JP3586218B2

JP3586218B2 - Coated cutting tool

Info

Publication number: JP3586218B2
Application number: JP2001140908A
Authority: JP
Inventors: 剛史石川
Original assignee: Hitachi Tool Engineering Ltd
Current assignee: Moldino Tool Engineering Ltd
Priority date: 2001-05-11
Filing date: 2001-05-11
Publication date: 2004-11-10
Anticipated expiration: 2021-05-11
Also published as: JP2002337006A

Description

【０００１】
【発明が属する技術分野】
本発明は金属材料等の切削加工に使用される被覆切削工具に関する。
【０００２】
【従来の技術】
切削加工の高能率化の要求に伴い高速マシニングセンターが普及し切削加工は高速化傾向にある。切削工具に被覆される皮膜もＴｉＮ、ＴｉＣＮに変わり、皮膜の耐酸化性を改善したＴｉＡｌＮ皮膜等を被覆した被覆切削工具が一般的である。しかしながら、更に切削加工の高速化に対応すべくＴｉＡｌＮにＳｉを添加し皮膜の耐酸化性の改善を試みた特許第２７９３７７３号公報、ＴｉにＳｉを添加しＴｉＡｌＮ以外の組成系を試みた特開平８−１１８１０６号、特開平９−１１００４号、また窒化物に異相を分散させ耐火性の改善を試みた特許第３１１７９７８号、若しくは窒化物を超多層にし異結晶体により耐摩耗性の改善を試みた特開平７−１３３１１１号、またＳｉを含有する皮膜においてＳｉ_３Ｎ_４及びＳｉ等の異相からなる独立した相を化合物中に存在させ耐摩耗性の改善を試みた特開２０００−３３４６０４号等に代表される皮膜の改善がなされている。
【０００３】
【発明が解決しようとする課題】
しかしながら、従来までのＴｉＡｌＮ皮膜をベースにしたＳｉの添加においてはＴｉＡｌＮの精々１．２倍未満の耐酸化性改善にしか至らず汎用的な切削環境下においては効果が認められるものの高速切削加工には十分対応できない。更にはＴｉにＳｉを添加した硬質皮膜においては、Ｓｉ添加により皮膜そのものの耐酸化性及び皮膜の高硬度化による静的な耐摩耗性はＴｉＮよりも改善されるものの著しい改善は認められない。これは単純にＳｉを添加しただけでは固溶体硬質相を形成し、固溶強化による改善が認められない事に起因する為である。また、皮膜が極めて脆くなり、この耐酸化性及び耐摩耗性を十分発揮できないばかりではなく、皮膜内部に発生する圧縮応力も非Ｓｉ含有皮膜と比べ著しく高くなり、この過剰な圧縮応力により成膜直後に剥離が発生してしまい、切削工具に適用するには至っていない。またＳｉ含有皮膜において、異相金属、異相窒化物等を分散させた硬質皮膜は皮膜そのものの耐欠損性が十分ではなく、同時に異相とマトリックスの結晶粒界を介し酸素が拡散する為、耐酸化性が十分であるとは言い難い。この事により、被切削物が高硬度若しくは切削環境が苛酷になるほど膜剥離や酸化進行に起因する異常摩耗及び欠損が生じてしまい実用化には至っていない。このように依然として高速切削加工において十分な切削特性の改善は得られてはいない。
【０００４】
本発明はこうした事情に鑑み、Ｓｉ含有皮膜特有の高硬度及び耐酸化性を更に改善し、かつ、高靭性で耐チッピング性に優れ、高速切削加工に最適である被覆切削工具を提供することを課題とする。
【０００５】
【課題を解決するための手段】
Ｓｉ含有皮膜においては前述の如く、Ｓｉ添加により皮膜の高硬度化による静的な耐摩耗性は改善されるが、皮膜が極めて脆くなり、同時に耐酸化性が十分ではなく酸化の進行に伴う摩耗が発生し、耐摩耗性を十分発揮できないばかりではなく、皮膜内部に発生する圧縮応力も非Ｓｉ含有皮膜と比べ著しく高くなり、この過剰な圧縮応力により成膜直後に剥離が発生してしまう。これらの理由から切削工具に適用するには至っていないのが現状である。しかしながら本発明者はこのＳｉ含有皮膜が脆くなる原因また過剰応力による皮膜剥離等を抑制する手段を見出し本発明に到達した。すなわち、切削工具基体に４、５、６族の金属元素及びＡｌのうち１種若しくは２種以上より選択された元素とＳｉ元素を含み、非金属元素として少なくともＮ、Ｂ、Ｃ、Ｏのうち１種若しくは２種以上より選択された元素を含むＳｉ含有皮膜を被覆してなる被覆切削工具において、該皮膜は同一相内に高Ｓｉ濃度領域と低Ｓｉ濃度領域を有する相を有することを特徴とする被覆切削工具である。
【０００６】
Ｓｉ含有皮膜が脆くなる要因の一つとして以下に示すことが判明した。即ち、現在一般的に使用されているＴｉＡｌＮ等の多元系窒化物の多くは立方晶ＮａＣｌ型の結晶構造を有する置換型の窒化物を形成する事が知られるが、このＳｉを含有した多元系皮膜においてはＳｉと他の金属元素が置換型の結晶構造をとりにくく、夫々の金属元素が窒化物等の結晶構造を形成し易い傾向にある為、このことが皮膜そのもの脆化若しくは過剰応力を誘発させると考える。同時に耐酸化性が不十分である要因としては、Ｓｉ窒化物とマトリックスとの間に形成される結晶粒界に沿って酸化が進行する事に起因する。
【０００７】
