Micro-Arc Oxidation Coatings ntawm Titanium: Hnav thiab Corrosion Performance

Qhov teeb meem lub txheej yuav tsum daws

Titanium alloys combine high specific strength, low density and good biocompatibility, which is why they are used in aerospace, defence and medical hardware. Qhov tsis muaj zog yog qhov chaw. Unalloyed thiab alloyed titanium ob leeg muaj tsis tshua muaj kev tiv thaiv rau abrasive thiab nplaum hnav, thiab hardness tsuas yog nruab nrab, yog li zawv zawg sib cuag nrog lwm yam hlau ua rau galling, hlau hloov thiab, nyob rau hauv seawater los yog chloride kev pab cuam, galvanic thiab crevice corrosion nyob rau hauv lub cheeb tsam. Bolted titanium sib dhos nrog stainless fasteners yog cov ntaub ntawv classic: cov zaj duab xis passive yog tawg mechanically, repassivation sib tw nrog kev tawm tsam hauv zos, thiab kev sib koom ua ke sai dua li qhov tsim tau xav.

Micro-arc oxidation, tseem hu ua plasma electrolytic oxidation, hais qhov no los ntawm kev loj hlob oxide zaj duab xis ntau dua li tso ib qho. Vim tias txheej txheej yog tsim los ntawm substrate, adhesion yog metallurgical thiab tsis muaj txheej txheej - substrate interface rau debond nyob rau hauv thermal cycling.

Yuav ua li cas zaj duab xis loj hlob: Plaub theem

Ib feem yog immersed nyob rau hauv ib tug alkaline electrolyte thiab ua lub anode ntawm ib tug pulsed mov. Kev loj hlob dhau los ntawm plaub theem pom tau.

Thawj theem zaum ua ntej sparking. Cov khoom siv tau hloov pauv, cov pa npuas ua rau ntawm qhov chaw, lub hnab ntim roj tsim, thiab cov zaj duab xis insulating passive ob peb kaum ntawm nanometers tuab tshwm. Current density rises rapidly to a peak and then falls.

Qhov thib ob theem yog sparking. Raws li qhov hluav taws xob txuas ntxiv nce cov zaj duab xis passive tawg, qhov ceev tam sim no nres thiab pib nce ntxiv, thiab qhov chaw muaj zog ntawm cov electrodes ionises lub hnab ntawv roj. Ntau lub txim me me txav mus thoob qhov chaw, ib txwm pom cov cheeb tsam nyias nyias ntawm zaj duab xis thiab tawg mus rau ntawd, yog li ntawd qhov chaw tawg yuav tsiv mus nyob.

Qhov thib peb theem yog qhov tseeb micro-arc. Dispersed micro- paug tawm tshwm sim, txav mus sai, nce siab thiab tom qab ntawd poob rau hauv tus lej ceev raws li cov yeeb yaj kiab thickens. Current density settles, and both film resistance and film thickness increase steadily.

Qhov thib plaub yog lub zos arcing. Arc me ntsis ua tsawg dua tab sis loj dua thiab muaj zog dua. Thaum cov arcs dominated, txheej txheej kev loj hlob qeeb thiab kev pheej hmoo ntawm kev puas tsuaj hauv cheeb tsam tau nce, yog li feem ntau cov sij hawm tsim khoom nres cov txheej txheem ua ntej lossis raws li theem no pib.

Electrolytes thiab txheej txheem Parameters

Cov electrolytes ntau lawm yog alkaline thiab feem ntau yog raws li silicate, phosphate los yog aluminate systems, singly los yog ua ke, nrog ntxiv uas tswj conductivity thiab pH. Silicate-raws li da dej nyiam cov yeeb yaj kiab tuab; phosphate da dej tsim cov txheej txheej uas ua kom nruj dua qhov ntev ntev; aluminate da dej thawb hardness siab dua. Cov electrolyte kuj txiav txim siab txheej txheej txheej, uas tseem ceeb vim hais tias cov rutile feem tswj kev ua haujlwm thaum lub sij hawm anatase feem cuam tshuam nrog bioactivity.

Ib tug phosphate los yog calcium-bearing da dej yog siv qhov chaw tiav lawm yuav tsum tau bioactive. Coatings zus nyob rau hauv calcium thiab phosphorus electrolytes txhawb cov pob txha ingrowth thiab yog siv nyob rau hauv orthopedic hardware, ib txoj hauv kev kuj pom nyob rau hauv cov kev cog lus specifications uas tswj tej chemistry, xws li ASTM F67 thiab ISO 5832-2 rau unalloyed titanium.

Ob lub ntsiab lus tseem ceeb tswj kev teem caij. Ua ntej, cov txheej txheem loj hlob ob sab nraud thiab sab hauv, yog li ib feem tau teev tseg rau qhov tiav tiav yuav tsum tau ua kom qis qis ua ntej; kwv yees li ib nrab ntawm zaj duab xis thickness yog noj substrate. Qhov thib ob, cov npoo ntse tsom rau tam sim no thiab tsim cov kev loj hlob hauv zos, yog li cov ntug dav dav dav yog qhov tsim nyog yuav tsum tau ua ntau dua li kev ua haujlwm yooj yim.

