Insights into surface modification and erosion of multi-element arc cathodes using a novel multilayer cathode design
16 Mar 2020-Journal of Applied Physics (AIP Publishing LLCAIP Publishing)-Vol. 127, Iss: 11, pp 113301
TL;DR: In this paper, a 10'μm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots.
Abstract: Nowadays, multi-element cathodes are frequently employed to grow multi-element thin films and coatings using cathodic arc deposition processes. During cathode erosion, the cathode spot sequentially ignites on the cathode surface and imposes melting–solidification cycles that lead to material intermixing and the formation of a modified layer on the cathode surface. To allow us to study these surface modifications, a 10 μm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode. This cathode was eroded by a dc steered arc discharge for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots. Furthermore, separated clusters of overlapping craters and a fully eroded surface caused by different stages of erosion were differentiated when scanning the erosion track in the lateral direction. Cross sections of single craters were prepared by focused ion beam techniques while metallographic methods were applied to obtain cross sections of overlapping craters and the modified layer. The layers of the multilayer coating acted as trace markers providing new insights into the material intermixing within craters, the material displacements during crater formation, the plasma pressure acting on the craters, and the temperature gradient (heat-affected zone) below the craters. The observations are discussed within the framework of established arc crater formation models.
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TL;DR: In this paper, the surface modified composite cathode is a promising candidate in alleviating arc ablation while retaining the matrix conductivity, and the arc discharge behaviors of BL Zr/Cu cathodes were investigated in the air atmosphere.
Abstract: The surface-modified composite cathode is a promising candidate in alleviating arc ablation while retaining the matrix conductivity. In this work, mono-layered (ML) and bi-layered (BL) Zr/Cu claddings were prepared on the copper substrate through laser cladding. The arc ablation behaviors of BL Zr/Cu cathodes were investigated in the air atmosphere compared to ML Zr/Cu cathodes. The surface zirconium contents for the ML and BL Zr/Cu cathodes are 5.42 at.% and 65.91 at.%, respectively. The high-dilution Zr/Cu cladding serves as the intermediate buffer layer and promotes metallurgical bonding between the cladding and the matrix. The tight interlayer bonding is well maintained after long-term arc discharge. Cathode arc discharge homogeneity is improved as the surface zirconium content increases. The arc ablation rate of the BL Zr/Cu cathode (1.28 μg C−1) is 39.0% lower than that of the ML Zr/Cu cathode (2.10 μg C−1). The improved arc discharge behaviors are attributed to the surface ZrO2 layer. The ZrO2 layer homogenizes the arc discharge process with generating type 1 cathode spots while the copper matrix conducts the input energy flux. The layered structure realizes a combination of ablation-resistant surface and conductive matrix, which enhances the service life of the cathode.
9 citations
TL;DR: In this article, the dynamics of phase changes in the material of a copper cathode during the explosion of a microprotrusion on its surface under the action of the explosive electron emission current has been numerically simulated.
Abstract: The dynamics of phase changes in the material of a copper cathode during the explosion of a microprotrusion on its surface under the action of the explosive electron emission current has been numerically simulated. Numerical data have been obtained that characterize the interaction of the liquid metal and the dense cathode plasma that are formed due to the microprotrusion explosion. It has been shown that, under the action of the pressure exerted by the plasma, the liquid metal is almost completely displaced from the zone of operation of the cathode spot of the vacuum discharge. This leads to the formation of a crater on the cathode surface with microirregularities at its edge. Thus conditions are created for the formation of new microprotrusions, which, when exploding, provide self-sustained and cyclic operation of the vacuum discharge.
9 citations
TL;DR: In this article , the effect of a second MeN layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties was reported.
Abstract: Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W2N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W2N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10−6 mm3/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb2O5 and WO3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions.
7 citations
TL;DR: In this paper, a multilayer cathode design was used to reveal temporal and spatial progress of cathode spots by enabling three-dimensional visualization of the craters left behind on the cathode surface.
Abstract: The cathode spot behavior influences the arc plasma chemistry and film growth conditions during reactive cathodic arc deposition of nitride and oxide films. Cathode spots can be studied using their characteristic craters left behind on the cathode surface. The multilayer cathode design used in this study reveals temporal and spatial progress of cathode spots by enabling three-dimensional visualization of the craters. The surface nitridation or oxidation of the cathode, also known as cathode poisoning, was found to give rise to a repeated switching between cathode spots of type 1 and 2. The surface oxide layers, however, more significantly promote the ignition of type 1 spots due to their thermodynamically privileged formation and/or their more favorable physical properties building up a stronger electric field within the insulating layer. The crater depths and their contribution to the surface modification of multilayered cathodes are discussed in detail. These results may contribute to a better understanding of macroparticle generation and arc plasma properties in cathodic arc deposition processes.
7 citations
TL;DR: A combination of both conventional and advanced high-resolution characterization techniques was applied to study the modified layers on the surface of three composite Al-Cr arc cathodes with identical nominal composition of Al-50 at.% Cr but varying powder grain sizes.