本発明者はこのＳｉ含有皮膜の過剰応力による脆化を抑制する手段として、Ｓｉ含有マトリックスに同一相からなる、Ｓｉが濃化した窒化物を皮膜内に分散させることにより皮膜内に残留する圧縮応力を著しく低減させ、皮膜の過剰応力に起因した脆化を抑制し、更にＳｉ濃度偏析相とマトリックス界面は同一結晶構造を有する為、比較的整合性があり格子欠陥が少なく、酸素の拡散を著しく低減させ、Ｓｉ含有皮膜の有する耐酸化性若しくは高硬度を犠牲することなく切削工具に対して十分にその特性が発揮されうる皮膜を成膜することを可能にした。
【０００８】
本発明の要旨は、切削工具基体に４、５、６族の金属元素及びＡｌのうち１種若しくは２種以上より選択された元素とＳｉ元素を含み、非金属元素として少なくともＮ、Ｂ、Ｃ、Ｏのうち１種若しくは２種以上より選択された元素を含むＳｉ含有皮膜を被覆してなる被覆切削工具において、該皮膜は同一相内に高Ｓｉ濃度領域と低Ｓｉ濃度領域を有する相を有することを特徴とする被覆切削工具であり、好ましくは透過型電子顕微鏡による観察で該Ｓｉ高濃度領域は２μｍ２以下であり、同一相内の低Ｓｉ濃度領域と格子が不連続であることを特徴とする被覆切削工具である。さらに、該Ｓｉ含有皮膜は金属元素としてＴｉ、Ｖ、Ａｌ、Ｃｒ、Ｙ、Ｎｂのうち１種若しくは２種以上より選択された元素を含み、該Ｓｉ含有皮膜のＳｉ含有量は金属元素成分のみの原子％で５０％未満であることを特徴とする被覆切削工具及び、該Ｓｉ含有皮膜とは別の少なくとも１層は金属元素として少なくともＡｌとＴｉを含み、非金属元素として少なくともＮを含むＡｌＴｉＮ系膜であることを特徴とする被覆切削工具、も本発明の範囲に含まれる。
【０００９】
このような構成を採用することで、高速切削加工及び高硬度材切削加工などの過酷な切削環境下においても、皮膜剥離を生ずることなく皮膜の耐酸化性及び硬さを大幅に改善し、切削性能が極めて良好となり、従来技術の課題を解決するに至った。すなわち、切削工具基体に４、５、６族の金属元素及びＡｌのうち１種若しくは２種以上より選択された元素とＳｉ元素を含み、非金属元素として少なくともＮ、Ｂ、Ｃ、Ｏのうち１種若しくは２種以上より選択された元素を含むＳｉ含有皮膜を被覆してなる被覆切削工具において、該皮膜は同一相内に高Ｓｉ濃度領域と低Ｓｉ濃度領域を有する相からなるＳｉ含有皮膜が極めて有効である。
【００１０】
【発明の実施の形態】
本発明のその構成要件について詳しく述べる。本発明である同一相内に高Ｓｉ濃度領域と低Ｓｉ濃度領域を有するＳｉ含有皮膜を解析した結果を以下に述べる。図１にＣｒとＳｉより構成されるＳｉ含有皮膜の透過型電子顕微鏡による格子像の観察結果をしめす。図２、図３に高Ｓｉ濃度領域及び低Ｓｉ濃度領域のエネルギー分散型分析による定量分析結果を示す。また図４、図５に高Ｓｉ濃度領域及び低Ｓｉ濃度領域の極微電子線回折像撮影による結晶構造の解析結果を示す。エネルギー分散型分析による定量分析は１ｎｍ角の分析領域を分析した。極微電子線回折像の撮影にはカメラ長を５０ｃｍ、ビーム径を２〜５ｎｍにて分析を行った。
【００１１】
図１より、領域２に示す部分は領域３に示す低Ｓｉ濃度領域のマトリックスに比べ極めて微細かつ不連続な格子像を示すことが明らかである。更に図２より、図１の領域２に示す高Ｓｉ濃度領域のＳｉの含有量は金属元素成分のみの原子比率で８．５０原子％、また領域３に示す低Ｓｉ濃度からなるマトリックスのＳｉの含有量は金属元素成分のみの原子比率で２．４３原子％であり、３倍以上のＳｉ含有量を示すものである。また図４に、図１の領域２に示すＳｉ濃度の高い領域の極微電子線回折結果を示すが、この高Ｓｉ濃度領域は低Ｓｉ濃度からなるマトリックスと同一のｆｃｃ構造を示すものである。更に図５に高Ｓｉ濃度領域の極微電子線回折パターンを示すがｆｃｃ構造の（２００）面に相当する領域において不明瞭なリング状の回折パターンが観察される。
【００１２】
図６に従来の成膜方法によりＳｉを含有させた皮膜と本発明皮膜のＸ線回折パターンを示す。本発明皮膜のＸ線回折パターンは従来の成膜方法でＳｉを含有させた皮膜のそれに対して（２００）面における回折ピークの広がりが認められる。これは図５の領域２に示す回折像と合わせて考察すると面間隔の異なる微細なＳｉの偏析を伴ったＳｉ含有窒化物が連続的に皮膜内部に形成している為であると考える。
【００１３】
この同一相からなる微細で不連続な高Ｓｉ濃度領域を有したＳｉ含有皮膜は、４、５、６族の金属元素及びＡｌのうち１種若しくは２種以上より選択された元素とＳｉ元素、より好ましくは金属元素としてＴｉ、Ｖ、Ａｌ、Ｃｒ、Ｙ、Ｎｂのうち１種若しくは２種以上より選択された元素とＳｉ元素からなり、更に非金属元素としてＮ、Ｂ、Ｃ、Ｏのうち１種若しくは２種以上より選択される元素からなるＳｉ含有皮膜において形成させることが可能である。
【００１４】
Ｓｉ含有皮膜中のＳｉ添加量は極少量である場合においてもＳｉが濃化した窒化物をＳｉ含有皮膜内に分散して形成させることが可能である。またＳｉ含有量が５０原子％を超える場合においては、異相を形成し易く、このことにより過剰応力に起因した破壊が発生し易い傾向にあり、Ｓｉ含有量としては５０原子％未満が好ましい。
【００１５】
