Titanium alloys muaj kev sib raug zoo rau cov pa oxygen thiab nitrogen ntawm qhov kub siab, uas ua rau muaj kev tsim cov nplai oxide tenacious thaum kub - ua haujlwm. Cov xim thiab tuab ntawm cov nplai no sib txawv raws li qhov kub thiab txias -xiav ntawm kwv yees li 600℃, greyish -liab ntawm kwv yees li 850℃, thiab grey ntawm 900℃. Raws li kev tsim kub nce, nplai thickness nce thiab adhesion rau lub substrate intensifies, ua kom tshem tawm ntau nyuaj. Scales generated saum toj no 900℃yuav tsum aggressive tshuaj stripping uas nquag compromises nyob rau hauv lub nto kev ncaj ncees.
Cov txheej txheem kev lag luam rau titanium alloy scale tshem tawm tseem yog ob -kauj ruam alkali-acid method: molten caustic conditioning tom qab acid pickling. Thaum ua tau zoo, cov kab ke no qhia txog ob qhov kev pheej hmoo loj ntawm metallurgical kev pheej hmoo - kev laus ntxov ntxov ntxov thiab hydrogen embrittlement- uas xav tau cov txheej txheem nruj heev.
Scale Formation thiab yam ntxwv
Titanium alloys tsim oxide nplai los ntawm kev sib kis- tswj oxidation thaum ua haujlwm kub. Cov nplai muaj ntau txheej txheej oxide, feem ntau TiO₂, nrog rau me me los ntawm Ti₂O₃ thiab TiO nyob ntawm cov pa oxygen ib nrab siab thiab lub sijhawm raug.
Qhov kub thiab txias - nplai kev sib raug zoo ua raws li tus qauv zoo sib xws hauv qib titanium alloy:
Ntawm 600 degree, oxide zaj duab xis tseem nyias thiab ntxeem tau, tso cai ncaj qha tshem tawm cov tshuaj lom neeg. Ntawm 850 degree, nplai thickening thiab sintering nce adhesion. Tshaj li 900 degree, qhov ntsuas densifies thiab bonds muaj zog nrog lub substrate; Kev tshem tawm yuav tsum tau txuas ntxiv nthuav tawm kev tawm tsam hnyav, ua kom muaj kev pheej hmoo ntawm kev tawm tsam substrate.
TC4 titanium alloy kub- ua rau saum npoo oxide tuab feem ntau ntsuas tsawg dua 2 μm, txawm li cas los xij, cov txheej nyias nyias no tuaj yeem cuam tshuam kev ua haujlwm tom qab yog tias tsis tshem tawm tag nrho.
Ob -Txoj Kev Descaling
Kauj Ruam Ib: Molten Caustic Conditioning
Thawj theem immerses lub scaled workpiece nyob rau hauv ib tug molten alkaline da dej. Lub caustic nruab nrab-feem ntau yog ib qho kev sib xyaw ntawm NaOH thiab NaNO₂ lossis NaOH thiab NaNO₃-reacts nrog cov nplai oxide, loosening nws cov qauv thiab txhawb detachment.
Common formulations muaj xws li:
- NaOH ntawm 700 g / L ntxiv rau NaNO₂ ntawm 250 g / L (supersaturated tov)
- Kub kub txog li 160 degree
- Lub sijhawm immersion mus txog 6 teev rau kev ua kom tiav
Lwm txoj hauv kev uas muaj molten oxidizing ntsev (piv txwv li, Virgo- hom formulations) kuj muaj pov thawj zoo rau kub - dov alloy scale tshem tawm.
Lub da dej caustic ua haujlwm los ntawm kev hloov tshuaj lom neeg: nws hloov cov oxide adherent mus rau hauv ib qho friable, conditioned txheej uas tom qab acid pickling tuaj yeem yaj.
Kauj Ruam 2: Acid Pickling
Tom qab ua kom txias txias thiab dej yaug, lub workpiece raug acid pickling. Cov txheej txheem pickling tov ua ke nrog nitric acid (HNO₃) nrog hydrofluoric acid (HF).
Yam khoom acid da dej parameter:
- HNO₃: HF ntim piv Ntau dua lossis sib npaug rau 5: 1 (tseem ceeb rau kev tiv thaiv hydrogen embrittlement)
- Pom zoo piv: 10: 1 HNO₃:HF
- Da dej kub: qis dua 60℃kom txwv hydrogen nqus
- Lub sij hawm immersion: 20 vib nas this mus rau ob peb feeb nyob ntawm qhov ntsuas thickness thiab alloy muaj pes tsawg leeg
Cov nitric acid ua hauj lwm raws li ib tug oxidizing tus neeg sawv cev uas passivates lub tshiab titanium nto, thaum hydrofluoric acid dissolves lub conditioned scale thiab underlying oxide- paug txheej.
