting forging method, can be said to be a production method suitable for a crucible having a relatively thick thickness as described in the examples (thickness 15 mm).

  Patent Document 4 discloses a crucible having a long life in which the size of crystal grains is controlled by a two-stage heat treatment technique for a crucible product finished in a crucible shape. The first stage is a relatively low temperature condition (800 ° C. to 900 ° C. in a hydrogen atmosphere, 1000 ° C. or higher in a vacuum), and the second stage is 2000 ° C. or higher in a vacuum. Although qualitative consideration is given to the effect of the gas impurities contained on the lifetime, there is no suggestion about the quantitative value. Although there is a reference to the pros and cons of degassing vacuum heat treatment of a flat disk before drawing, it is an invention of atmospheric heat treatment focusing on crystal grain control of crucible products.

  In Patent Document 5, the cause of defects during use is contained oxygen and contained metal impurities, and tungsten is alloyed with molybdenum to prevent coarsening of crystal grains. Furthermore, alloying tungsten, which is based on molybdenum and easily incorporates oxygen into the crystal, has a role to characterize oxygen that advances to the crystal surface. There is no disclosure regarding the quantitative relationship between lifetime and oxygen content.

  Patent Document 6 is an invention in which oxygen-adsorbed metal particles or oxide particles thereof are dispersed in a refractory metal crucible to prevent grain growth and to reduce the amount of oxygen contained in the refractory metal.

  The present inventor has included various gas impurities of C, N, and O contained in the crucible in order to achieve reduction of blistering problems frequently occurring in the corner R portion of the crucible used at a high temperature of 2000 ° C. or higher. Attention was paid to the amount and residual strain at the corner R (adopting Vickers hardness as a substitute characteristic).

  FIG. 1 is a cross-sectional view of a crucible according to an embodiment. Referring to FIG. 1, a crucible 1 is made of molybdenum or an alloy thereof, and an upper portion has an opening shape. A flange portion 12 extending in the circumferential direction and extending in the circumferential direction is provided on the upper portion.

  The crucible 1 has a bottomed shape, and a boundary portion between the bottom surface 15 and the side surface 13 is a corner R portion 16. The angle θ formed by the side surface 13 of the crucible 1 with respect to the vertical direction can be set variously.

  Single crystal sapphire can be produced by filling the crucible 1 with sapphire raw material powder (alumina) and heating, melting and solidifying the powder. After the single crystal sapphire is manufactured, the single crystal sapphire in the crucible 1 can be taken out by breaking the crucible 1.

  Since the gap between the raw material powders is filled by heating and melting, even if the raw material powder is filled as much as the internal volume of the crucible 1, single crystal sapphire smaller than the internal volume of the crucible 1 can be produced. Single crystal sapphire with the same volume cannot be produced. In order to manufacture a larger single crystal sapphire, a cylindrical guide member is provided on the upper portion of the crucible 1, and this guide member is engaged with the crucible 1. The raw material powder is filled not only in the crucible 1 but also in the guide member.

  The guide member is made of a heat resistant material, and is preferably made of the same material as the crucible. The raw material powder in the crucible 1 and the guide member is heated and melted to move into the crucible 1, and a large sapphire single crystal can be produced in the crucible 1. The guide member is detachably provided on the crucible.

1. In the crucible 1, the total of C, N, and O is 200 mass ppm or less, the Vickers hardness of the corner R portion 16 at the boundary between the bottom surface and the side surface is 150 HV or more and 300 HV or less, and molybdenum is 40 mass% or more. Including. The balance is tungsten and inevitable impurities. Preferably, C of the gas impurity contained is 30 mass ppm or less, N is 20 mass ppm or less, and O is 150 mass ppm or less.

A: Definition of gas impurity content (1) When C is 30 mass ppm or less; and exceeds 30 mass ppm, it is considered that the amount of solid solution and alloying in molybdenum or impurity elements increases. As a result, the crystal grain boundary is weakened, and the probability of occurrence of blistering defects increases.

  (2) N is 20 mass ppm or less; if it exceeds 20 mass ppm, it is considered that the same phenomenon as C occurs, and the probability of occurrence of blistering defects increases.

  (3) When O exceeds 150 ppm by mass; if it exceeds 150 ppm by mass, in addition to the same phenomenon as C and N, the amount accumulated in voids slightly existing at the crystal grain interface increases, so that swelling occurs. Is likely to occur.

  (4) The sum of C, N, and O is 200 mass ppm or less; the total amount of three types of gas impurities, mainly O, which is the largest amount of gas impurities after degassing treatment, is defined.

