Matrix embrittlement

Silicon may be present in high-chromium irons in amounts varying between 0-5 and 2-5%. Its effect is to increase fluidity in the foundry and improve the surface quality of castings. Further effects are to refine the eutectic carbides in the iron, to produce a more uniform structure and to raise the temperature at which the matrix transforms from ferrite to austenite with consequent dimensional changes. Additions above 2-5% have an embrittling effect. 

Tantalum and tantalum alloys react with hydrogen, nitrogen and oxygen at temperatures above 300°C. Hydrogen is dissolved in the metallic matrix above 350°C and evolved at higher temperatures of about 800°C . The dissolved hydrogen embrittles the tantalum and its alloys. This effect can be used to prepare tantalum powder. 

Chemical reaction This involves the formation of distinct compounds by reaction between the solid metal and the fused metal or salt. If such compounds form an adherent, continuous layer at the interface they tend to inhibit continuation of the reaction. If, however, they are non-adherent or soluble in the molten phase, no protection will be offered. In some instances, the compounds form in the matrix of the alloy, for example as grain-boundary intermetallic compound, and result in harmful liquid metal embrittlement (LME) although no corrosion loss can be observed. 

Moisture embrittlement must be distinguished from other forms of embrittlement. Brittleness of propellants at low temperatures is normally caused by binders which stiffen excessively with decreasing temperatures, owing to partial crystallization of the binder matrix (e.g.9 copolymers of butadiene with acrylonitrile, some hydrogenated polybutadienes, etc.). Such propellants are brittle at low temperatures whether they have been exposed to moisture or not. 

The inplane shear stress-strain tests reported here have been well demonstrated to be a reliable test for matrix-dominated properties in composites 141). For the selected mechanical properties that were monitored, their sensitivity to the thermal history was well demonstrated. In particular, the embrittlement process during the sub-Tg annealing or physical aging has been clearly observed. This decrease in molecular mobility, which gives rise to an increase in relaxation time and hence a decrease in toughness, can be rationalized as a decrease in free volume in an approach towards the equilibrium glassy state. 

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