Hard and Multifunctional Nano-Structured Coatings

Monday, April 28, 2014 10:00 AM in Room Sunset

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10:00 AM B5-1-1 Hard Multifunctional Hf-B-Si-C Films Prepared by Pulsed Magnetron Sputtering
Pavel Mares, Jiri Kohout, Jaroslav Vlcek, Jiri Houska, Radomir Cerstvy, Petr Zeman (University of West Bohemia, Czech Republic); Minghui Zhang, Jiechao Jiang, Efstathios Meletis (University of Texas at Arlington, US); Sarka Zuzjakova (University of West Bohemia, Czech Republic)
Hf–B–Si–C films were deposited on silicon and glass substrates using pulsed magnetron co-sputtering of a single B4C–Hf–Si target (at a fixed 15% Hf fraction and a varying 0-50% Si fraction in the target erosion area) in pure argon. We focus on the effect of the Si content. We found that the nanocolumnar Si-free Hf–B–C films exhibit a high hardness of 37 GPa and a high electrical conductivity (electrical resistivity of 1.8×10-6 Ωm). However, the high hardness of these films is accompanied by a high compressive stress of 4.9 GPa. The highly textured nanocolumnar Hf–B–Si–C films prepared at 1% Si fraction in the target erosion area exhibit a similar high hardness at a lower compressive stress of 1.8 GPa. A further increase in the Si fraction in the target erosion area to 7.5% results in a formation of nanocomposite Hf–B–Si–C films with a high hardness of 37 GPa, a low compressive stress of 0.9 GPa and significantly improved oxidation resistance in air (mass gain after annealing to 800 ºC is below 0.03 mg/cm2). We obtained a relatively high H/E* ratio of around 0.15, indicating a high elastic strain to failure, for all these nanostructured HfB2-based films. The highest oxidation resistance in air (almost no mass change after annealing up to 800 ºC) was achieved for the amorphous Hf–B–Si–C films prepared at 30% Si fraction in the target erosion area. All films exhibit very smooth defect-free surfaces with an average roughness below 1 nm. The films may be used as a new class of hard and electrically conductive protective coatings with a high oxidation resistance at elevated temperatures.
10:20 AM B5-1-2 Influence of Hf on the Structure, Thermal Stability and Oxidation Resistance of Ti-Al-N Coatings
Yuxiang Xu (Central South University, China); Li Chen (Central South University and Zhuzhou Cemented Carbide Cutting Tools Co., LTD, China); Yong Du (Central South University, China); Fei Pei (Central South University and Zhuzhou Cemented Carbide Cutting Tools Co., LTD, China); Yingbiao Peng (Central South University, China)

Alloying with transition metal (TM) elements into Ti-Al-N to improve its performance is attracting considerable interest. Here, we investigate the effect of Hf on structure, mechanical and thermal properties of Ti-Al-N coating with cubic structure. Alloying with 3 at.% Hf slightly promotes the spinodal decomposition of Ti-Al-N to form Al-depleted and Al-enriched domains during thermal annealing. According to TGA and DSC results, Hf-containing coating exhibits less oxidation below 1053 °C, which is attributed to the retarded transformation of anatase (a) TiO2 to rutile (r) TiO2. However, incorporation of Hf results in worse oxidation resistance above 1053 °C due to the deterioration of barrier effect of diffusion from large Hf atom. Ti-Al-Hf-N coatings onto Al2O3 substrates can retain most of dense unoxidized layer after oxidation at 850 °C for 10 h under synthetic air atmosphere and fully transform to oxides when oxidation temperature elevate to 950 °C. An oxidation of the coatings following the DSC curve during air up to 1100 °C shows that the oxide scales of Ti-Al-N and Ti-Al-Hf-N coatings are 3.45 and 3.87 μm, respectively.

The financial support from National Natural Science Foundation of China (grant nos. 51371201 and 51371199) and Zhuzhou cemented carbide cutting tools limited company of China is acknowledged.

10:40 AM B5-1-3 Growth of Hard Amorphous Ti-B-Si-N Coatings by Cathodic Arc Evaporation
Hanna Fager (Thin Film Physics Division, IFM, Linköping University, Sweden); Jon Andersson (Seco Tools AB, Swedon); Jun Lu, Jens Jensen, Lars Hultman (Thin Film Physics Division, IFM, Linköping University, Sweden)