この同一相からなる低Ｓｉ濃度マトリックスに比べ微細かつ不連続からなる高Ｓｉ濃度領域を含むＳｉ含有皮膜とすることで切削工具として安定したＳｉ含有皮膜を成膜することが可能となる。静的な酸化機構に関しては、高Ｓｉ濃度領域から優先的にＳｉが濃化した極めて微細なＳｉ酸化物を形成する。この微細酸化物により酸素の内向拡散に対して拡散障壁として作用し、その結果、大幅な耐酸化性の改善に寄与した。図７に切削過程における動的酸化の挙動を解析結果を示す。これは切削途中の工具逃げ面における皮膜摩耗部を深さ方向に元素分析したものである。尚、皮膜はＴｉにＳｉを含有させた窒化物における例を示す。図７より表面のＦｅ付着層と窒化物（皮膜）との間にＳｉが濃化した酸化膜を形成していることが明らかであり、動的な酸化においてもこのＳｉが濃化した酸化物によりそれ以後の酸化抑制に貢献している。また、切削工具表面のこのＳｉ酸化物は切削過程における潤滑効果をも有しているものと考えられこれらの相乗効果により高速切削特性が大幅に改善されたものと考える。更にＳｉ含有皮膜の欠点であった皮膜の靭性若しくは耐チッピング性に関しても、Ｓｉそのものによる結晶構造の歪発生に起因した高硬度を犠牲にすることなく従来までのＳｉ含有皮膜に対して格段に改善する結果となった。
【００１６】
上記、本発明皮膜は、静的及び動的条件下において耐酸化性、硬さ及び靭性を兼ね備えた優れた特性を有するものの、単一皮膜では十分な切削性能を示さない場合がある。このような使用環境下においては、耐摩耗性及び耐酸化性等の汎用的特性に優れる皮膜と併用することが有効であるが、この皮膜として現時点で最適であると考えられる皮膜は、金属元素として少なくともＡｌとＴｉを含み、非金属元素として少なくともＮを含むＡｌＴｉＮ系膜である。これを採用することで切削特性を補完することが可能である。より具体的な層構造としては、ＡｌＴｉＮ系膜と本発明皮膜を交互に、それぞれ１層以上積層することにより、高速切削に対応する被覆切削工具を得ることが可能となる。ＡｌＴｉＮ系膜は耐酸化性と耐摩耗性等の汎用的特性を有するばかりでなく、本発明皮膜との密着性が良好であり特性をさらに補完する。このとき、本発明皮膜は硬質皮膜の最上層に有ることが望ましいが、必ずしも最上層でなくとのその効果を十分に発揮するものである。また、基体との密着性改善を目的としたＴｉ窒化物等の引用若しくはＴｉの一部を少量の他元素による置換も本発明に含まれる。
【００１７】
本発明の被覆切削工具は、その被覆方法については、特に限定されるものではないが、被覆基体への熱影響、工具の疲労強度、皮膜の密着性等を考慮した場合、比較的低温で被覆でき、被覆した皮膜に圧縮応力が残留するアーク放電方式イオンプレーティング、若しくはスパッタリング等の被覆基体側にバイアス電圧を印加する物理蒸着法であることが望ましい。
【００１８】
本発明に係る上記、低Ｓｉ濃度マトリックスに比べ微細かつ不連続からなる高Ｓｉ濃度領域を含むＳｉ含有皮膜を基体表面に形成する方法としては、イオンプレーティング法やスパッタリング法等に代表される物理蒸着法が挙げられるが、例えばアークイオンプレーティング法による成膜においては以下による方法を用いれば良い。まず炉内を３×１０５Ｐａまで真空排気を行うと同じにヒーターにより基体の加熱を行う。その後Ａｒによる基体の清浄化及び活性化を行った後、炉内に複数配置されたアーク放電用蒸発源であるカソードに目的とした皮膜組成が得られる各合金ターゲットを設置し、アーク放電によりイオン化させた各種金属と窒素等の反応ガス雰囲気中でイオンプレーティングすることによって得られる。この時、複数のカソードから個々に各種金属をイオン化させるが、この各カソードからの各種金属の蒸発速度と皮膜形成に関与するイオンが放出するエネルギー（以下、イオンエネルギーと言う。）の調整を以下のように施した。
【００１９】
被覆時におけるイオンエネルギーの大小は主に基体に印加するバイアス電圧と反応ガスとの組み合わせによって決定する。ここで、基体に印加するバイアス電圧は負バイアス電圧と正バイアス電圧を周期的に変化させながら成膜を行う必要がある。結果として、皮膜内にイオンエネルギーの周期的な変化を誘発させ、Ｓｉ濃度の異なる皮膜を同一層内に形成させるものである。この周期的なイオンエネルギーの変化が本発明において極めて重要である。更にこの周期的なイオンエネルギーの変化と炉内に複数設置された合金ターゲットの蒸発速度を夫々のカソードにおいて同時に分散させながら基体を回転させることにより蒸気圧の異なるＳｉ含有皮膜のＳｉ偏析を皮膜内に誘発させるものである。
【００２０】
また、基体温度によっても皮膜中のＳｉ濃度差が変化する。具体的には、７００℃以上では同一相からなる低Ｓｉ濃度マトリックスに比べ微細かつ不連続からなる高Ｓｉ濃度領域が確認されない場合もあった。よって好ましい基体温度は５７０℃前後である。バイアス電圧を高くすると基体温度も上昇する傾向がある。基体材質の要求から温度が制限される場合は基体の冷却手段が必要となる場合がある。以下、本発明を実施例に基づいて説明する。
【００２１】
【実施例】
アークイオンプレーティング装置を用い、金属成分の蒸発源である各種合金製ターゲット、並びに反応ガスであるＮ２ガスを用い、被覆基体温度５５０℃とし、反応ガス圧力を５Ｐａ及び負バイアス電圧を３００Ｖ、正バイアス電圧を４０Ｖとし、その振幅は負を８０％、正を２０％に設定し、その周波数を２０ｋＨｚとした。また、基体を５ｒｐｍで回転させながら複数設置した各蒸発源の電流値の一方を３０Ａ、対向した蒸発源を３００Ａの電流を印加し成膜を行った。被覆基体には外径８ｍｍの超硬合金製６枚刃スケアエンドミル、Ｒ５ｍｍの超硬合金製２枚刃ボールエンドミル及び超硬合金製インサートを用い、全皮膜の厚みが３乃至は５μｍとなるように成膜した。また必要に応じてＡｌＴｉＮ系皮膜との多層膜とした。各試料の高Ｓｉ濃度領域を含むＳｉ含有皮膜の組成及び高Ｓｉ濃度領域の金属成分のみのＳｉ含有量を低Ｓｉ濃度領域の金属成分のみのＳｉ含有量で除した数値を示す。更に併用したＡｌＴｉＮ系膜の組成を表１に示す。
【００２２】
【表１】

