感应烧结制备高温自润滑涂层及其性能研究

PREPARATION AND PROPERTIES OF HIGH TEMPERATURE SELF LUBRICATING COATINGS BY INDUCTION SINTERING

通过高能球磨和感应烧结制备耐高温自润滑IS304涂层,涂层中自润滑相明显细化,其中Ag尺寸为5μm左右,BaF2/CaF2尺寸为1μm左右.研究表明,环境温度和组织对涂层的摩擦性能有较大影响,当温度为20—340℃时,2种涂层的摩擦系数都较高,磨损机理主要为微观脆性断裂;随着温度升高,由于磨损面上形成由氟化物和Ag组成的自润滑膜,涂层的摩擦系数急剧降低.当温度为340—700℃时,由于IS304涂层中润滑相尺寸细小且分布均匀,使得磨损面上形成的润滑膜完整,并且Ag膜尺寸细小、分布均匀,因此IS304涂层的摩擦系数明显低于润滑相粗大的PM304;当温度继续升高至700—800℃时,在摩擦力的作用下,软化的润滑膜表面出现塑性流变,涂层的摩擦系数明显增大.由于PM304涂层的磨损面上的Ag膜尺寸粗大,且Ag膜的塑性流变比氟化物膜更严重,使得PM304涂层的摩擦系数明显大于IS304.

NiCr-based self-lubricating PM304 coatings have been used successfully in many high-temperature, high-speed applications such as air cycle machines,bleed air turbo compressors and turbo expanders.However,coarse PM304 coatings are not fully dense,containing a few percentages of pores and cracks which are harmful not only to the coating＇s tribological properties but also to the coating＇s overall mechanical strength.Furthermore,fine IS304 was prepared by the methods of high energy ball milling and induction sintering.The size of self-lubricating phase was refined,with Ag particles of about 5μm and BaF_2/CaF_2 of about 1μm.The results show that temperature and microstructure have a great effect on wear properties of IS304 and PM304 coatings.At the temperature of 20—340℃,the friction coefficients of two types of coatings（IS304 and PM304） are higher,and the microscopic brittle fracture is the dominant wear mechanism.With the increase of the temperature,the coefficient of the coatings decreases rapidly due to the formation of self-lubricating film on the worn surfaces which consist of Ag and fluoride.At the temperature of 340—700℃,since the self lubricating phase is fine and uniformly distributed in the IS304 coatings,it makes the formation of an intact lubricating film as well as Ag film fine and well distributed.Thus,the friction coefficient of IS304 is lower than that of PM304.With a further increase at the temperature of 700—800℃,there is the plastic flow on the surfaces of the softened self-lubricating film under the influence of the friction force.Consequently, the friction coefficients of the coatings increase obviously.Comparing the PM304 with IS304 coatings, as the size of Ag film is large and the plastic flow of Ag film is much more severe than that of fluoride film,the friction coefficient of PM304 is higher than that of IS304.