Study On The High Speed Jet Electrodeposition Of Nano-crystalline Bulk Nickel And Their Micro-structure

High speed electrodeposition of pure nickel was carried out in jet flows of different electrolytes with and without additive. The influences of jet technological parameters, bath composition ,current parameters together with additive on the deposition speed, microstructure and surface morphology of the nickel coatings were investigated by optical microscope, instrumental microscope ,scanning electron microscope(SEM), transition electron niicroscope(TEM), X-ray diffraction(XRD), differential thermal analysis(DTA) and hardness tests. In addition, the thermostability of the nickel coatings. the mechanisms corresponding to the increment of deposition rate, to the refine of grain size ,as well as to the additive effect were also probed systematically. The experimental results indicate that:1.The bulk nickel with grain size of 10 to 30 nm and dimensions of maximum thickness of 0.8mm and diameter of 6mm, grain size of 9.8 ~- 1 mm and dimensions of 0.5mmX lOmmX 75mm were synthesized by lED processing under the conditions of jet flow was perpendicular to and horizontal to the cathode surfaces, respectively. The deposition rate of Ni2~ increased proportionally with the electrolyte flow speed and current density .When the applied current density is above the limit current density which depends on the flow speed, the corresponding deposition rate decreased with the current density. Further more, and there is the same relations between the coating thickness and the distance from the impingement center point to edge in radial direction.2.The grain size of lED nickel deposit decreases from 3Onm to 9.22nm with the additive (2.5g/L?g/L) addition .Meanwhile, microhardness of perpendicular lED layer is enhanced from Hv400 to Hv600,and texture component is transformed from previous (220) to (111) and (200). After heated at the temperature of 100 C to 400 .~ for 20mm, for horizontal deposited layers ,the grain size increases from 9.8nm to lOOnm or more. It was found that the deposition layer heated is very brittleness, the SEM fracture morphology shows that it was intragranular rupture. Microhardness decreases from Hv5 10 toabout Hv300.3.The deposition speed and current efficient of pulse current lED is higher than that of DC lED With the increasing of the duty cycle (20%~?0%),the speed of deposition increases from I .5mg/mm to 5.8mg/mm, and the current efficient increases from 55% to 93%.Meanwhile ,the grain size of perpendicular lED coatings begin to increase after the grain size to 9.45nm .On the other hand, the microhardness begin to decrease after they increase to Hv650. With the currentIIfrequency increases from 10kHz to 20kHz, the JED speed decreases ,and the current efficiency changes between 80% and 85%.