Study On Heat Treatment Process Of Flame Sprayed PEEK Coating

In this paper,PEEK coating was prepared on 17-4 substrate by subsonic flame spraying gun.After spraying,the coatings are cooled by air and water.Then thermal treatment at different temperatures(220??260??300?)and times(1 min?10 min?20 min?30 min)was carried out on the coatings.The coatings of PEEK were characterized by Fourier Transform Infra-Red(FTIR),Differential Scanning Calorimetry(DSC)and X-Ray Diffraction(XRD)measurements.The heat treatment process on microstructure and properties of PEEK coating were studied in this pape.The major work and conclusions of present paper are as follows :(1)The presence of acetylene during flame spraying can lead to surface modification of PEEK coatings,which is independent of cooling method.There are two reasons for the modification.One reason is that acetylene decomposes to carbon and hydrogen at high temperature,thus leading to the hydrogenation of aromatic groups into cyclohexane groups.Another is that scission of the covalent bond between the carbonyl group or the ether group and the adjacent ?-carbon along the polymer chain by photooxidation.Meanwhile,this scission caused formation of aldehyde bonds.Heat treatment are not a predominant parameter in degradation occurring at the surface of PEEK coatings.(2)Quenching coating can crystallize but air cooling coating can not during DSC scanning.The glass transition temperature and crystallization behavior of quenching coatings changed but air cooling had no change after heat treatment.The glass transition temperature of quenching coatings will increase slightly because of crystallization and crosslinking with increasing temperature and time.When the temperature is lower or the time is shorter,crystal peak was observed in the DSC because of imperfect crystallization.It is found that raising the temperature and prolonging soaking time of heat treatment promoting perfection of crystallization which causing the disappearance of crystal peak in DSC.When the heat treatment temperature reached 300? and time is more than 10 minutes,a small melting peak appears at 254? because of the existence of thin lamellae.(3)XRD determination results show that the quenching coating is amorphous and air cooling coating is semicrystalline structure.Semicrystalline coatings have higher hardness.Amorphous quenching coating became semicrystalline but air cooling coating almost had no change after heat treatment.With the increase of heat treatment temperature and time,the crystallinity and crystallization degree of coatings increase.(4)With the increase of heat treatment temperature and holding time,the crystallinity and crystallization degree of coatings increase and coating porosity decreases,which cause increase of hardness and reduction of friction coefficient.It is worth noting that the variation of friction coefficient is very weak.The increase of hardness of coatings is the main reason for the improvement of wear resistance.The wear mechanisms are adhesive wear and abrasive wear.There exists the friction-induced fatigue tearing in the process of friction.These phenomena will be gradually weakening or even disappearing with the increase of heat treatment temperature and holding time.