9705068 Gupta The objectives of this work are to establish experimental procedures for in-situ measurements of mechanical properties at interfaces under elevated temperatures, to develop a basic understanding of strength-structure-chemistry relationships for interfaces, and to generate data for elevated temperature interfacial strengths of several engineering systems. Because coated components used in machinery and device applications often undergo local temperature excursions during performance, the mechanical properties of the material interfaces and their relationships to interfacial structure and chemistry at elevated temperatures is important. An earlier one year grant permitted the development of a laser-generated, stress- pulse system that induces decohesion at the interface of dissimilar materials under elevated temperatures. In this renewal grant the tensile strengths of such interfaces are measured up to 1300 C in 1 to 3 micron thick coatings of Nb on substrates of sapphire. Interface chemistry and atomic structure are determined by using high resolution transmission electron microscopy (TEM) at the Massachusetts Institute of Technology. TEM at ambient temperature allows a determination of the influence of interface interdiffusion, void formation, coating grain size, new phases, and thickness of the amorphous layer on the measured interface strength at elevated temperatures. Once the strength-structure-chemistry relationships are developed at elevated temperatures for the Nb/sapphire interface, the tensile strengths of other representative systems chosen from applications in tribology (TiC coatings on Inconel substrates), thermal barriers (zirconia coatings on Inconel substrates), and microelectronics (Cu and Al coatings on nitrided surfaces of Si) will be determined up to 1300 C. %%% The grant is not only interdisciplinary in its approach, but also in its impact, as it serves particular needs in the composites, tribology, thermal spray, mi croelectronics, and other thin film industries. ***
