الفهرس 
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Abstract
I:rom the present study, which attacks the properties of the deposited layers produced by charged arc spray DROPlets by using induction charging electrode arrangements, the following conclusions can be drawn:
I) Electrostatic forces can be used as an effective tool for controlling the properties and construction of the sprayed deposits.
2) Charging the molten DROPlets by induction and thermionic emiSSIon are the most available and safe techniques. Charging the arc spray DROPlets with a positive charge (by negative potential) increases hardness, adhesion, cohesion and density of deposited layers and decreases porosity and the wear rate. On the contrary, negative charging for the spray DROPlcts (by positive potential) is found detrimental for the properties of the deposited layers. The arc spray gun (234) and spraying wIres (60E, 13% Cr) of Mitallization Limited are used in surfacing all standard test specimens.
3) ,By using long induction copper electrodes covering the arc zone and the workpiece, the lollowing results are relative to that obtained from examining the deposited layers produced by the conventional method.
a) At potential difference in the rang of (-12.5 kV to -14.5 kV ) between the charging electrodes and the workpiece , hardness increases to about (28.4 %),adhesion strength lI1creases to about (42.33 %), cohesion strength of the deposited layers increases to about (77.5 %) and percentage increase in specimen length in tension tests increases to about (64.0 %).
b) At potential difference of about (-14.4 k V) and using wear measuring by the decrease in diameter technique, wear values decreases to a minimum value of about (20.0 %) relative
to wear in deposited layers by the conventional method. Measuring the wear by the weight loss kchnique, wear values decreases to a minimum value of about (24.5 %)at the region of potential (-14.0 k V. to -15.0 kV).Measuring the wear by the change in surface roughness technique , it is found that at final test periods and at potential of(-12.8 kY), the minimum average R.M.S. of the surface irregularities is found about (63.7 %).
The further decrease in negative potential lower than (-15.0 kY), inverts the previous gain in all the results of wear measuring techniques.
c) Density of the deposited layers increases to about ( 3.9 %) at potential difference of (-14.4 kY).
4) To eliminate the secondary adverse attraction for the molten deposited DROPlets from the long induction electrodes,another short electrodes arrangement, covering the arc zone is used. Better results at lower potential difference are achieved.
a) Hardness increases to about (32.5 %) at the range of potential (-8.5 kY to -10.5 kY) and cohesion strength increases to about( 173.6 %)at a potential difference of (-13.4 k Y ).
b) Adhesion strength increases to about (26.8 %) at the range of potential (-10.0 k Y to -12.0 k V). The increase in adhesion strength is not like the maximum value gained by the long plates. It can be said that the adhesion strength decreases with the decrease in DROPlet charge.
5) Metallographic examination by using scanning electronic microscope of sections at the deposited layers produced by negative potential indicates that particles are arranged in the spraying direction with decrease in porosity, voids and oxide inclusions. Moreover as sprayed surfaces have sand dumes shape. On the contrary positive potential produces deposits with lamellar structure with long fissures.
Armed with the experience gained from the present work, a complete shooting for the advL:rsL: electrostatic forces in the spraying and charging techniq\!e is hoped in the near future. The future work will concentrate on:
A) Studying the ability of producing an integrated design for the spray gun with built in high voltage induction electrode. A copper ring induction electrode as shown in Fig. 5-1 (1\.), will be fixed around the gun nozzle. Potential difference and the clectrode dimcnsions will be studied to achieve minimum weight and potential with highest improve in the deposit properties.
8) Studying the ability of using the workpiece as charging electrode and meanwhile as a collecting electrode as shown in Fig. 5-1 (8). The workpiece will be completely isolated li’om the machine tool used [or spraying. The high voltage connection to the workpiece, will be through a spring loaded conducting brush. It is expected in the charging operation by using negatively charged workpiece that the electrostatic forces will directly attract the positivcly charged DROPlets towards the target. No adverse effect to DROPlets deposition will be expected. The surface area of the workpieces and their shape will affect the charging operation since they will change the electric field around the arc zone.
Robotized system for gun movements will be required for studying the second technique (8) as it is unsafe to the manual operation.