| Compared with traditional machinery,microdevices have more wear problems caused by surface friction and adhesion due to size effects.The lack of reliable lubrication severely limits the development and application of microdevices.Therefore,this paper attempts to use nano-magnetic fluid as lubricant.By constructing a matrix magnetic field,designing and fabricating a silicon-based microdevices for friction and wear test,to discuss the texture pattern and control methods of magnetic fluid on the silicon substrate surface under the external matrix magnetic field,study its tribological properties and lubrication mechanism.By calculating the force of the nano-magnetic fluid in the magnetic field,the main factors affecting the force of the nano-magnetic fluid are determined.Further,according to the magnetic field modified nano-magnetic fluid Bernoulli equation,the influence of the magnetic field on the distribution position of the nano-magnetic fluid is discussed.It provides theoretical basis for the design of matrix magnetic field and the magnetron lubrication of nano-magnetic fluid.According to the structure characteristics and working principle of the used pinon-disk reciprocating friction test rig,a pin-on-disk friction is designed which can provide the matrix magnetic field.Wherein,the lower specimen(disk)of the friction pair is a polished single crystal silicon wafer,and the thin cylindrical permanent magnets is used to form the matrix magnetic field which adjusted by changing the distance and height of the magnetic magnets.The upper specimen(pin)of the friction pair is a silicon-based microdevice with microlinear stripe fabricated by deep reactive ion etching(DRIE)technology,and the processing quality of microdevices was characterized by scanning electron microscopy and laser confocal microscopy.Based on the electromagnetic field theory,the ANSYS software was used to simulate the magnetic field of the designed lower specimens to determine the magnetic field distribution on the surface of the lower specimens when different magnetic fields were applied.Then,the image acquisition system was built to capture the texture pattern images of nano-magnetic fluid on the surface of different lower specimens,and to analyze the influence of matrix magnetic field on the texture pattern characteristics of nano-magnetic fluid.Using nano-magnetic fluid as the lubricant of silicon-based microdevice,the comparative friction tests were carried out under the condition of no magnetic field,single magnetic source magnetic field and matrix magnetic field.The friction data under different load and velocity were measured,the influence of magnetic fluid on the tribological properties of silicon-based microdevices under the matrix magnetic field were explored combining with Stribeck curve and the theory of liquid lubrication,and the optimal matrix magnetic field parameters which have the best antifriction effect were determined.The wear test was further designed according to the optimal matrix magnetic field parameters,and the wear surface morphology of the microdevices were characterized by optical microscope.The lubrication characteristics and mechanism of the nano-magnetic fluid applied to the silicon-based microdevice under the matrix magnetic field was investigated. |
