【発明の詳細な説明】[Detailed description of the invention]
（産業上の利用分野）
本発明は断熱性に優れた窒化珪素焼結部材に関
するものである。さらに詳しくは、表面にジルコ
ニアを被覆した表面近傍の熱伝導率の低い窒化珪
素焼結部材に関するものである。
（従来の技術）
窒化珪素焼結部材は高温における機械的強度、
耐熱性および耐熱衝撃性等の点で他の無機材料あ
るいは金属より優れているため、高温構造部材と
しての利用が考えられ、その用途開発が盛んに進
められている。
（発明が解決しようとする問題点）
しかしながら窒化珪素焼結部材は熱伝導率が高
く、断熱性が劣るという欠点がある。例えばエン
ジン燃焼室の耐熱性を高めるために壁面に窒化珪
素焼結部材を用いる場合にはエアギヤツプ等によ
り外部に対する断熱性は向上できるが、熱伝導率
が高いために給気が暖められ有効な吸入空気量が
得られない。この場合、窒化珪素焼結部材の表面
近傍の熱伝導率が問題となる。
耐熱性・耐食性・耐摩耗性向上を目的としてジ
ルコニアを表面被覆したものは特開昭55−28351
号、特開昭57−140876号および特開昭58−87273
号において基板が金属でプラズマ溶射による場合
が示されている。また特開昭57−135771号および
特開昭58−125679号には基板が炭素の場合にジル
コニアをその表面に被覆することが示されてい
る。しかしながら窒化珪素焼結部材を基板とし
て、しかも表面近傍の断熱性向上を目的とするも
のは例がない。
窒化珪素焼結部材に比べジルコニアは熱伝導率
が低く断熱性に優れているが、高温における機械
的強度が低い欠点がある。
（問題点を解決するための手段）
本発明は窒化珪素焼結体の表面に安定化または
部分安定化ジルコニアを被覆した高温構造部材用
窒化珪素焼結部材にある。
本発明においては窒化珪素焼結体表面に被覆す
るジルコニアは安定化または部分安定化ジルコニ
アであることが必要で、この安定化または部分安
定化ジルコニアはプラズマ溶射により窒化珪素焼
結体の表面に100μ以下の厚さに被覆することが
好ましい。
（作用）
本発明は高温強度は高いが、熱伝導率が高く断
熱性が悪い窒化珪素焼結部材表面を、熱伝導率の
低いジルコニアでその表面層を被覆し、表面近傍
の断熱性を改善することを目的とするものであ
る。
窒化珪素焼結部材とは窒化珪素常圧焼結体、加
圧焼結体、ホツトプレス焼結体、HIP焼結体ある
いは反応焼結体よりなるエンジン部品等の構造材
である。窒化珪素焼結部材はMgO、Al2O3あるい
はY2O3等種々の添加物を含む場合もあるが、本
発明の窒化珪素焼結部材の断熱性を改善する上で
添加物は本質的な問題ではない。本発明はこの窒
化珪素焼結部材の表面をジルコニアで被覆したも
のである。ジルコニアはY2O3、MgOあるいは
CaOで安定化あるいは部分安定化されたものを使
用する。ジルコニア層の厚さは100μｍ以下が好
ましい。これは、窒化珪素焼結部材とジルコニア
とは熱膨脹率が異なるので厚すぎると加熱・冷却
の繰り返しにより剥離や貫入が生じ易く、また表
面近傍の熱伝導率を有効に低下させるためには
100μｍ以下の厚さでも十分であるからである。
本発明のジルコニアを表面に被覆した窒化珪素
焼結部材の製造法を述べる。本発明のジルコニア
を表面に被覆した窒化珪素焼結部材は、窒化珪素
焼結部材の表面にジルコニアスラリーを塗布ある
いはスプレーによりジルコニアコート層を形成さ
せ焼成し焼き付けるか、好ましくはプラズマ溶射
によりジルコニアを被覆するなどして、窒化珪素
焼結部材の表面の一部あるいは全部をジルコニア
層で被覆したものである。窒化珪素焼結部材の表
面は一般に焼成面あるいは加工面であるためジル
コニア焼き付け層あるいは溶射層との結合力を高
めるために粗面化あるいは反応性を上げる処理が
必要である。それら処理は例えば砥粒による研磨
加工、空気中加熱による酸化あるいはフツ酸等に
よるエツチングである。粗面化あるいは反応性を
上げる処理は窒化珪素焼結部材の性質により最適
方法を見出す必要がある。また、ジルコニアコー
ト原料あるいは溶射原料はすでに安定化あるいは
部分安定化したジルコニアを用いても、ジルコニ
アと安定化剤とを焼成中あるいは溶射中に反応さ
せて安定化あるいは部分安定化ジルコニアとして
もよい。さらに、窒化珪素焼結部材とジルコニア
との熱膨脹率差による剥離や貫入を防止するた
め、中間の熱膨脹率を持つ中間層を予め形成させ
てもよい。
実施例
以下に本発明の実施例を示す。
実施例 １
SrO、MgO、CeO2およびZrO2を添加物とする
窒化珪素常圧焼結体より加工した直径10mm、厚さ
３mmの円板を空気中、1200℃で24時間酸化し表面
に酸化層を形成させ、プラズマ溶射溶融用基板と
した。この基板の片面に第１表の溶射剤を50〜
70μｍの厚さとなるようプラズマ溶射し、本発明
の窒化珪素焼結部材の熱伝導率測定用試料１、
２、３を得た。試料１、２、３と、ジルコニア被
覆をしない基板の比較例４および100μｍ以上被
覆した比較例11、純粋なジルコニアを被覆した比
較例12とのレーザーフラツシユ法による室温と
800℃における熱伝導率の測定結果を第１表に示
した。試料１、２、３のレーザーフラツシユ法に
よる熱伝導率の測定は被覆面にレーザーを照射し
て行つた。
(Industrial Application Field) The present invention relates to a silicon nitride sintered member with excellent heat insulation properties. More specifically, the present invention relates to a silicon nitride sintered member whose surface is coated with zirconia and has low thermal conductivity near the surface. (Prior art) Silicon nitride sintered members have high mechanical strength at high temperatures,
