JPH0585507B2 - - Google Patents
Info
- Publication number
- JPH0585507B2 JPH0585507B2 JP1077177A JP7717789A JPH0585507B2 JP H0585507 B2 JPH0585507 B2 JP H0585507B2 JP 1077177 A JP1077177 A JP 1077177A JP 7717789 A JP7717789 A JP 7717789A JP H0585507 B2 JPH0585507 B2 JP H0585507B2
- Authority
- JP
- Japan
- Prior art keywords
- type
- silicon nitride
- sintering
- nitride powder
- sintered body
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000005245 sintering Methods 0.000 claims description 39
- 239000002245 particle Substances 0.000 claims description 37
- 239000000843 powder Substances 0.000 claims description 37
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 35
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 35
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 11
- 229910052757 nitrogen Inorganic materials 0.000 claims description 9
- 229910052747 lanthanoid Inorganic materials 0.000 claims description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 5
- -1 lanthanide metal oxide Chemical class 0.000 claims description 5
- 229910044991 metal oxide Inorganic materials 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 230000000694 effects Effects 0.000 description 9
- 239000002994 raw material Substances 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 230000002159 abnormal effect Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 239000012535 impurity Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000000462 isostatic pressing Methods 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 238000007088 Archimedes method Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000007657 chevron notch test Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000001746 injection moulding Methods 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000013001 point bending Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Landscapes
- Ceramic Products (AREA)
Description
（産業上の利用分野）
本発明は、強度や熱衝撃抵抗が大きいため、自
動車部品やその他の機械部品への応用が期待され
ている高靱性窒化珪素焼結体の製造法に関する。
（従来の技術）
従来より、窒化珪素焼結体の焼結法としては、
ホツトプレス法、熱間静水圧法、常圧焼結法、ガ
ス圧焼結法等々が開発されている。原料粉末とし
ては、α型を主成分とする窒化珪素粉末が望まし
いとされており、一般的には、α率が85％以上
（すなわち、β率が15％以下）のものが市販され
ている。
このように高α率の窒化珪素粉末を用いるの
は、
α型は低温安定型なので、低い温度で合成で
き、コスト的に有利である。
α型は細かく焼結性が高い。
焼結中にα型がβ型に転移し、その際、柱状
粒子が発達する。破壊はクラツクが進むことに
よつて起こるが、この柱状粒子はクラツクの方
向を変え、焼結体の破壊靱性を上げる効果があ
る。
等の理由からであつた。
（発明が解決しようとする課題）
一方、破壊靱性は異常成長した粒子のアスペク
ト比（長軸／短軸比）に比例し、この粒子の形状
は原料中のα率に比例するとされてきたので、β
