High Temperature Tribology Property And Wettability Of HVOF And CS Sprayed Fe-based Amorphous Alloy Coatings

In the drilling process of unconventional oil and gas resources,the drill bit is very prone to"mud pack phenomenon",which means that muddy rock chips will be produced during the drilling process and cannot be discharged from the bottom of the hole in time when water is encountered and wrapped by the surface of the drill bit.And no matter what kind of drill bit is used,the phenomenon of mud pack will be produced,which will lead to stop drilling or jamming and other accidents in the hole.At the same time,the drilling process is often accompanied by the phenomenon of high temperature wear.One of the methods adopted by researchers in this field is to prepare a coating on the steel body surface of the drill bit,and prepare a coating with excellent hydrophobicity and wear resistance by spraying technology in order to solve the problem of mud-packing and service durability development of the drill bit.In this paper,Fe-Cr-Mo-C-B-Y system amorphous coatings were prepared on35Cr Mo steel substrate by HVOF and CS techniques,and the high-temperature(below glass transition temperature)tribological properties of Fe-based amorphous coatings were systematically discussed,and the differences in wear mechanisms between HVOF and CS coatings were compared.The laser weaving treatment of the coatings was also conducted to investigate the effect of weaving on wettability,as follows.(1)The Fe-based amorphous alloy coating prepared by CS technology has 90%amorphous content and no obvious crystallization phenomenon.Compared with the HVOF coating,the CS coating has the advantages of high density structure(porosity less than 1.5%),high hardness(Vickers microhardness up to 1104 HV_0.3),and better thermal stability.The high-temperature tribological properties of the coating were investigated by conducting ball-plate linear sliding tests at different temperatures(293K,473 K,673 K).The results show that the wear rates of the Fe-based amorphous alloy coatings all show an increasing trend with the increase of ambient temperature under dry frictional wear conditions,which is mainly due to the periodic growth,rupture,and peeling of the coating oxide layer significantly increasing the wear rates of the coatings under high temperature conditions.Compared with HVOF coatings,dry friction wear of CS coatings is more sensitive to ambient temperature.The high temperature wear mechanisms in air include fatigue wear,adhesive wear,and more severe oxidation wear.(2)Regularly arranged dot,groove and papillae structures were constructed using nanosecond pulsed laser,and the contact angles with deionized water and drilling fluid increased to 151.6°and 145°,respectively,after laser weaving of the coating surface.For the same weave,the smaller the spacing,the larger the water contact angle.The water contact angle of the papillae weave was greater than 145°,which showed excellent hydrophobic performance.Different micro-nano structures can be formed on the coating surface by adjusting the laser weaving parameters,and the weaving surface transforms from the Cassie-Wenzel state to the Cassie state as the weaving spacing decreases.