Research On Heat Transfer And Lubricant Material Transfer Characteristics At HAMR Head Disk Interface

With the approaching of big data and cloud computing,the demand for large storage density of hard disk is increasing.Heat Assisted Magnetic Recorading(HAMR)is developing rapidly,and it is just around the corner to meet this demand..Meanwhile,When the gap between the head/disk is extremely little,the bulges of the disk may affect the space between the head and the disk,which will influence aerodynamic pressure.When the head is at a low flying height,the physical quantities related to the nature of the gas shouldn't be regarded as constants,but variables depended on temperature and pressure.The lubricant's transferring between the magnetic head and disk will be affected on this condition,which is bad to the stability of the hard disk and even reduces the lifetime of hard disk.The modified Reynolds equation,based on the N-S equation and the continuity equation in fluid mechanics,is modified.It is suitable for the rarefied gas,the simplified heat flux equation is obtained by neglecting the heat generated by the gas viscous consumption and the boundary condition for heat transfer.Then based on the vaporization and condensation flux equation of gas,the lubrica nt's evaporating and condensing on the whole head is derived.Finally,the theory of molecular dynamics is studied.The total potential energy of the molecular system at any one time is obtained and then every atom's trajectory in the molecular system is obtained in any simulation time.The aerodynamic pressure on both plate head slider and Tri-pad head slider is discussed in this paper on different operating conditions and also is discussed when there are different sized bulges on disk.The related attentions to hard disk working are also given.It is found that the reasonable head slider's shape will make the pressure distribution on the head slider more reasonable,which improves the bearing capacity of the head slider.Under the gas rarefied effect physical quantities of gas,such as thermal conductivity,dynamic viscosity,gas density and molecular free range are studied when referring to heat transfer.When pressure and temperature are couple,the changes of average temperature on two kinds of head disk interface are studied under different working conditions.The effects of disk bulges on heat transfer are also taken into consideration,which may be used as a reference of the disk's surface design.Under the joint effect of hydrodynamic pressure and temperature,the influences of many factors on the lubricant's transferring between head and disk are studied,such as the head slider's flying attitude and flying height,the disk's speed,and the heat source's power and spot radius on the disk surface.The transfer of lubricant is further studied in terms of molecular dynamics.The main molecular models are built by using Materials Studio software,including four different lubricants' models,and the models of disk coat with different carbon content.Finally,the adsorption between lubricant and disk coat is simulated.The phenomenon are also explained by the method of dynamic equilibrium analysis when the adsorption energy between lubricant and disk coat is different under different molecular models.At the same time,the diffusion of lubricant to the air is studied and the potential factors influencing the diffusion coefficient are discussed.Finally,the advice of selecting corresponding lubricants for different hard disk coats is put forward to reduce the amount of lubricant transfer.