Amorphous metallic coatings are of high interest because of their good wear and corrosion resistance as well as their high hardness and toughness relative to the crystalline alloys with the same composition. Thermal spray that makes it possible to reach quenching rates in the order of 106-107 K/s, has the ability to deposit coatings with a high content of amorphous phase. However, very few studies dealt with the understanding of the spraying factors that affect the formation of the amorphous phase under thermal spray conditions. In this work, the relationship between temperature and velocity of the spray particles and coating characteristics is investigated. Special attention is given to the degree of amorphisation of the as-sprayed coatings. The latter were produced both by plasma and wire-arc spraying in order to get a larger range of particle parameters at impact and different particle heating history in the gas flow before impingement onto the substrate. A commercial iron-based alloy available both in powder and wire forms was used. Microstructural analyses show that the as-sprayed coatings are partially amorphous and that the proportion of the amorphous phases depends on the sizes of the sprayed particles as they control the heating and acceleration of particles in the gas flow and their cooling rate on the substrate.

Manufacturing of alloyed cast iron forming rolls is accompanied by generation of valuable solid waste as cutting and grinding swarf. The objective of this investigation was to evaluate the potential for mill debris to be used as a new source of inexpensive powders for thermal spraying of wear resistant coatings. More than 25 high-carbon iron alloy compositions are used in roll production. The structure of these cast irons usually includes from 2 to 4 phases (such as troostite, bainite, needled martensite, austenite, and graphite). The properties of powders obtained from mill debris were characterized in terms of particle size and shape, composition, structure, technological fluidity, and bulk density. The obtained powders were used for plasma spraying of wear resistant coatings. The results indicate that cutting and grinding swarf may be a feasible raw material source for economical alloyed powders, granules, and other materials for coatings. The composite plasma sprayed coatings obtained from powder mixtures of alloyed cast iron and nickel-base alloy have better tribological performance in comparison to coatings from any single powder alloy.

The high velocity oxy-fuel (HVOF) combustion spray technique has been shown previously to be an excellent solution for depositing crystalline matrix nano-reinforced polymer coatings. Dense polymer coatings can be produced by controlling both the particle dwell time in the HVOF jet and through substrate thermal management. In composite materials, it is often desirable to incorporate the maximum amount of reinforcing material into the polymer matrix to achieve optimum mechanical properties. The experiments described here were performed to determine the maximum amount of different scales of silica particles that could be incorporated into a nylon 11 matrix and the time required to do so. Ashing results indicated a maximum amount of silica that can be incorporated. Also, the maximum level of silica incorporation occurs in a shorter time than previously believed. Microscopy, however, indicated that other physical changes continued to occur within the powders when ball milling was allowed to continue beyond this time.

A wide range of manufacturing processes are used to supply yttria stabilized zirconia powders for plasma sprayed TBC applications. From previous studies it is known that the difference in coating properties can potentially result from variations in powder feedstock as a consequence of particle inflight behavior and particle impact. An additional strong contribution to splat variation results from changes in the particle in flight behavior. In order to understand the variation in particle condition as a consequence of different powder morphologies, a detailed diagnostic analysis was carried out for plasma densified (PD), fused and crushed (FC) and agglomerated & sintered (A&S) powders. In this study a “3D multiple sensors” based integrated approach was used to evaluate these differences. Direct feed back sensors were used for optimization and combined with sophisticated diagnostics for in-depth studies. To obtain comparable results, three batches of commercial powders were sized to the same specification. For a given set of spraying parameters the recorded spray stream characteristics such as plume position, particle temperature, size and velocity deviated strongly for the given morphologies. By optimizing injection, the different powders can be made to follow nominally similar trajectories. This study reveals the sensitivity of each powder to process parameters and the variability in particle state that can result from it. Some techniques are suggested to optimally inject the different powders and to achieve similar particle states for these morphologies

Two directions characterize the advances being made in thermal spraying today. On the one hand, the spray processes are becoming colder, as with cold spraying which facilitates the production of oxide-free coatings in the atmosphere. On the other hand, high-performance systems are being developed which enable a higher powder throughput, thus making production faster and more efficient. This development has made it more important than ever to maintain this time-saving advantage and not lose it as a result of cooling intervals. More and more applications require the use of CO 2 as a cooling medium to increase the cooling efficiency and, in turn, optimize the process. An ongoing objective of the gas industry is to offer the user hardware which not only exploits all the advantages of CO 2 , but which is also suited to new applications.