Our New SEM/EDS Capabilities
Late last year, Materials Engineering, inc. upgraded our scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) capabilities. You may have already noticed the difference in the SEM images and EDS spectra presented in our project reports. As we have always had excellent success with JEOL instruments in the past, we purchases anther JEOL scanning electron microscope (SEM), and equipped it with the WinEDS energy dispersive spectroscopy (EDS) systems and DIPS digital imaging system. The system is manufactured by Thompson Scientific and Point Electronics, and is distributed by TN Analyzer in Dane, Wisconsin.
The WinEDS/DIPS system is extremely user friendly, has a wide range of features and produces excellent quality images and spectra. The system is Microsoft Windows based and benefits from the flexibility and features intrinsic in Windows.
The SEM allows us to gather and print images on Polaroid film or in digital format. The high resolution digital images (up to 4000 by 3200 pixels) can be printed in 4" by 6" format on our color dye sublimation printer, or up to 81/2" by 11" on our inkjet printer. Dimensional measurements and annotation are easily added to the images. The images can be exported in many formats for e-mailing or burning to CDR for sending to you. The SEM also has a larger sample chamber than our old SEM, allowing us to analyze large samples without having to alter them so they will fit into the SEM chamber.
The primary uses of a scanning electron microscope (SEM) are determining the mode of failure, known as fractography, and looking at other microscopic features at high magnification. Energy dispersive spectroscopy (EDS) provides microscopic chemical analysis, and is used to determine the chemical elements present in contamination, residues, corrosion pits and metallurgical phases.
Use of dimensional measurement tool on semiconductor (left).
Microstructure of nickel-based super alloy (center).
Shrinkage defect on the fracture surface of a casting (right).

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The new EDS system has Quant Wizard, a one click semi-quantitative analysis tool, automatic element identification and labeling, overlaying and subtraction of spectra. The Dips and WinEDS work together to for dot mapping, providing a multicolor map of the location of elements in the sample. As with SEM images, the EDS spectra can be exported in many formats for e-mailing or burning to CDR for sending to you.
We would love the opportunity to show off our new SEM/EDS to you. The next time your require SEM/EDS analysis, call and arrange a time when you can be present during the analysis so we can show you all the capabilities of our new equipment.


Overview of Hardness Test Methods
Hardness testing is very popular because it is inexpensive, generally non-destructive, easy and provides quantitative results. These results are directly related to other material properties, such as strength and wear resistance. It is a powerful tool providing the first assessment to determine if a material or component has been properly processed.
The most common hardness testing is conducted using a Rockwell test machine, which operates by applying a fixed load to an indentor pushing it into the metal sample. The hardness value is derived from the depth of the penetration into the sample, read directly off a dial indicator. The indentor is either a diamond, for steels and hard materials, or a small (1/16") steel ball, for soft steels, aluminum, brass and other soft metals. The load varies from 60 to 150kg. Each combination of indentor and load represent a different Rockwell scale. The most common are the C Scale (HRC) which uses a diamond indentor and a 150 kg load, and the B Scale (HRB), which uses a 1/16" ball and a 100 kg load.
Rockwell superficial hardness is a special case of the Rockwell hardness method that applies a much lighter load. The most common is the Rockwell 15N scale, using a diamond indentor with a 15 kg gram load. With a lighter load, the depth of penetration is greatly reduced, making these scales useful for thin samples, or for steel samples which have been case hardened to shallow case depths.
Brinell (BHN) is the oldest of the common hardness test methods, developed in the late19th century by Dr. Brinell, a Swedish Engineer. Brinell testing utilizes the largest indentor and the heaviest load of the common hardness test methods. A 10 mm hardened steel or tungsten carbide ball is pressed into the test samples using 3000 kg load for ferrous metals or 500 kg load for non-ferrous metals. The round impression is read using a 20x microscope and converted into a hardness number.
Since a Brinell hardness impression covers the largest area, it is less sensitive to inhomogenities in material. It is commonly used for castings, forgings and larger components. Many specifications for cast irons report the hardness requirements in Brinell. Brinell hardness is also less sensitive to surface condition, requiring only a sufficient smoothness to read the impression diameter. However, due to the high load and large impression, Brinell cannot be used on thin materials, carburized steels, or small diameter bars.
Geometry of Brinell indentation (left). Geometry of Knoop and Vickers indentations (right).


Microhardness methods are similar to Rockwell hardness as they apply a load to a diamond indentor, but instead of calculating the depth of indentation, the size of the indentation is measured and converted into a hardness value. These methods are called microhardness because they apply very light loads, and the indentation must be measured using a microscope. The two major microhardness methods are Knoop (HK) and Vickers (HV).
Vickers was developed in England in 1925, and uses a pyramid shaped diamond (similar to Rockwell) that leaves a square indention of which the two axis are measured and averaged. Knoop was developed by the National Bureau of Standards (now NIST) in 1939 and produces an elongated diamond shaped indentation of which the major axis is measured. The indentation size is measured and the length converted to a hardness number through a mathematical calculation that is usually tabulated. Both scales can use loads from 5 grams to 1000 grams, although the 500 gram load is the most common.
Microhardness is measured on metallographically polished specimens and is therefore destructive. Microhardness allows characterization of microscopic features, such as hardness of a phase, decarburization or carburization. Effective case depth from carburization is usually defined as the depth at which the hardness is reduced to 50 HRC equivalent based upon microhardness measurements.
The test methods are controlled by ASTM E18, E10 and E384 specifications, which include the minimum material thicknesses each of the hardness scales require, as well as correction factors to be used when testing small diameter rods. Hardness values can be converted between the scales, with conversion tables provided in ASTM E140. Since the conversions are a potential source of error, you will always see our data reporting the exact scale which was used to test the components, with the conversion per ASTM E140 noted.
Materials Engineering, inc. offers hardness testing on all the scales and methods discussed in this article, and will be happy to advise you of which techniques best serves your needs.