型の窒化珪素粉末は原料として用いられていなか
つた。
しかし、高α率の窒化珪素粉末は、
細かく活性なため、保存中、或いは混合や成
形操作の際に、酸素や水蒸気と反応しやすい。
低温で合成する必要性から、非晶質を含む場
合があり、結晶化の際にガスを放出し、焼結を
阻害する。
破壊靱性を高める目的で柱状粒子の異方性を
大きくすると、焼結性が低下したり、欠陥が大
きくなり、強度が低いものとなる。
柱状粒子は異常成長粒子であり、原料や成形
焼結条件等の複雑な因子によつてその形、大き
さ、量が決定されるので、組織の制御は容易で
はない。
一定収率速度の条件下で焼結すると、より高
密度の焼結体が得られるが、α型は焼結挙動が
複雑で収縮速度が制御できない。
等々の問題点があつた。
本発明者の１人は、先に、高窒素下で高温での
焼結が可能になるガス圧焼結法を開発し提案した
（特許第1247183号）。ガス圧焼結法によると、従
来、焼結性が低いと考えられていたβ型窒化珪素
粉末を用いても高密度まで焼結し得ることは知ら
れているところである（“ジヤーナル・オブ・マ
テリアルス・サイエンス”、第11巻、p.1103〜
1107（1976）及び特公昭58−151371号公報参照）。
しかし、前記提案によれば、β型窒化珪素粉末を
用いて得られる焼結体は球状に近い粒子から成り
立ち、α型粉末を用いた場合における柱状粒子の
ようにクラツクを曲げる作用がないため、破壊靱
性の高い焼結体は得られなかつた。
本発明の目的は、上述の如くβ型窒化珪素粉末
を用いる従来法の問題点を解決するためになされ
たものであつて、高靱性の窒化珪素焼結体を製造
できる方法を提供するにある。
（課題を解決するための手段）
本発明者らは、高温で不安定なα型窒化珪素粉
末を用いると、焼結中に異常粒成長が起こり、得
られた焼結体の組織が不均一になり、強度分布が
大きくなることに鑑みて、β型窒化珪素粉末を使
用しても、高靱性で、かつ、均一組織を持つ焼結
体が得られる方法について鋭意研究を重ねた。そ
の結果、高温安定型の細かいβ型窒化珪素粉末を
用いると、均一な組織中に核が成長して大きな柱
状粒子が成長し、破壊靱性が大きな焼結体が得ら
れることを知見するに至り、本発明を完成したも
のである。
すなわち、本発明は、β型を主成分とし、平均
粒径1.5μｍ以下の窒化珪素粉末と、純粋なβ型で
平均粒径2.5〜5μｍの窒化珪素粉末とを重量比で
95：５〜75：25の割合で配合し、これに焼結助剤
を混合し、成形した後、２〜200気圧の窒素中で
1800〜2100℃にて焼結することを特徴とする高靱
性窒化珪素焼結体の製造法を要旨とするものであ
る。
以下、本発明について更に詳述する。
（作用）
β型を主成分とする窒化珪素粉末は、細かいも
のである必要があり、平均粒径1.5μｍ以下、望ま
しくは0.3〜1μｍのものを用いる。粒径が1.5μｍ
よりも大きいと焼結体の粒子が大きく、また大き
な残留気孔が存在することになるので、破壊靱
性、強度とも低くなり、好ましくない。β型を主
成分とする粉末は、β型が70〜100wt％、α型が
０〜30wt％のものが好ましいが、望ましくはβ
型が85〜100wt％、α型が０〜15wt％のものであ
る。α型の含有率が30wt％を超えると焼結中に
α→βの転移が起こり、それが粒成長を促進する
ので異常粒成長が起こり、不均一な組織となるの
で好ましくない。
窒化珪素は焼結助剤が生成した液相を通つて拡
散し焼結する液相焼結によるが、高温で不安定な
α型粉末の場合は、焼結と相変化が同時に起こ
り、異常粒成長が起こる。成長した粒子の形や大
きさが焼結体の破壊靱性を支配するが、初期に生
成したβ型粒子の核の形や数及び焼結条件等に大
きく依存し、制御することは困難である。一方、
高温安定型のβ型粉末の場合は、最初から核が存
在するので、焼結と共に小さな粒子が消滅し、大
きな粒子上に析出する反応が起こるだけである。
粒子は球状に近い形態を保つたまま一定の粒度分
布の幅を保つたまま粒成長する。そして、粒成長
のための核として、平均粒径2.5〜5μｍの純粋な
β型粉末を５〜25％（上記β型を主成分とする窒
化珪素粉末に対する重量比）配合すると、小さく
均一な粒子の間に大きな粒子が成長するため、破
壊の際、クラツクは一部の大きな粒子で曲げら
れ、破壊靱性は高くなる。この純粋なβ型粉末の
平均粒径は、望ましくは３〜４ミクロンであり、
混合割合は、望ましくは５〜15％である。粒径及
びその混合量がその下限値より小さいと核として
の効果がなく、大きすぎると組織全体が粗粒成
し、靱性や強度が低下するので好ましくない。
なお、原料粉末中の不純物は、金属は合計で
0.4wt％以下、酸素は1.5wt％以下のものが望まし
い。これら不純物は靱性値には大きな影響を及ぼ
さないが、高温強度を低下させるからである。
焼結助剤としては、Al2O3、Y2O3又はランタニ
ド金属酸化物のうちの２種類以上を用いる。単独
では焼結促進の効果が悪い。Al2O3は前記他の物
質よりも効果が大きいが、焼結体の高温強度を低
下させるので、その量は少ない方がよい。
すなわち、Al2O3と他の酸化物の混合物を使用
するときは合計で３〜10wt％、望ましくは４〜
8wt％とする。なお、Al2O3の量は0.3〜３重量
％、望ましくは１〜２重量％、Y2O3又はランタ
ニド金属の量はそれぞれ２〜7wt％、望ましくは
４〜6wt％である。
また、Y2O3又はランタニド金属酸化物の混合
物を用いる場合は、前記の場合よりも多量に必要
であり、合計で５〜15wt％、望ましくは７〜
12wt％とする。なお、この場合、焼結助剤の量
