Fatigue crack growth rates and fracture toughness of rapidly solidified Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloys
- PDF / 4,079,688 Bytes
- 10 Pages / 598.28 x 778.28 pts Page_size
- 85 Downloads / 193 Views
I.
INTRODUCTION
AI-Fe-V-Si alloys produced by rapid solidification techniques are promising alloy systems for elevatedtemperature applications, tt'2'3] The improved room- and elevated-temperature strengths of the alloys are due to dispersion strengthening provided by uniformly distributed fine dispersoids of an average composition mll3(Fe,V)3 Si. The alloys produced by the Allied-Signal, Inc., (Morristown, NJ) planar flow casting (PFC) process have been studied extensively. ]4-~5]The alloys have high creep resistance, adequate to moderate ductility, and high fracture toughness at room and elevated temperat u r e s . [6'7'8'9101 However, the microstructure of the extruded alloys consists of ribbon particles of approximately 1000 /~m in the longitudinal direction, 100 /xm in the transverse direction, and 20/xm in the short direction.[6] Because of the morphologies of particles, the fracture toughness at room and elevated temperatures depends on crack plane orientation and strain rate. ]5,6.1~ The anisotropy in fracture properties has been attributed to delaminations along prior powder particle boundaries. Delaminations relax the triaxial stresses within the process zone, increase the critical strain at fracture, and produce extrinsic toughening termed delamination toughening. Is'6"]2"]6"]7}However, the same delaminations result in significantly lower fracture toughness values in S. HARIPRASAD, Graduate Student, S.M.L. SASTRY, Professor of Metallurgy and Materials Science, and K.L. JERINA, Professor of Mechanical Engineering, are with the Mechanical Engineering Department, Washington University, St. Louis, MO 63130. R.J. LEDERICH, Senior Scientist, is with McDonnell Douglas Research Laboratories, St. Louis, MO 63166. Manuscript submitted May 18, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
certain orientations. The fatigue crack propagation resistance of the alloy in L-T orientation at room and elevated temperatures is equivalent to rapidly solidified dispersion-strengthened AI-Fe-Ce and AI-Fe-Ni-Cr alloys and the wrought alloy 2219-T87. tt4] At higher stress intensity ranges, the fatigue crack growth resistance is superior to conventional 2219 alloy. ~ Crack growth rates were observed to be higher at 205 ~ than at 315 ~ because of dynamic slxain aging, tHJS] The fatigue crack growth rates (FCGR) of the alloys increase with increasing stress ratio at 175 ~ and at 315 ~ in the moist air. The objective of the present investigation was to study the dependence of FCGR and fracture toughness on crack plane orientation in the AI-8.5 pet Fe-l.2 pet V-1.7 pet Si alloy processed by PFC and atomized melt deposition (AMD). Atomized melt deposition is an alternate rapid solidification technique involving deposition of rapidly solidified atomized melt droplets onto a substrate in an inert atmosphere, producing near net shape products. [~s] Variations of the process have been termed Osprey process, tl9] liquid metal dynamic compaction, t2~ and spray deposition, t2~] The deposits exhibit little or no evidence of individual pa
Data Loading...
