Bias Voltage Ub Research Articles

Cutting edge preparation of micro end mills by PVD-etching technology

Micromilling tools face significant challenges in achieving cutting edge preparation by mechanical processes due to their small size. To address these limitations, a new approach for cutting edge preparation of micro end mills by physical vapor deposition (PVD) etching technology is presented. By adapting the etching strategy, which is conventionally used as pre-treatment process for PVD technology to clean and condition the surface of cemented carbide substrate, cutting edges of micromilling tools were successfully modified. The high-energy process variation by Advanced Arc-Enhanced Glow Discharge (AEGD) offers the possibility of achieving high material removal rates on the tool surfaces and thereby altering the cutting edge geometry. Fundamental investigations on material removal as well as on the effects on surface topography, sub-surface properties, and coating adhesion of a subsequently applied PVD coating are performed. To influence the topography and the cutting edge geometry, the preparation time tp and bias voltage UB were selected. Subsequently, the machining performance of the modified tools is evaluated in a micromilling process of the hardened powder-metallurgical high-speed steel AISI M3:2 with a hardness of 62 ± 1 HRC. For this purpose, micro end mills of cemented carbide with a diameter of D = 1 mm were conditioned, achieving asymmetric geometric properties of cutting edges with varying average cutting edges rounding of S¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\overline S}$$\\end{document}= 5.8 … 14.8 µm and a form-factor of K = 2.0 … 2.7. Based on the application tests a positive influence on the process forces was found. Thus, an efficient approach to cutting edge preparation can be identified by specifically designing ion etching in the PVD coating process.

Fabrication of textured FeCo(110) and FeCo(200) films by DC magnetron sputtering

The results of study of bias voltage Ub and substrate temperature Ts influence on the texture of FeCo films with the thickness of 180 nm deposited on Si/SiO2 substrates by DC magnetron sputtering are presented. It is shown that the change of Ub from -250 V to 80 V leads to the growth of films with (110) texture. Further change of Ub from 80 V to 250 V causes the growth of films having (200) texture. Films deposited at Ub=0 and Ts=60-300oC have (200) texture. Further increase of Ts results in the change of film texture to (110). Keywords: FeCo films, magnetron sputtering, texture, coercitivity.

Получение текстурированных пленок FeCo(110) и FeCo(200) магнетронным распылением на постоянном токе

The results of study of bias voltage Ub and substrate temperature Ts influence on the texture of FeCo films with the thickness of 180 nm deposited on Si/SiO2 substrates by DC magnetron sputtering are presented. It is shown that the change of Ub from -250 V to ~ 80 V leads to the growth of films with (110) texture. Further change of Ub from 80 V to 250 V causes the growth of films having (200) texture. Films deposited at Ub = 0 and Ts = 60º – 300º C have (200) texture. Further increase of Ts results in the change of film texture to (110).

Effect of Bias Voltage and Deposition Rate on the Structure and Coercivity of NiFe Films

The effect of the bias voltage Ub and the deposition rate $${v}$$ on the structure, grain size D, and coercivity Hc of NiFe films with a thickness d from 30 to 980 nm, grown on Si/SiO2 substrates by DC magnetron sputtering, has been studied. In the case of Ub = 0, a decrease in $${v}$$ from values $${v}$$ ≈ 27 to ≈7 nm/min is accompanied by an increase in the values of the critical film thickness dcr from dcr ≈ 220 nm to dcr ≈ 270 nm. In this case, Hc in films with d < dcr is characterized by the dependence Hc ~ D6 and varies from ~1 to ~20 Oe. For Ub = –100 V, the effect of the deposition rate on the coercivity is much more noticeable. At $${v}$$ = 7 and 14 nm/min, the films exhibit soft magnetic properties (Hc ≈ 0.15–1.4 Oe) and the absence of dcr for the entire range of studied thicknesses. The films obtained at $${v}$$ = 21 and 27 nm/min pass into the “supercritical” state at d ≥ dcr ≈ 520 nm, and in the range d < dcr they are characterized by the dependence Hc ~ D3 and an increase in the coercivity from ~0.35 to ~10 Oe.