が所定量よりも少ないと効果が十分でなく、緻密
な焼結体は得られない。焼結助剤が多すぎるとコ
ストが高くなるだけでなく、耐酸化性等、高温で
の特性を低下させる。
上記窒化珪素粉末と焼結助剤の混合は、窒化珪
素の酸化を防ぐために有機溶媒中で行うのが望ま
しい。乾燥後、静水圧プレス、射出成形、鋳込み
成形等、通常の方法で成形する。
焼結は２〜200気圧の加圧窒素中で1800〜2100
℃の温度範囲で行う。窒素は、窒化珪素の熱分解
を防ぐために必要で、高温ほど高圧を用いる。必
要な最低圧は1800℃で２気圧、1900℃で５気圧、
2000℃で10気圧、2100℃で20気圧である。所定圧
力よりも低いと窒化珪素は熱分解し、窒素を放出
してシリコンとなるので望ましくない。所定圧よ
り高くてもよいが、装置が高価になる。窒素圧２
〜50気圧、温度1800〜2000℃で開気孔のない焼結
体を作り、第１段より更に高圧の条件下（50〜
200気圧）で1850〜2100℃にて焼結すると更に高
密度、高強度の焼結体を得ることができる。
焼結は、一般に10〜30℃／minの速度で昇温
後、所定範囲内の一定温度に30分〜４時間、望ま
しくは１〜３時間保持する。更に実際の焼結が起
こる1500℃以上においては、線収縮率を一定にし
て焼結すると、粒成長速度に比べ気孔除去速度が
大きくなるので、均一組織となり、高密度、高強
度の焼結体が得られるので望ましい。そのために
は線収縮率を0.5〜1.75％／minとするのが望まし
い。この範囲より低いと長時間要し実際的ではな
く、また高すぎると昇温速度を大きくする必要が
あり、大出力の電源が必要となる。線収縮率を一
定にするには、予め、昇温スケジユールと収縮率
の関係を、小さな試料を用い、差動変圧器を備え
た炉で求めておいて利用するとよい。大きな部品
でも昇温スケジユールを同じにすれば線収縮率は
一定に制御することは容易である。β型粉末は
1550〜1900℃の間に１段階で焼結するので収縮率
の制御は容易であるが、α型粉末は２段階で焼結
するので収縮率の制御は困難である。
上記のように、β型を主成分とする窒化珪素粉
末を用いると、焼結体中の粒子の粒度分布を一定
に保つことができる。また異常粒成長がないので
焼結条件の少しの変動は大きく影響しない。この
ため、β型粉末は焼結性がα型より高く、高密
度、高強度の焼結体が得られる。また、破壊の際
に大きな粒子がクラツクの方向を曲げ、破壊エネ
ルギーは大きくなり、破壊靱性は大きいものとな
る。α型から得られた焼結体が繊維強化型の高靱
性化機構を示すのに対し、β型から得られる焼結
体は粒子分散型の機構である。
（実施例）
次に本発明の実施例を示す。
実施例 １
α型窒化珪素粉末を10気圧の窒素中、1900℃に
１時間加熱して得た純粋なβ型窒化珪素粉末（平
均粒径3.0μｍ、金属不純物合計0.8wt％、酸素含
有率1.0wt％）と、β型を主成分とする窒化珪素
粉末（平均粒径0.8μｍ、β型／（α型＋β型）＝
0.9、金属不純物合計0.35wt％、酸素含有率1.2wt
％）を重量比で10：90に秤量し、これに焼結助剤
としてアルミナ（純度99.99％、平均粒径0.3μ
ｍ）、Y2O3（純度99.9％、平均粒径0.5μｍ）、ラン
タニド金属酸化物（純度＞99％、＜平均粒径0.8μ
ｍ）を第１表に示す所定量にて加え、ｎ−ヘキサ
ン中、窒化珪素製ボールミルで３時間混合した。
次いで、空気中、80℃で乾燥後、250Kg／cm2で
金型プレスした後、2ton／cm2で静水圧プレスし、
柱状の成形体とした。成形体を第１表に示す種々
の条件で焼結した後、水を用いたアルキメデス法
で密度を求め、気孔率を算出した。次いで、600
メツシユのダイヤモンドホイールで平面研削し、
約３mm×４mm×40mmの試料片とし、強度と破壊靱
性を調べた。それらの結果を第１表に併記する。
なお、強度はJISR1601によりスパン30mmの３
点曲げにより求めた。破壊靱性はシエブロンノツ
チ法で決定した。
第１表より、いずれも高靱性、高強度の焼結体
が得られていることがわかる。
(Industrial Application Field) The present invention relates to a method for producing a high toughness silicon nitride sintered body, which is expected to be applied to automobile parts and other mechanical parts because of its high strength and thermal shock resistance. (Conventional technology) Traditionally, the sintering method for silicon nitride sintered bodies is as follows:
Hot press methods, hot isostatic pressure methods, normal pressure sintering methods, gas pressure sintering methods, etc. have been developed. As a raw material powder, silicon nitride powder whose main component is α-type is said to be desirable, and those with an α rate of 85% or more (that is, a β rate of 15% or less) are generally commercially available. . The use of silicon nitride powder with such a high α rate is advantageous in terms of cost because the α type is stable at low temperatures, so it can be synthesized at low temperatures. The α type is fine and has high sinterability. During sintering, the α-type transforms into the β-type, and at this time, columnar particles develop. Fracture occurs as the crack progresses, and these columnar particles have the effect of changing the direction of the crack and increasing the fracture toughness of the sintered body. This was due to the following reasons. (Problem to be solved by the invention) On the other hand, it has been said that fracture toughness is proportional to the aspect ratio (major axis/minor axis ratio) of abnormally grown particles, and the shape of these particles is proportional to the α ratio in the raw material. ,β
Type silicon nitride powder was not used as a raw material. However, since high alpha ratio silicon nitride powder is fine and active, it easily reacts with oxygen and water vapor during storage or during mixing and molding operations. Because it needs to be synthesized at low temperatures, it may contain amorphous material, which releases gas during crystallization and inhibits sintering. If the anisotropy of columnar particles is increased for the purpose of increasing fracture toughness, the sinterability will decrease, defects will become large, and the strength will be low. Columnar particles are abnormally grown particles, and their shape, size, and amount are determined by complicated factors such as raw materials and shaping and sintering conditions, so it is not easy to control their structure. Sintering under constant yield rate conditions yields a denser sintered body, but the α type has complex sintering behavior and shrinkage rate cannot be controlled. There were other problems. One of the present inventors previously developed and proposed a gas pressure sintering method that enables sintering at high temperatures under high nitrogen conditions (Patent No. 1247183). It is known that gas pressure sintering can be used to sinter to a high density even when using β-type silicon nitride powder, which was previously thought to have low sinterability. Materials Science”, Volume 11, p.1103~
1107 (1976) and Japanese Patent Publication No. 58-151371).