【００２３】
また、比較例の被覆条件は同様にアークイオンプレーティング装置を用い、金属成分の蒸発源である各種合金製ターゲット並びに反応ガスであるＮ２ガスを用い、被覆基体温度４００℃とし、反応ガス圧力を５Ｐａ及び負バイアス電圧を７０Ｖにして表１に示す各組成の試料を作成した。なお表１において、組成の表示は金属成分、非金属成分を夫々あわせて１００となるよう、原子比で表記したが、これは金属成分と比金属成分の原子比が１：１であることを意味するものではない。得られた被覆エンドミル及び被覆インサートを用い切削試験を行った。エンドミルは切削長１００ｍ時での逃げ面摩耗幅を測定し、インサートにおいては欠損までの切削時間としその結果を表１に示した。
【００２４】
（超硬６枚刃スケアエンドミル切削条件）
工具：超硬６枚刃スケアエンドミル
切削方法：側面切削加工
被削材：ＳＫＤ６１（硬さＨＲＣ５２）
切り込み：軸方向８ｍｍ、径方向０．４ｍｍ
切削速度：５００ｍ／ｍｉｎ
送り：０．０７ｍｍ／ｔｏｏｔｈ
切削油：エアーブロー
【００２５】
（超硬２枚刃ボールエンドミル）
工具：超硬２枚刃ボールエンドミル
切削方法：底面直線仕上切削加工
被削材：ＳＫＤ１１（硬さＨＲＣ５６）
切り込み：軸方向１．５ｍｍ、ピックフィード０．２ｍｍ
切削速度：２２４ｍ／ｍｉｎ（接触最外径）
送り：０．０７ｍｍ／ｔｏｏｔｈ
切削油：エアーブロー
【００２６】
（超硬インサート切削条件）
工具：ＥＤＥＷ１５Ｔ４ＴＮ−１５
カッター径：６３ｍｍ
切削方法：面取り加工
被削材：ＳＫＤ６１（硬さＨＲＣ４５）幅５０ｍｍ×長さ２５０ｍｍ
切り込み：２．０ｍｍ
切削速度：２５０ｍ／ｍｉｎ
送り：０．５ｍｍ／ｒｅｖ
切削油：エアーブロー
【００２７】
表１より、本発明例１、２、３はＣｒにＳｉを含有させた場合の例であるが同一相からなる微細Ｓｉの偏析が膜内部に観察され、従来例２２、２３及び比較例１８、１９に対しても、３条件とも切削特性に優れる。また、本発明例４、５〜８はＴｉにＳｉを添加した同一相からなる微細Ｓｉの偏析を有した皮膜の例であるが、いずれの切削工具においても、耐摩耗性に優れる。本発明例９、１０はＡｌにＳｉを添加した同一相からなる微細Ｓｉの偏析を有した皮膜の例であるが、同様に切削特性に優れた。本発明例１１、１２、１３、１５は同一相からなる微細Ｓｉの偏析を有した３種の金属成分系の例であるが、いずれも切削特性に優れた。本発明例１４、１６はＳｉとＮｂ若しくはＶを用いた場合の例であるがいずれもＳｉの濃度差が確認され、ともに切削性能に優れた。本発明例は、比較例及び従来例に比して高速切削環境下においても安定した切削が可能である。
【００２８】
これらに対し、比較例１７はＭｎとＳｉの例であるがで、同一相からなる微細Ｓｉの偏析を伴わずＳｉの脆い特性が切削性能に影響を及ぼしたと考えられ本発明例に比して寿命が短い。比較例１８は本請求範囲内の金属元素及び組成ではあるが、従来の蒸着法により成膜した例であり、膜内部に同一相からなる微細Ｓｉの偏析を有することなく本発明例よりも劣る結果となった。比較例１９はＳｉ含有量が５０原子％以上の比較例であるがＳｉの過剰添加により脆くなってしまい、本発明例に比して性能が悪い。従来例２０〜２４は、いずれもこのような過酷な切削環境下においては短寿命である。
【００２９】
【発明の効果】
上記のように、本発明を適用することにより、膜の同一相内に高Ｓｉ濃度領域と低Ｓｉ濃度領域を有する皮膜を設けることにより、高速切削加工においても損傷が軽減され、耐摩耗性に優れた長寿命な被覆切削工具を売ることができた。
【図面の簡単な説明】
【図１】図１は、本発明例のＣｒとＳｉより構成されるＳｉ含有皮膜の透過型電子顕微鏡による格子像の観察結果を示す。
【図２】図２は、図１の高Ｓｉ濃度領域のエネルギー分散型分析による定量分析結果を示す。
【図３】図３は、図１の低Ｓｉ濃度領域のエネルギー分散型分析による定量分析結果を示す。
【図４】図４は、図１の高Ｓｉ濃度領域の極微電子線回折像撮影による結晶構造の解析結果を示す。
【図５】図５は、図１の低Ｓｉ濃度領域の極微電子線回折像撮影による結晶構造の解析結果を示す。
【図６】図６は、従来の成膜方法によりＳｉを含有させた皮膜と本発明皮膜のＸ線回折パターンを示す。
【図７】図７は、切削過程における動的酸化の挙動を、切削途中の工具逃げ面における皮膜摩耗部を深さ方向に元素分析した結果を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a coated cutting tool used for cutting a metal material or the like.
[0002]
[Prior art]
High-speed machining centers have become popular with the demand for high-efficiency cutting, and cutting has tended to be faster. The film coated on the cutting tool is also changed to TiN or TiCN, and a coated cutting tool coated with a TiAlN film or the like having improved oxidation resistance of the film is generally used. However, Japanese Patent No. 2,793,773, in which Si is added to TiAlN to improve the oxidation resistance of the film in order to cope with a higher cutting speed, and a composition system other than TiAlN in which Si is added to Ti is tried. No. 8-118106, Japanese Patent Application Laid-Open No. Hei 9-11004, and Japanese Patent No. 3179978 in which a different phase is dispersed in nitride to improve the fire resistance, or an attempt is made to improve the wear resistance by using a super-multi-layered nitride. JP-A-7-133111, and JP-A-2000-334604 in which an independent phase composed of a hetero phase such as Si ₃ N ₄ and Si in a Si-containing film is present in a compound to improve wear resistance. The improvement of the film represented by (1) has been made.
[0003]
[Problems to be solved by the invention]
However, the conventional addition of Si based on a TiAlN film only improves oxidation resistance to less than 1.2 times that of TiAlN and is effective under general-purpose cutting environments, but is effective for high-speed cutting. Can not cope enough. Furthermore, in a hard coating obtained by adding Si to Ti, the oxidation resistance of the coating itself and the static wear resistance due to the higher hardness of the coating are improved as compared with TiN, but no remarkable improvement is observed. This is because simply adding Si forms a solid solution hard phase and no improvement by solid solution strengthening is observed. In addition, the film becomes extremely brittle, and not only cannot exhibit its oxidation resistance and abrasion resistance sufficiently, but also the compressive stress generated inside the film becomes significantly higher than that of the non-Si-containing film. Immediately after peeling occurred, it has not been applied to cutting tools. In addition, in a Si-containing coating, a hard coating in which a different-phase metal, a different-phase nitride, etc. are dispersed does not have sufficient fracture resistance of the coating itself, and at the same time, oxygen diffuses through the crystal grain boundary between the different phase and the matrix, so that the oxidation resistance is high. Is hardly enough. As a result, abnormal wear and loss due to film peeling and oxidation progress occur as the workpiece becomes harder or the cutting environment becomes harsher, and it has not been put to practical use. As described above, sufficient improvement in cutting characteristics has not yet been obtained in high-speed cutting.
[0004]
In view of these circumstances, the present invention provides a coated cutting tool that further improves the high hardness and oxidation resistance specific to a Si-containing film, and that has high toughness and excellent chipping resistance, and is optimal for high-speed cutting. Make it an issue.
[0005]
[Means for Solving the Problems]
As described above, in the case of a Si-containing film, the addition of Si improves the static abrasion resistance due to the increase in hardness of the film, but the film becomes extremely brittle, and at the same time, the oxidation resistance is not sufficient and the abrasion accompanying the progress of oxidation is caused. Not only is it not possible to sufficiently exhibit wear resistance, but also the compressive stress generated inside the film is significantly higher than that of the non-Si-containing film, and peeling occurs immediately after film formation due to the excessive compressive stress. For these reasons, it has not yet been applied to cutting tools. However, the present inventor has found the cause of the brittleness of the Si-containing film and a means for suppressing the peeling of the film due to excessive stress, and has reached the present invention. That is, the cutting tool base contains an element selected from one or more of metal elements of

