Metal-induced embrittlement
Embrittlement caused by diffusion of metal in a base metal
- 2 min read
- 4 chapters
Related on Lably
Through Stress (mechanics), Copper and Melting point
- Diffusion through grain boundaries near the crack of matrix
- Diffusion of first monolayer heterogeneous surface embrittler atoms
- Second monolayer heterogenous surface diffusion of embrittler
- Surface diffusion of the embrittler over a layer of embrittler
The main mechanism of transport for SMIE is surface self-diffusion of the embrittler over a layer of embrittler that’s thick enough to be characterized as self-diffusion at the crack tip. In comparison, LMIE dominant mechanism is bulk liquid flow that penetrates at the tips of cracks.
Examples
Studies have shown that Zn, Pb, Cd, Sn and In can embrittle steel at temperature below each embrittler’s melting point.
Sign in to keep reading
3 more chapters are free with a Lably account.
Mechanics and temperature dependence
Similar to liquid metal embrittlement, solid metal-induced embrittlement results in a decrease in fracture strength of a material. In addition, a decrease in tensile ductility over a temperature range is indicative of metal-induced embrittlement. Although SMIE is greatest just below the embrittler’s melting temperature, the range over which SMIE occurs ranges from 0.75 × Tm to Tm, where Tm is the melting temperature of the embrittler. The reduction in ductility is caused by formation and propagation of stable, subcritical intergranular cracks. SMIE produces both intergranular and transgranular fracture surfaces in otherwise ductile materials.
Kinetics of crack onset and propagation via SMIE
Crack extension, as opposed to crack onset, is the rate determining step for solid induced-metal embrittlement. The main mechanism leading to solid metal induced embrittlement is multilayer surface self-diffusion of the embrittler at the crack tip. Propagation rate of a crack undergoing metal-induced embrittlement is a function of the supply of embrittler present at the crack tip. Crack velocities in SMIE are much slower than LMIE velocities. Catastrophic failure of a material via SMIE occurs as a result of the propagation of cracks to a critical point. To this end, the propagation of the crack is controlled by the transport rate and mechanisms of the embrittler at the tip of nucleated cracks. SMIE can be mitigated by increasing the tortuosity of crack paths such that resistance to intergranular cracking increases.
Susceptibility
SMIE is less common that LMIE and much less common that other failure mechanisms such as hydrogen embrittlement, fatigue, and stress-corrosion cracking. Still, embrittlement mechanisms can be introduced during fabrication, coatings, testing or during service of the material components. Susceptibility for SMIE increases with the following material characteristics:
- Increase in strength of high-strength material
- Increasing grain size
- Materials with more planar-slip than wavy-slip