Localized stress near and the thermal expansion of Al2Cu precipitates in an Al thin film matrix

The thermal expansion coefficient of Al2Cu precipitates embedded in an Al-C u thin film matrix is determined by in situ x-ray diffraction measurements on free films. The phases present and the thermal expansion or contraction are simultaneously observed during a temperature ramp. The Al2Cu precipitat e has a tetragonal structure. The thermal expansion coefficient of the Al2C u phase in the a direction is significantly smaller than that of the surrou nding Al matrix while the thermal expansion in the c direction is comparabl e to that of the Al matrix. Upon cooling from 500 degrees C, the mismatch o f the thermal expansion between the precipitate and the Al matrix results i n compressive and tensile stresses in the aluminum matrix near the precipit ates and in compressive stresses in the precipitates. Those stresses are es timated to be on the order of 100 MPa. (C) 2000 American Institute of Physi cs. [S0021-8979(00)00702-7].