The first step in preparing a specimen for metallographic or microstructural analysis is to locate the area of interest. Sectioning or cutting is the most common technique for obtaining this area of interest. Proper sectioning has the following characteristics:
- Flat and cut close to the area of interest
- Minimal microstructural damage
- Smeared (plastically deformed) metal
- Heat affected zones (burning during cutting)
- Excessive subsurface damage (cracking in ceramics)
- Damage to secondary phases (e.g. graphite flakes, nodules or grain pull-out)
The goal of any cutting operation is to maximize the desirable effects, while minimizing the undesirable effects.
Sectioning can be categorized as either abrasive cutting and precision wafer cutting. abrasive cutting is generally used for metal specimens and is accomplished with silicon carbide or alumina abrasives in either a resin or resin-rubber bond. Proper blade selection is required to minimize burning and heat generation during cutting, which degrades both the specimen surface as well as the abrasive blades cutting efficiency. Wafer cutting is achieved with very thin precision blades. The most common wafering blades are rim-pressed abrasive blades, in which the abrasive is located along the edge or rim of the blade. Precision wafering blades most commonly use diamond abrasives, however cubic boron nitride (CBN) is also used for cutting samples that react to dull diamond (e.g. high carbon, heat treated steels cut more effectively with CBN as compared to diamond). Wafer cutting is especially useful for cutting electronic materials, ceramics and minerals, bone, composites and even some metallic materials.
Selecting the correct abrasive blade is dependent upon the design of the cut-off machine and, to a large extent, the operator preference. Abrasive blades are generally characterized by their abrasive type, bond type and hardness. Determining the correct blade is dependent upon the material or metal hardness and whether it is a ferrous or a nonferrous metal. In practice, it often comes down to odor and blade life. Resin/rubber blades smell more because the rubber will burn slightly during cutting, however resin/rubber blades do not wear as fast and therefore last longer. On the other hand, resin blades are more versatile and do not produce a burnt rubber odor, but they do break down faster. Resin blades also provide a modestly better cut because the cutting abrasive is continually renewed and thus produces a cleaner cut.
Also note that the traditional “older” technology for producing abrasive blades resulted in very specialized resin/rubber blades. Finding the proper resin/rubber hardness, abrasive size, and blade thickness to match the sample properties and the cutting machine parameter required a lot of testing and experimentation. Thus, in the past, resin/rubber blades had been more popular in the US market; however, in more recent years as resins have improved, there has been more of a trend towards resin bonded abrasives. Conversely, resin bonded blades have typically been more widely used in the European and Asian markets for quite some time.Summary:
|Material||Composition||Recommended Blade||Blade Image|
|Soft non-ferrous metals
(aluminum, brass, zinc, etc.)
|Alumina/ resin bonded||MAX-E|
|Hard non-ferrou metals
(titanium, zirconium, etc.)
|Silicon carbide / resin-rubber bond||MAX-C|
|Soft steels||Alumina/ resin bonded||MAX-E|
|Hard and case hardened steels||Alumina/ resin bonded||MAX-VHS|
|General purpose blade for
steels and ferrous metals
|Alumina/ resin bonded||MAX-D|
|Universal thin resin/rubber blade||Alumina / resin-rubber bond||MAX-A|
|Industrial general purpose thin blade||Alumina / resin-rubber bond||MAX-I|
|Blade Thickness (inches)||10-inch||12-inch||14-inch||16-inch|
|Maximum Speed (rpm)||10-inch||12-inch||14-inch||16-inch|
Abrasive sectioning has primarily been used for sectioning ductile materials. Examples include metals, plastics, polymer matrix composites, metal matrix composites, plastics and rubbers. The proper selection of an abrasive blade requires an understanding of the relationship between the abrasive particle, abrasive bonding and the specimen properties.
