Laboratory control of thermal sprayed coatings_E

1、Laboratory control of thermal sprayed coatings Jrg Hochstrasser May 26th 2008 / 7/17/2021 / 2 Quality control of thermals sprayed coatings Materials Processing Surface Activation Coating Deposition MeltingPowderQuality Control Cleaning Grit Blasting Movement Transferred Arc - VPS Robotic Systems Man

2、ipulators Plasma Gun Design Control Systems Parameters Environmental Laser Light Scattering Morphology NDT Physical / Mechanical Tests Metallographic Criteria Degreasing Grit and Nozzle Wear, Pressure, Movement Surface Roughness Relative Movement Torch - Part Powder Plasma Gas Powder feed Environmen

3、tal Particle Size Distribution Morphology Controlled Metallographic Preparation Bond Strength Hardness Quality ControlQuality ControlQuality ControlQuality ControlQuality Control Automated ProcessAutomated Process Automated ProcessAutomated ProcessAutomated Process / 7/17/2021 / 3 Quality control of

4、 thermals sprayed coatings lMetallography 4 Metallographic preparation using reproducible standard methods 4 Evaluation according to internal- or customers specification (PWA, GE, etc.) 4 Lightmicroscope with Image archiving system (Acquiring, archiving and analyzing) 4 Scaning electron Microscope (

5、SEM) with Energy Dispersive X-ray Analyser 4 Microhardness (Vickers, Knoop) 4 Macrohardness (Rockwell superficial) / 7/17/2021 / 4 Mechanical testing 4 Bond strength (DIN EN 582, ASTM C633) 4 Lapshear 4 Bend test 4 cup test (Erichsen) Quality Control of thermals sprayed coatings / 7/17/2021 / 5 Qual

6、ity Control of thermals sprayed coatings Process of metallographical Operations Sample identification Cutting Mounting Grinding Polishing Etching (Optional) Evaluation / 7/17/2021 / 6 Quality Control of thermals sprayed coatings - Cut off - Mounting - Wet grinding - Polishing - - Etching - Micro-Exa

7、mination - Photomicrography - Skilled Metallographic Operations / 7/17/2021 / 7 Quality Control of thermals sprayed coatings The aim of metallographic sample preparation is to reveal the true structure of the sprayed sample. The easiest way to accomplish this is with a systematic preparation method.

8、 When our work routinely involves examining the same material, in the same condition, we want to achieve the same result each time. The preparation results must be Reproducible ! / 7/17/2021 / 8 Quality Control of thermals sprayed coatings Depending on the size or shape of the piece of material, it

9、may need to be sectioned. A plane surface, which as little deformation as possible, is required to facilitate and expedite further preparation. Consequently, the most appropriate sectioning method is abrasive wet cutting, which will introduce the least amount of damage in relation to the time needed

10、. Sectioning (Cutting) Choice of wheel:Wok pieceWheel material Binder Ceramicsdiamondsmetal Hard metalsdiamondsbakelite Ferrous metalsAluminium oxidebakelite Hard ferrous metalsCubic boron nitrid bakelite Non ferrous metalsSilicon carbidebakelite nHard materials Cut-off wheels with soft binder nSoft

11、 materials Cut-off wheels with hard binder / 7/17/2021 / 9 Quality Control of thermals sprayed coatings Sectioning (Cutting) Substrate Coating Direction of cutting Substrate Coating Or cut-off wheel Substrate Coating RightWrong Substrate Coating Rotation / 7/17/2021 / 10 Quality Control of thermals

12、sprayed coatings Cleaning For the best possible results, samples should be cleaned prior to mounting. The surface must be free from grease and other contaminants for the best adhesion of the resin to sample. Cleaning materials:Isopropylalkohol Ultra sonic (2 to 3 minutes) / 7/17/2021 / 11 Quality Co

13、ntrol of thermals sprayed coatings Mounting Generally it has to be distinguished between hot or cold mounting. Hot mounting: (Metals, Carbides) The sample is placed in the mounting press, the resin is added, and the sample is processed under heat and high pressure. Types of hot mounting resin: Acryl

14、ic Thermoplastic transparent mounts, low shrinkage Epoxy Thermosetting Edge retention, plainness, hard, good adhesion wear resistant, no shrinkage. Bakelite Thermosetting Serial mounting, medium shrinkage / 7/17/2021 / 12 Quality Control of thermals sprayed coatings Mounting Cold mounting:(porous me