  As for the chemical quantification method of gas impurities, both C and O are infrared absorption methods, and N is a thermal conductivity method.

B: Definition of Vickers hardness value of corner R part (1) Molybdenum (theoretical density 10.2 g / cm ³ ); residual plastic working strain is released by the vacuum high-temperature heat treatment of the present application, and the Vickers hardness after the vacuum high-temperature heat treatment is 150 HV To 200HV.

(2) 70 mass% molybdenum-30 mass% tungsten alloy (abbreviation 7 MW, theoretical density 11.88 g / cm ³ ); Vickers hardness increases with increasing tungsten content. The Vickers hardness after vacuum high temperature heat treatment is 170HV to 240HV.

(3) 40% by mass molybdenum-60% by mass tungsten alloy (abbreviation 4 MW, theoretical density 14.22 g / cm ³ ); Vickers hardness after vacuum high-temperature heat treatment is 190 HV to 260 HV.

(4) 30% by mass molybdenum-70% by mass tungsten alloy (abbreviation: 3 MW, theoretical density: 15.23 g / cm ³ ); Vickers hardness after vacuum high-temperature heat treatment is 200HV to 300HV.

The hardness was measured using a Vickers hardness meter and the load was 10 kg.
These preferred hardness ranges vary depending on the material, but in the case of numerical values that are lower than the lower limit of the respective hardness, recrystallization progresses, leading to a decrease in grain boundary strength, separation of the grain boundary, and swelling. Recrystallization that is allowed but below the above lower limit must be avoided. On the other hand, if the hardness is too high, a large amount of plastic strain remains, resulting in poor workability and an extremely low yield in forging. Therefore, it is desirable that the upper limit of hardness is not exceeded.

C: Definition of Molybdenum Content Range As a material constituting the crucible, molybdenum, tungsten, and molybdenum-tungsten alloy having a melting point that can withstand the sapphire melting temperature and high strength at high temperatures are used. If the tungsten content in the molybdenum-tungsten alloy exceeds 60% by mass, the alloying technique becomes high and the forging process becomes difficult. In addition to cost increase, the properties are similar to tungsten, so there are few merits to adopt.

2. Invention of manufacturing method <Details of process>
Step 1: Raw material FSSS (Fisher sub-sieve sizer) particle size of 1 μm to 10 μm, preferably 2 μm to 6 μm, molybdenum metal powder with a purity of 99.5% by mass, and FSSS particle size of 1 μm to 10 μm with a purity of 99.5% by mass Prepare tungsten metal powder. If the powder particle size is too fine, defects such as molding cracks are likely to occur, and if it is too coarse, the sintered density will be low.

Step 2: Mixing The required weight of powder is mixed with a V-shaped mixer for 0.5 to 3 hours. For mixing, a desired mixed powder can be obtained by using a general mixer such as a double cone mixer or a ball mill.

Step 3: Molding The powder that had undergone the required weighing was put into a rubber case and molded with a hydrostatic pressure press (CIP) at a pressure of 1 to 3 ton / cm ² .

Step 4: Sintering The powder compact is sintered in a hydrogen sintering furnace. The powder compact for molybdenum crucible was sintered at 1600-2000 ° C, the molybdenum-tungsten alloy crucible compact was sintered at 1800-2200 ° C, and the time was sintered for 5-20 hours.

Step 5: Vacuum degassing step C, N, O gas impurity content in order to reduce, 1500-2200 vacuum hot degassing of 1 to 10 hours 5 × 10 ^-6 torr at ° C. (5 × 10 ^{- 6} × 133 Pa) or less. This high temperature treatment improved the sintered density by about 1% or more.

Step 6: Forging and forming step Forming and forging were performed using a hot forging device. The sintered body is put into a heating furnace at 1100 to 1400 ° C., heated for 30 minutes, and then placed near the center of a hot forging die set in a forging apparatus. The mold is preliminarily coated with a carbon lubricant and then heated to about 200 ° C. Forging was initially forged several times from 2 TONm to 3 TONm, and then forged 5 to 6 times at 9 TONm to 10 TONm to rough finish the crucible material. During this period, reheating was not performed. The approximate dimensions of the coarse crucible were a bottom thickness of 14 mm, an opening diameter of 228 mm, and a total height of 79 mm. The density of the crude crucible after forging reached about 98.5% to 99% with respect to the respective theoretical densities. However, it still contains many gas impurities.

