Pulsed High Energy Density Plasma Research Articles

Multi-angle multi-pulse time-resolved Thomson scattering on laboratory plasma jets.

A single channel sub-nanosecond time-resolved Thomson scattering system used for pulsed power-driven high energy density plasma measurements has been upgraded to give electron temperatures at two different times and from two different angles simultaneously. This system was used to study plasma jets created from a 15 μm thick radial Al foil load on a 1 MA pulsed power machine. Two laser pulses were generated by splitting the initial 2.3 ns duration, 10 J, 526.5 nm laser beam into two pulses, each with 2.5 J, and delaying one relative to the other by between 3 and 14 ns. Time resolution within each pulse was obtained using a streak camera to record the scattered spectra from the two beams from two scattering angles. Analysis of the scattering profile showed that the electron temperature of the Al jet increased from 20 eV up to as much as 45 eV within about 2 ns by inverse bremsstrahlung for both laser pulses. The Thomson scattering results from jets formed with opposite current polarities showed different laser heating of the electrons, as well as possibly different ion temperatures. The two-angle scattering determined that the electron density of the plasma jet was at least 2 × 1018 cm-3.

Publisher's Note: "Talbot-Lau x-ray deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments (invited)" [Rev. Sci. Instrum. 87, 11D501 (2016)

Publisher's Note: "Talbot-Lau x-ray deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments (invited)" [Rev. Sci. Instrum. 87, 11D501 (2016)

Talbot-Lau x-ray deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments (invited).

Talbot-Lau X-ray deflectometry (TXD) has been developed as an electron density diagnostic for High Energy Density (HED) plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single Moiré image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grating survival and electron density mapping were demonstrated for 25-29 J, 8-30 ps laser pulses using copper foil targets. Moiré pattern formation and grating survival were also observed using a copper x-pinch driven at 400 kA, ∼1 kA/ns. These results demonstrate the potential of TXD as an electron density diagnostic for HED plasmas.

Hard TiCx/SiC/a-C:H nanocomposite thin films using pulsed high energy density plasma focus device

Thin films of TiCx/SiC/a-C:H were synthesized on Si substrates using a complex mix of high energy density plasmas and instability accelerated energetic ions of filling gas species, emanated from hot and dense pinched plasma column, in dense plasma focus device. The conventional hollow copper anode of Mather type plasma focus device was replaced by solid titanium anode for synthesis of TiCx/SiC/a-C:H nanocomposite thin films using CH4:Ar admixture of (1:9, 3:7 and 5:5) for fixed 20 focus shots as well as with different number of focus shots with fixed CH4:Ar admixture ratio 3:7. XRD results showed the formation of crystalline TiCx/SiC phases for thin film synthesized using different number of focus shots with CH4:Ar admixture ratio fixed at 3:7. SEM results showed that the synthesized thin films consist of nanoparticle agglomerates and the size of agglomerates depended on the CH4:Ar admixture ratio as well as on the number of focus shots. Raman analysis showed the formation of polycrystalline/amorphous Si, SiC and a-C for different CH4:Ar ratio as well as for different number of focus shots. The XPS analysis confirmed the formation of TiCx/SiC/a-C:H composite thin film. Nanoindentation results showed that the hardness and elastic modulus values of composite thin films increased with increasing number of focus shots. Maximum values of hardness and elastic modulus at the surface of the composite thin film were found to be about 22 and 305GPa, respectively for 30 focus shots confirming the successful synthesis of hard composite TiCx/SiC/a-C:H coatings.

Gas pressure dependence of composition in Ta–Ti–N films prepared by pulsed high energy density plasma

Tantalum titanium nitride (Ta–Ti–N) films were deposited on silicon wafer substrates by pulsed high energy density plasma (PHEDP), under different intake gas pressures, ranging from 0.1 to 0.4 MPa. The films were investigated by X-ray photoelectron spectroscopy. Results were analyzed in detail, which reveals that the contents of the metallic elements (Ta and Ti) tend to decrease with pressure, while that of nitrogen increases as expected. With increasing pressure, the films can be denoted as TaTi 3.9N 2.8, TaTi 4.7N 6.0, TaTi 2.2N 8.4 and TaTi 3.1N1 3.5, respectively. The bonding state of tantalum, titanium, as well as nitrogen was fitted and discussed. Our results demonstrate that almost all the titanium bonded with nitrogen. The Ta–N and Ti–N bonds have equal shares under low gas intake pressure, while the Ti–N bonds prevail under high pressure. The preferential sputtering between the coaxial electrodes should be responsible for this phenomenon. Under low nitrogen pressure, the preferential sputtering is quite significant; while it could be neglected under high pressure.