15、tals, ceramics) The sample is placed in a mould. The correct amounts of two or three components are measured carefully by ether volume or weight. Then they are mixed thoroughly and poured over the samples. Types of cold mounting resin: Acrylic Serial mounting, Edge retention, low viscosity (Mineral

16、fillers) very low shrinkage, wear resistant. Polyester / Acrylic Edge retention, plainness, very hard, (Mineral fillers) good adhesion, very low shrinkage. Epoxy Porous samples, vacuum impregnation good adhesion, no shrinkage,low vapourpressure low viscosity. / 7/17/2021 / 13 Quality control of ther

17、mals sprayed coatings Mounting Vacuum impregnation: (porous metals, ceramics) Porous materials (10%) as for example TBC-coatings, abradables and ceramics require vacuum impregnation. All pores connected to the surface fill with resin. Consequently, the resin reinforced these fragile materials. Prepa

18、ration artefacts like pull-outs, cracks ore unopened porosity (smearing) can be minimised. Only Epoxy resin can be used for vacuum impregnation, due to their low viscosity and their low vapour pressure. / 7/17/2021 / 14 Quality control of thermals sprayed coatings Mounting Vacuum impregnation / 7/17

19、/2021 / 15 Quality control of thermals sprayed coatings Grinding and Polishing Preparation parameters: Base (Disc):Paper, Cloth, Disc Abrasive:SiC, Al2O3 , Diamond Grit / Grain Size:200 mesh, microns Lubricant:Water, etc. Rotation speed:300 rpm Force, pressure:Newton Time:seconds, dependent of amoun

20、t of the samples All parameters are dependent of the amount of the samples / 7/17/2021 / 16 Quality control of thermals sprayed coatings Grinding and Polishing Proper grinding removes damaged or deformed surface materials, while introducing only limited amount of new deformations. The aim is a plane

21、 surface with minimal damage that can be removed easily during polishing in the possible time. Plane Grinding (PG) The first grinding step is always defined as Plane Grinding -SiC papers(soft materials) -Al2O3 grinding stones(ferrous metals) -Metal-bonded diadiscs(hard ferrous metals) -Diamondgrindi

22、ng discs(hard materials, like ceramics or carbides) / 7/17/2021 / 17 Quality control of thermals sprayed coatings Grinding and Polishing Fine Grinding (FG) Fine Grinding produces a surface with such a small amount of deformation that it can be removed during polishing SiC papers(soft materials) Diad

23、isc(hard ferrous metals) Diamondgrinding wheel(hard materials, like ceramics or carbides) Diamond polishing (DP) / Oxide polishing (OP) Like grinding, polishing must remove the damage introduced by previous operations. This is archived with steps of successively finer abrasive particles Napped cloth

24、(soft materials) No Napped cloth(hard materials) FAbrasive particles are applied during the process / 7/17/2021 / 18 Quality control of thermals sprayed coatings Metallographic preparation data sheet for thermal sprayed coatings (Example) Coating Materials:Cobalt Base:CoCrAIY, MCrAlY, etc. Nickel ba

25、se:NiAIMo, NiAI, NiCr, NiCrAIY, etc. Iron Base:FeCrAIY, FeNiAl, etc. Alloys 2.3 Sampling CuttingCut-off machine:Struers Discotom 2 Cut-off wheel:Struers 31 TRE MountingMounting mould:Dia. 30XDia. 4050 x70 Cold mountingMaterials:Struers Epofix or Caldofix Vacuum ImpregnationYes:No:XVacuum time:min. R

26、emarks: / 7/17/2021 / 19 Quality control of thermals sprayed coatings Metallographic preparation data sheet for thermal sprayed coatings Grinding / StepIIIIIIIVV EquipmentABRAMATIC DiscPaperPaperPaperPaper Grinding mediaSiCSiCSiCSiC Grit / Grain size1202205001000 Abrasive / Dosing- Lubricant / Dosin

27、gWaterWaterWaterWater Pressure (N)200150100100 Disc (RPM)300300300300 Rotation / Time (sec)2x60606060 Removal (mm)1 / 7/17/2021 / 20 Quality control of thermals sprayed coatings Metallographic preparation data sheet for thermal sprayed coatings Polishing / StepIIIIIIIVV EquipmentABRAMATIC(Optional)P

