The research of function of coating of CoCrAlY of spray of plasma of TiAl alloy surface
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SEM Observation Shows That The Bonding Between Thermal Barrier Coating And Substrate Is Good.
The Surface Hardness Of TiAl Alloy Is Improved After The Oxidation Test.
Show That The Oxidation Resistance Of The Samples Is Improved Remarkably of ℃ of The Oxidation Tests At 850.
The Phases And Microstructure Of The Thermal Barrier Coating Are Determined By SEM.
Key Words: Introductive Normal >TiAl alloy is ordered structure of face heart all directions, its density is small, hear resistance is good. Because it can form better aluminous surface coating, tiAl alloy has high high temperature strength, fight stability of fibre of creep function, high temperature and stretch model quantity. The material of construction of a kind of high temperature that use temperature can amount to 1000 ℃ [1] . But symmetry of crystal of the compound between TiAl metal is low, slippage is little, be good at electron counts covalence to hold proportion in the place in number of total prices electron bigger (about 30 ％ ) , accordingly alloy of the TiAl when room temperature appears fragile change. Often produce simple cleavage to rupture, produce plasticity to be out of shape in hot-working process hard. In 800 ℃ above its fight oxidisability to show apparent inadequacy, restricted what its fall in high temperature to use, after classics heat treatment, the organization shows inhomogenous sex to be put in thick any crystalline substance to rupture feature [2] . Although TiAl alloy has some effect,be apparent, but fall in more complex work environment, sheet relies on the function of its oneself to still cannot satisfy a requirement completely, fight the function such as oxidation to enhance what TiAl alloy falls in high temperature condition, we use technology of plasma thermal spraying to besmear in surface of TiAl alloy matrix normally MCrAlY of coating of a high quality, make matrix has the certain property of coating material thereby, if fight high temperature, fight oxidation to wait. MCrAlY in, m delegate: Co, Ni, Fe; Y is to serve as the function that increase and maintains protection oxidation coating (combinative sex, high temperature is able to bear or endure corrode sex and reduce interior to diffuse etc) this kind of coating, already caused the attention of people. In high temperature environment, MCrAlY coating and environmental interaction, built the Al2O3 oxidation layer that has protection or Cr2O3 oxidation layer, compact oxidation layer can keep apart matrix and aggressivity environment, lower the oxidation rate of matrix greatly. Add in coating 0.
1% ～ 1.
0% (Wt) Y, raised the chemical adhesion between oxidation layer and matrix not only, still make its fight circular oxidation ability to rise greatly, the Co of certain amount is added in coating, still can improve heatproof corrode ability [3] . CoCrAlY coating is used in this experiment. Among them, the char content of the organizes the γ solid solution that is Co-Cr and dispersion separate out chromium of CoCr alloy and tungsten and boride, have heat-resisting wear-resisting to fight corrode, the superior performance that fights the many sided such as the creep, tenacity that fights high temperature oxidation and tall rigid become reconciled, can be able to bear or endure especially H2S is corroded [4] . 1 experiment method 1.
Normal > TiAl alloy (45Ti-45Al-2Mn-2Nb-1B) the sample that great ability makes 1mm of × of 10mm × 10mm with cut of line cut machine, burnish the surface with sand paper before spray coating, with eliminate surface smeary with rusty spot, undertake gush sand preparation to sample surface again next, appearance is cleaned to wash sample face with ultrasonic after making the surface has certain surface roughness, clean sample with acetone, wait for the surface to blow after working, secure sample rotating on workbench, start rotate workbench, the made speed with 180r/s is rotational, sample is apart from the distance of spray gun to be 140mm. CoCrAlY(70Co-21Cr-8Al-0.
5Y) powder is put into powder feeder, equipment of spray of the plasma that start, connect proper argon gas and hydric, increase source current 600A from 450A, plasma jet arises, when CoCrAlY powder passes spray gun mouth, be fused, with glue state form from muzzle ejective, gush arrives sample surface, form coating stage by stage. Connect argon at the same time gas and hydric advocate if regard protection as atmosphere. 1.
Normal Align=left> undertakes with hot analysis balance high temperature oxidation experiments, its job sketch map sees a picture 1. Make balance and place hang sample balance above all, build asbestine spacer on heating furnace, insert oxygen therapy tube in oxidation canister. Heat to heat and connect oxygen next, open computer undertakes weightening finish compensates the job oxidizing. Every 5min records early days 1 times, after 5h every 0.