Nano-indentation and wear-resistance behaviors of TiCN films by pulsed plasma on cemented carbide cutting tool

Titanium carbonitride (TiCN) films were deposited on cemented carbide cutting tool substrates, by pulsed high energy density plasma (PHEDP). A nano-indentation system was employed to measure the nano-harness and Young's modulus of the films prepared under various conditions. The wear behaviors of the films were also investigated. The results show that the samples are significantly hardened, compared with the substrate. And more pulse of discharges creates harder films. On the other hand, the wear-resistance of the as-deposited samples has increased by times. These results strongly suggest that PHEDP is a promising way for fabricating films with good mechanical properties.

(Ti,Al)N Film on Normalized T8 Carbon Tool Steel Prepared by Pulsed High Energy Density Plasma Technique

Under optimized operating parameters, a hard and wear resistant (Ti,Al)N film is prepared on a normalized T8 carbon tool steel substrate by using pulsed high energy density plasma technique. Microstructure and composition of the film are analysed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning electron microscopy. Hardness profile and tribological properties of the film are tested with nano-indenter and ring-on-ring wear tester, respectively. The tested results show that the microstructure of the film is dense and uniform and is mainly composed of (Ti,Al)N and AlN hard phases. A wide transition interface exists between the film and the normalized T8 carbon tool steel substrate. Thickness of the film is about 1000 nm and mean hardness value of the film is about 26 GPa. Under dry sliding wear test conditions, relative wear resistance of the (Ti,Al)N film is approximately 9 times higher than that of the hardened T8 carbon tool steel reference sample. Meanwhile, the (Ti,Al)N film has low and stable friction coefficient compared with the hardened T8 carbon tool steel reference sample.

Characteristics of (Ti,Ta)N thin films prepared by using pulsed high energy density plasma

(Ti,Ta)N films were prepared by pulsed high energy density plasma (PHEDP) from a coaxial gun in N2 gas. The coaxial gun is composed of a tantalum inner electrode and a titanium outer one. Material characteristics of the (Ti,Ta)N film were investigated by x-ray photoelectron spectroscopy and x-ray diffraction. The microstructure of the film was observed by a scanning electron microscope. The elemental composition and the interface of the film/substrate were analysed using Auger electron spectrometry. Our results suggest that the binary metal nitride film, (Ti,Ta)N, can be prepared by PHEDP. It also shows that dense nanocrystalline (Ti,Ta)N film can be achieved.

Preparation of Ta(C)N films by pulsed high energy density plasma

The pulsed high energy density plasma (PHEDP) is generated in the working gas due to a high-voltage high-current discharge, within a coaxial gun. In PHEDP surface modification, discharge is applied for preparing the amorphous and nanostructured high-melting materials as thin films deposited on various substrates. In this investigation, Ta(C)N films were deposited using PHEDP on stainless steel. Pure tantalum and graphite were used as the inner and outer electrodes of the PHEDP coaxial gun, respectively. Nitrogen was used as the working gas and also one of the reactants. Preliminary study on the films prepared under different conditions shows that the formation of Ta(C)N is drastically voltage dependent. At lower gun voltage, no Ta(C)N was detected in the films; when the gun voltage reaches or exceeds 3.0 kV, Ta(C)N occurred. The films are composed of densely stacked nanocrystallines with diameter less than 30 nm, and some grains are within 10 nm in diameter.

Structure of the Coatings onto Ceramic Cutting Tools Deposited by Pulsed High Energy Density Plasma

With a newly-developed technique, pulsed high energy density plasma (PHEDP), TiN, TiCN, and (Ti,Al)N coatings were deposited onto silicon nitride and cemented carbide cutting tools. The structures of these coatings were systematically investigated in this paper. The average surface roughness (Ra) of the coated tools were ranged in 20~150 nm. The smooth surface of coated tools means that the coatings are promising candidate for cutting tools of high precision and it is in favor of reducing the fiction coefficients and flank wear of tools. The coating thickness varied, in the range of 3~20 µm, with the deposition conditions of the shot number of pulsed plasma, and the voltages between the inner and outer electrodes of the coaxial gun. The coating has a densified structure compared to the substrate structure and almost no pores and cracks exist in the coating surface. The grain sizes of the coating were small (<100nm), much finer than those of the substrate (>2 µm). Except for TiN-Si3N4 system, no apparent columnar grain structure as presented predominantly in typical vapor deposited coatings was observed. In fact, an equiaxed structure was presented, due to the pulsed mode of plasma bombardment and solid solution strengthening of C or Al into TiN lattices, resulting in disruption, through renucleation, of epitaxy on individual columns. A continuous and densified interface was observed. All these characteristics in structures promised an excellent performance of the coated tools.

