The Ohio State University
At Ohio State, the only university in the US that offers a doctorate in Welding Engineering, you'll find a Gleeble 1500 system in almost constant use. And for good reason: a nearly endless procession of graduate students and faculty members are conducting a variety of research projects aimed at improving their knowledge of how to effectively and economically join materials.
Dr. William A. "Bud" Baeslack, Professor in Ohio State's Depart-ment of Welding Engineering, says, "Most of the work involves joining advanced materials — such as non-ferrous alloys, stainless steels, nickel-based alloys, aluminum-lithium, and titanium — for a variety of applications, many of them in the aerospace field."
"We are constantly getting new problems from a joining standpoint," he says. "The projects are diverse because of the variety of the materials and because materials keep changing."
For General Electric Aircraft, Dr. Baeslack's colleagues are using the Gleeble to look at the weldability of cast Inconel 718 superalloys for turbine engines. They're examining the effect of alloy chemistry on cracking in the weld heat affected zone.
In a related project for the Edison Welding Institute, the Gleeble itself is being studied as a predictor of the weldability of 900 series superalloys. These superalloys exhibit very low expansion which makes them well suited for the high temperature environment inside a jet engine. Several different heats of the superalloys are tested using the Gleeble and then evaluated again using other weldability testing techniques. The results are then compared to see how well they correlate. According to Dr. Baeslack, preliminary results show "moderately good correlation."
Ohio State researchers are also performing continuous cooling phase transformation studies of advanced titanium aluminide alloys that may someday find application in the National AeroSpace Plane (NASP). Through careful control of the cooling rate, coupled with dilatometer measurements, they are able to simulate the HAZ structure of these materials so that structure and property analysis can be performed.
Another project, supported by the Office of Naval Research, involves simulating fusion zone specimens of aluminum-lithium alloys to see what effect different weld solidification rates have on the microstructure. A small quartz tube is clamped in the Gleeble's jaws, with a sample of the alloy inside. The sample is melted and then allowed to cool at a controlled rate. Dr. Baeslack reports that the structure of the resultant specimens closely parallels the structure found in samples produced through actual welding processes.
The US Army is supporting a fundamental research project at Ohio State involving diffusion bonding of advanced aluminum alloys for high temperature applications. Using the Gleeble, diffusion bonds with different characteristics are generated under precise temperature and pressure control. The quality, strength, and integrity of the bonds are then evaluated through a variety of methods, and the results are plotted against the bonding parameters. Ultimately this work could have possible application in missiles.
In the area of weld simulation with more conventional materials, Ohio State researchers are looking at duplex stainless steels — 50% ferrite, 50% austenite — to examine the effects of the thermal cycle on toughness, microstructure, and corrosion of the HAZ. By changing the peak temperature and cooling rate, they can determine which parameters produce welds that are well suited for applications in corrosive environments.
"The Gleeble's ability to simulate precisely the thermal and mechanical conditions present during welding is a key to this work," Dr. Baeslack says.
Dr. Baeslack adds, "Nearly every one of my students makes use of the Gleeble at some point in his or her research. It's an essential tool for what we are doing because it can control temperature, heating rates, and cooling rates, all very precisely. The Gleeble is also unique in its flexibility — it allows us to do a lot with just one piece of equipment."
This article first appeared in the Gleeble® Newsletter — Winter 1988/89.