5h is recorded. Experiment temperature is 850 ℃ . 1.
Aerobic bottle 2.
Oxygen therapy conduit 3.
Sample 4.
Oxidation canister 5.
Heating furnace 6.
Asbestine spacer 7.
Balance 8.
The computer pursues Fig of sketch map of experiment of oxidation of 1 high temperature.
1Result of test of Sketch Map Of The Oxidation Experimentation2 and analysis 2.
1 microstructure reachs hardness profile Normal > pursues 2 it is the sample after spray the microstructure after did not oxidize through high temperature and be being handled through oxidation of 850 ℃ high temperature, the left in the graph is material matrix, right is coating, macula is microscopical sclerometer impress. Can see from inside the graph CoCrAlY coating is compact be united in wedlock with matrix close together. And, what go up via the coating that high temperature oxidation handles is microscopical hardness impress is less than the impress after was not being handled through high temperature oxidation apparently. Explain through high temperature oxidation is handled, the element such as Co, Cr, Al, Y falls to form oxide with oxygen union in high temperature, those who make coating changes after passing heat treatment is very compact, hardness rises greatly. A) coating handles B without high temperature oxidation) the microstructure × 400 Fig of coating of 2 CoCrAlY of the graph after via 850 ℃ high temperature oxidation is handled.
2400 2 of × of Microstructures Of CoCrAlY Coating.
2Normal > pursues 3 it is picture of SEM of appearance of sample surface form, among them A) handle without high temperature, b) it is to pass processing of oxidation of 850 ℃ high temperature. From inside the graph we can see the pellet of sample surface coating that handles without high temperature submits a form for the most part, have a few showing elliptic, granuality is inhomogenous, be free among them hole. What handle temperature as high temperature oxidation is elevatory, the element such as the Co in CoCrAlY coating, Cr, Al, Y is united in wedlock with oxygen gradually, form oxide, cover face of Yu Tu layer, those who increased coating is compact degree. Can see coating is shown banding, and by the melt particle of shape of banding or irregular grain is built each other receive, chase an accumulation and become, the appearance of form of layer shape structure that has a typical case, one of main features that this is plasma coating [5, 6] . Normal Align=center>a) without B of high temperature oxidation) via 850 ℃ high temperature oxidation pursues Fig of appearance of form of 3 sample surface.
3SEM Micrograph Of Sample Surface2.
Normal > pursues 4 it is the sample after TiAl matrix and spray the weightening finish curve that oxidizes in static state of 100h of 850 ℃ classics. Should fall in 850 ℃ condition, when heat preservation time did not achieve 80h, the oxide weightening finish of CoCrAlY coating is apparent the oxide weightening finish of matrix of over TiAl alloy, but the speed of oxide weightening finish of CoCrAlY coating is compared with photograph of TiAl alloy matrix, apparent under TiAl alloy matrix. After heat preservation time achieves 80h, the oxide weightening finish of CoCrAlY coating gradually little the oxide weightening finish at TiAl alloy matrix, and speed of its weightening finish is apparent under YiAl alloy matrix. Accordingly, maintain when high temperature environment in longer inside, the oxide block that covers as a result of CoCrAlY coating surface its oxidize further, of CoCrAlY coating fight oxidisability matrix of alloy of apparent excel TiAl, can remove high temperature to fight the action of oxidation. Graph 4.
Fig of curve of oxidation weightening finish.
4Conclusion of Curves Of Oxidation Weight Gain 3 (1) use plasma spray law to be formed in TiAl alloy surface by coating of heat barrier of CoCrAlY pottery and porcelain. (2) the sample after spray is after processing of oxidation of course high temperature, the hardness of layer of exterior pottery and porcelain is remarkable heighten, show the advantage that CoCrAlY coating lays at high temperature ambient conditions aptly. (3) experiment of high temperature oxidation makes clear, maintain when high temperature environment in longer inside, the oxide block that covers as a result of CoCrAlY coating surface its oxidize further, of CoCrAlY coating fight oxidisability matrix of alloy of apparent excel TiAl, can remove high temperature to fight the action of oxidation. CNC Milling