Investigation on the Modification Methods to Ceramic Cutting Tools

There are too many methods to enhance the performance of ceramic cutting tools. All the methods can be sorted into two types: inner modification and surface modification. One of the main method to the inner modification of ceramic cutting tools is dispersion strengthening. Usually, in order to enhance the performance of ceramic cutting tools, some dispersed phases of TiN, TiC or TiCN, Al2O3, and/or ZrO2, and so on, and/or some whiskers, or fibers were added into the ceramic matrixes. And the new types of cutting tools, which possessed much more excellent performance than the original ones, were called composite ceramic cutting tools. For the composite Si3N4-based ceramic, Al2O3-based ceramic, and TiCN-based cermet, the cutting efficiency could be enhanced to 3~10 times, compared with cemented carbide tools. And they can be used for rough and finish machining of various cast iron workpieces and hardened steels, respectively, including milling and planning. Ion implantation is a surface modification for ceramic cutting tools. With certain doses of metals, for example, titanium, zirconium and chromium, and so on, implanted into the ceramics, the hardness, Young’s modulus, fractural toughness, and bending strength, etc., can be enhanced. For Al2O3 and Si3N4 ceramics, the hardness, Young’s modulus, and bending strength increased with a maximum factor of 50%, and the flank wear decreased with a factor of 2~12, compared with the unimplanted ceramic cutting tools. However, the main shortcoming of ion implantation to modify ceramics is the thickness of modified layers. They are, usually, too thin for cutting tools. The so-called PHEDP, pulsed high energy density plasma, is another surface modification method for ceramic cutting tools proposed recently. With such method, much thicker coatings of TiN, TiCN and (Ti,Al)N, etc, were deposited onto Si3N4 and WC ceramic cutting tools.The main merits involved in high hardness and Young’s modulus of the coatings, low residual stresses, and good adhesive strength between the coatings and substrates. And the flank wear of the as-depositedtools decreased with a factor of 5~10.

Titanium carbonitride films on cemented carbide cutting tool prepared by pulsed high energy density plasma

Hard films prepared by pulsed high energy density plasma (PHEDP) are characterized by high film/substrate adhesive strength, and high wear resistance. Titanium carbonitride (TiCN) films were deposited onto YG11C (ISO G20) cemented carbide cutting tool substrates by PHEDP at room temperature. XRD, XPS, SEM, AES, etc. were adopted to analyze the phases (elements) composition, microstructure and the interface of the films, respectively. The results show that, the uniform dense films are composed of grains ranging from 70 to 90 nm. According to the AES result, there is a broad transition layer between the film and the substrate, due to the ion implantation effect of the PHEDP. The transition layer is favorable for the film/substrate adhesion.

Preparation of silicon carbide nitride films on Si substrate by pulsed high-energy density plasma

Thin films of silicon carbide nitride (SiCN) were prepared on (111) oriented silicon substrates by pulsed high-energy density plasma (PHEDP). The evolution of the chemical bonding states between silicon, nitrogen and carbon was investigated as a function of discharge voltage using X-ray photoelectron spectroscopy. With an increase in discharge voltage both the C 1s and N 1s spectra shift to lower binding energy due to the formation of C Si and N Si bonds. The Si C N bonds were observed in the deconvolved C 1s and N 1s spectra. The X-ray diffractometer (XRD) results show that there were no crystals in the films. The thickness of the films was approximately 1-2 μm with scanning electron microscopy (SEM).

Microstructure and Wear Behaviour of WC Film Prepared byPulsed High Energy Density Plasma

A super hard and wear resistant WC film is in-situ prepared on a0.45% C steel substrate by pulsed high energy density plasma techniqueat ambient temperature. The microstructure and composition of the filmare analysed by x-ray diffraction, x-ray photoelectron spectroscopy,Auger electron spectroscopy and scanning electron microscopy. Thehardness profile and tribological behaviour of the film are determinedwith nano-indenter and wear tester, respectively. The results show thatthe microstructure of the film was dense and uniform and mainlycomposed of WC and a small amount of W2C. A wide mixinginterface exists between the film and the 0.45%C steel substrate. Thethickness of the film is about 2 μm. The hardness and Yang's modulus ofthe film are very high. The film has excellent wear resistance and lowfriction coefficient under dry sliding wear test conditions.

Study on the microstructure and properties of (Ti, Al)N film deposited by pulsed high energy density plasma

Hard and corrosion resistance (Ti, Al)N film was deposited by pulsed high energy density plasma on the substrate of 045% C carbon steel at ambient temperature. The microstructure of the film has been investigated by SEM,XRD,XPS and AES. The nanohardness of the film was tested by nanoindentation tester. The corrosion resistance of the film was tested by potentiodynamic polarization in 05 mol /L H2SO4 aqueous solution. The results indicate that the film mainly composed of (Ti, Al)N and a small amount of AlN. The nanohardness of the film approaches 26 GPa. The corrosion resistance of the film is improved by about one order of magnitude, compared with 1Cr18Ni9Ti austenitic stainless steel.

