Effects of Chemistry and Processing on the Fracture Related Properties of P/M Alloy CT91.
Final rept. Sep 80-May 84,
AIR FORCE WRIGHT AERONAUTICAL LABS WRIGHT-PATTERSON AFB OH
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With the single exception of fatigue crack propagation resistance, the development of high strength powder metallurgy PM aluminum alloys has been very successful. CT91, an example of this class of alloy, has been studied to determine the effect of chemistry Co content, deformation processing 38 and 64 uniaxial upset forging, and stress relief on engineering and fracture related properties. Stress relief by compression after solution heat treatment was found to have little effect on the properties studied and made no apparent change in the microstructure. A slight reduction in strength and slight improvement in fatigue crack propagation FCP resistance was noted in material that had been stress relieved. Co content had the largest effect of all program variables on strength - the 0.4 Co alloy exhibits a 28 MPa 4 ksi increase in both ultimate and yield strength compared to the 0 Co alloy. No effect of Co content on fracture toughness or FCP resistance was observed. Changing the uniaxial forging deformation from 38 to 64 produced no measureable effect on strength, toughness, or FCP resistance. There was a marked increase in scatter in the fracture related properties at the lower forging strain. This is attributed to the reduced degree of breakup and distribution of oxides found at the prior powder particle boundaries which provides sites for easy crack propagation. None of the major program variables had a significant effect on the Low Cycle Fatigue LCF behavior of the alloy. Author
- Properties of Metals and Alloys