METALLOGRAPHY ASSIGNMENT 1 - WordPress

Transcription

[METALLOGRAPHY] 1METALLOGRAPHYByMUHAMMAD AL-ASYRAF BIN DINMUHAMAD AMERUL MUKMIN BIN YAHAYAMUHAMMAD FADZILAN BIN ABD LATIFDEPARTMENT OF MATERIAL ENGINEERING, FACULTY OFMANUFACTURINGUNIVERSITY OF TECHNICAL MALAYSIA MELAKAThis report is submitted to the Faculty Of Manufacturing Engineering of UTeM as a partialfulfillment of the requirements in the subject of BMFB 3253 METALLURGY for Bachelor ofManufacturing Engineering (Engineering Materials). The member of the supervisory committeeis as follow:DR SHARIZA BT ISMAILSubmitted on 2 NOVEMBER 20151

2[METALLOGRAPHY]1.0 INTRODUCTIONMetallographyMetallography is the scientific discipline of examining and determining the constitution and theunderlying structure of (or spatial relationships between) the constituents in metals, alloys andmaterials or it can be materialography. It is also has relation to the properties, of metals andalloys. Moreover, the characterization of structure of alloys or metals can be seen mostly withoptic microscope. Microstructural analysis of a material's metallographic microstructure aids indetermining if the material has been processed correctly and is therefore a critical step fordetermining products reliability (Quality Control) and for determining why a material failed(Metallographic Failure analysis).MetalsMetal is an element that readily forms positive ions (cations) and has metallic bonds. Metals aresometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons.This material is typically hard, opaque, shiny, and has good electrical and thermal conductivity.AlloysAn alloy is a mixture of metals or a mixture of a metal and another element. Alloys are definedby metallic bonding character.MicrostructureThe structure which is in micro dimension. This structure only can be seen by using microscope.2.0 IMPORTANCE OF METALLOGRAPHYThe importance of metallography: The understanding of the metals behavior To determine the strength and other characteristics of new alloys. Examination of defects that appear in finished or partly finished products and studies ofparts that have failed in service.Metallographic ApplicationsMetallographic testing and Material Science failure analysis and quality control testing are usedin industries that require produce reliability such as:2

[METALLOGRAPHY] 3Industries AerospaceAdvanced MaterialsSuperalloysCeramic Matrix CompositesMetal Matrix CompositesPolymer Matrix CompositesBiomedical DevicesMedical ImplantsMaterials Science EducationMetallurgical EngineeringMechanical EngineeringAerospace EngineeringElectronicsSolder Joint analysisIntegrated IC chip failure analysisPrinted Circuit board or PCB qualitycontrol and failure analysisDielectric layer coating analysisAutomotiveHeat TreatingMetal FabricationForgingCastingsThermal SprayWeldingPowder MetallurgyDeep DrawingFastener TestingMining Metallurgical Testing Labs Metallographic ApplicationsGrain Size Analysis! ASTM E112Porosity! ASTM A276Phase Analysis! ASTM E566! ASTM E1245Inclusions! ASTM E454! ASTM E1245Graphite Nodularity! ASTM A247Coating Thickness! ASTM B487Decarburization! ASTM E1077Welding AnalysisHAZ SensitizationTwin BoundariesCracksDendritesCorrosionCarburizing thicknessNitriding thicknessIntergranular fractureWeld sensitizationFlow line stressMicrohardness testingRockwell hardness testingSuperficial hardness testing3.0 SAMPLE PREPARATIONThe sample preparation consists of five major steps: CuttingMountingGrindingLapping3

4[METALLOGRAPHY] PolishingCUTTINGWhen cutting a specimen from a larger piece of material, care must be taken to ensure that it isrepresentative of the features found in the larger sample, or that it contains all the informationrequired to investigate a feature of interest. One problem is that preparation of the specimen maychange the microstructure of the material, for example through heating, chemical attack, ormechanical damage. The amount of damage depends on the method by which the specimen is cutand the material itself. Cutting with abrasives may cause a high amount of damage, while the useof a low-speed diamond saw can lessen the problems. There are many different cutting methods,although some are used only for specific specimen types.1. Sawing"Using hacksaws, band saws, and wire saws"Hand-held hacksaws or band saws generally do not generate enough frictional heat toalter the microstructure"Saw cut surface are tough, and coarse grinding is required to obtain a flat surface2. Electric discharge machining (EDM)"Electric discharge machining (EDM), or spark machining is a proses that uses sparksin a controlled manner to remove material from a conducting workpiece in adielectric fluid like kerosene"The material is remove from the sample in the form of microscopic craters.3. Fracturing"Breaking specimens with blow of a hammer or by steadily applying pressure"Location of the fracture can be controlled by nicking or notching the material"Not recommended because it rarely follows desired directions and damage fromfracturing can mask inherent features4

