Effect of Boron Nitride Precipitation at Cavity Surface on Rupture Properties

Abstract

Compositions of type 304 austenitic stainless steels were modified with additions of boron, cerium and titanium. The additions of cerium and titanium removed free sulfur almost completely by formation of sulfides (Ce 2 O 2 S 2 and Ti 4 C 2 S 2 ), and led to precipitation of boron nitride onto creep cavity surfaces during creep exposure. Chemistries of the creep cavity surfaces, exposed by breaking creep exposed specimens at liquid nitrogen temperature under impact loading, were examined by Auger electron spectroscopy. The Auger spectra revealed the presence of boron nitride precipitating onto creep cavity surfaces. It was indicated that the boron nitride suppressed creep cavity growth and provided the steel with higher rupture strength and higher rupture ductility.

Evolution of Internal Crack in BCC Fe under Compressive Loading

“…It is possible that low strength materials might be made more reliable at a low cost if the crack healing is applied at an intermediate stage of their service life. The self-healing effect for creep cavitation in heat resisting stainless steels has been developed by alloy design, so micro-cracks can be constrained from propagating by automatically forming compounds on the crack surfaces although they may not be annihilated [1,2].…”

Self Healing of Mechanical Damage in Metallic Materials

“…Self healing of mechanical damage inside metallic materials has been thought to be difficult, since there is no means for delivery of healing agents in metallic materials. Recently Shinya group [1][2][3][4][5][6][7] and Lumley group [8,9] have proposed practical self healing methods for creep cavity in heat resisting steels and fatigue crack in Al alloys, respectively. Their self healing methods resemble each other and make use of solute atoms as healing agents.…”

“…Recently self healings of creep cavity and fatigue crack have been proposed by Shinya [1][2][3][4][5][6][7] and Lumley [8,9] groups, respectively. The self healing schemes proposed by them for creep cavity and fatigue crack are resemble each other, and their schemes are as follows: ① Solute elements with healing functions are added into metallic materials, and solid solution treated; ② The solute elements are delivered to damage sites autonomously through volume or pipe diffusion during high temperature or fatigue loading services of the materials; ③ The solute elements segregate on dislocations or creep cavity surfaces, or precipitate elemental substances or chemical compounds on surfaces of creep cavity and fatigue crack.…”

“…The detailed self healing method proposed recently by Shinya et al [1][2][3][4][5][6][7] is as follows. Creep cavity is thought to grow by diffusive transport of matter from creep cavity surface to grain boundary, which means that the physical property of creep cavity surface is closely connected to cavity growth.…”