ICMCTF2016 Session B5-1: Hard and Multifunctional Nano-Structured Coatings
Tuesday, April 26, 2016 1:50 PM in Room San Diego
Time Period TuA Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2016 Schedule
B5-1-2 Erosion and Self-Healing of Micro-architected Plasma-Facing Materials for Space Electric Propulsion
Nasr Ghoniem (University of California Los Angeles, USA)
The inﬂuence of surface nano architecture on the sputtering and erosion of tungsten and molybdenum is discussed. We present an experimental investigation of the effects of low energy (150 eV) Ar ions on surface sputtering in Mo and W nano-rods and nano-nodules at room temperature. Measurements of the sputtering rate from Mo and W surfaces with nano architecture indicate that the surface topology plays an important role in the mechanism of surface erosion and restructuring. Chemical vapor deposition (CVD) is utilized as a material processing route to fabricate nano-architectures on the surfaces of W and Mo substrates. First, Re dendrites form as needles with cross-sections that have hexagonal symmetry, and are subsequently employed as scaffolding for further deposition of W and Mo to create nano rod surface architecture. The sputtering of surface atoms in these samples shows a marked dependence on their surface architecture. The sputtering rate is shown to decrease at normal ion incidence in all nano- architecture surfaces as compared to planar surfaces. Moreover, and unlike an increase in sputtering of planar crystalline surfaces, the current measurements show a decrease in the net sputtering rate at oblique angles as compared to normal incidence. Energy deposition in the near surface layer shows that W is also amorphized at room temperature by low energy Ar ions to a depth of 5–10 nm. Long duration experiments in Ar plasmas show that sputtered atoms are re-deposited onto surface architechure, showing surface islands that increase in density and size with plasma exposure. These islands coalesce and re-build the surface achieving partial self-healing of the surface nano-architecture. A discussion of the theory of nano-patterning will be presented to explain the observed experimental features.
B5-1-4 Development of Hard, Tough, and Thermally Stable Intermetallic Coatings
Cameron Gross, Xingliang He, Yip-Wah Chung (Northwestern University, USA)
Most metal-based coatings, while tough, are relatively soft compared with ceramics-based coatings. One can improve the hardness of metals by decreasing the grain size to the nanometer regime, but such nanograined structure is not stable at elevated temperatures. Inspired by the ideas proposed by Weissmüller, Kirchheim, and Schuh, we propose the use of magnetron sputtering to synthesize tungsten (W)-titanium (Ti) intermetallic coatings with different Ti concentrations. The role of Ti is to provide thermodynamic stabilization of nanocrystalline grains in these W-Ti intermetallic coatings. In our work, we deposited coatings with thickness from 280 to 325 nm, with Ti atomic concentration from 10 to 20%. At room temperature, these coatings show high hardness of 28.5 ± 0.5 GPa. This hardness is almost unchanged after one hour annealing in vacuum at 600 °C, remaining at 27.1 ± 0.8 GPa. We expect such coatings to be tough because they are metal-based. This approach provides a unique method to synthesizing hard, tough, and thermally stable coatings.
B5-1-5 Toughness-Enhanced Coatings for Demanding High-Performance Tools
Marcus Morstein, Tobias Schär, Gunnar Lahtz, Andreas Lümkemann (PLATIT AG, Advanced Coating Systems, Switzerland); Bo Torp (PLATIT, Inc., USA)
Nanostructured coatings are increasingly exposed to a challenging combination of wear factors such as mechanical impact, abrasion and oxidation. This contribution will show ways how physical vapor deposition (PVD) coatings can be optimized to withstand these challenges.
Taking advantage of the benefits of the process flexibility offered by the lateral (LARC®) and central (CERC®) cylindrical rotating arc cathodes technology, coating properties can be adjusted to achieve a good balance of both hardness and toughness. Based on structural and physical optimizations, several coating families were designed for use in the most challenging operations such as milling and turning of hard and new, difficult to machine materials. Two design approaches were mostly followed, a multi-zone strategy for metal cutting applications and a dedicated multilayer structure for thick coatings on molds and dies. Substrate pre-treatment as well as plasma etching were taken into consideration in order to optimize coating adhesion on the respective substrate material.
For milling and drilling of hardened or difficult to machine materials, such as new steel types or Ni-base alloys, titanium-based nanocomposite coatings such as the multi-zone coatings nACo4, based on the TiAlN/SiNx nanocomposite, and TiXCo4, based on the TiN/SiNx nanocomposite, were found to provide the best performance. Here, a combination of good high-temperature mechanical properties and abrasion resistance was found to be crucial. In turning, adding an oxynitride top layer to any of these coating systems could up to double the performance in some applications.
