Laser Based Method of Evaluating the Behavior of Surfaces and Surface Treatments at Transient High Temperatures and Pressures.

Abstract : A set of experiments were performed in order to test the ability of a laser based system to simulate the chemical and thermal effects inside a gun barrel. It is expected that a laser based system would be a relatively inexpensive method for testing various materials and coatings for eventual gun barrel use, and to the present time, there are no publicly documented systems capable of such testing. An extensive literature review revealed that simulation of the mechanical effects would not be possible under the scope of this project, but thermal and chemical simulations could be done. A chamber was constructed to be used for both laser weld overlaying in an inert atmosphere, and for the simulations. Laser melting of titanium indicated that the chamber could provide an inert atmosphere in which no visual contamination of the titanium occurred. Parameters were developed to weld overlay titanium on AISI 4340 using 0.25 mm of preplaced powder, 1 ms pulses at a frequency of 50 Hz, and energy of 7.5 J/pulse, and a speed of 2.1 mm/s. This coating was then used as an interlayer for weld overlaying a 90tantaium-10tungsten alloy. Since titanium has a melting temperature close to the alloy steel, it was conjectured (correctly) that it could be more easily laser weld overlayed that the high melting temperature tantalum-tungsten alloy. Since Ta-Ti form a solid solution, rather than intermetallics formed by Ta-Fe, this was the best interlayer. The 90Ta- 10W alloy was overlayed using 0.25 mm of preplaced powder, 1 ms pulses at a frequency of 50 Hz, and energy of 7.5 J/pulse, and a speed of 5.2 mm/s. The coating was not continuous, but did appear to be melted and bonded in several locations. Other coatings were produced, including 0.25 mm of Stellite 6 on A36 mild steel, and 90 Ta-10W on commercially pure titanium.