However, according to the above proposal, the sintered body obtained using β-type silicon nitride powder is composed of nearly spherical particles and does not have the effect of bending cracks like columnar particles when α-type powder is used. A sintered body with high fracture toughness could not be obtained. The purpose of the present invention was to solve the problems of the conventional method using β-type silicon nitride powder as described above, and to provide a method for producing a highly tough silicon nitride sintered body. . (Means for Solving the Problem) The present inventors have discovered that when α-type silicon nitride powder, which is unstable at high temperatures, is used, abnormal grain growth occurs during sintering, resulting in a non-uniform structure of the obtained sintered body. In view of the fact that the strength distribution becomes larger, we conducted intensive research on a method that would allow us to obtain a sintered body with high toughness and a uniform structure even when using β-type silicon nitride powder. As a result, we found that when high-temperature stable fine β-type silicon nitride powder is used, nuclei grow in a uniform structure and large columnar particles grow, resulting in a sintered body with high fracture toughness. , has completed the present invention. That is, the present invention has a silicon nitride powder containing β-type as a main component and having an average particle size of 1.5 μm or less, and pure β-type silicon nitride powder having an average particle size of 2.5 to 5 μm in a weight ratio.
Blended in a ratio of 95:5 to 75:25, mixed with a sintering aid, molded, and then molded in nitrogen at 2 to 200 atmospheres.
The gist of this invention is a method for producing a highly tough silicon nitride sintered body, which is characterized by sintering at 1800 to 2100°C. The present invention will be explained in more detail below. (Function) The silicon nitride powder containing β-type as a main component must be fine, with an average particle size of 1.5 μm or less, preferably 0.3 to 1 μm. Particle size is 1.5μm
If it is larger than this, the particles of the sintered body will be large and large residual pores will be present, resulting in low fracture toughness and strength, which is not preferable. The powder whose main component is β type is preferably 70 to 100 wt% of β type and 0 to 30 wt% of α type.
The content of the type is 85-100wt% and the α-type is 0-15wt%. If the α-type content exceeds 30 wt%, an α→β transition occurs during sintering, which promotes grain growth, resulting in abnormal grain growth and a non-uniform structure, which is undesirable. Silicon nitride is produced by liquid phase sintering, in which the sintering aid diffuses through the generated liquid phase and sinters, but in the case of α-type powder, which is unstable at high temperatures, sintering and phase change occur simultaneously, resulting in abnormal grains. Growth occurs. The shape and size of the grown particles govern the fracture toughness of the sintered body, but this is difficult to control as it largely depends on the shape and number of the initially generated β-type particle nuclei and the sintering conditions. . on the other hand,
In the case of high-temperature stable β-type powder, since nuclei are present from the beginning, small particles disappear during sintering, and a reaction occurs in which they are precipitated on large particles.
The particles grow while maintaining a nearly spherical shape and a constant width of particle size distribution. When 5 to 25% (weight ratio to the silicon nitride powder mainly composed of the β type described above) of pure β type powder with an average particle size of 2.5 to 5 μm is blended as a nucleus for grain growth, small and uniform particles can be formed. During fracture, large particles grow, so when fracture occurs, the crack is bent by some of the large particles, increasing fracture toughness. The average particle size of this pure β-type powder is preferably 3 to 4 microns;
The mixing ratio is preferably 5 to 15%. If the particle size and the amount of the mixture are smaller than the lower limit, there is no effect as a nucleus, and if it is too large, the entire structure becomes coarse grained and the toughness and strength are reduced, which is not preferable. In addition, impurities in the raw material powder include metals in total.
It is preferable that the content of oxygen is 0.4wt% or less, and the oxygen content is 1.5wt% or less. This is because, although these impurities do not have a large effect on the toughness value, they reduce the high temperature strength. As the sintering aid, two or more of Al 2 O 3 , Y 2 O 3 or lanthanide metal oxides are used. When used alone, the effect of promoting sintering is poor. Although Al 2 O 3 has a greater effect than the other substances mentioned above, it lowers the high temperature strength of the sintered body, so it is better to have a smaller amount. That is, when using a mixture of Al 2 O 3 and other oxides, the total amount is 3 to 10 wt%, preferably 4 to 10 wt%.
8wt%. The amount of Al 2 O 3 is 0.3 to 3% by weight, preferably 1 to 2% by weight, and the amount of Y 2 O 3 or lanthanide metal is 2 to 7% by weight, preferably 4 to 6% by weight. In addition, when using Y 2 O 3 or a mixture of lanthanide metal oxides, a larger amount is required than in the above case, and the total amount is 5 to 15 wt%, preferably 7 to 15 wt%.