Влияние напряжения смещения и скорости осаждения на структуру и коэрцитивность пленок NiFe

Influence of the bias voltage Ub and the deposition rate  on the structure, grain size D, and coercivity Hc of NiFe films with the thickness d from 30 to 980 nm, grown onto Si / SiO2 substrates by DC magnetron sputtering, was studied. In the case Ub = 0, the decrease of  from ≈ nm/min to ≈ 7 nm/min is accompanied by the increase of the critical film thickness dcr from dcr ≈ 220 nm to dcr ≈ 270 nm. In this case, Hc in the films with d &lt; dcr is characterized by the dependence Hc ~ D6 and varies from ~ 1 to ~ 20 Oe. In the case of Ub = -100 V, the effect of the deposition rate on the coercivity is much more noticeable. At ν = 7 and 14 nm / min, the films demonstrate soft magnetic properties (Нс ≈ 0.15 - 1.4 Oe) and the absence of dcr for the entire range of studied thicknesses. The films obtained at ν = 21 and 27 nm / min turn into the “supercritical” state at d ≥ dcr ≈ 520 nm, and, in the region d &lt; dcr, they are characterized by the dependence Hc ~ D3 and by the increase of coercivity from ~ 0.35 to ~ 10 Oe.

AFM-tip written normal and anomalous domains in PMN-0.4PT crystals

At present, crystals of the solid solutions Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) are under intensive investigation due to their excellent piezoelectric characteristics. Studies in domain engineering are of importance for an insight into the contribution from the domain formation and resulting domain-wall density to piezoelectric coefficients. In this work, the fabrication of domains by dc AFM-tip voltages was studied in the tetragonal PMN-0.4PT crystals. Two types of domains were observed, either uniformly polarized along the poling field (the “normal” ones), or, following the commonly accepted term, “anomalous” ones containing a small area with the polarization directed oppositely to the poling field. In this work, for the first time, the correlation between the domain shape and the local piezoelectric hysteresis loops Hω−Utip was found, namely, the larger is the local bias voltage Ub, the higher is the tip voltage Utip at which the anomalous domains appear. This finding relates the observed scatter in the exposure conditions corresponding to the anomalous domains formation, to the nonuniform spatial distribution of the local bias fields. The domain diameter D vs Utip and pulse duration tp were investigated for Utip ≤ 50 V and tp from 10 ms to 10 s. The exposure characteristics are independent of the domain shape. For a given tp, D(Utip) is described by a unified linear function in the whole Utip range. The curves D(tp) follow a power law D∼tpk with the exponent k varying very weakly with Utip. The relaxation kinetics of anomalous domains depends on the writing conditions. The normal domains are found to decay significantly faster than the anomalous ones, with the decay kinetics depending on the domain spacing.

The Properties of Cr–Co–Cu–Fe–Ni Alloy Films Deposited by Magnetron Sputtering

In spite of great efforts undertaken to produce and examine the properties of new high-entropy alloys (bulk or film alloys), the available information is still insufficient for creating scientific ideas that would connect the properties and process parameters of these alloys. We studied the dependence of the composition and structure of Co–Cr–Cu–Fe–Ni films deposited by magnetron sputtering on the physical parameter such as energy flux delivered to the growing film surface. This parameter is directly related to process parameters such as magnetron discharge current (Id) and substrate bias voltage (Ub). The films have a nanocrystalline microstructure and crystallize as a two-phase fcc and bcc solid solution with the following lattice parameters: a = 0.363 nm for the fcc phase and a = 0.294 nm for the bcc phase. Ion bombardment of the growing film induced by bias voltage Ub varying from 0 to –300 V in the substrate influences the film structure and composition. Thus, the films deposited at ~300 eV are noticeably depleted of copper, while the composition of the films deposited without ion bombardment is the same as that of the target. Greater energy flux delivered to the growth surface (higher Id and/or Ub in the substrate) increases the growth surface temperature, leading to grain coarsening and film texturing. The bcc phase also substantially decreases in volume, vanishing in the films deposited at Ub = –300 V. The films formed by the bombardment of ions with ≈100 eV energy showed the maximum (~19 GPa) microhardness.

Superhard CrN/MoN coatings with multilayer architecture

Main regularities of the formation of microstructure and properties of multilayer nanostructured CrN/MoN films with periodically changing architecture of layers were considered. Coatings were fabricated by vacuum-arc evaporation of the cathodes (Arc-PVD) in nitrogen atmosphere (pN was 0.4, 0.09 and 0.03 Pa). CrN and γ-Mo2N nitride phases with fcc lattices and a small volume of metastable MoNx cubic phase were formed in the films at pN = 0.4 Pa. The decrease of pN to 0.09 Pa causes the formation of β-Cr2N hexagonal phase. Preferential crystallographic orientation changes from [311] to [111] and [200] when bias voltage Ub is −20, −150 and −300 V respectively. The nanocrystallites size in coatings with bilayer thickness λ = 44 nm decreases to 5.8 nm. The microdeformation grows from 0.4 to 2.3% when Ub changes to −20 V. Coatings show high hardness of 38–42 GPa and H/E = 0.107. In a couple with results of tribological tests, coatings demonstrate strong wear resistance, which makes them appropriate and promising for industrial applications as protective ones. The effect of deposition conditions (pN, Ub, λ) on composition, structure, hardness, toughness and wear resistance was studied to achieve superior mechanical and physical properties of coatings with long lifetime in harsh environment.

