Phase transformations in phosphorus ion implanted 304L stainless steel

Abstract

Phosphorus ions accelerated to 175 keV were implanted into electropolished 304L stainless steel specimens near room temperature to fluences from 2.4 × 10 16 P + cm -2 to 1.9 × 10 18 P + cm -2. Microstructural characterization of the samples with an analytical electron microscope revealed an f.c.c. to b.c.c. transformation at fluences of around 1.0 × 10 17 P + cm -2, followed by amorphous phase formation from the b.c.c. matrix at greater fluences. Fully amorphous specimens were produced at a fluence of 3.5 × 10 17 P + cm -2. Further P + implantation precipitated the hexagonal M 2P phase from the amorphous matrix at 3.75 × 10 17 P + cm -2, while implantation to 7.2 × 10 17 P + cm -2 produced the orthorhombic MP phase from the crystalline M 2P phase. Here “M” represents the stoichiometric mixture of iron, chromium, nickel and manganese atoms present in the steel. Auger depth profiling analysis of implanted specimens indicated the b.c.c. transformation occurred at approximately 10 at.% P. Fully amorphous samples were found to contain around approximately 30 at.% P and the precipitation of the M 2P phase corresponded to an implanted layer composition of approximately 33 at.% P. Recrystallization of partially amorphous specimens with less than 22 at.% P at 600 °C for 1 h produced the orthorhombic FeCrP phase while similar heat treatments of samples with more than 22 at.% P resulted in the hexagonal M 2P phase as well as the FeCrP phase. Rebombardment of specimens containing less than 22 at.% P with 1.0 × 10 16 Fe + cm -2 ions accelerated to 310 keV produced to 310 keV produced some amorphous phase, while similar rebombardment of specimens containing more than 22 at.% P induced no change.