Since it is superior to other inorganic materials or metals in terms of heat resistance and thermal shock resistance, it is considered to be used as a high-temperature structural member, and the development of its use is actively progressing. (Problems to be Solved by the Invention) However, silicon nitride sintered members have the disadvantage of having high thermal conductivity and poor heat insulation properties. For example, when using silicon nitride sintered materials on the walls to increase the heat resistance of the engine combustion chamber, the insulation against the outside can be improved by using an air gap, etc., but due to its high thermal conductivity, the supply air is warmed and the intake air becomes effective. Air volume cannot be obtained. In this case, the thermal conductivity near the surface of the silicon nitride sintered member becomes a problem. JP-A No. 55-28351 describes a product whose surface is coated with zirconia for the purpose of improving heat resistance, corrosion resistance, and abrasion resistance.
No., JP-A-57-140876 and JP-A-58-87273
In this issue, the case where the substrate is made of metal and is made by plasma spraying is shown. Furthermore, Japanese Patent Laid-Open Nos. 57-135771 and 1987-125679 disclose that when the substrate is made of carbon, the surface thereof is coated with zirconia. However, there is no example of one that uses a silicon nitride sintered member as a substrate and aims to improve heat insulation near the surface. Compared to silicon nitride sintered members, zirconia has a lower thermal conductivity and excellent heat insulation properties, but it has the disadvantage of low mechanical strength at high temperatures. (Means for Solving the Problems) The present invention resides in a silicon nitride sintered member for high-temperature structural members, in which the surface of a silicon nitride sintered body is coated with stabilized or partially stabilized zirconia. In the present invention, the zirconia coated on the surface of the silicon nitride sintered body must be stabilized or partially stabilized zirconia. It is preferable to coat to the following thickness. (Function) The present invention coats the surface of a silicon nitride sintered member, which has high high-temperature strength but high thermal conductivity and poor insulation properties, with zirconia, which has low thermal conductivity, to improve insulation properties near the surface. The purpose is to The silicon nitride sintered member is a structural material such as engine parts made of silicon nitride pressureless sintered body, pressure sintered body, hot press sintered body, HIP sintered body, or reaction sintered body. The silicon nitride sintered member may contain various additives such as MgO, Al 2 O 3 or Y 2 O 3 , but the additives are essential in improving the heat insulation properties of the silicon nitride sintered member of the present invention. It's not a problem. In the present invention, the surface of this silicon nitride sintered member is coated with zirconia. Zirconia is Y 2 O 3 , MgO or
Use one stabilized or partially stabilized with CaO. The thickness of the zirconia layer is preferably 100 μm or less. This is because the silicon nitride sintered member and zirconia have different coefficients of thermal expansion, so if it is too thick, it is likely to cause peeling or penetration due to repeated heating and cooling, and in order to effectively reduce the thermal conductivity near the surface.