Wear behaviour of wear-resistant adaptive nano-multilayered Ti-Al-Mo-N coatings

Coating samples in the Ti-Al-Mo-N system were obtained by arc-PVD method at variable bias voltage Ub applied to the substrate, and the partial pressure of nitrogen P(N2) used as a reaction gas. The deposited coatings were characterized by a nanocrystalline structure with an average grain size of 30–40nm and multilayered architecture with alternating layers of (Ti,Al)N nitride and Mo-containing phases with a thickness comparable to the grain size. Coatings of (Ti,Al)N-Mo-Mo2N and (Ti,Al)N-Mo2N compositions were obtained by changing deposition parameters. The obtained coatings had hardness of 40GPa and the relative plastic deformation under microindentation up to 60%. (Ti,Al)N-Mo2N coatings demonstrated better physicomechanical characteristics, showing high resistance to crack formation and destruction through the plastic deformation mechanism without brittle fracturing, unlike (Ti,Al)N-Mo-Mo2N. The friction coefficient of the study coatings (against Al2O3 balls under dry condition using a pin-on-disc method) reached the values of 0.35 and 0.5 at 20°C and 500°C respectively, without noticeable wear within this temperature range. These tribological properties were achieved by forming MoO3 acting as a solid lubricant. At higher temperatures the deterioration in the tribological properties is due to the high rate of MoO3 sublimation from friction surfaces.

Influence of the bias voltage on the structure and mechanical performance of nanoscale multilayer CrAlYN∕CrN physical vapor deposition coatings

The effects of bias voltage on the microstructure and the related tribological properties of CrAlYN∕CrN nanoscale multilayer superlattice coatings were investigated. The coatings were deposited at 450°C substrate temperature by combined high power impulse magnetron sputtering (HIPIMS) and unbalanced magnetron sputtering techniques. The substrates were 304 stainless steel, M2 high speed steel for structural analysis and mechanical testing, as well as cemented carbide substrates end mills for dry high speed milling applications. Substrates were pretreated by HIPIMS etching. The bias voltage Ub was varied between −75 and −150V. The chemical composition was determined by neutral mass spectroscopy. The microstructure was characterized by x-ray diffraction and cross sectional transmission electron microscopy. All coatings had a single phase B1 fcc structure. The chemical composition was not affected by the bias voltage. Local epitaxial or axiotaxial growth attributed to the HIPIMS etching pretreatment was observed on the large surface areas of the substrate crystals. This turned to columnar growth with {110} texture at low bias voltages Ub between −75 and −120V, while at Ub=−150V an equiaxed structure of large crystal sizes developed with {111} texture. At the same time the waviness of the superlattice significantly decreased. An increase in bias voltage resulted in a significant rise in both residual stress levels (from −3.3to−9.5GPa) and plastic hardness (from Hp=34–51GPa), while the coating/substrate adhesion decreased from 61to45N. The friction coefficient increased from 0.43 (at Ub=−75V) to 0.55 (at UB=−120V), while the initial sliding wear rates decreased remarkably (2.6×10−16m3N−1m−1 at UB=−75V to 3.7×10−17m3N−1m−1 at Ub=−150V). The life time of 8mm ball-nosed cemented carbide end mills decreased from 39min at Ub=−75V to 19min when Ub was raised to −150V. These results highlight that the combination of HIPIMS substrate treatment and designed deposition parameters provides good opportunity to tailor coating structures with optimized properties.

Chromium nitride/niobium nitride nano-scale multilayer coatings deposited at low temperature by the combined cathodic arc/unbalanced magnetron technique

