J. Piekoszewski

Generation of high-intensity pulsed ion and plasma beams for material processing

The paper reviews the principles of operation of the present sources of high intensity pulsed ion and plasma beams. Limitations of the ion beam intensity are presented. The concept of magnetic insulation is discussed in some detail. Methods of high-density plasma generation are outlined. Characteristics of the existing devices are listed. It is shown that the existing sources cover a wide range of parameters and can be matched to almost any type of experiment on material processing.

Surface modification of constructional steels by irradiation with high intensity pulsed nitrogen plasma beams

Abstract This paper presents the results of the modification of two types of constructional steels induced by irradiation with multiple pulses of nitrogen plasma generated in two facilities: IBIS (at Swierk, Poland) and PROSVET (at Kharkov, Ukraine). The duration of pulses is in the microsecond range and the energy density attains a value of up to 20 J/cm 2 . The treatment leads to melting and solidification of a surface layer of a thickness of few micrometres, with simultaneous introduction of a significant concentration of nitrogen. Irradiation results in marked improvement of the wear properties. Several analytical techniques such as conversion electron Mossbauer spectroscopy (CEMS), conversion X-ray Mossbauer spectroscopy (CXMS), nuclear reaction analysis (NRA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to reveal the nature of this improvement. Possible mechanisms of modification are discussed. It is concluded that the improvement of the wear properties should be associated with the formation of austenitic fcc γ N phase in which an Fe atom has an interstitial N atom as the nearest neighbour.

Kinetics of the pulsed erosion deposition process induced by high intensity plasma beams

Abstract Intense pulsed ion and/or plasma beams can modify the surface properties of materials by melting their near surface region and doping and/or coating with foreign atoms reaching doses in the order of 10 17 cm −2 in a single pulse. Such processes can be performed using a Rod Plasma Injector (RPI), where plasma pulses are generated as a result of a low-pressure, high current discharge between two concentric, cylindrical sets of rod-type electrodes. The discharge is initiated by a HV pulse applied with a delay time τ d after the moment of injection of working gas into the inter-electrode space. Depending on τ d , two modes of operation are possible. If τ d is sufficiently long, the plasma contains almost exclusively the elements of the working gas (PID mode). For short τ d in addition to the generation of plasma of the working gas rapid erosion of the metallic electrodes also occurs (DPE mode). This metal is deposited and in some cases mixed into the substrate. The aim of the present work was to get insight into the kinetics of the DPE process. Several experiments with different working gases (N, Ar, and Xe), different electrode materials (Ti, W) and substrates (Al 2 O 3 , Cu) were performed. Energy density was approximately 5–7 J/cm 2 and pulse duration was approximately 1 μs, respectively. The two main conclusions have been derived. (a) Metal atoms eroded from electrodes do not undergo ionization and acceleration during the discharge (as it is the case with the working gas). Vapor and low energy ions reach the surface when it is already solidified after being melted first by the working gas plasma. The metallic coating is molten and mixed into the substrate during the subsequent pulse. (b) Erosion of electrodes is caused by some thermal effects as a result of heating by ions and electrons — but not by sputtering.

Irradiation of silicon with a pulsed plasma beam containing Mo ions

Abstract This paper presents preliminary results of a new approach to forming a refractory metal (Mo) layer on Si, using intense pulses of Mo-N plasma. The new approach overcomes an inherent difficulty of mixing two materials with dissimilar surface tensions in the liquid state when using proton beam pulses for melting the predeposited surface layer of a refractory metal. Previous attempts to mix a refractory metal with Si using the latter pulses were unsuccessful owing to a tendency of the pulse-melted refractory metal layer to collect into droplets and splash off. Since in the new approach the plasma-borne Mo atoms “sink” in the molten Si layer, there is no opportunity for them to form a separate Mo layer and an effective mixing between Mo and Si takes place. This mixing is demonstrated by the Mo in Si profiles obtained by Auger electron spectroscopy.

Resistance to high-temperature oxidation in B+Si implanted TiN coatings on steel

Moulds for light-alloy die casting are usually made of TiN-coated AISI H13 tool steel. During operation the moulds undergo wear caused (among others) by high-temperature corrosion (oxidation). Recently it has been shown that Ti-Si-B-N coatings prepared by reactive sputtering from multi-element Ti-Si-B targets exhibit excellent resistance to high-temperature corrosion, and that such resistance can also be obtained by ion implantation of Si and B into TiN coating on H13 steel. However, the B-ion beam cannot be produced in MEVVA-type ion sources. Therefore an attempt was made to improve the high-temperature oxidation resistance of the TiN coating by implanting Si ions alone. Thermogravimetry measurements show that 1×1017 cm−2 Si ions implanted from modified MEVVA-type ion source operated at 75 kV results in more than twofold reduction of the oxidation rate at 630¼.

Intense plasma pulses: two modes of the use for surface processing purposes

The stainless steel substrates AISI321 were irradiated with high intensity pulsed plasma beams containing copper and nitrogen ions at various proportions. The mass change, the total copper content and elemental composition of the surface layer were examined. An effective mixing of Cu and N atoms with the substrate material accompanied by mass ablation has been revealed for N rich plasma beams. Also, an evidence of segregation effects caused by pulse melting has been found. The origin of the observed ablation effect is discussed in terms of evaporation and sputtering mechanisms.

Pulse implantation doping - concentration profiles and surface morphology

Abstract A new method of doping semiconductions in which the implantation and damage annealing processes are reduced to a single-step operation owing to the use of a high-power pulsed plasma beam is described. We present the results of SIMS boron profile measurements, obtained at various pulse-energy density level and discuss them in terms of the surface melting model. The changes observed on the sample surface using an electron microscope also confirm the effect of melting. Some previous results on the RBS spectra of the processed samples and on their electrical parameters are also included.

Deposition and mixing of cobalt, titanium and tungsten on the pulse melted surfaces of substrates

A new method for the formation of thin metallic coatings on steel substrates is demonstrated. The method is based on the use of high intensity plasma pulses. Depending on the choice of operational conditions of the plasma pulse generator, it is possible to form pulses containing either both nitrogen and metal plasma or pure metallic plasma. In the present experiments plasma pulses of Ti, Co and W, are used. The feasibility of a two-step process is shown. In the first step there is a mixing of deposit-substrate components induced by melting and mutual diffusion. In the second one, there is a deposition of the metal coating of practically unlimited thickness on the intermediate mixed layer.

Alloying the near Surface Layer of Stainless Steel with Rare Earth Elements (REE) Using High Intensity Pulsed Plasma Beams (HIPPB)

Addition of some active elements such as yttrium, cerium, lanthanum and other rare earths elements (REE) to austenitic stainless steels helps to improve their high temperature oxidation resistance and tribological properties. The high intensity plasma pulses were used to introduce Ce and La into AISI 316L austenitic stainless steel. The plasma pulses contained both ions/atoms of Ce-La and those of the working gas. The pulse energy densities were sufficient to melt the near surface layer of the steel and introduce those elements into the surface layer. Scanning electron microscopy (SEM) as well as energy dispersion spectroscopy (EDS) was used during each one part of surface characterisation. Obtained results allowed us to make decision about directions of modified material successive investigations.