Gathering Contamination Samples: A Reminder
The energy dispersive spectroscopy (EDS) system on our scanning electron microscope (SEM) is a powerful tool used to determine the chemical elements present on a microscopic level, such as contamination, embedded particles, stains/discoloration, corrosion products, sludges and residue on components. Once identified, the source of contamination can be traced down and the problem eliminated.
Our experience shows that our success in identifying the contamination is often linked to the method used to gather, handle and ship the sample. Problems in the gathering, handling, storing or shipping of the sample can lead to unreliable data no matter how good the analytical procedures are. While sample type and size may effect the handling methods, some basic guidelines can be followed for most samples.
"Do's"
Use clean implements to gather the sample
Be careful and disturb the samples as little as possible.
Obtain a sample that is representative, including multiple colors or textures
Send a sufficient amount. While we can analyze small amounts, more is better.
Store in a clean sealed protective container, such as a jar or ziplock bag
Cut samples far away from area of interest to prevent overheating
Identify/Label multiple samples
Consider photographing the sample before removal
Provide possible sources of contamination for comparison
Provide an uncontaminated reference sample for comparison
If corrosion is of concern, be sure to send a sample of the substrate
Provide backgrounds on the product and application
Provide history of contamination, when it was first noticed, etc.
Provide details of material, processing
Acquire residues or powder samples by scraping methods whenever possible
"Don'ts"
Touch area of interest with fingers as they contain salts and oils
Clean the sample with solvent, water or detergents
Cut parts with coolants or lubricant
Heat parts if you have to cut the sample
Use adhesive tapes to collect samples
Use cotton swabs to collect samples

Following these guidelines will help us provide you with a proper analysis: When in doubt, please give us a call before you try to gather the sample. We can provide you with specific methods and techniques, or travel to your facility to inspect the hardware and gather the samples ourselves. We will do what ever is necessary to insure that the sample is properly gathered so that you can have meaningful results.


Meet Jennifer
Most of you have noticed there is a new voice answering the phone when you call us. That voice belongs to Jen Lowe, who recently jointed our staff as an administrative assistant. Jen is in charge of running our office, including keeping track of project flow, suppliers, purchase orders, past due invoices, evidence, receiving and returning samples. We know she will help us to serve you better.
Jen is always busy with her two children (Cassie 7 and D'Artagnan 2) and three horses (Rebel, Lexus and Max). She lives in nearby Maple Park, but is looking to find a home with more land for her horses. She is president of a trail riding club and invites anyone who is interested to join the club for a ride. The club has a web site, which was designed by Jennifer, can be seen at www.loweriders.com.


CCD OES Chemical Analysis Coming!
Materials Engineering expects delivery on a SPECTROLAB Optical Emission Spectrometer (OES) this fall. The spectrometer uses the latest CCD detector technology with traditional arc and spark excitation to determine the chemical composition of metal samples. The unit will be specially equipped for analysis of small samples down to 5mm in diameter and wire or fasteners to 3mm, greatly expanding the range of samples that can be easily analyzed for chemical composition.
We were very impressed with the capabilities of the SPECTROLAB during a recent demo, and are excited to be adding it to the range of services we offer. The unit is expected to be fully operational by November. Look for more details in our next newsletter.


The "What Is It?" Contest
The scanning electron microscope (SEM) is a powerful tool, capable of magnifications up to 180,000 times. It allows us to reveal information which is critical to metallurgical investigations, such as fracture modes and surface characteristics.
The SEM can also be fun to play with, because it allows one to view the surface of anything at high magnification with great depth of field. All of us have been amazed by the pictures of various insect parts, especially the eye of a fly.
In our contest, we take a look at an object on the SEM that should be familiar to all of you. In this issue, our image shows something that many of you have first hand experience with, especially while on summer vacation.


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Please fax, mail or e-mail us (don't call) with your answer. We will draw a winner from all correct entries received by June 6. The correct answer and the winner will be published in the next issue Of Materials Interest.
The prize is a $50 restaurant gift certificate, so put on your thinking caps.
Results:
Last issue, we showed you images of three fabrics that were famous for sweaters, from the orient and the fabric of our lives. Many people correctly matches the fibers as wool, silk and cotton.
Our winner, drawn at random from the correct entries, was Jim Blankenship of Velsicol Chemical Company in Chattanooga, Tennessee. His efforts earned he and his wife a nice dinner at The Chop House in there. Velsicol produces intermediate chemicals with names only a chemist could love, used in the manufacture of may consumer products.
Congratulations, Jim.