Skip to main content

Samples Preparation for Metallurgical testing

Getting together

SAMPLE PREPARATION:-


  • Selecting a representative sample of the materials
  • Sectioning the sample to avoid altering or destroying the structure of interest
  • Mounting the section without damage to the test sample
  • Grinding to achieve a flat sample with a minimum amount of damage to the sample surface
  • Polishing the mounted and ground sample
  • Etching in the proper etchant to reveal the microstructural details

SELECTING

Selecting a representative test sample to properly characterize the microstructure or the features of interest is a very important first step. For example, grain size measurements are performed on transverse sections, whereas general microstructure evaluations are performed on longitudinal sections. Therefore, it is important to provide the laboratory with information about the orientation or the rolling direction of the test specimen.







SECTIONING

Test samples are carefully sectioned to avoid altering or destroying the structure of the materials. If an abrasive saw is used, it is important to keep the sample cool with coolant or lubricant so it doesn’t burn or overheat. However, no matter how carefully abrasive sawing or electric discharge machining is performed, a small amount of deformation occurs on the sample surface. This deformation must be removed during subsequent preparation steps.



MOUNTING

After the test sample is sectioned to a convenient size, it is mounted in a plastic or epoxy material to facilitate handling and the grinding and polishing steps. Mounting media must be compatible with the sample with respect to hardness and abrasion resistance. Typical mounting materials are thermosetting phenolics such as Bakelite, and thermoplastic materials such as methyl methacrylate (Lucite). Mounting involves putting the sample in a mold and surrounding it with the appropriate powder. When the mold is heated and pressurized at the correct levels, setting or curing of the media occurs. The mounted sample is removed from the mold. If the use of heat or pressure might alter the structure of the sample of interest, then castable cold mounting materials such as epoxies are employed.





GRINDING & POLISHING

Grinding follows mounting to remove the surface damage that occurred during the sectioning step and to provide a flat surface. Grinding generally involves the use of water lubricated abrasive wheels and the use of a series of progressively finer abrasive grits. This procedure provides a flat surface that is nearly free of the disturbed or deformed metal that has been introduced by the previous sample preparation steps.

Polishing:-

Final polishing abrasives are selected based upon specimen hardness and chemical reactivity. The most common polishing abrasives are alumina and colloidal silica. Alumina abrasives are primarily used as mechanical abrasives because of their high hardness and durability. They also exist in either the softer gamma (mohs 8) or harder alpha (mohs 9) phases. 






ETCHING


The final step that might be used is etching to show the microstructure of the test sample. This step reveals features such as grain boundaries, twins and second phase particles not seen in the unetched sample.


NitalEthanol
Nitric acid		100 ml
1-10 ml		Immersion up to a few minutes.Most common etchant for Fe, carbon and alloys steels and cast iron - Immerse sample up from seconds to minutes; Mn-Fe, MnNi, Mn-Cu, Mn-Co alloys


PicralEthanol
Picric acid		100 ml
2-4 grams		Seconds to minutes
Do not let etchant crystallize or dry –explosive		Recommended for microstructures containing ferrite, carbide, pearlite, martensite and bainite. Also useful for magnetic alloys, cast iron, high alloy stainless steels and magnesium.




Thanks & regards
Aviansh Sharma

Labels

Labels:

Comments

Post a Comment

Popular posts from this blog

Rockwell test procedure.

INFORMATION. Rockwell hardness test, a differential-depth method, the residual depth of the indent made by the indenter is measured.  The deeper a defined indenter penetrates at a defined test force into the surface of a workpiece (specimen), the softer the tested material. In the Rockwell method, the total test force is applied in two stages. This allows the impact of specimen surface roughness (e.g. grooves in the specimen) and measuring errors caused by backlash in indentation depth measurement to be eliminated. THE INDIVIDUAL ROCKWELL METHODS ARE DISTINGUISHED FROM EACH OTHER AND. The five resulting Rockwell methods use five different indenters (diamond cone with 120 o  curvature or a hard metal ball made from tungsten carbide with diameters of: 1/16",1/8",1/4",1/2") and six different total test forces (15, 30, 45, 60, 100, 150 kgf).. This results in 30 different - standardised according to ISO 6508 and ASTM E18 – Rockwell scales (e.g. A, B, C, 30N, ...
Post a Comment
Read more

INCLUSION RATING TESTING

INCLUSION RATING TESTING:- Non-metallic inclusions process :- Non-metallic inclusions are chemical compounds and non metals that are present in steel and other alloys. They are the product of chemical reactions, physical effects, and contamination that occurs during the melting and pouring process. Sources of inclusions formation Non-metallic inclusions that arise because of different reaction during metal production are called natural or indigenous. They include oxide , sulfide , alumina silicate and Globular oxide .Singl Globular oxide Apart from natural inclusions there are also parts of Slag, refectories , material of a casting mould (the material the metal contacts during production) in the metal. Such non-metallic inclusions are called foreign, accidental or exogenous. Most inclusions in the reduction smelting of metal formed because of admixture dissolubility decreasing during cooling and consolidation. Non-metallic...
2 comments
Read more

Case Carburizing process.

  Case hardening Process Case hardening is a material processing method that is used to increase the hardness of the outer surface of a metal. Case hardening results in a very thin layer of metal that is notably harder than the larger volume of metal underneath of the hardened layer. - It is mainly used on low-carbon steels. The part is heated to 871–954 °C (1600–1750 °F) - Attempt to harden an entire metal object. One reason is efficiency. Less energy and less time are required to heat the outermost surface of a metal as opposed to its entire cross section. - A hard outside shell and a more ductile interior. What Types of Metals Can Be Case Hardened? Metals that can be case hardened are generally limited to ferrous materials, although there are special cases such as the Nitriding of some titanium or aluminum alloys. The ferrous metals commonly case hardened are. Gears Fasteners Camshafts Rods Pins   --BENEFITS OF CASE HARDENING Creating a more durable product Increases wea...
Post a Comment
Read more