The ultra‐small‐angle X‐ray scattering (USAXS) technique has been used to investigate and to quantify the morphology and size distribution of second‐phase particles in Zircaloy‐4 under various heat‐treatment conditions. The alloy samples were solutionized in the β phase field at 1293 K for 15 min and then cooled at different rates, including water quenching, air cooling and furnace cooling. The water‐quenched samples were subsequently subjected to a thermal aging treatment at 873 K for different aging times (30, 60, 120 and 300 min). The USAXS results show that water quenching and air cooling from the β phase field produces a narrow size distribution of fine‐size precipitates with an average diameter of 300–800 Å, while furnace cooling resulted in coarsening of the particles, with a broad size distribution having an average precipitate size of 600–1200 Å. Further, the furnace‐cooled sample shows a higher volume fraction of particles than the water‐quenched or air‐cooled sample. The USAXS results on the quenched then aged samples show that aging at 873 K for 10 min resulted in very fine size precipitates with an average diameter of 200–350 Å. A rapid precipitation with the highest number density of second‐phase particles amongst all the heat‐treated samples (4.3 × 1020 m−3) was observed in the sample aged for 10 min at 873 K. Particles of larger size and with a broad size distribution were observed in the sample aged at 873 K for 300 min. A bimodal type of particle size distribution was observed in all the heat‐treated samples. Important parameters in the characterization of second‐phase particles, such as the average size, size distribution, volume fraction and number density, were evaluated and quantified. These parameters are discussed for both β heat‐treated and aged specimens. Transmission and scanning transmission electron microscopy characterization were carried out on all heat‐treated samples, to assist in interpretation and to substantiate the results from the USAXS measurements.
Journal of Applied Crystallography – Wiley
Published: Feb 1, 2015