Groups

4, 5, and 6 and Al and an Si element, and at least N, B, C, and O as nonmetal elements. A coated cutting tool coated with a Si-containing coating containing at least one element selected from the group consisting of a phase having a high Si concentration region and a low Si concentration region in the same phase. Coated cutting tool.
[0006]
The following has been found as one of the factors that make the Si-containing film brittle. That is, it is known that many of multi-component nitrides such as TiAlN which are generally used at present form substitution-type nitrides having a cubic NaCl-type crystal structure. In the film, Si and other metal elements are unlikely to have a substitutional crystal structure, and each metal element tends to easily form a crystal structure such as a nitride. Think to induce. At the same time, the reason why the oxidation resistance is insufficient is that oxidation proceeds along a crystal grain boundary formed between the Si nitride and the matrix.
[0007]
As a means for suppressing the embrittlement of the Si-containing film due to excessive stress, the inventor disperses the Si-enriched nitride having the same phase in the Si-containing matrix into the film, thereby compressing the Si-containing film. It significantly reduces stress, suppresses embrittlement caused by excessive stress in the film, and has the same crystal structure between the Si concentration segregation phase and the matrix interface, so it has relatively consistent, few lattice defects, and reduces oxygen diffusion. It is possible to form a film capable of exhibiting the characteristics sufficiently for a cutting tool without significantly reducing the oxidation resistance or high hardness of the Si-containing film without sacrificing.
[0008]
The gist of the present invention is that a cutting tool base contains an element selected from one or more of metal elements belonging to