This is because a thickness of 100 μm or less is sufficient. A method for manufacturing a silicon nitride sintered member whose surface is coated with zirconia according to the present invention will be described. The silicon nitride sintered member whose surface is coated with zirconia according to the present invention can be obtained by coating or spraying a zirconia slurry on the surface of the silicon nitride sintered member to form a zirconia coat layer, followed by baking, or preferably coating the zirconia by plasma spraying. A part or all of the surface of the silicon nitride sintered member is coated with a zirconia layer. Since the surface of a silicon nitride sintered member is generally a fired or processed surface, it is necessary to roughen the surface or increase reactivity in order to increase the bonding strength with the zirconia baked layer or thermally sprayed layer. These treatments include, for example, polishing with abrasive grains, oxidation by heating in air, and etching with hydrofluoric acid. It is necessary to find an optimal method for surface roughening or increasing reactivity depending on the properties of the silicon nitride sintered member. Further, as the zirconia coating raw material or thermal spraying raw material, zirconia that has already been stabilized or partially stabilized may be used, or zirconia and a stabilizer may be reacted during firing or thermal spraying to produce stabilized or partially stabilized zirconia. Furthermore, in order to prevent peeling or penetration due to the difference in coefficient of thermal expansion between the silicon nitride sintered member and zirconia, an intermediate layer having an intermediate coefficient of thermal expansion may be formed in advance. Examples Examples of the present invention are shown below. Example 1 A disk with a diameter of 10 mm and a thickness of 3 mm processed from a pressureless sintered silicon nitride containing SrO, MgO, CeO 2 and ZrO 2 as additives was oxidized in air at 1200°C for 24 hours to oxidize the surface. A layer was formed to provide a substrate for plasma spraying and melting. Apply 50 to 50% of the thermal spraying agent listed in Table 1 on one side of this board.
Sample 1 for thermal conductivity measurement of the silicon nitride sintered member of the present invention, which was plasma sprayed to a thickness of 70 μm.
I got 2 and 3. Samples 1, 2, and 3, Comparative Example 4 with a substrate without zirconia coating, Comparative Example 11 with a substrate coated with 100 μm or more, and Comparative Example 12 with a pure zirconia coating were measured at room temperature by the laser flash method.
Table 1 shows the measurement results of thermal conductivity at 800°C. The thermal conductivity of Samples 1, 2, and 3 was measured by the laser flash method by irradiating the coated surface with a laser.
【表】
安定化剤MgO、Y2O3、CaOを24〜５重量％含
むジルコニアを被覆した本発明品１、２、３は室
温と1200℃との間の20回の加熱・冷却の繰り返し
によつても剥離や貫入が生じなかつた。
これに対し安定化剤を含まない純粋なジルコニ
アを被覆した比較例12のものは剥離発生し使用に
耐えないことが確認された。また、安定化剤
Y2O3を20重量％含むジルコニアを110μｍ被覆し
た窒化珪素焼結体にも貫入発生があつた。このこ
とは安定化または部分安定化ジルコニアの被覆の
厚みは100μｍ以下がよいことを示している。
実施例 ２
Y2O3、MgOおよびCeO2を添加物とする窒化珪
素常圧焼結体より加工した直径10mm、厚さ３mmの
円板を50℃の濃弗酸中に１時間浸漬し表面をエツ
チングし、プラズマ溶射用基板とした。この基板
の片面に第２表の溶射剤を50〜70μｍの厚さにプ
ラズマ溶射し、本発明の窒化珪素焼結部材の熱伝
導率測定用試料５、６を得た。試料５、６とジル
コニア被覆をしない同じ基板の比較例７との実施
例１と同じ方法による熱伝導率の測定結果を第２
表に示した。[Table] Products 1, 2, and 3 of the present invention coated with zirconia containing 24 to 5% by weight of stabilizers MgO, Y 2 O 3 , and CaO were heated and cooled 20 times between room temperature and 1200°C. No peeling or penetration occurred even when the coating was applied. On the other hand, it was confirmed that Comparative Example 12, which was coated with pure zirconia containing no stabilizer, suffered from peeling and was not usable. Also, stabilizers
Penetration also occurred in the silicon nitride sintered body coated with 110 μm of zirconia containing 20% by weight of Y 2 O 3 . This indicates that the thickness of the stabilized or partially stabilized zirconia coating is preferably 100 μm or less. Example 2 A disk with a diameter of 10 mm and a thickness of 3 mm processed from an atmospheric pressure sintered body of silicon nitride containing Y 2 O 3 , MgO and CeO 2 as additives was immersed in concentrated hydrofluoric acid at 50°C for 1 hour. was etched and used as a substrate for plasma spraying. One side of this substrate was plasma sprayed with the thermal spraying agent shown in Table 2 to a thickness of 50 to 70 μm to obtain samples 5 and 6 for thermal conductivity measurement of silicon nitride sintered members of the present invention. The results of measuring thermal conductivity using the same method as Example 1 for Samples 5 and 6 and Comparative Example 7 of the same substrate without zirconia coating are shown in the second example.
Shown in the table.
