【正文】 othertemperaturewear,forspecificuponmaterialsmatchedcanIndividualimportantsingleprobablyThisChoicepartautomationdependingentireovermoreisthermalbuildupTheThickness2).o Uniformpatternsnodensityalmostappliedcandifficult.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 Denserqualityofmakingparametersthesolutiontheconductivityaffectespeciallyplating.o TanknotthatmaskdifficultitpletelymustBecausetime.o Maskingincreasewillproblems.thereforestresseshighmaybuildupcreateshigh.densitywhereedgecornerbuildupexcessNodulesBuildupsizeon25μmthicknessdeposithourrequiresTypicallyThroughputandpartprocesseswithPlatingthecouldtechnology,toviableofferingissprayingrisks.thebutchrometosimilarthatalternativetotechnology－ Thermalitsdisposalandplatingtheimposedandenvironmentaltheduesteadilyhaveyears,pastOverininstancesinsize,buildup,ono Disadvantages:surfaceunitcostamanyreclamationandcorrosionwear,Solution available.67Cold Spray Process Advantages:p Low temperature process, no bulk paticle melting l retains position/phases of initial particles l very little oxidation l high hardness, cold worked microstructure 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: beingonlystageandtheprimarilyisspraycoated.u Thethanerodesubstratesorparticles.theactionthecanthoselimitedareSubstratematrixapositesappliedmayform,thesprayednotceramicsmaterialsandalloys.copper,stainlesslikeductilelimitedpresentwelding.u Coatingsortobondingheatinghighgeneratinghighsurfaceschemicallycontactfilmsofcausesurfacesandtheinteractionandimpactthesubstrate. particle of plastic cause energyonBondingcolddeformationchangeswiththephaseschemistryoriginalretainingaidtemperaturesprocesses.thermalthemostreactionsliquid/solidtension not pression stressed to coatings impact,inducedhighwithcooling,shrinkagevery resultlowandNoaidscleansurfacesmaterial,theoxidationtoimpartsThestateisonbulksorelativelyandsolidinparticles and moderately heated to a certain velocity and temperature where on impact with a substrate they deformstrongdenseauparesult the impact particles hot of kiicTheamanyisThiseachbarrelpurgeusednitrogenpulsebarrel.downsupersonic powder accelerates heats resulting andgasigniteusedsparkpowder.chargewithbarrelintoismostfuelOxygenandforinletbarrelwateraconsistsgun.High Velocity Oxygen Fuel Thermal Spray Process HVOF61Characteristics of HVOFl The coatings produced by HVOF are similar to those produce by the detonation process. HVOF coatings are very dense, strong and show low residual tensile stress or in some cases pressive stress, which enable very much thicker coatings to be applied than previously possible with the other processes.l The very high kiic energy of particles striking the substrate surface do not require the particles to be fully molten to form high quality HVOF coatings. This is certainly an advantage for the carbide cermet type coatings and is where this process really excels.l HVOF coatings are used in applications requiring the highest density and strength not found in most other thermal spray processes. New applications, previously not suitable for thermal spray coatings are being viable.62High velocity oxyfuel(HVOF) sprayingthe versatile, high deposition rate thermal spraying proces