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Thin Film and Plasma Characterization of PVD Oxides

機譯：PVD氧化物的薄膜和等離子體表征

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摘要

The state-of-the-art tools for machining metals are primarily based on a metal-ceramic composite(WC-Co) coated with different combinations of carbide, nitride and oxide coatings. Combinations of these coating materials are optimized to withstand specific wear conditions. Oxide coatings are especially desired because of their possible high hot hardness, chemical inertness with respect to the workpiece, and their low friction. This thesis deals with process and coating characterization of new oxide coatings deposited by physical vapor deposition (PVD) techniques, focusing on the Cr-Zr-O and Al-Cr-Si-O systems. The thermal stability of α-Cr0.28Zr0.10O0.61 deposited by reactive radio frequency (RF)-magnetron sputtering at 500 °C was investigated after annealing up to 870 °C. The annealed samples showed transformation of α-(Cr,Zr)2O3 and amorphous ZrOx-rich areas into tetragonal ZrO2 and bcc Cr. The instability of the α-(Cr,Zr)2O3 is surprising and possibly related to the annealing being done under vacuum, facilitating the loss of oxygen. The stabilization of the room temperature metastable tetragonal ZrO2 phase, due to surface energy effects, may prove to be useful for metal cutting applications. The observed phase segregation of α-(Cr,Zr)2O3 and formation of tetragonal ZrO2 with corresponding increase in hardness for this pseudo-binary oxide system also opens up design routes for pseudo-binary oxides with tunable microstructural and mechanical properties. The inherent difficulties of depositing insulating oxide films with PVD, demanding a closed circuit, makes the investigation of process stability an important part of this research. In this context, we investigated the influence of adding small amount of Si in Al-Cr cathode on plasma characteristics ,process parameters, and coating properties. Si was chosen here due to a previous study showing improved erosion behavior of Al-Cr-Si over pure Al-Cr cathode without Si incorporation in the coating. This work shows small improvements in cathode erosion and process stability (lower pressure and cathode voltage) when introducing 5 at % Si in the Al70Cr30-cathode. This also led to fewer droplets at low cathode current and intermediate O2 flow. A larger positive effect on cathode erosion was observed with respect to cleaning the cathode from oxide contamination by increasing cathode current with 50%. However, higher cathode current also resulted in increased amount of droplets in the coating which is undesirable. Through plasma analysis the presence of volatile SiO species could be confirmed but the loss of Si through volatile SiO species was negligible, since the coating composition matched the cathode composition. The positive effect of added Si on the process stability at the cathode surface should be weighed against Si incorporation in the coating. This incorporation may or may not be beneficial for the final application since literature states that Si promotes the metastable γ-phase over the thermodynamically stable α-phase of pure Al2O3, contrary to the effect of Cr, which stabilizes the α-phase.
機譯：用于加工金屬的最新工具主要基于涂覆有碳化物，氮化物和氧化物涂層的不同組合的金屬陶瓷復(fù)合材料（WC-Co）。這些涂料的組合經(jīng)過優(yōu)化，可以承受特定的磨損條件。特別期望氧化物涂層，因為它們可能具有高的熱硬度，相對于工件的化學惰性以及低的摩擦力。本文研究了通過物理氣相沉積（PVD）技術(shù)沉積的新氧化物涂層的工藝和涂層特性，重點研究了Cr-Zr-O和Al-Cr-Si-O系統(tǒng)。在高達870°C的溫度下退火后，研究了通過反應(yīng)射頻（RF）-磁控濺射在500°C下沉積的α-Cr0.28Zr0.10O0.61的熱穩(wěn)定性。退火后的樣品顯示出α-（Cr，Zr）2O3和富含ZrOx的非晶態(tài)區(qū)域轉(zhuǎn)變?yōu)樗姆絑rO2和bcc Cr。 α-（Cr，Zr）2O3的不穩(wěn)定性令人驚訝，并且可能與在真空下進行退火有關(guān)，從而促進了氧氣的流失。由于表面能的影響，室溫亞穩(wěn)態(tài)四方ZrO2相的穩(wěn)定化可能被證明可用于金屬切削應(yīng)用。對于該準二元氧化物體系，觀察到的α-（Cr，Zr）2O3的相偏析和四方ZrO2的形成以及相應(yīng)硬度的增加，也為具有可調(diào)節(jié)的微結(jié)構(gòu)和機械性能的準二元氧化物開辟了設(shè)計路線。用PVD沉積絕緣氧化膜的固有困難，需要閉路，這使得對工藝穩(wěn)定性的研究成為該研究的重要部分。在這種情況下，我們研究了在Al-Cr陰極中添加少量Si對等離子體特性，工藝參數(shù)和涂層性能的影響。在此選擇Si是因為先前的研究表明，與純Al-Cr陰極相比，Al-Cr-Si的腐蝕行為有所改善，而沒有在涂層中摻入Si。當在Al70Cr30陰極中引入5 at％的Si時，這項工作顯示出陰極腐蝕和工藝穩(wěn)定性（較低的壓力和陰極電壓）的小改進。這也導(dǎo)致在低陰極電流和中間O2流量下液滴減少。通過將陰極電流增加50％，可以清潔陰極免受氧化物污染，從而對陰極腐蝕產(chǎn)生了更大的積極影響。然而，較高的陰極電流也導(dǎo)致涂層中液滴的數(shù)量增加，這是不希望的。通過等離子體分析，可以確認存在揮發(fā)性SiO種類，但是由于涂料組成與陰極組成相匹配，因此通過揮發(fā)性SiO種類造成的Si損失可以忽略不計。應(yīng)權(quán)衡添加的Si對陰極表面工藝穩(wěn)定性的積極影響，以防Si摻入涂層中。這種摻入對于最終的應(yīng)用可能有好處，也可能沒有好處，因為有文獻指出，與純Al2O3的熱力學穩(wěn)定的α相相比，Si促進了亞穩(wěn)態(tài)γ相，這與使α相穩(wěn)定的Cr的作用相反。

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  • 作者

    Land?lv, Ludvig;

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  • 年度 2017
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  • 正文語種 eng
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