A unique process for producing powder whose individual particles contain both chromium carbide and nickel/chromium is discussed. This process involves agglomeration of fine chromium carbide with nickel/ chromium-bearing materials using a proprietary binder system. The agglomerates are subsequently sintered, melted in a plasma flame, and sized. This powder does not exhibit the segregation and inhomogeneity problems associated with conventional mechanical blends of chromium carbide and Nichrome powders. Jet Kote* coatings created from the prealloyed powders have uniform microstructures, high hardnesses, and wear characteristics superior to those of plasma-sprayed coatings from the conventional blends.

Thin ZrO2 -Y2 O3 coatings ranging in composition from 3 to 15 mole % Y2 O3 were produced by rf sputter deposition. This composition range spanned the region on the equilibrium ZrO2 -Y2O3 phase diagram corresponding to partially stabilized zirconia (a mixture of tetragonal ZrO2 and cubic solid solution). Microstructural characteristics and crystalline phase composition of as-deposited and heat treated films (1100°C and 1500°C) were determined by transmission electron microscopy (TEM) and by x-ray diffraction (XRD). Effects of substrate bias (0 ∼ 250 volts), which induced ion bombardment of the film during growth, were also studied. The as-deposited ZrO2-Y2O3 films were single phase over the composition range studied, and XRD data indicated considerable local atomic disorder in the lattice. Films produced at low bias contained intergranular voids, pronounced columnar growth, and porosity between columns. At high bias, the microstructure was denser, and films contained high compressive stress. After heat treatment, all deposits remained single phase, therefore a microstructure and precipitate distribution characteristic of toughened, partially stabilized zirconia appears to be difficult to achieve in vapor deposited zirconia coatings.

Multiple arc discharges enable more than one arc to be operated in close proximity supplied from the same supply. This enables reduced individual electrode current to be used. Multiple electrodes may be used in d.c. arc furnaces and d.c. plasma furnaces for melting, liquid-phase smelting and particulate phase processes. Non-consumable multiple electrodes may be used to replace graphite electrodes in arc furnaces. Other applications include high temperature gas heating and in flight plasma reactions.

Plasma properties as a function of heat conduction are approximated by the power-law relation, for instance, σ= σo (S*/So)nσ. Then, the temperature effect on the dimensionless number is allowed for by a factor, (S*/So)γ, the value of which is estimated by equating the dominant number or the whole set of numbers to unity. Substituting this value into the generalized equation gives the form of the correlation function. A relative contribution of each number, K1, is determined from the comparison of the exponents of the dimensionless numbers with the experimental ones.

Topics discussed: (a) The dissipative structure (DS) composed of the plasma bulk (PB), near-to-surface plasma layer (PL), surface and the adjacent material layer (ML) coupled by mass, electric charge, etc. fluxes and applications to plasma deposition. (b) The transient local dissipative structure (TLDS) formed by a single plasma ion impinging on the surface and associated with sputtering, etc.

In the method described here, oxygen and air plasmas were generated at pressure of 1 – 10 Torr in quartz tube placed inside various kinds of microwave cavieties. Cavieties were supplied by 10 to 500 W of microwave power / f=2.45 GHz /. Processed fiber was fastly moved across the plasma region by special driving system. Experimentally the optimal process conditions, i.e. treatment time and gas pressure, were found. Moreover, a special construction of a “long” plasma reactor for industrial application of the process was worked out.

A system is described for mass spectrometric detection of transient gaseous species involved in reactive plasma deposition of materials. The equipment comprises a three stage differentially pumped UHV quadrupole mass spectrometer chamber, which permits modulated molecular beam sampling over a short path-length, direct from the plasma at 0.1–1.0 torr pressure. Operation of the system and optimum conditions for maximum signal-detection are detailed, and preliminary results for species formed in a silane-argon high-power rf discharge are reported. Spectra mostly agree with those obtained by Turban and Catherine using a lower power rf plasma, although some evidence is observed for the formation of increased SiH species at higher power.

A novel high-temperature plasma tube has been developed that overcomes the meltdown problem of the conventional water- and gas-cooled quartz plasma tubes commonly used. The key feature of this system is the placement of heavywalled, water-cooled copper fingers inside a quartz mantle to shield the mantle from the intense radiation of the plasma. The copper fingers act as transformers to couple the plasma to the applied rf field.

This system has been used to produce ultrafine, ultrapure silicon carbide powder by reaction of silane and methane. Powder of β-SiC has been obtained with a BET surface area of >160 m2 /g and a particle size range of 10 to 20 nm as measured by TEM. Likewise, powder of silicon nitride has been synthesized by reaction of silane and ammonia in the plasma. The resulting powder is approximately 50% Si3N4 with a mixture of α- and β-polymorphic forms. Boron carbide has also been successfully synthesized from diborane and methane.

Optical emission intensities have been measured as a function of composition for silane-argon and silane-hydrogen mixtures used in the deposition of hydrogenated amorphous silicon. It was found that changes in silane fraction have a large effect on the electron concentration and energy distribution in the discharge.

The plasma transferred arc (PTA) process has been traditionally used to deposit wear resistant coatings on iron base alloy substrates, but has not been employed to coat lightweight alloys due to processing problems. In the current study, use of the PTA process to deposit TiC, WC, and Cr3C2 coatings on titanium substrates has been explored. The resistance of these coatings to dry abrasive wear has been measured and compared to that of the base metal. The variation in wear resistance of these coatings is discussed in terms of the carbide particle size and the microstructure of the deposit. A comparison is also made to coatings prepared by a laser surface melting and carbide particle injection process.