Ua pov thawj ntawm Txheej: Kev Xeem thiab Txais

Ib txheej txheej tsuas yog siv tau yog tias nws tuaj yeem raug lees paub zoo ib yam li cov substrate. Microindentation hardness nyob rau hauv ASTM E384 yog tus qauv txheej txheem rau zaj duab xis hardness, qhia raws li HV nrog ib tug teev kev xeem load vim hais tias qhov kev nyeem ntawv ntog li loads ntawm ib tug ntxeem tau ceramic. Kev hnav yog ib txwm suav los ntawm tus pin- ntawm- disc kuaj ib ASTM G99, nrog tungsten carbide los yog alumina counterface, qhia tshwj xeeb hnav tus nqi ntau dua li raw ntim poob kom cov txiaj ntsig sib piv ntawm cov chaw sim.

Corrosion kuj ntawm MAO-kho titanium yog soj ntsuam los ntawm nruab nrab ntsev tsuag ib ASTM B117, qhov chaw kho mob ib txwm tuav li ob peb puas teev tiv thaiv dawb corrosion khoom nyob rau hauv lub cheeb tsam, thiab los ntawm electrochemical polarization kom quantify qhov txo nyob rau hauv corrosion tam sim no ntom, uas feem ntau poob los ntawm ib tug mus rau ob qho kev txiav txim. Qhov twg yog qhov chaw cog, ASTM F2129 electrochemical kuaj rau corrosion tsis kam ntawm cov khoom cog yog cov txheej txheem cuam tshuam.

Qhov twg siv zaj duab xis

Marine thiab offshore qauv yog daim ntawv thov ntim loj tshaj plaws, vim tias cov txheej txheem nyuaj, cov txheej txheem ceramic ntawm cov khoom siv titanium txhim kho kev ua haujlwm hauv dej hiav txwv thiab txo cov galvanic siab qhov twg titanium ntsib tooj liab alloys lossis hlau. Automotive heat-shield components benefit from the combination of wear resistance and thermal barrier behaviour, particularly where a sprayed thermal layer would spall and an in-situ ceramic film does not. Textile machinery siv MAO-coated yarn qhia qhov twg abrasive action ntawm filament yuav txwv tsis pub txiav rau hauv liab qab hlau.

Cov khoom siv hluav taws xob thiab hluav taws xob hluav taws xob siv cov txheej txheem rau kev tiv thaiv kev sib nqus thiab tiv thaiv siab - hluav taws xob hluav taws xob. Hauv cov kev pabcuam nruj dua, cov yeeb yaj kiab nqa cov khoom siv siab, siab thiab siab kub ib txhij, uas yog qhov ua haujlwm ntev ntawm ib qho hauv -situ ceramic txheej ntaus ib qho kev tso nyiaj.

Cov lus nug nquag

Q:Puas micro-arc oxidation hloov qhov ntev ntawm ib feem tiav?
A: Yog. Kev loj hlob ntawm zaj duab xis ua ke nrog kev loj hlob sab nraud nrog kev noj cov substrate, yog li cov khoom yog machined undersize ua ntej kev kho mob thiab ib tug nominal 20 µm zaj duab xis hloov sab nraud nto los ntawm kwv yees li ib nrab ntawm cov nyiaj.

Q:Cov qib titanium twg tuaj yeem kho tau?
A: Txhua qib uas tuaj yeem ua anodised hauv alkaline electrolyte, suav nrog cov qib tsis sib xws ntawm ASTM B265 thiab alpha-beta alloys xws li Ti-6Al-4V. Kev xaiv qib feem ntau cuam tshuam rau cov txheej txheem kev loj hlob thiab theem kev sib xyaw, tsis yog cov txheej txheem ua haujlwm.

Q:Yuav ntsuas qhov hardness ntawm ib zaj duab xis ceramic li cas?
A: Los ntawm microindentation nyob rau hauv ASTM E384, nrog rau kev kuaj load qhia nrog rau qhov tshwm sim. Vim tias cov txheej txheej yog ntxeem tau thiab nyias, kev nyeem ntawv poob qis thaum thauj khoom nce, yog li daim duab hardness tsis muaj qhov teev tseg tsis sib piv.

Q:Cov txheej txheem tuaj yeem siv rau kev sib dhos ua tiav?
A: Tsuas yog rau qhov chaw uas tuaj yeem raug hluav taws xob cais tawm thiab ua rau tag nrho. Masking yog ib qho nyuaj, threaded nta sau tam sim no thiab overgrow, thiab tiv tauj cov chaw uas yuav tsum tau nyob conductive yuav tsum tau tiv thaiv los yog machined tom qab.

Q:MAO zaj duab xis piv nrog cov txheej anodised li cas?
A: Pa anodising hlob ib zaj duab xis ob peb micrometers tuab ntawm tsawg voltage. Micro-arc oxidation ua haujlwm nyob rau hauv kev tso tawm, ua kom tuab dua, nyuaj thiab ntau dua crystalline oxide uas nqa lub nra hnyav dua li tsuas yog tiv thaiv corrosion.

Q:Cov yeeb yaj kiab puas muaj sia nyob thermal cycling?
A: Zoo dua li cov txheej txheej tso rau hauv feem ntau, vim tias nws tau loj hlob los ntawm substrate thiab tsis muaj kab ntawv cog lus. Thermal expansion mismatch tseem teeb tsa qhov kev ntxhov siab, thiab cov txheej txheej yuav tsum tau sib phim rau qhov kev caij tsheb kauj vab.