The content shall be 12wt%. In this case, if the amount of the sintering aid is less than the predetermined amount, the effect will not be sufficient and a dense sintered body will not be obtained. Too much sintering aid not only increases cost but also reduces properties at high temperatures, such as oxidation resistance. The mixing of the silicon nitride powder and the sintering aid is preferably carried out in an organic solvent to prevent oxidation of the silicon nitride. After drying, it is molded using conventional methods such as isostatic pressing, injection molding, and cast molding. Sintering is performed in pressurized nitrogen at 2 to 200 atmospheres at a temperature of 1800 to 2100
Perform at a temperature range of ℃. Nitrogen is necessary to prevent thermal decomposition of silicon nitride, and the higher the temperature, the higher the pressure used. The minimum pressure required is 2 atm at 1800℃, 5 atm at 1900℃,
The pressure is 10 atm at 2000℃ and 20 atm at 2100℃. If the pressure is lower than a predetermined pressure, silicon nitride will thermally decompose and release nitrogen to become silicon, which is not desirable. Although the pressure may be higher than the predetermined pressure, the equipment becomes expensive. Nitrogen pressure 2
A sintered body with no open pores was made at ~50 atm and a temperature of 1800~2000℃, and then sintered at a higher pressure than the first stage (50~2000℃).
By sintering at 1850 to 2100°C at 200 atm), a sintered body with even higher density and strength can be obtained. In sintering, the temperature is generally increased at a rate of 10 to 30° C./min, and then maintained at a constant temperature within a predetermined range for 30 minutes to 4 hours, preferably 1 to 3 hours. Furthermore, at temperatures above 1500℃, where actual sintering occurs, if sintering is performed with a constant linear shrinkage rate, the pore removal rate will be greater than the grain growth rate, resulting in a uniform structure and a high-density, high-strength sintered body. This is desirable because it provides the following. For this purpose, it is desirable to set the linear shrinkage rate to 0.5 to 1.75%/min. If it is lower than this range, it will take a long time and is not practical, and if it is too high, it will be necessary to increase the temperature increase rate, and a high output power source will be required. In order to keep the linear shrinkage constant, it is best to use a small sample to determine the relationship between the temperature increase schedule and the shrinkage in a furnace equipped with a differential transformer. Even for large parts, it is easy to control the linear shrinkage rate to a constant level by keeping the temperature rise schedule the same. β-type powder is
Since it is sintered in one step between 1550 and 1900°C, it is easy to control the shrinkage rate, but α-type powder is sintered in two steps, so it is difficult to control the shrinkage rate. As described above, by using silicon nitride powder containing β type as a main component, the particle size distribution of particles in the sintered body can be kept constant. Furthermore, since there is no abnormal grain growth, slight variations in sintering conditions do not have a large effect. Therefore, the β-type powder has higher sinterability than the α-type powder, and a sintered body with high density and high strength can be obtained. Furthermore, during fracture, large particles bend the direction of the crack, increasing fracture energy and fracture toughness. While the sintered body obtained from the α type exhibits a fiber-reinforced type high toughness mechanism, the sintered body obtained from the β type has a particle dispersion type mechanism. (Example) Next, an example of the present invention will be shown. Example 1 Pure β-type silicon nitride powder obtained by heating α-type silicon nitride powder at 1900°C for 1 hour in nitrogen at 10 atmospheres (average particle size 3.0 μm, total metal impurities 0.8 wt%, oxygen content 1.0) wt%) and silicon nitride powder mainly composed of β type (average particle size 0.8 μm, β type/(α type + β type) =
0.9, total metal impurities 0.35wt%, oxygen content 1.2wt
%) in a weight ratio of 10:90, and add alumina (purity 99.99%, average particle size 0.3μ) as a sintering aid to this.
m), Y 2 O 3 (purity 99.9%, average particle size 0.5μm), lanthanide metal oxide (purity >99%, <average particle size 0.8μm)
m) was added in the predetermined amount shown in Table 1, and mixed in n-hexane for 3 hours using a silicon nitride ball mill. Next, after drying in air at 80°C, mold pressing was performed at 250 kg/cm 2 , followed by isostatic pressing at 2 ton/cm 2 .