Groups

4, 5, and 6 and Al and an Si element, and at least N, B, and C as nonmetal elements. , O, a coated cutting tool coated with a Si-containing coating containing at least one element selected from the group consisting of a phase having a high Si concentration region and a low Si concentration region in the same phase. A coated cutting tool characterized in that the high Si concentration region is preferably 2 μm 2 or less as observed by a transmission electron microscope, and the low Si concentration region and the lattice in the same phase are discontinuous. Coated cutting tool. Further, the Si-containing film contains at least one element selected from Ti, V, Al, Cr, Y, and Nb as a metal element, and the Si content of the Si-containing film is only the metal element component. And at least one layer other than the Si-containing coating contains at least Al and Ti as metal elements and at least N as non-metal elements. A coated cutting tool characterized by being a system film is also included in the scope of the present invention.
[0009]
By adopting such a configuration, even under severe cutting environments such as high-speed cutting and cutting of high-hardness material, the oxidation resistance and hardness of the film are significantly improved without peeling off the film, and cutting is performed. The performance was extremely good, and the problem of the prior art was solved. That is, the cutting tool base contains an element selected from one or more of metal elements of

Groups

4, 5, and 6 and Al and an Si element, and at least N, B, C, and O as nonmetal elements. A coated cutting tool coated with a Si-containing coating containing at least one element selected from the group consisting of a phase having a high Si concentration region and a low Si concentration region in the same phase. Is extremely effective.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The constituent elements of the present invention will be described in detail. The result of analyzing the Si-containing coating having a high Si concentration region and a low Si concentration region in the same phase according to the present invention will be described below. FIG. 1 shows the results of observation of a lattice image of a Si-containing film composed of Cr and Si by a transmission electron microscope. 2 and 3 show the results of quantitative analysis of the high Si concentration region and the low Si concentration region by energy dispersive analysis. 4 and 5 show the results of analyzing the crystal structure of the high Si concentration region and the low Si concentration region by micro electron beam diffraction imaging. In the quantitative analysis by the energy dispersive analysis, an analysis area of 1 nm square was analyzed. The analysis was performed with a camera length of 50 cm and a beam diameter of 2 to 5 nm for capturing an ultra-fine electron beam diffraction image.
[0011]
It is apparent from FIG. 1 that the portion shown in the region 2 shows an extremely fine and discontinuous lattice image as compared with the matrix of the low Si concentration region shown in the region 3. Further, from FIG. 2, the Si content in the high Si concentration region shown in region 2 of FIG. 1 is 8.50 atomic% in atomic ratio of only the metal element component, and the Si content of the matrix having a low Si concentration shown in region 3 is low. The content is 2.43 atomic% in atomic ratio of only the metal element component, and shows the Si content three times or more. FIG. 4 shows the result of microelectron beam diffraction of the region having a high Si concentration shown in region 2 of FIG. 1. The high Si concentration region shows the same fcc structure as a matrix having a low Si concentration. Further, FIG. 5 shows a microelectron beam diffraction pattern in a high Si concentration region, and an unclear ring-like diffraction pattern is observed in a region corresponding to the (200) plane of the fcc structure.
[0012]
FIG. 6 shows the X-ray diffraction patterns of the film containing Si by the conventional film forming method and the film of the present invention. In the X-ray diffraction pattern of the film of the present invention, the spread of the diffraction peak on the (200) plane is recognized as compared with that of the film containing Si by the conventional film forming method. Considering this together with the diffraction image shown in region 2 of FIG. 5, it is considered that Si-containing nitrides with fine Si segregation having different plane spacings are continuously formed inside the film.
[0013]
The Si-containing film having a fine and discontinuous high Si concentration region composed of the same phase is composed of an element selected from one or two or more of the metal elements of