Pickling tshem tawm cov seem seem thiab rov ua kom cov xim hlau ua tiav. Rau cov khoom siv tshuaj milled, ntsev - yuav tsum tau da dej txias kom tshem tawm cov pa oxygen - cov kab mob paug hauv qab qhov ntsuas.
Cov Txheej Txheem Tseem Ceeb
Risk Ib: Kev laus ntxov ntxov ua kom muaj zog
Lub molten caustic da dej ua haujlwm ntawm kwv yees li 450 degree. Qhov kub no poob rau hauv lossis ze rau qhov kub ntawm qhov kub ntawm + thiab titanium alloys.
Thaum lub sij hawm caustic txias, ib nrab- cov khoom tiav tuaj yeem ua rau cov nag lossis daus uas tsis tau npaj siab ntxiv lawm - cov nucleation thiab kev loj hlob ntawm theem nrab lossis intermetallic theem hauv matrix. Qhov kev laus ntxov ntxov no ua rau muaj ntau yam kev puas tsuaj:
- Ntxiv hardness thiab txo ductility hauv kev ua haujlwm txias tom ntej
- Kev pheej hmoo siab ntawm kev tawg thaum lub sijhawm ua haujlwm ntxiv
- Compromised seem stability nyob rau hauv cov khoom tiav
Qhov tshwm sim tshwj xeeb tshaj yog nyob rau hauv - nplua nuj alloys qhov twg cov laus kinetics nrawm ntawm qhov kub siab tshaj 400℃. Tsis zoo li kev tswj xyuas kev laus ua tau raws li kev soj ntsuam nruj, caustic- da dej tshwm sim yam tsis xav txog qhov kev kub ntxhov ntawm cov hlau, qhia txog qhov sib txawv ntawm cov khoom siv kho tshuab thoob plaws ntau lawm.
Risk Ob: Hydrogen Embrittlement
Hydrogen embrittlement yog qhov kev hem thawj tshaj plaws hauv titanium alloy ua. Titanium thiab nws cov alloys nkag tau yooj yim nqus hydrogen los ntawm cov kev daws teeb meem, ntxuav chav da dej, thiab txawm tias qhov chaw ntawm qhov kub siab.
Lub mechanism ua haujlwm raws li hauv qab no:
Thaum lub sij hawm acid pickling, HF tivthaiv tawm tsam titanium nto, tsim atomic hydrogen raws li ib tug byproduct ntawm lub dissolution cov tshuaj tiv thaiv. Ib feem ntawm no atomic hydrogen diffuses rau hauv titanium lattice es tsis recombining rau hauv molecular H₂ thiab khiav.
Thaum nqus tau, hydrogen nyob hauv qhov chaw nruab nrab hauv -Ti lattice. Ntawm qhov siab tshaj qhov kev txwv tsis pub solubility, hydrogen precipitates li brittle titanium hydride (TiHₓ) platelets raws li cov ciam teb nplej thiab plam dav hlau. Cov hydrides no:
- Txo cov pob txha toughness thiab qaug zog ua haujlwm
- Txhawb intergranular cracking nyob rau hauv tensile kev nyuaj siab
- Accelerate subcritical crack loj hlob nyob rau hauv kev pab cuam ib puag ncig
Qhov chaw pib hydrogen embrittlement sib txawv los ntawm cov alloy muaj pes tsawg leeg thiab microstructure, tab sis cov concentrations tsawg li 150-200 ppm tuaj yeem ua rau ntsuas qhov degradation hauv cov khoom siv tshuab.
Ob peb yam ua rau hydrogen picks ntau dua - thaum lub sij hawm pickling:
- HF concentration ntau tshaj qhov pom zooaccelerates lub dissolution cov tshuaj tiv thaiv thiab generates ntau atomic hydrogen
- Kub da dej siab tshaj 60 degreence hydrogen diffusivity thiab nqus kinetics
- Depleted HNO₃ cov ntsiab lustxo cov nyhuv passivating uas yuav txwv tsis pub hydrogen ingress
- Ntxiv lub sij hawm immersionprolongs kev raug hydrogen
- Titanium ion tsub kom siab tshaj 12 g / LNyob rau hauv lub da dej hloov cov tshuaj chemistry thiab txhawb nqa hydrogen absorption
Hydrogen absorption tuaj yeem tiv thaiv tau tag nrho los ntawm kev tshem tawm cov hlau thiab npib tsib xee saum npoo av nyob rau hauv cov tshuaj nitric acid ua ntej scale txias. Qhov kev kho ua ntej no tshem tawm cov teebmeem galvanic coupling uas ua kom cov hydrogen pick- thaum lub sij hawm tom qab raug cov kua qaub.