A columnar molded body was obtained. After the molded bodies were sintered under various conditions shown in Table 1, the density was determined by the Archimedes method using water, and the porosity was calculated. Then 600
Surface grinding with Metsuyu's diamond wheel,
A sample piece of approximately 3 mm x 4 mm x 40 mm was used to examine strength and fracture toughness. The results are also listed in Table 1. In addition, the strength is 3 with a span of 30 mm according to JISR1601.
Obtained by point bending. Fracture toughness was determined by the Chevron-Notch method. From Table 1, it can be seen that sintered bodies with high toughness and high strength were obtained in all cases.
【表】
実施例 ２
実施例１の試験No.１と同じ原料粉末及び焼結助
剤を用い、同様の操作で直径14mm、長さ15mmのペ
レツトを作つた。これを、10気圧の窒素中で差動
変圧器により収縮率を測定しながら1500℃以上で
は収縮速度が0.75％minになるように温度を調節
し、1950℃に到達後、その温度に30分保つた後、
冷却した。次いで、実施例１と同じ成形体を作製
し、上記の温度スケジユールで昇温し、焼結体を
得た。焼結体の気孔率は0.3％、破壊靱性値は
7.9MN／m3/2、強度は820MPaであつた。実施例
１の場合に比べ、破壊靱性はあまり向上していな
いが、強度は大きくなつた。
（発明の効果）
以上説明したように、本発明によれば、従来は
焼結用原料として望ましくないとされていたβ型
窒化珪素粉末を使用しても、高密度に焼結するこ
とができ、高靱性の窒化珪素焼結体が得られる。[Table] Example 2 Using the same raw material powder and sintering aid as in Test No. 1 of Example 1, pellets with a diameter of 14 mm and a length of 15 mm were made in the same manner. While measuring the shrinkage rate using a differential transformer in nitrogen at 10 atm, the temperature was adjusted so that the shrinkage rate was 0.75% min at temperatures above 1500℃, and after reaching 1950℃, the temperature was kept at that temperature for 30 minutes. After keeping
Cooled. Next, the same molded body as in Example 1 was produced, and the temperature was raised according to the above temperature schedule to obtain a sintered body. The porosity of the sintered body is 0.3%, and the fracture toughness value is
The strength was 7.9MN/m 3/2 and 820MPa. Compared to the case of Example 1, the fracture toughness was not significantly improved, but the strength was increased. (Effects of the Invention) As explained above, according to the present invention, even if β-type silicon nitride powder, which has conventionally been considered undesirable as a raw material for sintering, is used, it is possible to sinter with high density. , a highly tough silicon nitride sintered body is obtained.
Claims (1)
化珪素粉末と、純粋なβ型で平均粒径2.5〜5μｍ
の窒化珪素粉末とを重量比で95：５〜75：25の割
合で配合し、これに焼結助剤を混合し、成形した
後、２〜200気圧の窒素中で1800〜2100℃にて焼
結することを特徴とする高靱性窒化珪素焼結体の
製造法。 ２ 前記β型を主成分とする窒化珪素粉末が70〜
100wt％のβ型と、０〜30wt％のα片とからなる
ものである請求項１に記載の方法。 ３ 前記焼結助剤として、Al2O3：0.3〜3wt％
と、Y2O3：２〜7wt％及びランタニド金属酸化
物：２〜7wt％の１種類以上とを合計量で３〜
10wt％用いる請求項１に記載の方法。 ４ 前記焼結助剤として、Y2O3及びランタニド
金属酸化物の２種類以上とを５〜15wt％用いる
請求項１に記載の方法。 ５ 前記焼結を、1500℃以上における線収縮率が
0.5〜1.75wt％／minの範囲内となるように行う請
求項１に記載の方法。[Scope of Claims] 1 Silicon nitride powder whose main component is β type and has an average particle size of 1.5 μm or less, and a silicon nitride powder that is pure β type and has an average particle size of 2.5 to 5 μm.