Step 7: Lathe cutting A rough crucible was set on an NC vertical lathe, and a surplus portion and burrs on the end face of the opening were cut and removed with a carbide tool to finish a crucible product. The finished dimensions are a wall thickness of 7 mm, a bottom thickness of 9.5 mm, an opening inner diameter of 200 mm, and a total height of 200 mm. The Ra of the cut and removed surface was 2 to 3 μm, and defects such as cracks and voids were not recognized by visual inspection and ultrasonic flaw inspection, and were good.

Step 8: Vacuum degassing step For the purpose of reducing gas impurities adsorbed in the hot forging step, the crucible after finishing was subjected to vacuum high temperature degassing. The heating temperature was 1800 ° C. to 2000 ° C. for the molybdenum crucible, and 2000 ° C. to 2200 ° C. for the molybdenum-tungsten alloy crucible, respectively, for 1 hour. The ultimate vacuum was 5 × 10 ⁻⁶ torr (5 × 10 ⁻⁶ × 133 Pa) or less.

  In addition, the sintering process of the said process 4 can be replaced with another sintering method. For example, when encapsulating in HIP processing, sealing is performed after evacuation while baking at a temperature of 500 ° C. to ˜1000 ° C. Thereafter, the HIP sintering treatment may be performed at a temperature of 1100 ° C. to ˜2000 ° C. for about 3 hours to about 10 hours.

  Further, in the sintering step of Step 4, the hydrogen dew point may be appropriately adjusted and sintered in an atmospheric pressure hydrogen atmosphere furnace depending on the sintering temperature, time, hydrogen flow rate, arrangement of the hydrogen inlet, and the like.

  In the sintering step, the total content of gas impurities C, N and O is 100 mass ppm or less, the C content is 30 mass ppm or less, the N content is 20 mass ppm or less, O If the crucible with a content of 50 mass ppm or less and a hardness and a hardness at the corner R of the boundary between the bottom surface and the side surface of 150 HV or more and 310 HV or less is obtained, the vacuum degassing treatment steps 5 and 8 in the above steps are performed. It can be omitted.

<Example>
Using a single crystal sapphire growing device, the occurrence of swelling problems was investigated. Each manufactured crucible was filled with alumina powder, heated and melted at 2100 ° C., held for 10 hours, and cooled to 500 ° C. as one cycle, and the situation after 5 cycles was observed visually. The crucible of the present invention and the crucible of the comparative example were evaluated by applying the same cooling load. The purpose of applying a cooling load along with high-temperature heating is to increase the frequency of occurrence of blistering defects by accelerating thermal stress on the crystal grain interface of the polycrystalline material that constitutes the crucible. The evaluation results are shown in Table 1.

  Here, sample no. 1-3, 6-8, 11-13, and 16-18 are examples. 4, 5, 9, 10, 14, 15, 19, and 20 are comparative examples using test specimens cut out from the crucible manufactured in the process up to the cutting process up to the process 7. It was found from the table that in order to prevent blistering, it is necessary to reduce the amount of gas components by vacuum degassing.

  No. Nos. 16 to 18 are insufficient even if the amount of gas components is reduced to some extent by the primary vacuum degassing process, and the hardness is high, causing problems in workability in the forging process, and the frequency of occurrence of cracks at the corner R is high. It is not at the level at which the secondary vacuum degassing treatment is performed, and industrial production is impossible, and the amount of tungsten added to molybdenum is limited to 60% by mass or less.

  It is important to balance the vacuum heat treatment conditions and the hardness after the vacuum heat treatment. If the temperature and time of the vacuum heat treatment are excessive, recrystallization proceeds and the residual amount of gas components decreases, but swelling occurs due to a decrease in grain boundary strength due to recrystallization.

  On the contrary, if the temperature and time of the vacuum heat treatment are insufficient, the residual strain is reduced and the amount of degassing is insufficient, and the material is brittle and internal cracks are likely to occur during processing. Residual gas components tend to concentrate due to diffusion through the grain boundaries, resulting in accumulation of gas components, increasing the frequency of cracks, and eventually leading to blistering.

  The present invention can be used in the field of crucibles.

  1 crucible, 12 flange part, 13 side face, 15 bottom face, 16 corner R part.

Claims (2)

Molybdenum containing molybdenum 40 wt% or more - a crucible of forgings tungsten alloy or molybdenum, C, and the total content of N and O is 200 mass ppm or less, at the corner R portion of the boundary of the bottom and sides A crucible having a hardness of 150 HV or more and 300 HV or less, a C content of 30 mass ppm or less, an N content of 20 mass ppm or less, and an O content of 150 mass ppm or less. Filling the crucible according to claim 1 with alumina powder;
And a step of forming single crystal sapphire in the crucible by solidifying the alumina powder after being heated and melted.

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