Extended Al(Mn) solution in a rapidly solidified Al-Li-Mn-Zr alloy
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fewer striations are visible. After the transverse deflection of the crack path, only white dots (transverse section images of SiC whiskers) and dimples are seen. It has been known that in the period of stable fatigue crack growth, the maximum stress intensity factor Kmax is less than the critical stress intensity factor Kc, i.e., gmax < g c. On the other hand, during the tensile fracture or the overload fracture following the stable fatigue crack growth, Km~x-> Kc- Taking this into account, the results of this study can be summarized as follows. (1) The SiC whiskers are aligned in the extrusion direction. (2) During stable fatigue crack growth under loading with Km~ < Kc, the crack growth path is nearly parallel to or along the longitudinal interface of the aligned SiC whiskers. In this stage, fatigue striations are developed on a longitudinal matrix crack plane. (3) During the tensile fracture or the overload fracture following stable fatigue crack growth under loading with Km~x --> K~, the crack path is transverse to the aligned SiC whiskers. In this stage, dimples are formed in the matrix.
Extended AI(Mn) Solution in a Rapidly Solidified AI-Li-Mn-Zr Alloy M. RUHR, E.J. LAVERNIA, and J.C. BARAM In the present communication, the effect of cooling rate on the extension of Mn solid solubility in A1 and on the relative amount of MnA1 (MnAI6 and MnA14) secondary phases during gas atomization and spray deposition is critically examined, ll.2] An alloy of composition A1-6.5Mn-2.3Li-0.65Zr (wt pct) currently being investigated for applications requiring high strength and low density at high temperatures was selected for this study. The material was exposed to various solidification histories by altering gas pressure and powder size during solidification. The resulting six distinct cooling rates were characterized for the following samples (labeled A through F): (1) Sample A consisted of high pressure argon gas atomized powders sieved in the
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