28、lanapol(*) DiscDP-DURDP-MOLDP-NAPOP-CHEM Grinding mediaDiamondDiamondDiamondOP-U Grit / Grain size6 m3 m1 m0.04 m Abrasive / DosingMeMeMeManual Lubricant / DosingRed/MeRed/MeRed/MeWater Pressure (N)10010010090 Disc (RPM)150150150150 Rotation / Time (sec)906060120 (*) Planapol with Pedemax REMARKS: T

29、he preparation methods are designed for three mounted samples of 30 mm diameter, clamped in a sample holder of 160 mm diameter. The specimen area should be approximately 40 % of the mount, with a coating thickness of 150-300 microns. For thinner / thicker coatings reduce / increase only the time. If

30、 you need more information or if you want to improve the results, see STRUERS Metalog Guide or in the literature. / 7/17/2021 / 21 Quality control of thermals sprayed coatings Porosity (Holes) Impurities (Oxides) unmelted particles (unreacted) Cracks (horizontal,vertical) Interface contamination (Bo

31、nding) Surface roughness Coating Thickness Hardness (Micro,Vickers / Macro, Rockwell) Bond strength Coating evaluation / 7/17/2021 / 22 Quality control of thermals sprayed coatings Spraying direction Schematically coating structure / 7/17/2021 / 23 Quality control of thermals sprayed coatings Smooth

32、 surfaces The world of Surfaces Sticky surfacesHot surfacesFragile surfaces Reflectin surfacesHard surfacesSoft surfacesMissing surfaces / 7/17/2021 / 24 Quality control of thermals sprayed coatings Preparation artefacts Smearing: The plastic deformation of larger samples areas is called smearing In

33、stead of being cut, the material is pushed, moved across the surface The reason is an incorrect application of abrasive, lubricant or polishing cloth, or a combination of these. Which makes the abrasive act as if it was blunt. There are three possibilities to avoid smearing: 1. Increase the amount o

34、f lubricant 2. Change the cloth 3. Use larger grain size Mag.: 500 x / 7/17/2021 / 25 Quality control of thermals sprayed coatings Pull-outs: Pull-outs are the cavities left after grains or particles which are torn out of the sample surface during abrasion. They are found in hard and brittle materia

35、ls, and in materials with inclusions. Preparation artefacts / 7/17/2021 / 26 Quality control of thermals sprayed coatings Preparation artefacts Gaps: Gabs are voids between mounting resin and sample materials. Mag.: 50 x Mag.: 200 x / 7/17/2021 / 27 Quality control of thermals sprayed coatings Prepa

36、ration artefacts Cracks: Cracks are fractures in brittle materials and materials with different phases. The energy used to machine the sample is greater than can be absorbed. The surplus energy results in the cracks. When cutting coated samples, the wheel should pass through the layer fist, so that

37、the base material can act as support. For brittle materials, hot compression mounting should be avoided and cold mounting, preferably vacuum impregnation, should be used instead. Be careful not to use mounting materials with high shrinkage. They might pull layers away from the base materials. 500:1

38、200:1 WC 17Co ZrO2-Y2O3 / 7/17/2021 / 28 Quality control of thermals sprayed coatings Preparation artefacts Porosity: Plasma coatings have natural porosity. It is important to get the correct values, and not wrong readings because of preparation faults. Depending on the properties of the material, t

39、wo contrary effect regarding porosity can be seen. 1.Soft and ductile materials can be deformed easily. Therefore pores can be covered by smearing materials. An examination might show readings which are too low. 2.Hard brittle materials often get fractures at the surface during the first mechanical

40、(Cutting) preparation steps. The surface might show a porosity higher than real one. 200 :12.1. / 7/17/2021 / 29 Quality control of thermals sprayed coatings Preparation artefacts Scratches: Scratches are grooves in the surface of a sample, produced by the points of abrasives particles. Make sure th

41、at after PG (plan grinding) the surface of all samples in the specimen holder show the same uniform scratch-pattern over the whole surface. Mag.: 50 x Mag.: 200 x Repeat PG in necessary! Clean samples and sample holder carefully after every step, to avoid contamination of the grinding / polishing surface through large abrasive particles from a pre