Group

4, 5, and 6 and Al, More preferably, the metal element is composed of one or more elements selected from Ti, V, Al, Cr, Y, and Nb and the Si element, and the nonmetallic element is one of N, B, C, and O. It can be formed on a Si-containing coating made of one or more elements selected from two or more.
[0014]
Even when the amount of Si added to the Si-containing film is extremely small, it is possible to disperse and form the nitride in which Si is concentrated in the Si-containing film. When the Si content exceeds 50 atomic%, a heterophase is likely to be formed, which tends to cause breakage due to excessive stress, and the Si content is preferably less than 50 atomic%.
[0015]
By using a Si-containing film including a high Si concentration region that is finer and discontinuous than the low Si concentration matrix composed of the same phase, a stable Si-containing film can be formed as a cutting tool. As for the static oxidation mechanism, an extremely fine Si oxide in which Si is preferentially concentrated from a high Si concentration region is formed. This fine oxide served as a diffusion barrier against inward diffusion of oxygen, and as a result, contributed to a significant improvement in oxidation resistance. FIG. 7 shows an analysis result of the dynamic oxidation behavior in the cutting process. This is a result of elemental analysis in the depth direction of the film wear portion on the flank of the tool during cutting. In addition, the film | membrane shows the example in the nitride which made Si contain Ti. It is apparent from FIG. 7 that an oxide film in which Si is concentrated is formed between the Fe-adhered layer on the surface and the nitride (film). This contributes to the suppression of oxidation thereafter. Further, it is considered that this Si oxide on the surface of the cutting tool also has a lubricating effect in the cutting process, and it is considered that the high-speed cutting characteristics are greatly improved by the synergistic effect of these. In addition, the toughness or chipping resistance of the coating, which was a disadvantage of the Si-containing coating, is significantly improved compared to conventional Si-containing coatings without sacrificing the high hardness caused by the occurrence of crystal structure distortion due to Si itself. Results.
[0016]
Although the coating of the present invention has excellent characteristics having both oxidation resistance, hardness and toughness under static and dynamic conditions, a single coating may not show sufficient cutting performance in some cases. Under such usage environment, it is effective to use together with a film having excellent general-purpose properties such as abrasion resistance and oxidation resistance. Is an AlTiN-based film containing at least Al and Ti, and at least N as a nonmetallic element. By adopting this, it is possible to supplement the cutting characteristics. As a more specific layer structure, by alternately laminating one or more layers of the AlTiN-based film and the film of the present invention, a coated cutting tool corresponding to high-speed cutting can be obtained. The AlTiN-based film not only has general-purpose properties such as oxidation resistance and abrasion resistance, but also has good adhesion to the film of the present invention and further complements the properties. At this time, the coating of the present invention is desirably provided on the uppermost layer of the hard coating, but it is not necessarily the uppermost layer and sufficiently exerts its effect. Further, the present invention includes reference to Ti nitride or the like for the purpose of improving adhesion to a substrate, or substitution of a part of Ti with a small amount of another element.
[0017]
The coated cutting tool of the present invention is not particularly limited in its coating method, but is coated at a relatively low temperature in consideration of the thermal effect on the coated substrate, the fatigue strength of the tool, the adhesion of the coating, and the like. It is preferable to use a physical vapor deposition method in which a bias voltage is applied to the coated substrate side, such as arc discharge ion plating or sputtering, in which a compressive stress remains in the coated film.
[0018]
As a method for forming a Si-containing film including a high Si concentration region which is finer and discontinuous than the low Si concentration matrix according to the present invention on a substrate surface, physical methods such as ion plating and sputtering are used. Although a vapor deposition method is mentioned, for example, the following method may be used for film formation by the arc ion plating method. First, the substrate is heated by the heater in the same manner as when the inside of the furnace is evacuated to 3 × 105 Pa. After cleaning and activating the substrate with Ar, each of the alloy targets capable of obtaining the desired coating composition is installed on the cathodes, which are the plurality of evaporation sources for arc discharge, arranged in the furnace, and ionized by arc discharge. It is obtained by ion plating in a reaction gas atmosphere of various metals and nitrogen or the like. At this time, various metals are individually ionized from the plurality of cathodes. Adjustment of the evaporation rate of the various metals from each cathode and the energy released by ions involved in film formation (hereinafter, referred to as ion energy) will be described below. It was applied as follows.
[0019]
The magnitude of the ion energy during coating is determined mainly by the combination of the bias voltage applied to the substrate and the reaction gas. Here, the film needs to be formed while periodically changing the negative bias voltage and the positive bias voltage as the bias voltage applied to the base. As a result, a periodic change in ion energy is induced in the film, and films having different Si concentrations are formed in the same layer. This periodic change in ion energy is extremely important in the present invention. Further, by rotating the substrate while simultaneously dispersing the periodic change in ion energy and the evaporation rate of the alloy targets installed in the furnace at each cathode, Si segregation of the Si-containing films having different vapor pressures is caused in the film. Is to induce.
[0020]
Further, the difference in the Si concentration in the film changes depending on the substrate temperature. More specifically, at 700 ° C. or higher, a fine and discontinuous high Si concentration region may not be observed in some cases as compared with a low Si concentration matrix composed of the same phase. Therefore, the preferred substrate temperature is around 570 ° C. Increasing the bias voltage also tends to increase the substrate temperature. When the temperature is limited due to the requirement of the base material, a cooling means for the base may be required. Hereinafter, the present invention will be described based on examples.
[0021]
【Example】
Using an arc ion plating apparatus, various alloy targets as metal component evaporation sources, and N2 gas as a reaction gas, the coating substrate temperature was 550 ° C., the reaction gas pressure was 5 Pa, the negative bias voltage was 300 V, and the positive bias voltage was 300 V. The bias voltage was set to 40 V, the amplitude was set to 80% for negative and 20% for positive, and the frequency was set to 20 kHz. In addition, while rotating the substrate at 5 rpm, a current of 30 A was applied to one of the plurality of installed evaporation sources, and a current of 300 A was applied to the opposed evaporation source to form a film. The coated substrate is made of a cemented carbide 6-flute scare end mill with an outer diameter of 8 mm, a cemented carbide 2-flute ball end mill of R5 mm and a cemented carbide insert, so that the total thickness of the coating is 3 to 5 μm. Was formed. If necessary, a multilayer film with an AlTiN-based film was formed. The numerical values obtained by dividing the composition of the Si-containing film including the high Si concentration region and the Si content of only the metal component in the high Si concentration region of each sample by the Si content of only the metal component in the low Si concentration region are shown. Table 1 shows the composition of the AlTiN-based film used together.
[0022]
[Table 1]

