Metals failure mechanisms

McEvily, A. J., Metal Failures Mechanisms, Analysis, Prevention, Wiley, New York, 2002. 

Perhaps the most important stress factor affecting corrosion fatigue is the frequency of the cyclic stress. Since corrosion is an essential component of the failure mechanism and since corrosion processes typically require time for the interaction between the metal and its environment, the corrosion-fatigue life of a metal depends on the frequency of the cyclic stress. Relatively low-stress frequencies permit adequate time for corrosion to occur high-stress frequencies may not allow sufficient time for the corrosion processes necessary for corrosion... 

At elevated temperatures where titanium alloys could be the adherend of choice, a different failure mechanism becomes important. The solubility of oxygen is very high in titanium at high temperatures (up to 25 at.%), so the oxygen in a CAA or other surface oxide can and does dissolve into the metal (Fig. 12). This diffusion leaves voids or microcracks at the metal-oxide interface and embrittles the surface region of the metal (Fig. 13). Consequently, bondline stresses are concentrated at small areas at the interface and the joint fails at low stress levels [51,52]. Such phenomena have been observed for adherends exposed to 600°C for as little as 1 h or 300°C for 710 h prior to bonding [52] and for bonds using... 

Problems of short-term and long-term overheating, which leads to fatigue and metal failure, also are associated with deposition on boiler surfaces and restricted BW flow—the particular mechanisms depend on the nature and quantity of the waterside deposits formed. 

It is generally agreed that the causes and effects of poor water chemistry, mechanical problems, boiler section corrosion, metal failure, and poor boiler plant operation are all closely interrelated. Thus, effective control over the various corrosion processes that may occur in a boiler and its auxiliary equipment is fundamental to the realization of the full life expectancy and safe operation of the plant. Corroded and wasted metal cannot be replaced easily, and the failure of a boiler in service is both potentially dangerous and expensive. 

Where stress plays a part, the resultant metal failure may be present as either a transgranular (transcrystalline) or an intergranular ( intercrystalline) mechanism. 

Environmental Cracking The problem of environmental cracking of metals and their alloys is very important. Of all the failure mechanism tests, the test for stress corrosion cracking (SCC) is the most illusive. Stress corrosion is the acceleration of the rate of corrosion damage by static stress. SCC, the limiting case, is the spontaneous cracking that may result from combined effects of stress and corrosion. It is important to differentiate clearly between stress corrosion cracking and stress accelerated corrosion. Stress corro-... 

Figure 1 provides several electrochemical windows of important, relevant processes, including the reduction of alkyl carbonates, ethers, Li insertion into graphite, and Li metal deposition. Recent studies revealed two major failure mechanisms of graphite electrodes in repeated Li insertion/ deinsertion processes 21... 

There are two possible mechanisms that can lead to catastrophic vessel failure upon rapid depressurization, which is typically caused by metal failure or relief device actuation (Melhem et al., 1994) ... 

Beachmarks appear as in the case of metals. Detailed mechanism of crack growth differs from metals and fatigue failure in polymers is not characterized by an endurance limit... 

A. G. Evans and A. Rana, High Temperature Failure Mechanisms in Ceramics, Acta Metall., 28, 129-141 (1980). 

From a more fundamental point of view, the selection of different inden-ter geometries and loading conditions offer the possibility of exploring the viscoelastic/viscoplastic response and brittle failure mechanisms over a wide range of strain and strain rates. The relationship between imposed contact strain and indenter geometry has been quite well established for normal indentation. In the case of a conical or pyramidal indenter, the mean contact strain is usually considered to depend on the contact slope, 0 (Fig. 2a). For metals, Tabor [32] has established that the mean strain is about 0.2 tanG, i.e. independent of the indentation depth. A similar relationship seems to hold for polymers although there is some indication that the proportionality could be lower than 0.2 for viscoelastic materials [33,34], In the case of a sphere, an... 

The last failure mechanism involves defects in the underlying support layer that are transferred to the thin permselective layer. Examples include surface irregularities (such as pits or cracks), and particles on the support surface. Sintered stainless steel supports may be especially prone to residual particles of metal powder that can pierce the thin permselective metal layer during use. Shock and vibration may cause damage (such as cracking) to a ceramic support layer that then results in damage to, and failure of, the permselective layer. 

To increase the wear resistance of surfaces, silicon and metals are often coated with a hard nitride, carbide, boride, or oxide film. Nanoindentation and fracture simulations have been used extensively to elucidate failure mechanisms of these typically more brittle surfaces, which include crack propagation and film delamination. Considerable attention has also focused on nanocomposite materials, which possess nanocrystalline inclusions in an otherwise amorphous matrix. The nanocrystalline component is sufficiently small to preclude the formation of stable dislocations, and thus provide a higher hardness. 

A number of integrated circuit (IC) failure mechanisms are related to the presence of water and impurities at device surfaces. The most catastrophic failures are open or short circuits resulting from electrochemical attack on substrate metallization. Other, more subtle maladies include increased capacitive coupling between conductors (1.), reduced bipolar current gain (2), shifted MOS threshold voltages (3.4), and parasitic MOS devices (5.6). These problems arise from spurious electrical conduction processes in the presence of moisture and ionic contaminants. Polymer encapsulants, such as silicone rubber, provide barriers that prevent the formation of conductive water films on IC surfaces. 

It was mentioned above that the simulation method of Termonia [67-72] can be used to calculate the stress-strain curves of many fiber-reinforced or particulate-filled composites up to fracture, including the effects of fiber-matrix adhesion. Such systems are morphologically far more complex than adhesive joints. Many matrix-filler interfaces are dispersed throughout a composite specimen, while an adhesive joint has only the two interfaces (between each of the bottom and top metal plates and the glue layer). If one considers also the fact that there will often he a distribution of filler-matrix interface strengths in a composite, it can be seen that the failure mechanism can become quite complex. It may even involve a complex superposition of adhesive failure at some filler-matrix interfaces and cohesive failure in the bulk of the matrix. 

Metal Failure in Electrolytes Under Mechanical Stresses... 

Next, we will apply the general equations to the problem of electromigration in a metal. In this case, the components of the mixture will be conduction electrons and metallic ions. The motion of the metallic ions in the interconnect constitutes a failure mechanism, which has received renewed interest as production circuit dimensions approach one micron (5). In this work, the ions are considered to constitute a linearly "elastic material 2). The results will be compared to previous work by approximations, and a set of equations with initial and boundary conditions, which could be solved numerically, will be presented for the first time. 

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