Nanometer grain titanium carbonitride coatings with continuously graded interface onto silicon nitride cutting tools by pulsed high energy density plasma

Nanometer grain ternary Ti(C,N) coatings of excellent mechanical properties with continuously graded surface onto Si3N4 cutting tools were deposited at room temperature via a newly developed equipment, pulsed high energy density plasma coaxial gun. The maximum critical load by nanoscratch tests of the coatings onto Si3N4 substrates is approximately 100 mN. The maximum hardness of the coatings is more than 50 GPa by nanoindentation tests. Compared with the uncoated tools, the tribological properties of the coated tools, which were evaluated by the cutting performances in turning hardened CrWMn steel under industrial conditions, were improved dramatically with the flank wear reduced by a factor of 6-8. (C) 2004 Elsevier B.V. All rights reserved.

Ti(C,N) Hard Coatings Prepared by Pulsed High Energy Density Plasma

A new technique, namely pulsed high energy density plasma, has been developed to deposit hard coating of metals and various compound materials on ceramic and metal substrates. In this system, the plasma density was in the range of 10(14)-10(16) cm(-3) in the glow discharge space; the electron temperature was in the range of 10(5)-10(6) K; the power density was varied from 10 5 to 101 W(.)cm(-2); the pulse width is about 60 mus and the pulse frequency is 10(-2) s(-1). In this study, Ti(C,N) hard coatings were deposited on Si3N4 ceramic cutting tool substrates at room temperature, resulting coatings with high hardness and excellent adhesion to the substrates. The adhesion force of the Ti(C,N) coatings is in the range of 80-100 mN measured by nanoscratch tests, and the nanohardness of the coatings varied from 40 GPa to 50 GPa as measured by a nanoindenter. The tribological properties and the cutting performances of the coated tools were evaluated by turning HT 250 (HB230) steel under industrial conditions. The wear resistance and edge life of the tools were improved dramatically because of the deposition of Ti(C,N) coatings. From the structural analyses, these improvements were attributed to a combination of three effects: deposition, ion implantation and quenching.

Preparation of titanium nitride films by pulsed high-energy-density plasma and investigation of the tribological behavior of the film

Supper hard and wear resistant titanium nitride films were deposited onto 0.45% carbon steel substrate by pulsed high-energy-density plasma(PHEDP) technique at ambient temperature. The microstructure, surface compositions and depth profile of the film were analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM).The hardness profile and tribological behavior of the film were determined with nano-indenter and MM200 wear tester, respectively. The results showed that the microstructure of the film was dense and uniform and mainly composed of titanium nitride phases. A wide mixing interface existed between the film and the substrate. The film possessed a very high value of nanohardness. The wear resistance of the film was excellent and the value of the friction coefficient of the film was low under dry sliding wear test conditions.

Microstructure and mechanical properties of titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard, wear-resistant and well-adhesive titanium nitride coatings on cemented carbide cutting tools were prepared by the pulsed high energy density plasma technique at ambient temperature. The results of Auger spectra analysis indicated that the interface between the coating and substrate was more than 250 nm. Under optimized deposition conditions, the highest critical load measured by nanoscratch tester was more than 90 mN, which meant that the TiN film was well adhesive to the substrate; the highest nanohardness and Young’s modulus according to nanoindentation tests were near to 27 and 450 GPa. The results of cutting tests evaluated by turning hardened CrWMn steel in industrial conditions indicated that the wear resistance and edge life of the cemented carbide tools were enhanced dramatically because of the deposition of titanium nitride coatings. These improvements were attributed to the three combined effects: the deposition and ion implantation of the pulsed plasma and the becoming finer of the grain sizes.

Hard and wear-resistant titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard and wear-resistant titanium nitride coatings were deposited by pulsed high energy density plasma technique on cemented carbide cutting tools at ambient temperature. The coating thickness was measured by an optical profiler and surface Auger microprobe. The elemental and phase compositions and distribution of the coatings were determined by Auger microprobe, x-photon electron spectroscope, and X-ray diffractometer. The microstructures of the coatings were observed by scanning electron microscope and the roughness of the sample surface was measured by an optical profiler. The mechanical properties of the coatings were determined by nanoindentation and nanoscratch tests. The tribological properties were evaluated by the cutting performances of the coated tools applied in turning hardened CrWMn steel under industrial conditions. The structural and mechanical properties of the coatings were found to depend strongly on deposition conditions. Under optimized deposition conditions, the adhesive strength of TiN film to the substrate was satisfactory with the highest critical load up to more than 90 mN. The TiN films possess very high values of nanohardness and Young’s modulus, which are near to 27 GPa and 450 GPa, respectively. The wear resistance and edge life of the cemented carbide tools were improved dramatically because of the deposition of titanium nitride coatings.