Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology

The Preparation Technology and Properties of CrN Coating Deposited by Superimposed Pusle Bias Cathodic Arc Ion Plating

Author YangJuan
Tutor ChenZhiQian;NieChaoZuo
School Southwestern University
Course Materials Physics and Chemistry
Keywords CrN coatings cathodic arc ion plating pulse bias voltage microstructure and properties theoretical calculation
CLC TG174.4
Type Master's thesis
Year 2009
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Transtent subgroup metal nitride coatings have been widely used in the modification of cutting and confectioning tools due to their excellent properties including highly microhardness,low friction coefficients and good wear resistance, which can reduce the mechanical abrasion,chemical corrosion and high temperature oxidation of various kinds of components effectually,for the sake of impr-oving their abradability,reliability and prolong the operational life span.Many methods,such as molecular beam epitaxy(MBE),ion beam assisted deposition(IBD),cathodic arc ion plating(CAIP),triode sputtering(TS),unbalanced magnetron sputtering(UMS),and so on,have been conducted to deposited nitride coatings.Recent researches show that CrN Coatings have better erosion resistance and dry-type machinability,besides their higher microhardness,lower innerstress,better toughness and wear resistant,and much easier to thicken coatings,comparing to TiN extensively applied in industry.Furthermore,its easily controllable preparation technology enable its multitudinous industry production, which has more practical meaning.Thereby,CrN coatings are the most prospective material to replace TiN.In this paper,the direct current superimposed pulse bias cathodic arc ion plating process was used to deposite CrN coatings with high cohesion and good synthetical properties on high speed steel substrates.The depostion technology of CrN coatings was studied,and different voltage levels was used to modify the CrN coatings.The aim is to systematically investigate their effect on the basic characteristics of CrN coatings,such as surface morphologies,phase formation,microhardness,and so on.Various standard Characterization techniques and equipments,such as X-ray diffraction,ball-on-disc friction tester,surface profilometer,scanning electronic microscopy,microindention system,nano-scratching device,atomic force microscopy,electrochemistry analyser and optical microscopy,were used to analyze and qualify the surface morphology,the microstructure,the mechanical and tribological properties,corrosion resistant and machinability.The comparing study of CrN,TiN,TiAlN coatings’ properties was also executed,and the friction,wear,corrosion and machining mechanics of CrN coatings were disclosured theoretically;Moreover,the effect of pulse bias on the cathodic arc ion plating ion sheath’s electric potential distribution and the stress of specific microparticles of cathodic arc ion plating in the ion sheath were calculated by calculation software.The study results show as following:1.The direct current superimposed pulse bias cathodic arc ion plating technique is an effective method of realizing the preparation of CrN coatings with high quality at low temperature.The CrN coatings,which are nearly 2.4μm thick,have dense microstructure and high binding force with HSS substrates,and the ones prepared at -100 V show the best combined property.2.The deposition conditions determine the surface quality and the phase structure of the CrN coatings directly.With the increasing of the substrate bias voltage,the growing speed decreases,causing the thickness’ reducing,the number of macroparticles decreases,surface roughness reduces,inducing more smooth surface,and the cohesion increases.CrN coatings fabricated at differrent bias consists of Cr2N and CrN phase, with no monoatomic Cr phase;The crystallinity and grain sizes increase,and the preferred orientations change,mainly happening at the directions of CrN(211),Cr2N (110) and Cr2N(220),when the the substrate bias voltage increase.3.The bias critically influences the microhardness and the tribological properties of CrN coatings.With the increasing of the substrate bias voltage,the microhardness increases to nearly 2800HV,and then decreases,and the coefficient of friction raises to 0.68,and reduces to the level of the ones deposited at lower bais afterwards,while the specific wearability exhibits reverse changing tendency.The tests results show that CrN coatings prepared at -100 V show the highest microhardness and the best wear resistance enhancement.The friction coefficient decrease with the increasing of friction speed and loading weight,and is always lower than the HSS substrate.The friction mechanism are principally occuring distortion and micro tear friction,and the abrasion chiefly attributes to grain-abarsion and surface fatigue wear between CrN coatings and tribo-opposition GCr15 ball.4.Proper superimposed pulse bias is benefitial to the deposition of CrN coatings with high quality.With increasing of the substrate bias voltage,the corrosion resisting property of CrN coatings,which is better than TiN,but a little inferior to that of TiAlN,increases at first,and decrease later,CrN coatings obtained at the condition of -100 V exhibit the best corrosion resistance,and its corrosion mechanism is minipore corrosion in the NaCl solution cardinally,at the same time,the slot corrosion and electric couple corrosion also occur during the electrochemistry test.The drawbacks breakthroughing the whole coating,e.g.pin holes or microparticles,notablely reduce the corrosion resisting property of CrN coatings,so the reduction of these disadvantages and refining the crystalline grains can significantly improve the corrosion resistance of the coatings.5.The machinability of the CrN coatings is superior to TiN and TiAlN coatings, and evidently outgo that of HSS drill at the condition of dry-type drilling.CrN coatings do not adhere and flake from the drill at the same working environment,when having drilled 25 holes,indicating that CrN coating is more suitable to machining Al alloy than TiN,TiAlN and HSS drills.With the raising of the rotational speed,all of the cutting longevity increase at the beginning,and decrease at the end,and when the number of revolution is 2230r/min,the coatings shows the best cutting performance,the lifespan of the CrN coatings deposited at the optimized technology is five times of uncoated HSS drills.The attrition wear of CrN,TiN and HSS is binding wear chiefly,while the abrasion of TiAlN is mainly peeling and adhesion,and all these processes belong to physical change.6.The calculation results show that repelling force,the microparticles subjected, increases with the increasing substrate bias,for certain size of the microparticles,i.e.the higher the substrate bias value and the bigger of the microparticles’size,the larger the ion shaking force and the electrical field force.Therefore,the experimental phenomenon that the microparticles created in the process of cathodic arc ion plating are deactivated explicitly under the condition of utilizing the superimposed pulse bias is justified by the theoretical calculation.Above of all,the systematically study results show that the direct current superimposed pulse bias cathodic arc ion plating technique is an effectual method to deposit CrN coatings in order to improving the abradabilities,corrosion resisting properties and the machinabilities of various kinds of tools,and the paper has guiding function to the technology optimization of CrN coatings’ deposition.

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