Txheej txheem tswj cov tswv yim
Caustic Conditioning Controls
Kev tswj qhov kub thiab txias tseem yog qhov tseem ceeb ntawm kev tiv thaiv kev laus ntxov ntxov. Thaum 450℃sawv cev rau qhov chaw ua haujlwm zoo sib xws, qis dua -cov qauv kub kub muaj nyob. NaOH-NaNO₂ cov tshuab ua haujlwm nyob ze 160℃(boiling aqueous tov) muab lwm txoj hauv kev uas txo cov kev pheej hmoo ntawm kev laus thaum tswj kev ua haujlwm kom zoo.
Lub sij hawm minimization txwv thermal raug. Lub sijhawm txias yuav tsum yog qhov tsawg kawg nkaus uas yuav tsum tau ua kom ua tiav qhov ntsuas qhov xoob- feem ntau txiav txim siab los ntawm kev kuaj daim coupon rau txhua qhov alloy-qib thiab nplai- tuab ua ke.
Alloy-cov txheej txheem tshwj xeeb account rau qhov sib txawv ntawm kev laus rhiab heev. -nplua nuj alloys yuav tsum tau ntau conservative kub-lub sij hawm tsis tshaj los yog nyob ze - alloys.
Acid Pickling Controls
HNO₃: HF piv kev saib xyuas saum toj no 5: 1 (zoo dua 10: 1) yog ib qho tseem ceeb tshaj plaws kev tswj tsis tau rau kev tiv thaiv hydrogen embrittlement. Cov nitric acid concentration yuav tsum tsis txhob poob qis dua li ntawm 10%, raws li qhov chaw pib no qhia txog thaj tsam ntawm kev nyab xeeb passivation thiab nquag nqus hydrogen.
Qhov ntsuas kub qis dua 60℃txo ob qho tib si hydrogen absorption kinetics thiab cov nqi corrosion.
Kev saib xyuas da dej suav nrog kev tshuaj xyuas tsis tu ncua ntawm cov kua qaub thiab cov ntsiab lus titanium yaj. Kev hloov da dej yuav tsim nyog thaum titanium concentration ntau dua 12 g / L.
Tshaj tawm -pickling yaug nrog dej kub ua raws li dej txias thiab yuam kom ziab kom tsis txhob muaj cov kua qaub corrosion thiab txo qis hydrogen ingress thaum tuav tom ntej.
Lub sij hawm qhov rais txwv yuav tsum tau acid pickling nyob rau hauv ib teev ntawm caustic txias kom tiv thaiv oxidation theem nrab ntawm cov conditioned nto.
Xaus
Ob -cov kauj ruam molten caustic txias thiab acid pickling txheej txheem tseem yog tus qauv kev lag luam rau titanium alloy nplai tshem tawm. Nws cov txiaj ntsig tau muab los ntawm kev ua tiav ntawm caustic scale loosening tom qab los ntawm acid dissolution. Txawm li cas los xij, cov txheej txheem qhia txog ob qhov kev pheej hmoo loj hauv metallurgical - kev laus ntxov ntxov ua kom muaj zog los ntawm 450℃caustic raug thiab hydrogen embrittlement los ntawm kev tswj tsis tau HF-HNO₃ pickling.
Kev ua tiav tau zoo xav tau kev tswj xyuas nruj ntawm qhov ntsuas kub, lub sijhawm, thiab kev daws teeb meem chemistry. HNO ₃: HF piv yuav tsum tsis tu ncua tshaj 5: 1 kom tiv thaiv hydrogen nqus. Caustic da dej kub thiab ntev yuav tsum tau txo qis kom tsis txhob muaj cov lus teb tsis zoo.
Rau qhov chaw tsim khoom ua cov qib sib txawv ntawm titanium alloy thiab cov qauv khoom, cov txheej txheem sib txawv - ua ke nrog hauv - kev saib xyuas thiab kev tsom xam da dej tsis tu ncua - muab txoj hauv kev txhim khu kev qha zoo tshaj plaws rau kev tshem tawm cov nplais tsis muaj kev cuam tshuam cov khoom siv lossis cov khoom siv ruaj khov.
