This study assesses the strength and adherence of VPS titanium coatings on ultrahigh molecular weight polyethylene (UHMWPE) substrates. Four-point bend tests show the existence of a critical tensile strain of 1% corresponding to the onset of cracking. For strains up to 6%, crack density increases with no observed debonding. Fatigue tests over 106 cycles reveal that the coating remains uncracked at a strain of 1% and stays in a stable cracked state without debonding as strain is increased to approximately 6%. A laser shock test developed specifically for titanium-polymer interfaces revealed the existence of a debonding threshold corresponding to the adhesion strength. The results serve as a guide for the design of orthopedic implants on which VPS titanium coatings are used and, more generally, open the way for systematic measurement of adhesion between metallic coatings and polymer substrates.

This paper investigates the effect of chamber pressure on plasma jet expansion characteristics. It presents images of the plasma jet corresponding to different chamber pressures and torch parameters and correlates them with enthalpy probe and pressure measurements recorded in different areas of the torch nozzle. A transition from an over-expanded to an under-expanded flow regime, as evidenced by a change in jet topology, is shown to be a function of chamber pressure. This transition pressure strongly depends on torch parameters and is characterized by an estimation of a rarefaction parameter based on nozzle exit and chamber pressure. At low chamber pressures, a progressive change from a continuum to a transition flow regime is shown by the thickening of the shock structures. Paper includes a German-language abstract.

This paper describes an experimental investigation of plasma jet properties of a DC torch operated at low pressure (below 10 mbar). A modified enthalpy probe system is described, which allows gas sampling from the plasma jet at pressures down to the mbar range. Measurements of the specific enthalpy, temperature and velocity throughout the jet for different pressures are presented and discussed. In the pressure range investigated, the jet flow is supersonic and compressible theory is used to infer the velocity from the dynamic pressure measured at the probe tip. In addition, optical emission spectroscopy of the plasma jet is used to evidence the differences of these low-pressure plasmas with respect to common, atmospheric pressure thermal jets. These preliminary measurements are the starting points towards a better understanding of plasma jets at low operating pressures in view of new process development and optimisation.

Plasma spray coating has achieved outstanding technological and commercial progress. However the underlying fundamentals still require a better understanding to overcome some limitations coming from, in particular, the instabilities of the arc and the strong erosion of the electrodes. In this paper we present experimental investigations of the fluctuating behavior of a Sulzer Metco F4 gun operated at atmosphere. The temporal evolution of the torch voltage and current, and of the plasma jet emission have been measured, hi addition, an optical fiber inserted inside the gun allows to measure fluctuations of the arc emission directly. Depending on the external parameters, different modes of operation have been identified. In the "restrike" mode which prevails for spraying-relevant operation conditions, detailed analysis of the voltage signals and corresponding arc and jet light emission reveals different categories of voltage drops corresponding to arc interruptions or reconnections. Spectral analysis of the different fluctuation signals shows clearly-defined peaks in the frequency range 3-30 kHz which are attributed to the arc motion and restrike inside the torch. The dependence of these peaks on operation conditions in terms of gas flows and composition, and gas injection geometry is presented. In addition a study of the effect of electrode aging on the torch fluctuations is reported.

The ability of high damping iron-chromium-aluminium alloys and coatings to absorb noise and vibrations has been investigated over a wide range of frequencies and amplitudes. The damping capacity was determined using a cantilever method based on the modal analysis technique of the flat beams and was found to be very sensitive to internal stress of specimens. Heat treatment usually enhanced the loss capability, but only an optimised annealing restored the maximum damping capacity. The influence of vibration amplitude evidenced by appearance of a maximum around ε = 10-4”, while the vibration frequency did not influence 'damping behaviour significantly. The position of the maximum damping was shifted towards lower strains with annealing time and temperature. The structure of magnetic domains was observed using the magneto-optical Kerr effect and their modification following to an applied stress or magnetic field was associated with different values of the damping capacity. Accordingly, the beneficial effect of annealing on damping capacity arises on the one hand from improved mobility of unpinned domain walls and on the other hand from growth of 90° domains considered as the principal responsible of damping. Addition of aluminium between 1-8 wt%. improved the damping values notably around 4 wt%.