For applications in dry or wet high-performance milling, but also for mold and dies, a toughness optimization of chromium-based coatings by structural design on the nano- and microscale produces versatile yet performant coatings. In milling, significant advances were achieved using nACRo4 (based on the CrAlN/SiNx nanocomposite) and ALL4 (a nanolayered AlCrTiN with an AlCrN base layer). Here, both an optimized coating internal stress and an adjusted nanostructure were the keys to achieve stable high performance. For thick coatings on hot-working dies, a multilayer strategy was applied, containing an AlTiCrN-based temperature resistant coating together with rather soft interlayers, thus making the coatings more compliant even at a total thickness of up to 10 μm.
Additional tests and properties of these structurally optimized coating generations are shown for coatings produced by the recently introduced π1511 large-volume coating unit, featuring a combination of newly developed big LARC® cathodes and flexible traditional arc cathodes.
B5-1-6 Ti4AlN3 Formation by Solid State Reaction of Substoichiometric Solid Solution (Ti0.52Al0.48)N0.45 Thin Films
Isabella Schramm (Linköping University, IFM, Sweden); Mats Johansson-Jõesaar (Seco Tools AB, Fagersta, Sweden); Per Eklund (Linköping University, IFM, Thin Film Physics Division, Sweden); Frank Mücklich (Saarland University, Germany); Magnus Odén (Linköping University, IFM, Nanostructured Materials, Sweden)
The MAX phase Ti4AlN3 was confirmed and characterized in the late 90´s, with a slight deviation from stoichiometry, i.e. Ti4AlN3-δ (δ ≈ 0.1) , . The synthesis route was optimized to achieve a fully dense single-phase bulk material while reducing the aluminium loss during annealing. For technical purposes there is an interest to obtain MAX phases as thin films, reducing the synthesis temperature, and suppress the formation of metastable phases. Here we report a route to form Ti4AlN3 by solid state reaction from arc-deposited N-deficient (Ti,Al)Ny (y<1) coatings.
Reactive cathodic arc-deposition was used to grow substoichiometric solid solution cubic (c)-(Ti0.52Al0.48)N0.45 thin films at a temperature of 450 °C. The films were then heated in an Ar-environment to 1400 °C and the formation of Ti4AlN3 via solid state high temperature reactions was established. Characterization of the reaction path was performed using a combination of X-ray diffractometry, differential scanning calorimetry, scanning- and transmission electron microscopy, and atom probe tomography. The solid state reaction of c-(Ti0.52Al0.48)N0.45 started with the formation of w-AlN and Al3Ti at 1000 °C followed by Ti2AlN formation at 1100 °C. At 1300 °C two MAX phases, Ti2AlN and Ti4AlN3, coexist and finally at 1400 °C only Ti4AlN3, w-AlN and c-TiN were observed. Highly nitrogen-deficient c-TiAlN solid solutions have a strong driving force for precipitation of metallic Al or Al-Ti mixtures, resulting in an Al-depleted matrix. It has been suggested that such situation favors the formation of hexagonal MAX phases . In our case, this is consistent with the formation of intermetallic Al3Ti and Ti2AlN. Additionally, we note that in the subsequent reaction step, the presence of Ti2AlN (and its stability up to 1300 °C) is necessary for obtaining Ti4AlN3, possibly via deintercalation of aluminium layers.
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B5-1-7 Investigation and Optimization of the Tribo-mechanical Properties of CrAlCN Coatings using Design of Experiments
Wolfgang Tillmann, Dominic Stangier (TU Dortmund University, Germany)
The control of friction as well as its adaption is essential for forming operations. Thin hard coatings have a significant influence on the performance of production processes and the service life of tools, especially for Sheet-Bulk Metal Forming processes with high contact normal stresses and issues concerning the filling of filigree functional elements.
To handle these challenges, the coating system CrAlCN is generated by means of bipolar-pulsed reactive magnetron sputtering, using Design of Experiments. A Central Composite Design is selected investigating the cathode power, bias voltage, as well as the reactive gas flow composition (nitrogen and acetylene). The aim is to evaluate the correlations and the interaction of the investigated process parameters on the morphology as well as the tribo-mechanical behavior of the CrAlCN coating and to develop models to obtain the desired coating properties.
As substrate material the high speed steel AISI M3:2 (material number 1.3344) with a hardness of 62 ± 1 HRC, which is typical of forming tools, is used for the deposition process. To investigate the mechanical and tribological properties, the coated specimens are analyzed by nanoindentation, a ball‑on‑disc‑tribometer with different counter parts (100Cr6, WCCo and Al2O3), a scratch-tester, and by utilizing a scanning electron microscope, including energy dispersive X-ray analyses. To determine the elemental composition of the CrAlCN coatings, Glow Discharge Optical Emission Spectroscopy (GDOES) as well as XRD for phase analyses are used.