Transition metal nitrides are used in many applications because of their high hardness, mechanical wear resistance, high thermal stability, and good oxidation resistance. For these materials, much research has concerned nanocrystalline films and nanocomposites. Especially in the development of hard ceramic coatings for wear-resistant applications, microstructural design has been of great importance, as has the correlation between microstructure and mechanical properties. Recently, we have directed focus to a less studied area: amorphous transition metal nitrides. We propose amorphous multicomponent transition metal nitrides for a new class of durable materials that could extend the range of possible applications, due to the material’s homogeneous structure, lack of weak grain boundaries, and mixed character of bonding. We previously showed that the addition of Al and Si to TiN in Ti1-x-yAlxSiyN distorts nanocrystalline growth and promotes renucleation and an amorphous structure in cathodic arc evaporation [1]. We concluded that the coatings were amorphous when the Ti content 1-x-y<0.34. Isothermal annealing experiments showed that the amorphous coatings were thermally stable up to 900 °C and exhibited age hardening up to 1100°C with an increase in hardness from 19.4 GPa to 31.6 GPa. Here, we exchange Al for B and explore the Ti1-x-yBxSiyN system. B is a well-known grain refiner, and a good choice for promoting growth of amorphous phases, since it can be both three- and fourfold coordinated. Also, B-N bonds are stronger than Si-N ones, which is beneficial for hard coating applications. The coatings were grown onto cemented carbide substrates in an industrial scale cathodic arc evaporation system using Ti-Si and Ti-B cathodes in a pure N2 atmosphere. Compositional analysis of the as-deposited films was performed by elastic recoil detection analysis, and the structural information and phase composition was gained by X-ray diffraction, and analytical transmission electron microscopy. Mechanical properties of the coatings are characterized by nanoindentation. We show that the structure of as-deposited films remain amorphous up to a Ti content of 0.63. The structure changes to nanocrystalline for Ti content 1-x-y>0.70. The hardness of the as-deposited amorphous coatings is 17.1-18.9 GPa depending on composition. In addition, we will present results for the phase composition, thermal stability, and crystallization behavior of the coatings, as well as from metal cutting tests.

[1] H. Fager et al., Surf. Coat. Technol. (2013), 10.1016/j.surfcoat.2013.07.014

11:00 AM B5-1-4 Structure, Oxidation Resistance and High Temperature Tribological Properties of CrTiAlN Coatings
Jianliang Lin, Kent Coulter, Peter Lee (Southwest Research Institute, US); William Sproul (Reactive Sputtering, Inc., US)

CrTiAlN coatings with different Cr/Ti ratios have been reactive sputtered from a CrAl and a Ti target, which were powered by pulsed dc magnetron sputtering and deep oscillation high power pulsed magnetron sputtering (DOMS), respectively. DOMS is an alternative high power pulsed magnetron sputtering technique that uses large voltage oscillation packet to achieve high power pulses for sputtering. The coatings were deposited onto WC-Co, AISI 304 steel coupons, and Si wafers at room temperature using a -60 V dc negative substrate bias voltage. The microstructure, mechanical properties, and oxidation and tribological behavior at elevated temperatures of the CrTiAlN coatings were investigated and compared to the Cr0.7Al0.3N baseline system.

By varying the Cr/Ti ratio, while maintaining the Al content in the metal lattice lower than 30 at.%, the CrTiAlN coatings exhibited a large variation in the hardness between 26 GPa to 38 GPa, which showed great improvement as compared to 30 GPa for the Cr0.7Al0.3N coating. Appropriate addition of Ti into CrAlN coatings improved the oxidation resistance of the coatings. The onset oxidation temperature has been successfully delayed to 1000 oC for the TiCrAlN coatings as compared to 800 oC for the low Al concentrated Cr0.7Al0.3N coating. However, excessive addition of Ti is detrimental to the oxidation resistance of the coatings. At the end of the study, high temperature wear resistance of the CrTiAlN coatings from 400 to 700 oC in an ambient air will also be reported.
11:20 AM B5-1-5 Growth of AlYB14 Thin Films by HPPMS
Oliver Hunold, Denis Music, Yen-Ting Chen, Stanislav Mráz, Jochen Schneider (RWTH Aachen University, Germany)

Icosahedral boron-rich solids, containing B12 clusters, exhibit outstanding physical properties1 such as high hardness, a Young’s modulus above 500 GPa2 and a melting point on the order of 2400 °C. Calculations3,4 and experiments5 have shown that these materials provide very favorable properties for wear resistant applications. Furthermore, spontaneous self-healing1 has been reported after radiation induce vacancy formation. Among others AlYB14 (space group: Imma) belongs to this group of boron-rich solids. However, synthesizing crystalline XYB14, where X and Y are metals, is challenging both with respect to the incorporation of impurities5 and the required synthesis temperature: 1400 °C.6

The influence of the duty cycle ton/(ton+toff) on the structure evolution of AlYB14 was studied using high power magnetron sputtering (HPPMS). The film structure was analyzed by X-ray and electron diffraction. Depending on the duty cycle the formation of crystalline AlYB14 was obtained at a temperature of 800 °C. Our data indicate that crystalline AlYB14 grains grow within an amorphous matrix.

References:

1 D. Emin, J. Solid State Chem. 179 (9), 2791 (2006).

2 J. Emmerlich, N. Thieme, M. to Baben, D. Music, and J. M. Schneider, J. Phys.: Condens. Matter 25 (33), 335501 (2013).

3 J. E. Lowther, Physica B 222 (2002).

4 Y. Lee and B. N. Harmon, J. Alloys Compd. 338 (2002).

5 B. A. Cook, J. L. Harringa, T. L. Lewis, and A. M. Russell, Scripta Mater. 42 (2000).

6 M. M. Korsukova, T. Lundström, and L.-E. Tergenius, J. Alloys Compd. 187 (1992).