CrN/NbN nano-scale multilayered coatings have been successfully grown at a deposition temperature of 250 °C. The coatings have been grown by the combined cathodic arc/unbalanced magnetron technique (Arc Bond Sputter) and were deposited at two different thicknesses namely ∼1.0 and ∼3.0 μm at bias voltages UB between −75 and −150 V. In all cases the stresses were compressive and increased from −4.4 GPa at UB=−75 V to −9.5 GPa at UB=−150 V. Coatings in all cases developed a pronounced {111} texture that tended to a maximum at a bias voltage of −95 V. The experiments indicated that the {111} texture developed by a competitive growth mechanism from a randomly oriented or {100} initial starting texture. Measurements of coefficients of friction and sliding wear show a decrease in the coefficients of friction and sliding wear with increasing bias voltage. The coefficient of friction decreases from μ=0.7 at UB=−75 V to μ=0.5 at UB=−150 V while in parallel the coefficient of sliding wear decreased by an order of magnitude from 1.3×10−14 at UB=−75 V to 2.8×10−15 at UB=−150 V. These decreases in coefficients of friction and sliding wear appear to mirror the increases in intensity of the {111} texture. The adhesion as measured by scratch test shows a distinct maximum of 72 N at a bias voltage UB of −95 V, which is a remarkably high value for a low temperature process in a coating with a compressive stress of −5.4 GPa.

Microwave plasma nitriding of a low-alloy steel

A low-alloy steel was nitrided in the downstream zone of an electron cyclotron resonance (ECR) discharge at low pressure (0.15–0.25 Pa). Structure and properties of the nitrided surfaces were primarily controlled by the substrate temperature Ts (300–550 °C), the nitrogen–hydrogen–argon gas mixture composition, and the substrate bias voltage Ub (−1000 to +40 V) at a typical value of the incident microwave power Pi=900 W, the distance of the substrate from output aperture of the ECR source was d=250 mm, and the nitriding time t=2 h. Optical emission spectroscopy was used to study the behavior of significant atomic and molecular species, such as N2, N2+, NH, H, Fe, Ar, and Ar+, in front of the nitrided sample. It has been found that due to a high plasma reactivity, nitriding is effective at substrate temperatures Ts⩾500 °C, when the surface hardness is about 1200 HV0.05 and a diffusion layer thickness up to 120 μm has been achieved for t=2 h. The presence of 10%–30% H2 in a nitrogen–hydrogen gas mixture enhances the efficiency of nitriding in comparison with treatment in pure nitrogen under the same conditions. For Ts⩾500 °C, the process is effective even for substrates at positive potential (Ub=+30 V) and for a lower amount of N2 (10%–30%) in a nitrogen–hydrogen–argon gas mixture, for which no compound layer is formed on the nitrided surface. However, the negative substrate bias voltage Ub enhances considerably the efficiency of nitriding only at lower substrate temperatures (Ts≈400 °C), when the nitriding is relatively weak.

RFA as control method of the reactive sputtering process of TiN films

In-situ X-ray fluorescence (XRF) analysis has been used to control the deposition process of Ti-N films on steel substrates during reactive sputtering. The analysis system consisted of a tungsten X-ray tube, secondary targets of Cu, Fe and Cr and a Si (Li) detector. The sputtering off the Ti target has been determined indirectly by plasma monitoring using optical emissions spetroscopy (OES) of the Ti atoms, and the film growth has been measured directly by XRF analysis of the surface mass of Ti atoms deposited on the substrate. For zero bias voltage and varying N2 flow the increment of surface mass per deposition time has been found to incrase linearly with the intensity of the OES signal of Ti. A negative bias voltage UB≥100 V changes strongly the growth rate by resputtering effects, especially in the range where stoichiometric TiN is formed.

Thermal gas effusion from hydrogenated amorphous carbon films

Hydrogenated amorphous carbon (a-C:H) films, deposited onto negatively biased substrates in a 13.56-MHz hydrocarbon glow discharge system, have been investigated by mass spectroscopic thermal effusion measurements. Depending on the bias voltage UB as the most important deposition parameter, hydrocarbons and/or H2 molecules are desorbed at threshold temperatures between 300 and 600 °C. The threshold temperature increases with increasing bias voltage while the mass of the desorbed molecules decreases. a-C:H films deposited at low bias release H2, CH4, and higher hydrocarbons whereas from hard a-C:H films deposited at UB≳500 V, only H2 is released. Using double-layer a-C:H/a-C:D films, it is shown that H2 and CH4 molecules are formed in the volume of the film followed by molecular diffusion through the a-C:H network. For high-bias voltages (UB≳500 V), the reduced pore size of the strongly crosslinked a-C:H network is shown to prevent diffusion of hydrocarbon molecules, while the films are still permeable for hydrogen.

Influence of substrate bias and pressure on microstructure of TiN x films reactively sputtered by cylindrical post magnetron

This contribution analyzes the influence of the bias voltageUb and the total pressure of working gas mixturepTOT=pAr+pN2 on the microstructure of grown TiNx films and the direction of growth of crystallites in the films with respect to the film-substrate interface.