Microstructures And Properties Of Surface Layers Strengthened By TiC/TiN On Steel Substrates

Those mechanical parts that are usually used in the media environments withhigh-speed, heavy load and corrosion, should withstand the severe shock, wearresistance and corrosion resistance, which are the essential requirements for them towork dependable. In the field of modern industry, it has become an important way torepair, strengthen and prolong the service life of the parts, by cladding materials ofhigh hardness, great wear resistance and good corrosion resistance on the surface ofthe easily damage and easy-to-corrode parts.The research of strengthening the substrate surface with the thin hard coatingsprepared by TiC and TiN has been studying for years. TiC and TiN as reinforcingphases of cemented carbide coatings exhibit excellent mechanical properties becauseof their high hardness, wear resistance. They were widely and successfully applied intools that caused a Tools Revolution in the1970s.There are many reports about the study on the preparation of TiC and TiNstrengthening coating. Vapor deposition method is a common method, includesphysical vapor deposition and chemical vapor deposition. But the binding forcebetween the coating and substrate is bad, so the coating is easy to fall off. Laser gasnitriding is one of the emerging technologies now, which introduces laser technologyinto gas nitridation technology then uses the high temperature reaction of them toproduce the coating. But laser equipment is high in price that needs to invest greatproduction cost. Since recent years, arc cladding technology has been arousingpeople’s attention and research because of its simple machining technology andflexible construction. In this way, good metallurgical bonding can be obtainedbetween the coating and steel substrate.In this paper, according to arc cladding technology, the test prepared the layer ofstrengthen phrases with TiC/TiN on the surface of45steel and stainless steel321substrates. Gas argon and nitrogen are used as arc atmospheres. The nitrogen is notonly a protective gas, but also the resource of nitrogen in the reaction. Precoat titanium powder and graphite powder on the surface, under the high temperature theprecoat powder will melt and cause reaction of Ti+Câ†'TiC. Nitrogen will decomposeinto nitrogen atom or nitrogen ion, and by adsorption and diffusion they will havereaction of Ti+Nâ†'TiN with molten titanium powder in the molten pool. This paperhas systematically analyzed and studied on microstructures and mechanical properties,and also discussed the effect of parameters.The result shows that the strengthening phases of TiC and TiN present twodistribution patterns on the surface layers. The dendrites and the granule, smoothgrains of TiC distribute in the layer of containing none or less nitrogen, whereas thesquare grains and the block structure of TiN distribute in the layer of rich nitrogen.In the test of45steel substrate, arc current was200A and arc travelling speedwas4mm/s, changing the gas proportion of Ar and N2to pure argon,the highestmicro-hardness was up to780HV which was improved third times more than thesubstrate itself. Changing the arc current to180A when the atmosphere ratio was6:4L/min and the arc travelling speed was4mm/s. The highest micro-hardness was upto579.4HV which was increased two fold comparing to the original substrate. Whenthe atmosphere ratio was6:4L/min and the arc current was200A, transforming the arctravelling speed to8mm/s, the highest micro-hardness was up to865.9HV that wasenhanced more than three times, too.In the test of stainless steel321substrate, arc current was180A and arc travellingspeed was4mm/s, changing the gas proportion of Ar and N2to pure argon, the highestmicro-hardness was up to319HV that was also improved more than doubled to thesubstrate itself. When the atmosphere ratio was6:4L/min and the arc travelling speedwas4mm/s, changing the arc current into180A, the highest micro-hardness was up to276.9HV that was doubled to the original substrate. The result of abrasive wear testsshowed that under the optimizing technology parameters, there were shallow furrowson the coating layer which had the best wear resistance property to hinder pressingand resist plastic deformation.