COMPARISON OF Mo COATING DEPOSITED BY TWAS AND APS SinplexPro THERMAL SPRAY TECHNIQUES

The wear resistant Mo coatings were deposited using SmartArc Electric Arc Wire Spray System and advanced SinplexPro high throughput atmospheric plasma spray gun. The coatings were analyzed in terms of microstructure, mechanical properties and tribological characteristics, including wear rate and wear mechanism. It was shown that despite of the differences in deposition process principles, the properties of the coatings don’t differ with respect to their functional properties. Both coatings reached comparable hardness, microhardness, wear resistance and coefficient of friction. The economic aspects remain the main argument for the recommendation of the most suitable thermal spray deposition technique for the application of molybdenum coatings.

Research and Application Status of Atmospheric Plasma Spray Torch in Internal Feedstock Mode

In comparison with typical external feedstock mode, powders internal injecting method can effectively enhance plasma sprayed ceramic coatings performance and improve powder deposition efficiency. In this feedstock mode, spray powders were injected into the hotter regions of a plasma jet, which had enough heat capacity to melt most of the particles instantly. Currently, several plasma spray guns in internal feedstock mode, such as Axial III and SG100, have been developed and commercialized. In this paper, characteristics of plasma spray guns in internal and external feedstock methods were summarized. And the research status of the plasma spray torch in internal feedstock mode was particularly presented. Finally, the development trend of different feedstock modes adopted by plasma spray gun was discussed.

Motion Analysis of Powder Particle in Plasma Jet

In order to do research on the motion time of plasma spray gun in powder particle flame plating, the paper made an analog computation to powder particle motion process of plasma spray gun by establishing powder particle equation of motion and thermal evolution equation, after that the motion time of powder particle in electric arc was obtained. It provided advantageous theoretical basis for plasma spray gun design after confirming the computation results by making use of high-speed photography technology.

Performance Evaluation of Hydroxyapatite Coatings Thermally Sprayed on Surgical Fixation Pins

Today, in the period of one year, in Brazil and throughout world, hundreds of thousands of surgical implants, both permanent and temporary, are carried out with a high cost for the patients, especially those of SUS – Sistema Único de Saúde. In addition, the SUS costs for treatment of infections that appear as a result of introduction of an implant into the human body create expenses about three times greater than the use of implants coated with biomaterials. Hydroxyapatite (HA) constitutes the base of one important group of biomaterials with excellent implant characteristics. Hydroxyapatite has been extensively studied, but the adherence relationship at the coating/substrate interface is not yet well understood. The coatings in this study were produced using substrates of AISI 316L stainless steel shaped as external fixation pins, with HA applied by a high energy plasma spray gun (HEP). The coating thicknesses were between 15µm and 98µm. The mechanical evaluation of coating adhesion was conducted by scratch testing with progressive loads. Results show an increase of failure load with an increase in thickness. The clinical evaluation was carried out in the Trauma and Orthopedics Sector of the Baleia Hospital, and shows a significant decrease in inflammatory response in the human body.

The Effect of Tungsten Contamination from the Spray Gun on the Performance of a Thermal Barrier Coating

A traditional plasma spray gun consists of an anode and a cathode. During spraying small particles of anode material of either copper or tungsten, depending on the brand of the gun, will be worn off and deposited in the coating. The size and frequency of the particles from a copper anode has generally a dramatic appearance (in the beginning or at the end of its life) whereas a tungsten nozzle normally behaves more randomly during its life. Tungsten particles can therefore be expected anywhere in a plasma sprayed coating. Unfortunately the material properties of tungsten is not very compatible with a thermal barrier coating of partially stabilized zirconia and it is shown that a contamination will cause a catastrophic failure, if located in, for a thermal barrier, a critical region. The behavior of tungsten at elevated temperatures is investigated and clearly show the detrimental effect of tungsten on the life and performance of a thermal barrier coating.