超声波对镀层影响

Thin Solid Films, 120 (1984) 153-159 PREPARATION AND CHARACTERIZATION 153 THE EFFECT OF ULTRASONIC VIBRATION ON HARD CHROMIUM PLATING IN A MODIFIED SELF-REGULATING HIGH SPEED BATH E. NAMGOONG AND JOHN S. CHUN Depariment of Materials Science, Korea Advanced Institute of Science and Technology, Seoul (South Korea) (Received August 17, 1983; accepted June 20, 1984) The effect of ultrasonic vibration on the current efficiency, microhardness, preferred orientation and microstructure of chromium deposits was investigated. A comparison was made between the results obtained with an ultrasonic agitating bath and those obtained with a modified self-regulating high speed bath. Using ultrasonics, the ensuing cavitation causes a higher temperature and a higher pressure at an electrode surface. This method activates the electrode surface, which results in a change in the physical and mechanical properties of the deposits such as a slightly lower current efficiency, a higher microhardness and more cracking. Also, brighter unstained deposits were obtained in the ultrasonically agitated bath. Very strong (111) preferred orientation with a columnar structure was obtained both with and without ultrasonics. 1. INTRODUCTION Hard chromium plating is used to increase resistance to heat, wear, corrosion and friction. In recent years various alterations such as a modification of the plating bathle3 and its operation conditions 4-6 have been widely applied to increase the efficiency of plated products. An improvement in the chromium plating bath was secured in the modified self-regulating high speed (SRHS) bath with ultrasonics in this work. Ultrasonics produce shock waves and cavitation and thus reduce the ionic concentration gradient by inducing microstreaming at the electrode-electrolyte interface’-‘, thereby accelerating the electrolytic metal deposition process and changing the properties of deposits’O_“. However, there are no reports on the effect of ultrasonics on hard chromium plating in an SRHS bath. In our study a comparison between the use of ultrasonics and the conventional method has been made. We studied the effect of ultrasonics on the current efficiency, microhardness, preferred orientation and microstructure as a function of the temperature and current density in a modified SRHS bath. Research has been conducted to improve the physical and mechanical properties of chromium deposits with the use of ultrasonics. 0040-6090/84/$3.00 0 Elsevier Sequoia/Printed in The Netherlands 154 E. NAMGOONG. J. S. CHUN 2. EXPERIMENTAL PROCEDURES 2.1. Plating bath and apparatus The experimental apparatus used in this investigation is represented schemati- cally in Fig. 1. Ultrasonic vibrations were generated with a magnetostrictive transducer connected to an oscillator, at a working frequency of 20 kHz and with an output of 145 w. Fig. 1. Schematic diagram of the ultrasonic plating cell and accessories: a, d.c. power supply; b, oscilloscope; c, ultrasonic generator; d, transducer; e, conical horn; f, stirrer; g, thermocouple; h, thermometer; i, anode; j, cathode; k, on-off low temperature controller; I, heater; m, water jacket; n, polystyrene. The cathode and magnetostrictive transducer were coupled with a conical horn made from aluminium alloy. A d.c. power supply was used for chromium plating with a calibrated ammeter. The cathodes consisted of 15 mm x 55 mm panels cut from a commercial low carbon steel sheet 1.2 mm thick. The anodes were made from a Pb-Sb alloy