[0023]
The coating conditions of the comparative example were similarly set using an arc ion plating apparatus, using various alloy targets as the evaporation source of metal components and N2 gas as a reaction gas, setting the coating substrate temperature to 400 ° C, and setting the reaction gas pressure to Samples having the compositions shown in Table 1 were prepared at 5 Pa and a negative bias voltage of 70 V. In Table 1, the composition is represented by an atomic ratio so that the total of the metal component and the non-metal component is 100 in total. This means that the atomic ratio of the metal component and the specific metal component is 1: 1. It does not mean. A cutting test was performed using the obtained coated end mill and coated insert. The end mill measured the flank wear width at a cutting length of 100 m, and the result was shown in Table 1 as the cutting time until fracture in the insert.
[0024]
(Carbide 6 flute Scare end mill cutting conditions)
Tool: Carbide 6-flute Scare end mill Cutting method: Side cutting Work material: SKD61 (hardness HRC52)
Cut: 8 mm in axial direction, 0.4 mm in radial direction
Cutting speed: 500m / min
Feed: 0.07mm / tooth
Cutting oil: air blow [0025]
(Carbide 2-flute ball end mill)
Tool: Carbide 2-flute ball end mill Cutting method: Bottom straight finish cutting Work material: SKD11 (hardness HRC56)
Cut: 1.5 mm in axial direction, 0.2 mm in pick feed
Cutting speed: 224m / min (outermost contact diameter)
Feed: 0.07mm / tooth
Cutting oil: air blow [0026]
(Carbide insert cutting conditions)
Tool: EDEW15T4TN-15
Cutter diameter: 63mm
Cutting method: Chamfering Work material: SKD61 (hardness HRC45) width 50 mm x length 250 mm
Cut: 2.0mm
Cutting speed: 250m / min
Feed: 0.5mm / rev
Cutting oil: air blow [0027]
Table 1 shows that Examples 1, 2, and 3 of the present invention are examples in which Cr contained Si, but segregation of fine Si having the same phase was observed inside the film, and that of Conventional Examples 22, 23, and Comparative Example 18 , 19, the cutting characteristics are excellent in all three conditions. In addition, Examples 4 and 5 to 8 of the present invention are examples of coatings having fine Si segregation consisting of the same phase in which Si is added to Ti, and all of the cutting tools are excellent in wear resistance. Examples 9 and 10 of the present invention are examples of films having segregation of fine Si composed of the same phase in which Si is added to Al, and also have excellent cutting characteristics. Inventive Examples 11, 12, 13, and 15 are examples of three kinds of metal component systems having segregation of fine Si having the same phase, and all of them were excellent in cutting characteristics. Examples 14 and 16 of the present invention are examples in which Si and Nb or V were used, but a difference in the concentration of Si was confirmed in both cases, and both were excellent in cutting performance. The example of the present invention enables more stable cutting even under a high-speed cutting environment than the comparative example and the conventional example.
[0028]
On the other hand, Comparative Example 17 is an example of Mn and Si, and it is considered that the brittle properties of Si did not affect the cutting performance without segregation of fine Si having the same phase. Life is short. Comparative Example 18, which is a metal element and a composition within the scope of the present invention, is an example in which a film is formed by a conventional vapor deposition method, and is inferior to the present invention without segregation of fine Si having the same phase inside the film. The result was. Comparative Example 19 is a comparative example in which the Si content is 50 atomic% or more, but becomes brittle due to excessive addition of Si, and has poor performance as compared with the examples of the present invention. Conventional examples 20 to 24 all have a short life under such a severe cutting environment.
[0029]
【The invention's effect】
As described above, by applying the present invention, by providing a film having a high Si concentration region and a low Si concentration region in the same phase of the film, damage is reduced even in high-speed cutting, and wear resistance is improved. Excellent long-life coated cutting tools could be sold.
[Brief description of the drawings]
FIG. 1 shows the results of observation of a lattice image of a Si-containing coating composed of Cr and Si of the present invention by a transmission electron microscope.
FIG. 2 shows the results of quantitative analysis of the high Si concentration region in FIG. 1 by energy dispersive analysis.
FIG. 3 shows a quantitative analysis result by an energy dispersive analysis of the low Si concentration region in FIG. 1;
FIG. 4 shows an analysis result of a crystal structure of the high Si concentration region shown in FIG. 1 by imaging with a micro electron beam diffraction image.
FIG. 5 shows an analysis result of a crystal structure of the low Si concentration region in FIG. 1 by imaging with a micro electron beam diffraction image.
FIG. 6 shows X-ray diffraction patterns of a film containing Si by a conventional film forming method and a film of the present invention.
FIG. 7 shows the results of an elemental analysis of the behavior of dynamic oxidation in the cutting process in the depth direction of the film wear portion on the flank of the tool during cutting.

Claims

The cutting tool base includes an element selected from one or more of metal elements of Groups 4, 5, and 6 and Al and an Si element, and at least one of N, B, C, and O as a nonmetallic element Alternatively, in a coated cutting tool formed by coating a Si-containing coating containing an element selected from two or more, the coating has a phase having a high Si concentration region and a low Si concentration region in the same phase. Coated cutting tools.

2. The coated cutting tool according to claim 1, wherein the high Si concentration region is 2 μm ² or less as observed by a transmission electron microscope, and the low Si concentration region and the lattice in the same phase are discontinuous. Coated cutting tools.

2. The coated cutting tool according to claim 1, wherein the Si-containing coating contains one or more elements selected from the group consisting of Ti, V, Al, Cr, Y, and Nb as metal elements. A coated cutting tool, wherein the Si content is less than 50% in atomic% of only the metal element component.

2. The coated cutting tool according to claim 1, wherein at least one layer other than the Si-containing film is an AlTiN-based film containing at least Al and Ti as metal elements and at least N as a nonmetal element. Coated cutting tools.