This work evaluates the microstructure and composition of zirconia films produced by thermal plasma chemical vapor deposition (TPCVD). The results show that TPCVD has the potential to produce durable ceramic films with columnar structure, even in open air. Paper includes a German-language abstract.

In this paper, spectroscopic and electrostatic probe measurements are made to examine the characteristics of a supersonic dc plasma jet near the surface of titanium plate during a nitriding treatment. The low-pressure nitriding process is done using a mixture of ammonia, nitrogen, and hydrogen gasses. Heating effects from the plasma are evaluated with nickel slug and thermocouple attached to the plate. The authors present the results of their study along with observations, insights, and suggestions on how to improve plasma nitriding processes. Paper includes a German-language abstract.

Electromagnetic acceleration plasma generators, which are called Magneto-Plasma-Dynamic (MPD) arcjet generators, can produce higher-velocity, higher-temperature and higher-density plasmas than those of conventional thermal plasma torches, because MPD arcjet plasma is efficiently accelerated by electromagnetic body forces in MW-class input power operation. These properties are effective for deposition of rigid coatings adhering strongly to substrate surfaces. In the present study, we newly developed an ablation type MPD arcjet generator for titanium nitride (TiN) reactive spray coatings. The coatings were deposited onto steel substrate. The phase structure and the composition of the coatings were analyzed by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their Vickers hardness were measured. These analyses showed that the MPD spray process could successfully form dense and uniform titanium nitride coatings. The properties of the titanium nitride coatings were highly sensitive to the titanium cathode diameter and discharge current.

Spectroscopic and electrostatic probe measurements were carried out to understand the plasma feature inside and outside a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle. Ammonia and a mixture of nitrogen and hydrogen were used as the working gas. The NH3 and N2+3H2 plasmas in the throat were expected to be nearly in a temperature-equilibrium condition, although the plasmas in the expansion nozzle and in the downstream plume without substrate plates were in thermodynamical nonequilibrium states. As a result, the H-atom excitation temperature and the N2 rotational excitation temperature decreased from 7000-11000 K in the throat to about 4000 K and to 1000-1500 K, respectively, on the nozzle exit at 0.1-0.2 g/s, although the NH rotational temperature did not show an axial decrease even in the nozzle. On the other hand, each temperature was almost kept a small range in the downstream plume without substrate plates under an ambient pressure of 130 Pa except for the NH rotational temperature for NH, working gas, although in the case with a titanium plate the nonequilibrium plasma came to a temperature-equilibrium one as approaching the plate.

Since plasma jets, which have been used as heat sources of thermal plasma spraying process, expand adiabatically under a low pressure environment, the plasma temperatures drastically fell down to 2000K at the nozzle out let at 30Pa chamber pressure. However, the plasma jets still had enough reactivity to form hard nitride layer on the surface of the titanium samples by only a few minutes treatment. In this study, in order to obtain useful information for the practical applications of this plasma as low temperature and high rate surface modification processes, nitriding of nitriding steel and carbon steel using supersonic expanding hydrogen/ nitrogen mixture plasma jets were carried out. Consequently, though surface hardening was occurred slightly in the case of carbon steel, surface hardening was obviously promoted in the case of nitriding steel. In both cases, surface hardening was promoted with increasing hydrogen flow rate and thermal damages of the samples due to heat transfer from plasma jets weren't observed. Besides, according to the results of wear testing, wear mass loss of nitrided samples were much lower than that of non-nitrided samples. From these results, this process was found to have a high potential even in the case of surface modification of steel materials.

In this paper, as a basic study of the plasma jet process under a low pressure, the nitriding of titanium plates and atmospheric plasma sprayed titanium coatings are carried out using nitrogen and hydrogen added nitrogen plasma jets at 30Pa. The plasma torch used in this paper is equipped with a supersonic expansion nozzle to improve the acceleration efficiency of plasma jets. The effects of ambient pressures and supersonic expansion nozzles on transformation of plasma particles are examined from gas-dynamical viewpoints. It was observed that from the results, the supersonic plasma jet process under a low pressure was proved to have a high potential for nitriding. Paper includes a German-language abstract.

The quasi-steady magneto-plasma-dynamic (MPD) arcjet generator is a promising plasma accelerator, which has a coaxial electrode structure similar to those of conventional plasma torches. The MPD arcjet generator utilizes principally electromagnetic acceleration of the interaction between the discharge current of kiloamperes and the azimuthal magnetic field induced by the discharge current, although the working gas is accelerated aerodynamically through a nozzle in a thermal arcjet generator. In this paper, ablation-type MPD arcjet generators are developed for ceramic coatings. Discharge voltages and ablation rates of ceramic materials are examined, and front velocities of ablated atoms of ceramic component are also estimated using a streak camera. The Vickers hardness of coating is measured. Their cross sections are observed with a scanning electron microscope, and their surfaces are analyzed by means of x-ray diffraction and x-ray photoelectron spectroscopy. Paper includes a German-language abstract.

Ammonia and a mixture of nitrogen and hydrogen are used for material processing. Since these gases are chemically active, the processing efficiency is enhanced. This article describes a study to understand the physical properties of ammonia and a mixture of nitrogen and hydrogen plasmas inside and outside an arcjet generator. Spectroscopic measurement is made, and several plasma properties are determined from the data. The result shows that the H-atom electronic excitation temperature and the nitrogen rotational excitation temperature decreased from 7000-11000 K in the constrictor to about 4000 K and to 1000-1500 K, respectively, on the nozzle exit with mass flow rates of 0.1-0.2 g/s at input powers of 7-12 kW. However, the NH rotational excitation temperature did not show a significant axial decrease even in the downstream plume. Paper includes a German-language abstract.