NanoSIMS

Hanis Ayuni Mohd Yusof

Hanis is using the NanoSIMS to investigate grain boundary segregation in a statistically significant number of grain boundaries in bulk samples. This project will explore the application of this technique to model system of sulphur segregation in nickel including industrially relevant samples of boron segregation in steel, tungsten and nickel based superalloys and phosphorus segregation in copper. These projects are in collaboration with University of Nantes (France), Tata Steel (UK), Swedish Nuclear Fuel and Waste Management Co. (Sweden), Fission and Fusion group and Engineering Science (Oxford).

Research projects:

Sulphur and phosphorus segregation

Impurity segregation and its influence on the mechanical properties of metals and alloys has been studied for many years. Segregation to grain boundaries can lead to, for example, grain boundary fracture as a result of temper brittleness, creep embrittlement, stress relief cracking of welds, environmentally assisted fatigue, grain boundary corrosion, and some forms of intergranular stress corrosion cracking.

Sulphur is known to segregate to grain boundaries and cause brittle intergranular fracture in nickel, iron, stainless steels and other alloys. Phosphorus grain boundary segregation contributes to the degradation of mechanical properties of steels and copper. Therefore diffusion and segregation data concerning sulphur and phosphorous in metals are of great importance.

Boron segregation

Unlike many other segregants, boron does not cause grain boundary embrittlement in steel. Boron is a trace solute impurity commonly found in stainless steels with a strong tendency to segregate at grain boundaries. Grain boundary strengthening, in most instances, is considered to be caused by the segregation of boron to grain boundaries where it is incorporated into precipitates and alters the character of the grain boundary or matrix/particle interface. It is essential to prevent boron precipitating into nitrides or carbides because its positive effect on hardenability requires it to be in solid solution. Therefore, it is necessary to develop techniques to localise boron in steel to determine if it is in precipitates or segregated at grain boundaries to understand the mechanisms involved. The difficulty in detecting boron, and especially small amounts of boron, as well as a strong tendency for the formation of boron carbides and boron nitrides make it difficult to clearly identify the mechanism responsible for the beneficial boron effect.