5 citations
References
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TL;DR: In this paper, a review of arc cathode spots, mainly based on the investigation of arcs in a vacuum with cold cathodes, is given, and experiments are presented that study the temporal and spatial behaviour of the spots with high time and space resolution of less than 10 ns and less than 5 µm, respectively.
Abstract: A review is given on arc cathode spots, mainly based on the investigation of arcs in a vacuum with cold cathodes. For the latter and after a short description of general features and theoretical concepts, experiments are presented that study the temporal and spatial behaviour of the spots with high time and space resolution of less than 10 ns and less than 5 µm, respectively. With the help of these observations the various spot types described in the literature are ordered into three levels: level A corresponding to the proper spot with typical diameters of 50-100 µm, level B associated with spot fragments having a size of 10-20 µm and level C comprising a substructure of the fragments. The structures undergo periodic fluctuations of brightness and position with characteristic times that can be arranged in a hierarchy from a few nanoseconds through about 100 µs. The analysis of these fluctuations shows that the spot operates in cycles that include both extremely non-stationary periods with time constants of less than 10 ns and more stationary periods in the microsecond range. In the presence of an external magnetic field, the latter periods lead to unstable plasma configurations that give rise to retrograde motion. Finally, for vacuum arc spots the basic parameters are summarized. After that, the peculiarities of spots in gases with cold electrodes are discussed, followed by a presentation of spots with hot cathodes at high pressures.
362 citations
TL;DR: In this paper, the influence of three magnetic field configurations on the kinetic energy has been investigated, and it has been found that the kinetic ion energy is higher at the beginning of each discharge and approximately constant after 150 μs.
Abstract: Because plasma production at vacuum cathode spots is approximately proportional to the arc current, arc current modulation can be used to generate ion current modulation that can be detected far from the spot using a negatively biased ion collector. The drift time to the ion detector can used to determine kinetic ion energies. A very wide range of cathode materials have been used. It has been found that the kinetic ion energy is higher at the beginning of each discharge and approximately constant after 150 μs. The kinetic energy is correlated with the arc voltage and the cohesive energy of the cathode material. The ion erosion rate is in inverse relation to the cohesive energy, enhancing the effect that the power input per plasma particle correlates with the cohesive energy of the cathode material. The influence of three magnetic field configurations on the kinetic energy has been investigated. Generally, a magnetic field increases the plasma impedance, arc burning voltage, and kinetic ion energy. However, if the plasma is produced in a region of low field strength and streaming into a region of higher field strength, the velocity may decrease due to the magnetic mirroreffect. A magnetic field can increase the plasma temperature but may reduce the density gradients by preventing free expansion into the vacuum. Therefore, depending on the configuration, a magnetic field may increase or decrease the kinetic energy of ions.
351 citations
TL;DR: In this article, the Debye-H{umlt u}ckel approximation of the nonideal plasma for all metals of the Periodic Table and for boron, carbon, silicon, and germanium was calculated under the assumption that the spot plasma experiences an instantaneous transition from equilibrium to nonequilibrium while expanding.
Abstract: Vacuum arc plasmas are produced at micrometer-size, nonstationary cathode spots. Ion charge state distributions (CSD{close_quote}s) are experimentally known for 50 elements, but the theoretical understanding is unsatisfactory. In this paper, CSD{close_quote}s of vacuum arc plasmas are calculated under the assumption that the spot plasma experiences an instantaneous transition from equilibrium to nonequilibrium while expanding. Observable charge state distributions are the result of a freezing process at this transition. {open_quotes}Frozen{close_quotes} CSD{close_quote}s have been calculated using Saha equations in the Debye-H{umlt u}ckel approximation of the nonideal plasma for all metals of the Periodic Table and for boron, carbon, silicon, and germanium. The results are presented in a {open_quotes}periodic table of CSD.{close_quotes} The table contains also the mean ion charge state, the neutral vapor fraction, and the effective plasma temperature and density at the freezing point for each element. The validity of the concepts of {open_quotes}instantaneous freezing{close_quotes} and {open_quotes}effective temperature and density{close_quotes} is discussed for low and high currents and for the presence of a magnetic field. Temperature fluctuations have been identified to cause broadening of CSD{close_quote}s. {copyright} {ital 1997} {ital The American Physical Society}
302 citations
TL;DR: In this article, a time-of-flight diagnostic was used to monitor the energetic ion beam produced by a metal vapor vacuum arc ion source. The arc was operated in a pulsed mode with pulse length 0.25 ms: arc current was 100 A throughout.
Abstract: Vacuum arc ion charge-state spectra have been measured for a wide range of metallic cathode materials. The charge-state distributions were measured using a time-of-flight diagnostic to monitor the energetic ion beam produced by a metal vapor vacuum arc ion source. Data were obtained for 48 metallic cathode elements: Li, C, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn Fe, Co, Ni, Cu, Zn, Ge, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er Yb, Hf, Ta, W, Ir, Pt, Au Pb, Bi, Th, and U. The arc was operated in a pulsed mode with pulse length 0.25 ms: arc current was 100 A throughout. The measured distributions are cataloged and compared with earlier results. Some observations about the performance of the various elements as suitable vacuum arc cathode materials are also presented. >
206 citations