of silicon nitride powder in a weight ratio of 95:5 to 75:25, mixed with a sintering aid, molded, and then heated at 1800 to 2100°C in nitrogen at 2 to 200 atmospheres. A method for producing a highly tough silicon nitride sintered body, which is characterized by sintering. 2 The silicon nitride powder mainly composed of the β type is 70~
The method according to claim 1, comprising 100 wt% of the β type and 0 to 30 wt% of the α piece. 3 As the sintering aid, Al 2 O 3 : 0.3 to 3 wt%
and one or more of Y2O3 : 2-7wt% and lanthanide metal oxide: 2-7wt% in a total amount of 3-3%.
The method according to claim 1, wherein 10 wt% is used. 4. The method according to claim 1, wherein 5 to 15 wt% of Y 2 O 3 and two or more types of lanthanide metal oxides are used as the sintering aid. 5 The linear shrinkage rate of the sintering at 1500°C or higher is
2. The method according to claim 1, wherein the rate is within the range of 0.5 to 1.75 wt%/min.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1077177A JPH02255573A (en) | 1989-03-29 | 1989-03-29 | Production of high-toughness silicon nitride sintered body |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1077177A JPH02255573A (en) | 1989-03-29 | 1989-03-29 | Production of high-toughness silicon nitride sintered body |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02255573A JPH02255573A (en) | 1990-10-16 |
| JPH0585507B2 true JPH0585507B2 (en) | 1993-12-07 |
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ID=13626522
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1077177A Granted JPH02255573A (en) | 1989-03-29 | 1989-03-29 | Production of high-toughness silicon nitride sintered body |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2506519B2 (en) * | 1991-09-25 | 1996-06-12 | 科学技術庁無機材質研究所長 | Low-temperature low-pressure sintered silicon nitride sintered body manufacturing method |
| JPH0753615B2 (en) * | 1991-09-25 | 1995-06-07 | 科学技術庁無機材質研究所長 | Method for manufacturing silicon nitride sintered body |
| US5401450A (en) * | 1991-12-20 | 1995-03-28 | Nissan Motor Co., Ltd | β-silicon nitride sintered body and method of producing same |
| JP2670221B2 (en) * | 1993-01-22 | 1997-10-29 | 日本碍子株式会社 | Silicon nitride sintered body and method for producing the same |
| JP2725761B2 (en) * | 1993-12-27 | 1998-03-11 | 本田技研工業株式会社 | Silicon nitride ceramic material and method for producing the same |
| JP2002029850A (en) * | 2000-07-17 | 2002-01-29 | Denki Kagaku Kogyo Kk | Sintered silicon nitride compact and method for manufacturing the same |
| CN114787102B (en) * | 2019-12-20 | 2023-08-04 | 可乐丽则武齿科株式会社 | Method for producing zirconia sintered body |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58151371A (en) * | 1982-02-25 | 1983-09-08 | 住友電気工業株式会社 | Manufacture of silicon nitride sintered body |
| JPS62297269A (en) * | 1986-06-16 | 1987-12-24 | 住友電気工業株式会社 | Silicon nitride sintered body and manufacture |
| JPS63252967A (en) * | 1987-04-09 | 1988-10-20 | 京セラ株式会社 | Manufacture of silicon nitride base sintered body |
| JPH01145380A (en) * | 1987-11-30 | 1989-06-07 | Kyocera Corp | Production of silicon nitride sintered form |
-
1989
- 1989-03-29 JP JP1077177A patent/JPH02255573A/en active Granted
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58151371A (en) * | 1982-02-25 | 1983-09-08 | 住友電気工業株式会社 | Manufacture of silicon nitride sintered body |
| JPS62297269A (en) * | 1986-06-16 | 1987-12-24 | 住友電気工業株式会社 | Silicon nitride sintered body and manufacture |
| JPS63252967A (en) * | 1987-04-09 | 1988-10-20 | 京セラ株式会社 | Manufacture of silicon nitride base sintered body |
| JPH01145380A (en) * | 1987-11-30 | 1989-06-07 | Kyocera Corp | Production of silicon nitride sintered form |
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