[METALLOGRAPHY] 5"Also lengthy coarse grinding may be required to obtain a flat surface.4. Shearing"Low-carbon sheet steel and other thin, soft materials can be cut to size by shearing"The area affected by shearing must be removed by grindingMOUNTINGMounting of specimens is usually necessary to allow them to be handled easily. It also minimizesthe amount of damage likely to be caused to the specimen itself. The mounting material usedshould not influence the specimen as a result of chemical reaction or mechanical stresses. It5

6[METALLOGRAPHY]should adhere well to the specimen, and if the specimen is to be electropolished later in thepreparation then the mounting material should also be electrically conducting. Specimens can behot mounted (about 150 C) using a mounting press either in a thermosetting plastic, examplephenolic resin, or a thermosoftening plastic example acrylic resin. If hot mounting will alter thestructure of the specimen a cold-setting resin can be used example epoxy, acrylic or polyesterresin. Porous materials must be impregnated by resin before mounting or polishing, to preventgrit, polishing media or etchant being trapped in the pores, and to preserve the open structure ofthe material. A mounted specimen usually has a thickness of about half its diameter, to preventrocking during grinding and polishing. The edges of the mounted specimen should also berounded to minimize the damage to grinding and polishing discs.6

[METALLOGRAPHY] 7GRINDINGSurface layers damaged by cutting must be removed by grinding. Mounted specimens are groundwith rotating discs of abrasive paper, for example wet silicon carbide paper. The coarseness ofthe paper is indicated by a number: the number of grains of silicon carbide per square inch. So,for example, 180 grit paper is coarser than 1200 grit. The grinding procedure involves severalstages, using a finer paper (higher number) each time. Each grinding stage removes the scratchesfrom the previous coarser paper. This can be easily achieved by orienting the specimenperpendicular to the previous scratches. Between each grade the specimen is washed thoroughlywith soapy water to prevent contamination from coarser grit present on the specimen surface.Typically, the finest grade of paper used is the 1200, and once the only scratches left on thespecimen are from this grade. The series of photos below shows the progression of the specimenwhen ground with progressively finer paper.Specimen ground with 180 grit paperSpecimen ground with 400 grit paperSpecimen ground with 800 grit paperSpecimen ground with 1200 grit paper7

88[METALLOGRAPHY]

[METALLOGRAPHY] 9LAPPINGThe lapping process is an alternative to grinding, in which the abrasive particles are not firmlyfixed to paper. Instead a paste and lubricant is applied to the surface of a disc. Surface roughnessfrom coarser preparation steps is removed by the micro-impact of rolling abrasive particles.POLISHINGPolishing discs are covered with soft cloth impregnated with abrasive diamond particles and anoily lubricant or water lubricant. Particles of two different grades are used a coarser polish typically with diamond particles 6 microns in diameter which should remove the scratchesproduced from the finest grinding stage, and a finer polish – typically with diamond particles1 micron in diameter, to produce a smooth surface. Before using a finer polishing wheel thespecimen should be washed thoroughly with warm soapy water followed by alcohol to preventcontamination of the disc. The drying can be made quicker using a hot air drier.Specimen polished to 6 micron levelSpecimen polished to 1 micron levelMechanical polishing will always leave a layer of disturbed material on the surface of thespecimen. Electropolishing or chemical polishing can be used to remove this, leaving anundisturbed surface.9

