in Vol. 16 - July Issue - Year 2015
Stressed Out? Determine Component Stresses with X-Ray Diffraction Testing
Beth Matlock, Senior Materials Engineer in the Materials Testing Division of TEC
TEC works closely with its customers. Sam Abston of Applied Ultrasonics reviews test plan and data on an important ORNL project.
Beth Matlock puts the finishing touch on a sample setup for residual stress measurement
MFN was able to get an interview with Beth Matlock, Senior Materials Engineer in the Materials Testing Division of TEC.
(?) MFN: Who is TEC, and what industries do you serve?
(!) B. M.: Technology for Energy Corporation is a high-tech company in Knoxville, TN. We've been in business for 40 years supplying simple solutions to complex problems for our customers in many industries including the aerospace, automotive, heavy equipment and electric utility industries. We have four divisions, each supplying innovative products and services with a different focus.
The Materials Testing Division has x-ray diffraction products to measure residual stress and retained austenite. Our first system was delivered in April 1984. This system is still in operation today attesting to the quality and reliability of our products. We also have an A2LA-accredited laboratory to provide services in our lab or at your facility.
(?) MFN: What is your role at TEC, and how long have you been with the company?
(!) B. M.: I'm the Senior Materials Engineer in the Materials Testing Division, and I've had a wonderful relationship with the company for 31 years. It's been an exhilarating experience since I've "grown up" with the development of the systems and the beginning of the services lab.
Over the years, TEC has launched two successful diffraction systems - the 1600 and 4000 series. We are now preparing to launch MAX (Miniature Advanced X-Ray Diffraction System), an impressive system which is truly compact. This exciting new product is super portable, precise, and will permit measurements of residual stress and retained austenite. Although it can be used in a lab environment, MAX is especially well-suited for measurements in previously inaccessible locations. We are currently working on commercializing a third generation of our MAX product for release later this year.
Our services lab started as an applications lab, where we performed applied research. Due to popular demand, we initiated the measurement services. When our customers started requesting accreditation, we worked hard to put an excellent quality program in place. The company has ISO 9001 certification, and the lab is accredited by A2LA to ISO Guide 17025. The services lab has matured to provide competitively priced measurements with excellent customer support and the fastest turnaround times in the industry. Our standard turnaround is two to four weeks, and we offer one-week and two-day expedited service. We can, in some situations, offer same-day service for super-critical needs. We are able to measure samples as small as traces on a circuit board to components weighing tons. In our on-site laboratory, we can accept parts weighing up to a ton.
(?) MFN: What are residual stress and retained austenite? Why is it important to have these measured?
(!) B. M.: Residual stress is the stress that remains after all external loads are removed. It occurs during the manufacturing process and during service life. Basically, anything that you do to a part will affect its residual stress. Shot peening, grinding, welding, casting, machining, and heat-treating are a few examples of processes that result in changes in the residual stresses. Although stress has a negative connotation, beneficial stresses do exist. The challenge is to know what your stresses are, and to put beneficial stresses in the part before it goes into service. We can help you determine what your stresses are.
Retained austenite is a phase in steel. The amount of retained austenite affects part longevity where dimensional tolerances are critical. Bearings and large structures are examples where the amount of retained austenite is important. X-ray diffraction is the preferred measurement technique when the amount of retained austenite is less than 10-15%.
(?) MFN: What products and services are available from TEC's Materials Testing Division that capture these measurements?
(!) B. M.: We currently offer the TEC 4000 system. This product is a rugged, versatile instrument that can make measurements in just a few minutes. We offer nine different peak-fitting routines that allow you to pick the algorithm which best fits your data. The system is easy to operate - even a Ph.D can do it! Since the system is portable and centerless, you can make non-destructive surface measurements on large parts and parts with complex geometries. It's also easy to reconfigure the system to measure different alloys. The system is approved for open beam operation, which means that it does not need to be kept in a safety enclosure. It works equally well in a climate-controlled laboratory, or out in a field environment. In addition to measurements in a specific direction, the 4000 can make principle stress and triaxial stress measurements. If you need to know the stress versus depth into a part, the analysis package corrects the data for stress gradient and layer removal to give more accurate results.
The 4000 quickly and accurately measures retained austenite. The system measures two martensite/ferrite peaks along with two austenite peaks for a comprehensive analysis. ASTM E975 requires that at least two austenite peaks are measured to correct the data for factors such as carbide interference. The 4000 is capable of detecting retained austenite levels as low as 0.1%.
Our services lab is known for fast turnaround along with excellent customer service. We work with our customers to develop a concise measurement program that will answer their questions with the minimum number of measurements. Once our customers have their data, we continue to work with them to help them understand the significance of the data. We provide our expertise to our customers to ensure their understanding of our measurements while learning what is most important and vital to their operations.
(?) MFN: What's new at TEC?
(!) B. M.: This year is a banner year for the Materials Testing Division. Will McAlexander joined us in February. Will has a Master's Degree in Materials Engineering from the University of Tennessee. He has a strong background in x-ray diffraction and instrumentation. He also has an engaging personality, and is an excellent addition to our team.
Our second notable happening is the introduction of MAX. MAX is a miniature x-ray diffraction system with the same powerful software used by our 4000 system. This portable system will measure residual stress and retained austenite, making it a powerful tool in a small package. MAX is designed to fit inside an 8" orifice and make measurements within a couple of minutes. It is packaged in two briefcase-sized cases. Along with a laptop computer, this system can boldly go where no x-ray system has gone before. It was originally developed under an SBIR program for the US Air Force. The Air Force needed a method for determining stresses in aircraft components without having to remove the component from the aircraft. MAX has proved its value by measuring stresses in aircraft components on the flight line and in the hangar.
(?) MFN: What are the benefits of the 4000 and MAX, and how can these features benefit my bottom line?
(!) B. M.: Both the 4000 and MAX provide precise residual stress and retained austenite measurements quickly in the lab or a field environment. They can be safely used in any environment by employing the safety interlocks incorporated in the systems. MAX, with a 4W x-ray tube, is easily shielded to minimize any x-ray exposure to personnel. Both systems use a position-sensitive proportional counter detector, which gathers hundreds of data points in seconds. These features translate into products that can detect detrimental stresses in parts before they're put into service. In turn, the identification of stresses allows a company to alter or add processes that can improve and provide beneficial stresses resulting in superior products that last. It's more cost effective to detect detrimental stresses early in the manufacturing process to prevent the costly failure of critical components during normal operation. With x-ray diffraction, the stresses can be measured at each step in the manufacturing process to make changes before a company makes significant financial investment. These measurements can also confirm new designs, contribute to research and development, provide quality control, and assist in failure analysis.
Likewise, retained austenite measurements can confirm that components such as bearings will meet manufacturing specifications. Having the correct amount of retained austenite improves the probability that components will survive during service history.
Since TEC offers both products and services, we can provide the benefits of residual stress and retained austenite measurements in a package that makes sense to our customers. Customers that have production requirements, proprietary operations and large measurement requirements might choose to purchase their own systems. Those customers that have an occasional need for measurements may prefer to make use of our services. Since we can provide services in our Knoxville, TN laboratory or at our customer's site, our services option can be a cost-effective way to quickly determine the stress state in products. Either way, TEC will work with a customer to help them determine the best use of their resources to obtain quick return on investment.
MFN would like to thank Beth Matlock for this interview!