Thermo-mechanical behavior of NiAl thin films by Weller P.

By Weller P.

This paintings describes the impression of movie thickness (0.2 to 3.1 чm) and Al content material (45 to fifty two at-% Al) at the yield power, the fracture sturdiness and the creep power of polycrystalline NiAl movies. The NiAl movies have been sputter-deposited on Si substrates and have been thermally cycled as much as seven hundred °C. the strain evolution in the course of thermal biking used to be measured utilizing a laser-optical substrate-curvature strategy.

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7. 7). 7 and table 3-2). If the parameter Z is known, the total energy release rate Gc in equation (3-2) can be calculated from the film thickness, fracture stress and plane-strain elastic modulus of the film (table 3-2). 4 J/m2 for fracture along {111} Si planes [69]. Solving equation (3-5) for Γf and inserting the ratio of substrate crack length to film thickness and the total energy release rate as determined according to equation (3-2) yields the fracture energy of the NiAl films. 5 . 9 MPa m1/2.

5 times the film thickness was chosen. 4). Such a trend can be seen in the cross sectional SEM and FIB observations. However, due to the lack of contrast a more precise analysis of substrate crack lengths was not possible. 3 Cracking behavior during cooling The stress measurements during cooling showed that, once cracking occurred, the film stress continuously decreased with decreasing temperature (see figures 3-4, 3-5 and 3-6). This implies that the film stiffness is continuously lowered by further crack propagation.

The plane strain modulus of the {211} texture component was calculated by averaging the plane strain modulus along < 0 1 1 > and < 1 1 1 > directions. It turned out that the plane strain moduli of {111} and {211} orientations have similar values with 235 GPa for {111} and 231 GPa for {211} oriented grains. Consequently, the texture and thus the chemical composition of the Al-rich films have a negligible influence on the plane strain modulus of the Al-rich NiAl films. Therefore, the elastic mismatch between the brittle NiAl films and the Si substrates was assumed to be independent of the Al content.

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