Abrasive Type - Today's high performance abrasive blades use alumina or silicon carbide abrasives. Alumina is a moderately hard and relatively tough abrasive which makes it ideal for cutting ferrous metals. Silicon carbide is a very hard abrasive which fractures and cleaves very easily. Thus, silicon carbide is a self-sharpening abrasive and is more commonly used for cutting nonferrous metals.
Bonding Material - The hardness and wear characteristics of the sample determine which resin system is the best-suited for abrasive cutting. In general, the optimum bonding material is one that breaks down at the same rate as the abrasive dulls; thus, exposing new abrasives for the most efficient and effective cutting operation.
Abrasive Cutter Speed - Variable speed saws allow the user to better control the abrasive cutting process by matching the cutting speed with the hardness of the blade in order to minimize damage while maximizing the cutting speed. Typically softer metals are cut at slower speeds to reduce the cutting burr or smearing of the metal. Harder samples are cut at medium to high speeds in order to break down the wheel bond in order to expose new / sharp abrasives. Note for hardened steels the recommended cutting speed for the MAX-VHS blades in approximately 50% the maximum MOS in order to prevent overheating and burning at the specimen surface.
Lubrication and swarf removal during abrasive cutting and diamond wafer cutting are required in order to minimize damage to the specimen. For some older abrasive cutters, the proper cutting fluid can also have the added benefit of coating cast iron bases and the fixtures in order to reduce or eliminate corrosion.
TIP: Most abrasive cutters have a hood, which can produce a corrosive humidity chamber when not in use. In order to reduce these corrosive effects, keep the hood open when not in use.
Abrasive Cutting Fluid - The ideal cutting fluid for abrasive cutting is one that removes the cutting swarf and degraded abrasive blade material. It should have a relatively high flash point because of the sparks produced during abrasive sectioning.
|Chipped or broken blade||
-Secure sample properly-
-Reduce cutting force
-Secure sample properly
-Reduce cutting force
|Bluish burnt color on specimen||
-Incorrect cutting fluid
-Improper blade or excessive force
-Use proper cutting fluid|
-Consult applications guideline
or use a blade with a softer resin
Soft non-ferrous materials
(aluminum, brass, zinc, etc.)
Hard non-ferrous materials
(titanium, zirconium, etc.)
|Hard and case hardened steels||MAX-VHS250||MAX-VHS300||MAX-VHS350||MAX-VHS400|
|General steels and ferrous metals||MAX-D250T||MAX-D300||MAX-D350||MAX-D400|
|Universal Thin Blade||MAX-A250||MAX-A300||MAX-A350||MAX-A400|
|Industrial general purpose thin blade||MAX-I250||MAX-I300||MAX-I350||MAX-I400|
|MAXCUT Cutting Fluid (32 oz)||32 oz||MAXCUT-1000-32|
|MAXCUT Cutting Fluid (1/2 gallon)||1/2 gallon||MAXCUT-1000-64|
|MAXCUT Cutting Fluid (1 gallon)||1 gallon||MAXCUT-1000-128|
|MAXCUT Cutting Fluid (5 gallons)||5 gallons||MAXCUT-1000-5G|
|MAXCUT 2 Cutting Fluid (with corrosion inhibitor ) (32 oz)||32 oz||MAXCUT2-1000-32|
|MAXCUT 2 Cutting Fluid (with corrosion inhibitor ) (1/2 gallon)||1/2 gallon||MAXCUT2-1000-64|
|MAXCUT 2 Cutting Fluid (with corrosion inhibitor ) (1 gallon)||1 gallon||MAXCUT2-1000-128|
|MAXCUT 2 Cutting Fluid (with corrosion inhibitor ) (5 gallons)||5 gallons||MAXCUT2-1000-5G|
|MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (32 oz)||32 oz||MAXCUT-OL-1000-32|
|MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (1/2 gallon)||1/2 gallon||MAXCUT-OL-1000-64|
|MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (32 oz)||1 gallon||MAXCUT-OL-1000-128|
|MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (32 oz)||5 gallons||MAXCUT-OL-1000-5G|