PNNL

Abstract

Metals and alloys have been crucial for humans for 1000s of years. Specifically many precipitate strengthened high-temperature alloys are currently used in safety-critical applications such as jet engines, turbines, airplanes, nuclear reactors, and in industrial infrastructure. Understanding precipitate stability and solute segregation mechanisms between precipitates and the matrix at high temperatures is key to designing high-strength alloys with consistent mechanical properties at high temperatures. Rapid in situ approaches that can quantitatively analyze the solute segregation between precipitate phases and the matrix can therefore be pivotal in accelerating the alloy design process. Hereby using the test case of a promising high-temperature Al-Cu-Mn-Zr alloy, we demonstrate the value of in situ atom probe tomography coupled with in situ transmission electron microscopy to reveal atomic-scale mechanisms that lead to the emergence of non-equilibrium solute segregation, especially during the early stages of high-temperature annealing. Mn and Zr segregation at precipitate-matrix interfaces extends the thermal stability of the strengthening precipitates (?') to 350?. We show that Mn rapidly segregates to the interfaces thus providing a kinetic barrier for phase transformation from metastable ?' to the thermodynamically stable ? phase. Mn segregation allows additional time for the even slower diffusing Zr to segregate to the ?'-matrix interface. The Zr-rich pockets and nucleation of Al3Zr on the ?' interfaces further raise the kinetic barrier for the strengthening phase to transform to the unfavorable ? phase. This rapid approach can essentially eliminate lengthy heat treatments, metallographic preparations, and ex-situ characterization steps and thus help accelerate the process of high-temperature alloy design.