This study investigated the effect of alloying on the behavior of Fe-Cr-Ni base alloys in boiling MgCl2 solutions. Alloys included commercial Fe-Cr-Ni alloys; ternary Fe-Cr-Ni alloys to 40% Cr; fourth-component alloys with specific alloy bases; fourth-, fifth-, and sixth-component alloys. The primary experimental measurements were time-to-breaking of wire specimens. In addition, polarization, potential time, current decay, constant potential cracking, and metallographic studies were conducted. Alloys of very substantial improvement in resistance to cracking were found. The most effective alloy additions were found to be aluminum, beryllium, and carbon. Lowering chromium to the 10-15% range was also found to be very effective in preventing cracking. The results are discussed in terms of the slip-step dissolution model of stress corrosion cracking.
Post-failure analyses of Type 316L stainless steel implants have frequently implicated stress corrosion cracking as the mode of failure. If stress corrosion cracking of this stainless steel is likely in vivo, this material would have questionable utility for such applications. However, this material is widely used by manufacturers and approved by government regulating agencies. This study was designed to critically evaluate this issue. No susceptibility to stress corrosion cracking of 316L was found in manufactured implants or in specimens from implant quality material in vitro by both static loading and slow strain rate testing techniques. An adjunct in vitro fatigue study disclosed multiple fatigue cracks with branching tendencies. It is concluded that crack branching and secondary cracking in 316L implants are not adequate indicia of stress corrosion cracking of implants.
This paper is based upon an actual post-crash investigation of a high-performance single-engine aircraft that crashed in mountainous terrain resulting in a post-crash fire. A detailed metallurgical study of the fuel system separations was undertaken to identify which fittings or fuel lines had suffered mechanical damage during the initial impact sequence and which had been damaged by the post-crash fire or in subsequent handling of the wreckage. This paper discusses some of the basic metallurgical theories used in failure analyses of aluminum alloy components involved in post-crash fire studies. Its primary purpose is to discriminate between thermal effects of fire and mechanical overload, specifically for fuel system components. Metallurgical characteristics cause certain specific signatures or 'witness marks' in mechanically induced separations and different features in post-crash fire separations. Discussed are frequently observed metallurgical signatures that may be used to evaluate post-crash, post-tire damage. Based on the metallurgical evidence and the principles described in this paper, it was obvious that the root cause of damage to these fuel system components was either thermal exposure during the post-crash fire or breakage after the fire during handling of the wreckage. Therefore, it was concluded that the fuel system components described herein had not been compromised during the initial impact, but rather had released fuel only after the post-crash tire. These principles can be utilized in similar investigations but it is important to recognize the chaotic nature of severe crashes and the wide range of possible damage features that may result. Each investigation must, of necessity, be based upon both basic principles and an overall assessment of the quality of the evidence as well as the need to resolve what may appear to be conflicting or questionable features of the available evidence.
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