【表】
安定化剤を含むジルコニアを被覆した本発明品
５、６も室温と1200℃との間の20回の加熱・冷却
の繰り返しによつても剥離や貫入が生じなかつ
た。
これに対し、安定化剤を含まない純粋なジルコ
ニアを被覆した比較例14のものでは剥離発生し使
用に耐えないものであることが確認された。ま
た、安定化剤を含むジルコニアを被覆した比較例
13のものでも被覆の厚みが100μｍを越えるもの
は貫入が発生し好ましくないことが確認された。
実施例 ３
MgOを添加物とする窒化珪素ホツトプレス焼
結体より加工した直径10mm、厚さ３mmの円板を
＃400のSiC砥粒で研磨し表面を粗面加工し、ス
ラリー塗布用基板とした。この基板の片面に第３
表の塗布剤と成型助剤であるポリビニルアルコー
ルとを水に懸濁させたスラリーを塗布し、乾燥
後、窒素雰囲気中、1500℃で１時間加熱し、90〜
100μｍの厚さの焼き付け層を形成させ、本発明
の窒化珪素焼結部材の熱伝導率測定用試料８、９
を得た。試料８、９とジルコニア被覆をしない同
じ基板の比較例10とを実施例１と同じ方法により
熱伝導率を測定し、その結果を第３表に示した。[Table] Products 5 and 6 of the present invention coated with zirconia containing a stabilizer did not cause peeling or penetration even after repeated heating and cooling 20 times between room temperature and 1200°C. On the other hand, in Comparative Example 14, which was coated with pure zirconia containing no stabilizer, peeling occurred and it was confirmed that it was unusable. Also, a comparative example coated with zirconia containing a stabilizer.
It was confirmed that even in No. 13, coatings with a thickness exceeding 100 μm are undesirable because penetration occurs. Example 3 A disk with a diameter of 10 mm and a thickness of 3 mm processed from a silicon nitride hot-pressed sintered body containing MgO as an additive was polished with #400 SiC abrasive grains to roughen the surface and used as a substrate for slurry application. . 3 on one side of this board
A slurry made by suspending the coating agent shown above and polyvinyl alcohol, which is a molding aid, in water is applied, and after drying, it is heated at 1500℃ for 1 hour in a nitrogen atmosphere, and then
Samples 8 and 9 for thermal conductivity measurement of silicon nitride sintered members of the present invention were prepared by forming a baked layer with a thickness of 100 μm.
I got it. The thermal conductivity of Samples 8 and 9 and Comparative Example 10, which was the same substrate without zirconia coating, was measured by the same method as in Example 1, and the results are shown in Table 3.
【表】
本発明品８、９も室温と1200℃との間の20回の
加熱・冷却の繰り返しによつても剥離や貫入が生
じなかつた。
これに対し安定化剤を含まない純粋なジルコニ
アを被覆した比較例16のものでは剥離発生し使用
に耐えないものであることが確認された。
また安定化剤を含むジルコニアを被覆した比較
例15のものでも、被覆の厚みが100μｍを超える
ものは貫入が発生し好ましくないものであること
が確認された。
第１、２、３表に示したとおり本発明のスラリ
ー塗布あるいはプラズマ溶射により安定化または
部分安定化ジルコニアを表面に被覆した窒化珪素
焼結部材は熱伝導率が低く優れた断熱性を示すも
のであることが確認された。
（発明の効果）
以上のように本発明のジルコニアを表面に被覆
した窒化珪素焼結部材は窒化珪素焼結部材の高温
強度とジルコニアの断熱性を兼ね備えたものであ
り、エンジン部品等高温構造材料へ適用すること
により、耐熱性と断熱性とを同時に改善できるも
のであつて、このため工業上大なる利益がある。[Table] Inventive products 8 and 9 also showed no peeling or penetration even after repeated heating and cooling 20 times between room temperature and 1200°C. On the other hand, in Comparative Example 16, which was coated with pure zirconia containing no stabilizer, peeling occurred and it was confirmed that it was unusable. Furthermore, even in Comparative Example 15, which was coated with zirconia containing a stabilizer, it was confirmed that if the thickness of the coating exceeded 100 μm, penetration would occur, which is undesirable. As shown in Tables 1, 2, and 3, the silicon nitride sintered member whose surface is coated with stabilized or partially stabilized zirconia by slurry coating or plasma spraying of the present invention exhibits low thermal conductivity and excellent heat insulation properties. It was confirmed that (Effects of the Invention) As described above, the silicon nitride sintered member whose surface is coated with zirconia of the present invention has both the high-temperature strength of the silicon nitride sintered member and the heat insulation properties of zirconia, and is suitable for high-temperature structural materials such as engine parts. By applying it to, heat resistance and heat insulation properties can be improved at the same time, and therefore there is a great industrial benefit.