Präzipitationshärtung

Präzipitationshärtung, also known as age hardening or precipitation hardening, is a heat treatment technique used to increase the yield strength of malleable metals. This process relies on the formation of extremely small, uniformly dispersed precipitate particles within the metal's matrix. These precipitates act as obstacles to the movement of dislocations, which are line defects in the crystal structure of metals. By impeding dislocation motion, the material becomes stronger and harder.

The process typically involves three main steps. First, solution treatment, where the alloy is heated to a temperature where the alloying elements are completely dissolved in the matrix, forming a homogeneous solid solution. Second, quenching, where the alloy is rapidly cooled to a lower temperature, trapping the dissolved alloying elements in a supersaturated solid solution. This supersaturated state is unstable. Third, aging, where the alloy is held at an intermediate temperature or at room temperature for a period of time. During aging, the supersaturated solid solution decomposes, and fine precipitate particles form within the matrix. The size, distribution, and coherency of these precipitates with the matrix determine the extent of hardening.

Different aging treatments can be employed. Artificial aging involves heating the material to an elevated temperature to accelerate precipitation. Natural aging occurs at room temperature over a longer period. The optimal properties are achieved when the precipitates are coherent with the matrix. Over-aging can occur if the aging time or temperature is too high, leading to the formation of larger, incoherent precipitates which can reduce strength. Präzipitationshärtung is widely used in aluminum alloys, nickel-based superalloys, and some steels to achieve high strength-to-weight ratios.