Adding X-Ray Diffraction to LSP Technologies’ toolkit

Adding Speed and Precision to Laser Peening Application Development

Posted: June 20, 2019
By: mmahoney

LSP Technologies (LSPT) has enhanced its in-house measurement of compressive residual stress in metals, installing a new X-ray Diffraction (XRD) instrument. New XRD measurements will help LSPT to develop laser peening prescriptions for customer needs more quickly and accurately for complicated geometries and parts.
“Customers are increasingly asking for the kind of precision which XRD measurements can yield,” said Dr. Micheal Kattoura, a Materials Research Engineer for LSPT. “Now we can prove out the benefits of laser peening on even the most complicated geometries efficiently with XRD measurements.”

Laser peening, a cold deformation process for metal improvement, induces deep levels of compressive residual stress in metal to prevent fatigue, corrosion, cracking, flaking, and other cases of metal failures, increasing the useful life of metal components by 5x or more.
To document the benefits of laser peening, the labs at LSPT’s Materials Science Center of Excellence provide customers with detailed reports on the depth and character of residual stress levels below the surface of metals.
The new XRD device, Stresstech’s Xstress G3, can access small spaces and complex geometries, including many of the industrial shapes and components typically treated by LSPT’s laser peening processes.
The XRD is made by Stresstech and serviced by its affiliate, American Stress Technologies, Inc., in Pittsburgh, PA. Learn more at the Stresstech website and view a page about the XStress-G3 equipment now installed at LSP Technologies.
In most cases, XRD exceeds the precision of slitting tests, formerly used by the materials lab, in measuring compressive residual stress, which is measured in mega-Pascals (MPa or Ksi).
In slitting tests, a wire slitter slices through the surface of metal parts, and electronic strain gauges provide data that matches a residual stress profile. Due to the strain gauges being mounted on the back of the sample, slitting can’t capture near surface residual stresses with high certainty. The process used at LSPT is designed for rectangular shaped samples, but not for complex metal shapes such as blades, gear teeth, or the interior of tubes.
XRD involves aiming X-rays at a material. The reflecting rays “bounce,” sending a unique diffracted fingerprint that reveals patterns of residual compressive stress. The process is ideal for examining metals because the wavelength of X-rays is at the same magnitude as the distance between grain layers in metals.
“XRD testing overcomes many of the problems with slitting, but I think the real advantages of in-house XRD testing is our ability to improve our cycle time on delivering results to customers,” Kattoura said.
Here’s why. For new alloys and shapes of components, laser peening must deliver precise levels of residual compressive stresses at precise locations. That may take some experimentation at several different levels of power density (GW/cm2), different layering of peening spots, and other variables available with LSPT’s Procudo® Laser Peening System, the only commercially available laser peening system.
“Now, with XRD in our toolkit, we can test quickly and accurately, seeing the stress levels we achieved in the critical locations within hours, not days, over a wide range of variables, and then we can meet customer requirements accurately and economically,” Kattoura said.
Other advantages of in-house XRD testing will include:
• Consistent pinpointing of the component spots and depths at which compressive residual stress must be measured.
• Using electropolishing – removing a layer of material with an electrolyte solution (saltwater or acid solution) and electricity – to measure stress levels at progressively deeper layers of material.
• A standardized XRD measurement reporting system that will capture all the XRD parameters, material parameters, and other information related to component processing.
“The XRD testing capability will help us understand more about the benefits of laser peening, and that can only help customers we serve and customers we hope to serve in the future,” Kattoura said.
Stresstech is headquartered in Finland and has offices in Germany, the United States, and India. For more than 30 years, Stresstech has been providing non-destructive and destructive testing solutions for process control and quality inspection.

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