S A David, Group Leader & Corporate Fellow,
Emeritus, Oak Ridge National Laboratory,
Oak Ridge, TN 37831, USA
You are highly recognized for your extensive contributions towards welding science and solidification through innovative experimental techniques and associated theories. Please introduce a more about you?
I am an American of Indian origin. I hail from India and I was Born in Kolar Gold Fields and had all my education in Bangalore India. BSc (St Joseph’s college) B.E and ME (Indian Institute of Science, India) Got my PhD from the University of Pittsburgh , United States. Joined Oak Ridge National Laboratory (ORNL) in 1977 as a Research staff and became a corporate fellow. This is the highest technical position at the laboratory of about 4000 staff. I was the leader of the Materials Joining Group and led the group in developing one of the world’s best welding science programs. I live in Knoxville Tennessee with my wife Bertha David who is a retired psychiatrist, son Kevin David who is an Oncologist at Rutgers University in NJ and a daughter Cheryl David Amar who is a lawyer Pittsburgh PA I have four grand children. Currently, I am a Corporate Fellow Emeritus at ORNL and continuing to do some research. I have been fortunate to receive several recognition’s and awards from the professional societies (ASM,TMS, AWS and IIW). I am a Fellow of ASM,TMS, AWS, IIW. I have organized 10 International conferences on Trends in Welding Research and edited their proceedings and I am one of the founding editors along with Prof DebRoy Pennsylvania State University and Sir Harry Bhadeshia of Cambridge university of the journal Science and Technology of Welding and Joining published by Francis & Taylor in the U K. J have published about 350 technical papers and have edited 11 conference proceedings.
What has been your role with Oak Ridge National Laboratory (ORNL)?
I was appointed to develop and lead a world class research program in welding. In the last three decades we have been in the forefront in the field in the world. Worked on process modeling, Transport phenomenon, process development, phase transformation, welding metallurgy, residual stress, neutron scattering and properties of weldments.
What is your say on the welding science and technology scenario in US?
In the past, welding has progressed more as an art than science. In the last four decades, there has been an increase in the scientific underpinning of the welding technology. Researchers from all over the world are making contributions. We are one of the few countries holding leadership in the science of welding.
Could you brief us on the major welding projects of US?
Activities related to welding and weldability of materials for Light weight vehicles, aerospace, advanced fossil fueled power plants dissimilar materials joining and intelligent manufacturing etc.
What is the country’s effort towards encouraging welding as a career?
Most of the activities related on this topic comes from the American Welding Society (AWS ). They provide scholarships to students from vocational schools and universities. AWS trains and certifies welders. There are government supported welding research programs supporting welding.
You were one among the three man team (Steve Spooner and Cam Hubbard) to measure for the first time in the United States, residual stresses in weldments using neutron scattering. Please elaborate. How has been your experience?
One of the consequences of welding is the development of residual stresses and distortion in the weldment. They are very detrimental to the welded structure and can cause internal fracture, degrade corrosion resistance and reduce fatigue strength. One would like to get a complete picture of the distribution of the stresses in the whole weldment that is very thick. In order to do that, you have to penetrate deep in to the material. The existing techniques such as hole drilling which is a destructive technique and X-ray that can penetrate only the surface (may be a mm) cannot do the measurements in thick materials. Neutrons can penetrate inches of steel and aluminum. The principle of the technique is to determine the lattice parameter of the weldment at various places (using Braag’s Law) and determine the strain in the lattice and calculate the stress. I had the opportunity to work with two physicists (Spooner and Hubbard ) and using the neutron beam available in our research reactor, we embarked on a project to characterize the residual stress distribution in an austenitic steel weldment and we were very successful in accomplishing that. We were able to establish a residual stress measuring capability at ORNL may be the first one such capability in the US.
What has been your contribution towards stainless steel?
I did research on the solidification behavior of austenitic stainless steels, phase stability and creep properties. Besides, also identified the effect of cooling rate on the microstructure and ferrite content in austenitic stainless steel welds. Carried out very fundamental studies on the development of solidification microstructure in the weld pools using Fe-15Cr -15Ni alloy single crystals.
Weld and weld repairs is highly important into the success completion of any project? What are your efforts towards this?
We have done lot of work on welding of single crystal stainless steel and nickel base
superalloys. We have used the basic knowledge developed to repair weld nickel base
superalloy single crystal turbine blades.
You have also performed novel in-situ experiments using Transparent Organic Metal Analog
Systems and Time Resolved X-ray Diffraction (TRXRD). Please elaborate, as these studies are
critical to the design of welding consumables.
Some organic systems make a good metal analog system to simulate solidification behavior
of metals. So we used an organic system to investigate weld pool solidification. Also what we understand from the conventional microstructural analysis using optical and other advanced characterisation techniques is a postmortem analysis. For example: when you observe the solidification microstructure, one does not know what really happened at elevated temperature. By using insitu X-Ray studies we can for sure understand the events that occur at elevated temperatures.
In the area of joining of ductile ordered intermetallic alloys, you clearly hold the leadership in the world. That’s amazing
I have done a lot of work on the welding of ductile intermetallics. I have contributed in a major way to the welding metallurgy of intermetallic alloys.
What has been your contribution towards NASA’S mission?
For safety Iridium alloy for encapsulating fuel elements used in radioisotope thermoelectric power system for deep space missions (Voyager, Cassini) was developed by Dr C T Liu at ORNL. I investigated the welding and weldability of the alloys (see the figures).
I am glad to participate in this interview. I am glad to share some of my experiences related to welding research. ORNL has been extremely encouraging and supportive of my efforts. In recent years, enormous progress is being made in welding science and technology. In the last few decades, welding has evolved from an empirical art to an activity combining advanced tools of basic and applied sciences. Oak Ridge National Laboratory (ORNL) has contributed and continues to extensively to this effort. India has a great potential to contribute to this effort. A focused program on the science and technology of welding would be in the right direction. I wish you all the best.