【正文】 l eliminates solidification stresses, enables thicker coatings l low defect coatings l lower heat input to work piece reduces cooling requirement l possible elimination of grit blast substrate preparation p No fuel gases or extreme electrical heating required p Reduce need for masking68Cold Spray Process Disadvantagesl Hard brittle materials like ceramics can not be sprayed without using ductile binders l Not all substrate materials will accept coating l High gas flows, high gas consumption. Helium very expensive unless recycled l Still mainly in research and development stage, little coating performance/history data 69Possible Uses for Cold Spray Coatingsl Corrosion protection, where the absence of processinduced oxidation may offer improved performance l Electrical and thermal, where the absence of processinduced oxidation may offer improved conductivity l Preplacement of solders and coatings where purity is important 70In summary:Cold spray process Powder pressed gas (helium), heat71Hard chrome platingo Advantages:Solutionforwear,erosion,corrosionresistanceanddimensionalreclamationformanyyears.areasonablecostperunitofsurfacearea,o Disadvantages:limitationsonthicknessbuildup,partsize,andinsomeinstancesperformanceinservice.Overthepastfewyears,costshavebeensteadilyescalatingduetothegrowingenvironmentalpressuresandlegislationimposedonthechromeplatingprocessandthedisposalofitsbyproducts.o Alternativetechnology－ Thermalsprayingtofindalternativeprocessesthatoffersimilarcharacteristicstohardchromeplating,butwithouttheconsequentrisks.Thermalsprayingtechnologyisincreasinglyofferingaviablealternativetothistechnology,andcouldprovidetheChromePlatingindustrywithplimentaryprocessesforpartprotectionandreclamation.72Benefits of Hard Chrome Platingo High Hardness Hardness value of Vickers 7001000.o History Well known, well established process with known properties and limitations.o Surface Coverage Not a line of sight process, will work on inside diameters, and on plex geometry.o Excellent Surface Finish A surface finish. o Economical For Thin Deposits Chrome plating is economical and reliable for very thin deposits, 25 to 100um ( ”).73Limitations of Hard Chrome Plating(1)o Adhesion Two primary reasons cause poor adhesion, especially on ironbased materials such as ductile and cast iron. 1. The first is improper or poor surface preparation and 2. the second is excessive micro cracking throughout the chrome plating. Microcracks, which extend from the surface, occur in the plating due to residual stresses (figure 1). When the microcracks extend all the way down to the substrate, separation of the plating may occur.74Limitations of Hard Chrome Plating(2)o SlowThroughputTypicallyplatingrequiresaboutonehourtodepositathicknessof25μm(”)onanysizepart.o Nodules/UnevenBuildupNodulesofexcessplatingbuildupontocornerandedgeareaswherecurrentdensityishigh.Thiscreatesunevenbuildupandmaycausehighresidualstressesandthereforeadhesionproblems.Itwillalsoincreasefinishingtime.o MaskingBecausepartsmustbepletelysubmerged,itisdifficulttomaskareasthatdonotrequireplating.o TankContaminationContaminants,especiallyiron,affecttheconductivityoftheplatingsolutionandtherelatedparametersinvolvedmakingreproductionofplatingqualitysometimesdifficult.75Benefits of Thermal Spraying(1)o Low Capital Investment Compared to a chrome plating installation, a low capital investment in equipment required. Also, installation of a thermal spray system takes much less time and associated installation costs are low.o Waste Disposal Wastes from thermal spraying are not toxic, but do contain elements requiring special disposal. Typically they are dry powders, some of which can be reactive. o Competitive Application Costs When parts are large enough and the coating thickness requirement is high, thermal spraying bees very cost petitive with chrome plating.o No Limitation On Size 0f Part The thermal spray process has no real limitations on part size because there is no need for immersion in plating tank.o High Deposition Rates Most of the thermal spray processes have a higher deposition rate than chromium plating.o OnSite Capability Thermal spray equipment is portable and has onsite capability.o Fewer Process Steps Thermal spray coatings require fewer process steps to apply than chrome plating.o Thicker Coatings The thermal spray process has the ability to economically apply thicker coatings, in some cases up to 10mm.76Benefits of Thermal Spraying(2)o DenserCoatingsCoatingscanbeappliedwithalmosttheoreticaldensitywithnocrackpatterns(figure2).o UniformCoatingThicknessThecoatingbuildupwiththermalsprayingismuchmoreuniformovertheentirepart,dependingonautomationandpartgeometry.o MaterialsChoiceThisisprobablythesinglemostimportantbenefit.Individualapplicationscanbematchedtomaterialsdependinguponthespecificrequirementsforcorrosion,wear,servicetemperatureorotherfactors.77Other benefits include:o No Hydrogen Embrittlement No base metal hydrogen embrittlement problems.o No Post Heat Treatment No post heattreatment or stress relief required.o No Fatigue Debit Chrome plating reduces the fatigue life of parts it is applied to, whereas, some thermal spray coatings can increase it.o Finish With Conventional Grinding Thermal spray coatings can be finished with convention