10 [METALLOGRAPHY]ETCHINGEtching is used to reveal the microstructure of the metal through selective chemical attack. Inalloys with more than one phase etching creates contrast between different regions throughdifferences in topography or the reflectivity of the different phases. The rate of etching isaffected by crystallographic orientation, so contrast is formed between grains, for example inpure metals. The reagent will also preferentially etch high energy sites such as grain boundaries.This results in a surface relief that enables different crystal orientations, grain boundaries, phasesand precipitates to be easily distinguished. The specimen is etched using a reagent. For example,for etching stainless steel or copper and its alloys, a saturated aqueous solution of ferric chloride,containing a few drops of hydrochloric acid is used. This is applied using a cotton bud wipedover the surface a few of times The specimen should then immediately be washed in alcohol anddried. Following the etching process there may be numerous small pits present on the surface.These are etch pits caused by localized chemical attack, and in most cases they do not representfeatures of the microstructure. They may occur preferentially in regions of high local disorder,for example where there is a high concentration of dislocations. If the specimen is over etched oretched for too long, these pits tend to grow, and obscure the main features to be observed as seenin the images below:Etched specimen10Over etched specimen

[METALLOGRAPHY] 11Cleaning specimens in an ultrasonic bath can also be helpful, but is not essential. Ideally thesurface to be examined optically should be perfectly flat and level. If not, then as the viewingarea is moved across the surface it will pass in and out of focus. In addition, it will make itdifficult to have the whole of the field of view in focus - while the centre is focused, the sideswill be out of focus. By using a specimen leveling press (shown below) this problem can beavoided, as it presses the mounted specimen into plasticene on a microscope slide, making itlevel. A small piece of paper or cloth covers the surface of the specimen to avoid scratching.4.0 MICROSCOPIC ANALYSISDuring microstructure analysis, the structure of a material is studied under magnification. Theproperties of a material determine how it will perform under a given application and theseproperties are dependent on the material’s structure. Metallographic analysis can be used as atool to help identify a metal or alloy, to determine whether an alloy was processed correctly, toexamine multiple phases within a material, to locate and characterize imperfections such as voidsor impurities, or to observe damaged or degraded areas in failure analysis investigations. Themethod most often used in such evaluations is microscopy. Both optical and scanning electronmicroscopy with energy-dispersive x-ray analysis can be useful in metallographic analysis. X-11

12 [METALLOGRAPHY]ray photoelectron spectroscopy is also useful in the measurement and identification of carbidesand graphitic inclusions and intermetallic formation.Metallographic analysis may determine such issues as: Grain size and growth Grain structure resulting from processing Intermetallic phase microstructures Carbide formation at surfaces and grain boundaries Equiaxed or columnar grains Chemical microsegregation Microshrinkage and porosity Inclusions Planar, cellular, and dendritic interfaces Microstuctures as a function of cooling rate Grain size as a function of work hardening Graphite structures in cast irons Graphite replacing bulk carbides near surfaces Silicon structures in Al-Si alloys5.0 PRINCIPLE AND PRACTICEThe mechanical properties of the materials are strongly affected by their microstructures.Metallography is one of the most used methods in metallurgy in order to characterize themicrostructures of the materials. This method allows the study and characterization of metals,ceramics and polymers. Optical and electronic microscopy are the major techniques used toobtain images of the characteristic microstructures of the materials.Metallography MethodThe process is done according the following:12

[METALLOGRAPHY] 13Sample CuDngAquisiEion ofMicrosctructure'simageSample CleaningMetallographyMehthodAcid EtchingSample MounEngPolishingGrindingAcquisition of material structures – Optical ExaminationOptical microscopy is still one of the most important techniques to analyze the microstructure of thematerials. Their major components, Illumination system (light source with variable intensity),Condenser lenses (adjustable lenses for focusing the light beam) and objective lens (It forms the imagebeing the most important component of the microscope)13

14 [METALLOGRAPHY]There are two examination modes, which are: 14Bright FieldVertical illuminationMost used method to the observation ofthe surface structuresLight passes through the objective lensand impinges on the sample surfaceSt

This report is submitted to the Faculty Of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements in the subject of BMFB 3253 METALLURGY for Bachelor of Manufacturing Engineering (Engineering Materials). The member of the supervisory committee is as follow: DR SHARIZA BT ISMAIL Submitted on 2 NOVEMBER 2015 . 2 [METALLOGRAPHY] 2 1.0 INTRODUCTION Metallography .