The Basic Research Of Vanadium Nitride Coatings By Chemical Vapor Deposition

As the science and technology develop rapidly, the status of machining in manufacturingindustry is becoming increasingly vital, and the tool plays the most important role, whoseperformance affects cutting efficiency and the cost of the processing. The traditional cutter ofcemented carbide has been unable to meet the requirements for the development ofcontemporary society, therefore, the research and development of coated tools for newmaterials are particularly urgent.On the one hand, this paper focuses on researching the vanadium nitride coating on thesurface of T12hacksaw with V2O5、H2and N2as raw materials using CVD. In considerationof the main process parameters which affect the chemical vapor deposition of vanadiumnitride coatings, a series of orthogonal experiments were designed and implemented forfabricating the vanadium nitride coating samples under the different parameters condition,then character and test the samples, the main results are:(1) Observation of the images obtained by SEM show that vanadium nitride coatingsurface coating sample diffuses tiny holes, the aperture is in a few hundred nanometers whichform a mesh structure.(2) In diffraction peak, only the α-Fe and VN peak appears, no other impurity peak,which shows that the VN coating specimens has high purity, the emergence of α-Fe peak iswith the influence of the substrate T12steel. VN average crystallite size is34.36nm.(3) In these samples of vanadium nitride coating, In addition to the1#sample thethinnest which is12.60μm,2#sample is15.77μm, other samples thickness is around20μm.According to the analysis of orthogonal, the optimal parameter combination of the thincoating is obtained: Pre heat preservation is5min, deposition temperature is900℃,deposition time30min; the optimal parameter combination of thick coating is obtained: Preheat preservation is15min, deposition temperature is1100℃, deposition time90min.(4) Through the test of vanadium nitride coating sample film adhesion, getting thecritical load Lcn values.1#sample film base bonding strength the lowest is9.1N, the criticalload value Lcn maximum of5#samples is27.2N. To produce VN coating film base combinedwith high intensity, analyzing the orthogonal, selecting the optimal parameter combination,the parameter combination is: Pre heat preservation is10min, deposition temperature is1000℃, deposition time90min.(5) Roughness of vanadium nitride coating samples is tested. The roughness Ra value of1#,2#,3#sample is less than2μm, the roughness Ra value of the rest VN coating samples isabove2μm, the roughness Ra value of6#is maximum, its value is close to3.28μm. To get one smaller roughness VN coating, referring to orthogonal analysis, the optimal parametercombination is selected, the parameter combination is: Pre heat preservation is5min,deposition temperature is900℃, deposition time60min.(6) Friction coefficient of vanadium nitride coating samples is tested. The averagefriction coefficient of Preparation VN coating samples is between0.3~0.5. To get a relativelyhigh coefficient of friction for VN coating, referring to orthogonal analysis, the optimalparameter combination is selected, the parameter combination is: Pre heat preservation is15min, deposition temperature is900℃, deposition time60min.(7) The amount of wear vanadium nitride coating samples is tested. The wear volume1#,2#,3#sample is above0.05mm3, wear quantity is large,4#,5#,6#sample wear volumereduction, wear volume of7#,8#,9#sample is at least between0.05mm3~0.03mm3range,no more than0.02mm3. To fabricate the VN coating which possesses low wear and excellentwear resistance, referring to orthogonal analysis, the optimal parameter combination isselected, the parameter combination is: Pre heat preservation is15min, deposition temperatureis1000℃, deposition time90min.(8) Corrosion behavior is investigated by putting VN coating sample in3.5%NaClsolution for72h.1#sample weight loss of2.5mg, corrosion is most serious, followed by2#sample, reducing weight is1.8mg, reduction weight of the rest is below1.5mg. To produceVN coating with good resistance to corrosion, by orthogonal analysis, the optimal parametercombination is selected, the parameter combination is: Pre heat preservation is10min,deposition temperature is1100℃, deposition time90min.On the other hand, taking thermodynamics calculation and analysis and deposition rateinto consideration, the chemical vapor deposition sedimentation mechanism of vanadiumnitride coating is discussed briefly. The conclusions can be summarized as follows:(1) During the temperature range from943k to1600k,V2O5(g)+5H2(g)+N2(g)=2VN(s)+5H2O(g)standard reactionΔG θT<0，Δ GθTincreases with therising of temperature T. This shows that the temperature is too high to make thereaction take place smoothly.(2) During the process of chemical vapor deposition VN coating, if the reactiontemperature is different, deposition rate is different, In high temperature (above1000℃)belong to the gas phase diffusion control, In low temperature area (below1000℃) depositionrate is the process of surface reaction control. Given the same reaction temperature, thedeposition rate is changed with the distance change between sample and V2O5.